Polymer Science Overview - American Chemical Society

13 Polymers in the World of Tomorrow W. O. BAKER

Downloaded by CORNELL UNIV on July 20, 2016 | http://pubs.acs.org Publication Date: December 10, 1981 | doi: 10.1021/bk-1981-0175.ch013

Bell Telephone Laboratories, Murray Hill, NJ 07974

As we have said in reporting the establishment of the national materials program two decades ago, the ages of civilization have long been named according to the materials used in the technology of those times (Stone - Tin - Bronze - Iron - Steel). In the world of today synthetics - plastics - fibers play a large part in civilization. So do electronic and optic materials, the semiconductors and magnetics and now lasers and light guides to facilitate communications and information, on which order in modern life so much depends. Communication and information handling may be dominant modes of easing the strenuous demands for food, shelter, energy transport and security, as well as health and education. And the former remain also primary demands for raw materials in a crowded planet. So in looking toward tomorrow, the role of polymers would extend beyond the major part they play already in the conventional functions of society which we have noted. We should emphasize as w e l l , however, that those convent i o n a l f u n c t i o n s are a l s o ever expanding. They extend i n the case of s y n t h e t i c rubber to more than 2-1/2 m i l l i o n metric tons/year i n the United States alone. Likewise f o r p l a s t i c s , annual usage of 30 b i l l i o n pounds of thermoplastics and about 5 b i l l i o n s of thermosetting systems added to 10-1/2 b i l l i o n pounds of f i b e r s (of which only about a b i l l i o n are c e l l u l o s e d e r i v e d ) , all indicate the magnitude of s e r v i c e already provided by macromolecules. In Western Europe, c u r r e n t l y about 28 b i l l i o n pounds of bulk thermoplastics are a p p l i e d , with about 5% being for special engineering f u n c t i o n s . Among these, uses of polyethylene and polybutylene terephthalates are expanding at about 22% per year, polyphenylene oxides by about 11% annually, with polysulpones, polyaryl, other ketones, polyphenylene s u l f i d e s and polyamide imides by about 13%. These a p p l i c a t i o n s of course, w i l l be extended i n ingenious and unforeseen ways i n the world of tomorrow. Our point i s , however, that new and e q u a l l y compelling functions of polymers are s t e a d i l y appearing. These have e s p e c i a l l y to do with the Age of Information, i n which

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Stahl; Polymer Science Overview ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


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the v e r s a t i l i t y of the polymeric s t a t e , ranging e l e c t r o m a g n e t i c a l l y from the superb e l e c t r i c a l i n s u l a t i o n of polyethylene and polystyrene to the semiconducting p r o p e r t i e s of polymer carbon, rubbers and widely used s i l v e r and gold f i l l e d epoxy and p o l y imide adhesives, makes them v i t a l elements i n the vast and growing global network of communication and information processors. Indeed these q u a l i t i e s have been developed since the midCentury so that i n a p a r t i c u l a r segment of the i n f o r m a t i o n i n d u s t r y such as telephones and communications, our volume of s y n t h e t i c polymers used annually exceeds that of any other c l a s s of m a t e r i a l s , although the a c t u a l tonnage of m e t a l l i c and i n o r g a n i c matter s t i l l leads. For the world of tomorrow, we f i n d m i c r o e l e c t r o n i c s , t h i n f i l m c i r c u i t r y and systems and, e s p e c i a l l y now photonics, with l a s e r s and l i g h t guides, to be dominant components. A l l of these s t r o n g l y use polymers, for their s p e c i a l p h y s i c a l - c h e m i c a l as w e l l as f a m i l i a r mechanical and electro-optical qualities. We shall illustrate some of these developing r o l e s , as symbolic of major trends i n polymer technology. E s p e c i a l l y these uses depend a l s o on polymer s c i e n c e . Thus we s h a l l expect to see an even more intimate l i n k than up to now between b a s i c understanding and t e c h n i c a l u t i l i z a t i o n - an i n t e r a c t i o n of high importance i n a l l modern i n d u s t r i a l society.(_1) There i s , however, an a d d i t i o n a l element i n the vigorous p u r s u i t of polymer science and technology i n c y b e r n e t i c s . For i t i s i n these uses of t h i n membranes, with exposure to electromagnetic f i e l d s and charged p a r t i c l e s , that the i n t e r s e c t i o n s and analogy with l i v i n g matter, with the t i s s u e s of plants and animals, become manifest. And here indeed i s a great f r o n t i e r i n the world of tomorrow. Every scientific element of v i t a l processes c a l l s f o r more d i s c o v e r y , but none more f o r c e f u l l y than how s i g n a l s are sent i n l i v i n g t h i n g s , and how the nerves r e g u l a t e , and u l t i m a t e l y the b r a i n computes. Polymer behavior i s prominent i n every one of these a c t i o n s , yet we s t i l l do not know the elementary process i n a s i n g l e one of them. The elegant chemistry of a c e t y l c h o l i n e at synapses, and of adenosine i n i t s energy r e g u l a t i o n s , are s t i l l undefined i n respect to an a c t u a l s i g n a l system. And beyond a l l t h i s , the marvelous mystery of t i s s u e assembly, of c e l l u l a r communication and i n t e l l i g e n c e , ( 2 , 3 ) i n v o l v e s yet other polymer behavior whose understanding may indeed be aided by the f i l m s and f u n c t i o n s of polymers i n e l e c t r o - t e c h n o l o g y . Probably we should emphasize the p o s i t i o n of polymers i n the world of tomorrow a l s o with reference to other strong s o c i a l and economic f a c t o r s derived from the growing f i e l d of communication and information p r o c e s s i n g . Prime among these i s energy, where the transport of people f o r communicating as w e l l as moving of records, papers, f i l m s e t c . are s u b s t a n t i a l f a c t o r s i n energy usage. For i n s t a n c e , the energy used f o r a t y p i c a l telephone



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conversation has diminished i n the past s i x years by 1/3, from about 320 BTU's to 220· The point i s that i f , as we s h a l l show, polymers are e s s e n t i a l elements of communications and information systems, then polymers w i l l p a r t i c i p a t e i n the d r i v e to reduce energy usage. As noted, a telephone c a l l l i n k i n g people over some t y p i c a l d i s t a n c e of tens of miles takes about only 224 BTU's or l e s s than the energy i n 1/2 tablespoon of g a s o l i n e . This usage supports a complete network, i n c l u d i n g the b u i l d i n g c o s t s , network operation, transmission equipment, computers and motor v e h i c l e maintanance resources. I f only 10% of personal d r i v i n g were replaced by telephone s e r v i c e s , a n a t i o n a l saving of at l e a s t 625,000 b a r r e l s of crude o i l d a i l y or 10% of imports would be p o s s i b l e , with a concordant improvement of balance of payments of more than 6-1/2 b i l l i o n d o l l a r s per year. So the f u n c t i o n s of polymers should be sought ever more widely i n the times ahead, d e s p i t e t h e i r extensive part i n modern l i f e already. Let us now peer b r i e f l y i n t o p r o p e r t i e s and potent i a l s which provide these new parts i n forwarding the output of human minds and meanings. A primary f u n c t i o n i n t h i s information system of the world of tomorrow i s transforming the communication modes of human beings i n t o some mode capable of high v e l o c i t y and q u a n t i t y . This i s achievable by methods such as the analog and d i g i t a l coding of speech and p i c t u r e s , e l e c t r o m a g n e t i c a l l y , i n c l u d i n g optically. Techniques of conversion f o r speech and hearing have been the c l a s s i c schemes. Here, microphones and vibrating membrane r e c e i v e r s and loud speakers are the c r u c i a l elements i n the h i s t o r i c e v o l u t i o n of telephone, and l a t e r of broadcast radio. Polymer-related matter has played a part since the beginning, e s p e c i a l l y i n Edison's carbon p a r t i c l e microphone, the primary speech transducer i n telephones up to the present p e r i o d . In the condenser microphones, types of e l e c t r e t were used more than 50 years ago. In these, waxes were charged and functioned crudely d e s p i t e t h e i r small capacitance. In 1948 i t was shown that many f i l m s of a c r y l i c s and c e l l u l o s e e s t e r s , polystyrene and vinyls could be charged,(4) but i n subsequent study and a c o n t i n u i n g examination of p o s s i b i l i t i e s , no s u c c e s s f u l usage was achieved. Then, i n work of Sessler and West at Bell L a b o r a t o r i e s , (_5) a new course was taken, on the b a s i s of modern polymer science and technology. They produced high performance e l e c t r e t s from t h i n polymer f i l m s m e t a l l i z e d so as to y i e l d high capacitance. Both e l e c t r i c a l and mechanical p r o p e r t i e s of these transducers have been remarkable examples of how a p p l i c a t i o n s of science of s o l i d s , i n c l u d i n g knowledge of e l e c t r o n t r a p s , conduction processes i n i n s u l a t o r s and the v i s c o e l a s t i c phenomena of s e m i c r y s t a l l i n e polymers, can be combined.(6) I n c i d e n t a l l y , s i m i l a r ideas have been a p p l i e d to o p t i m i z a t i o n of the p r o p e r t i e s of p a r t i c l e microphones, through assemblies of p e r f e c t l y m i c r o s p h e r i c a l polymer carbon systems. These have shown what l i m i t s of performance



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could be expected in that sort of sound-electricity conversion.(7) These e f f o r t s now assure, i n the world of tomorrow, a generic c a p a b i l i t y f o r transforming voice and other mechanical s i g n a l s , i n c l u d i n g even the v i b r a t o r y movements of pen or s t y l u s on paper, into appropriate electromagnetic s i g n a l s , through polymer e l e c t r e t f i l m s . Modern e l e c t r o n i c telephones produced commerically i n Japan, and p r e s e n t l y (with novel designs) i n t h i s country, are based on these low power transducers. These enable for the f i r s t time a l l of the advantages of s o l i d state integrated circuitry also to be included i n the telephone instrument. Recorders, tape systems, a host of new high f i d e l i t y sound processors use these elements. A large v a r i e t y of device designs i s now a v a i l a b l e which can e x p l o i t the remarkable s t a b i l i t y of charged p o l y t e t r a f l u o r e t h y l e n e . Its sensitivity i n such membranes f o r microphones d e c l i n e s by l e s s than one dB a f t e r being at 95% relative humidity and 50°C f o r a year, an a c c e l e r a t e d aging which would hardly ever be encountered i n practice. Thus i s offered a wide range of options f o r transforming mechanical motion of almost any s o r t , from the smallest to r e l a t i v e l y large amplitude, i n t o e l e c t r o n i c s i g n a l s . But a l s o i n the course of t h i s work, fundamental q u a l i t i e s of polymer s t r u c t u r e s have been found that open wide paths f o r other future engineering. B a s i c a l l y , i t was long recognized that a p p l i c a t i o n of e l e c t r i c f i e l d s to d i e l e c t r i c m a t e r i a l at elevated temperatures, with the d i e l e c t r i c then subsequently cooled, would y i e l d i n j e c t e d space charges and d i p o l e o r i e n t a t i o n , as seen i n F i g . 1.(8) Modern s o l i d s t a t e studies i n d i c a t e , however, that charge i n j e c t i o n by corona discharge, high voltages exceeding breakdown i n the sample, or by l i q u i d contacts and e l e c t r o n beams are p r e f e r a b l e schemes. The d i r e c t e l e c t r o n beam r a d i a t i o n , analogous i n i t s charge implantation to what we have developed p r a c t i c a l l y f o r semiconductors and a whole v a r i e t y of other s o l i d s , i s an e f f e c t i v e method f o r e l e c t r e t formation, F i g . 2. Films of about 25 micrometer thickness of p o l y f l u o r o e t h y l e n e propylene ( T e f l o n FEP) and p o l y t e t r a f l u o e t h y l e n e ( T e f l o n ) were found to capture charges effectively, associated with the e l e c t r o n e g a t i v i t y of the bonds and p o s i t i o n s of the d i p o l e s . The p e n e t r a t i o n of the charge i n t o the polymer was followed by measurements with a s p l i t Faraday cup. Here i t i s found that at the end of a given r a d i a t i o n i n d u c t i o n , charges q± and q on the f r o n t and rear e l e c t r o d e s of the f i l m y i e l d mean s p e c i a l depth "d" of the t o t a l charge i n the form where D i s sample t h i c k n e s s . I t i s seen that at modest e l e c t r o n energies, there i s about 10% or so depth of charge i n j e c t i o n i n the 25 micrometer FEP specimens, F i g . 3. During r a d i a t i o n with beams of about 40 KEV energy and 10~ amperes/cm current density, the c o n d u c t i v i t y of the volume penetrated r i s e s to about 1 0 ~ ohm cm. But a f t e r about ΙΟ* s e c , t h i s c o n d u c t i v i t y reaches a l e v e l of about 10" ohm cm., and would r e q u i r e years f o r r e s t o r a t i o n of 2

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Implantation of electrons in polytetrafluoroethylene films to form electric transducer of high stability and sensitivity.

Details of methods of charging polymer films that function as electromechanical transducers and also information storage elements.


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Figure 3.

Depth in micrometers of charge injection in a 25-fxm fluoroethylene polymer film as a function of energy of injected electrons.


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the 10" ohm cm. of the original unirradiated material. Nevertheless the uncharged p o r t i o n seems to have r e t a i n e d i t s o r i g i n a l low c o n d u c t i v i t y . So an i n t e r e s t i n g trap l o c a l i z a t i o n and m o d i f i c a t i o n of i n t e r n a l f i e l d s seem to be c o n t r o l l a b l e . Levels of breakdown strength of the polymer rather than the d e n s i t y of trap s i t e s seem to l i m i t c a p a b i l i t i e s f o r charge storage. Thus p o l y t e t r a f l u o r e t h y l e n e can maintain .5 χ 10" C/cm (ohms per square centimeter), polyethylene terephthalate 1.4 χ 10" C/cm , each corresponding to a few megavolts per centimeter of e l e c t r i c f i e l d . The trap d e n s i t i e s , however, exceed 10" /cm . Thermally d i s t r i b u t e d current from these charged f i l m s gives f u r t h e r d e t a i l s of the behavior of the charges. Thus, i t i s indicated that the polyester and the polytetrafluorethylene environments had trapping l e v e l s with a c t i v a t i o n energies for l i b e r a t i n g the charges between 0.4 and 2.2 e l e c t r o n v o l t s and with m o b i l i t i e s of about 10" °/cm v.(9) The complex issue of traps and charge d i s t r i b u t i o n s i n polymer films suggests much f u t u r e investigation. Static electricity also remains a puzzling phenomenon i n nature. However, the s i g n i f i c a n c e of these e f f e c t s i n t e c h n i c a l mechanisms i s j u s t now being revealed. They appear widely i n electrographic and xerographic recording and duplicating processes ( 10) such as a p p l i e d i n our l a b o r a t o r y so many years ago by Mr. Chester Carlson. I t has been assumed that these traps i n v o l v e various s t r u c t u r a l u n i t s , such as p r i m a r i l y of course the atoms w i t h i n the polymer, but also groups of a s s o c i a t e d chain segments and a l s o e v e n t u a l l y at i n t e r f a c e s with v a r y i n g l e v e l s of c r y s t a l l i n i t y . As f i g u r e s show, a s t e p - l i k e charge decay suggests a s e r i e s of traps, F i g . 6.(11) Obviously the chemical ( e s p e c i a l l y i o n i c ) behavior of these systems may a l s o be a f f e c t e d by such traps and charging. As example of continued i n v e s t i g a t i o n i n t h i s report i s measurement of induced c o n d u c t i v i t y of T e f l o n FEP f i l m a f t e r r a d i a t i o n of 35 micrometer f i l m s by 50 to 100 k i l o v o l t s x-rays (Mo t a r g e t ) and currents between 2.5 mA and 20 mA. Seventy-five k i l o v o l t x-rays, with dosages between 25 rads per second and 220 rads per second, produced c o n d u c t i v i t y that was studied under 90 v o l t s of a p p l i e d e x t e r n a l f i e l d , equivalent to 3.75 x \Φ volts per cm. After r a d i a t i o n , a strong upsurge i n c o n d u c t i v i t y then decreased and l e v e l e d o f f a f t e r about an hour. This was analyzed i n terms of trap f i l l i n g , which showed a l i n e a r dependence on the exposure r a t e , X, at the r a d i a t i o n induced current I r . For t h i s polymer, mobility of the holes greatly exceeded that of electrons.(12) Additional studies done by electron pulse i o n i z a t i o n near the surface y i e l d e d c o n s i s t e n t behavior of the hole c u r r e n t s . ( 13) Low hole m o b i l i t y , u = 2 χ 10" cm. ^ V s e c , i s i n reasonable accord with e a r l i e r f i e l d independent values. Excellent devices f o r telephone speech transducing are now manufactured from these polymers, F i g . 5. 6

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Figure 4. Relative charge density persisting in various polymer compositions as a junction of time after initial charging. The polytetrafluoroethylene system traps retain charge indefinitely whereas those in the polyethylene terephthalate decay relatively quickly.

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Practical telephone transmitter unit now manufactured, using polymer foil electrets.



Figure 6. Diagram of the possible charge distribution in insulating polymer films into which electrons have been injected. The states suggested are symbolic of the wide range of electromagnetic effects to be expected in polar structures of macromolecular solids.


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These t r a p s , ( F i g . 6) and s i m i l a r e f f e c t s i n the motion of holes and other charges through polymers, would e v e n t u a l l y be c o r r e l a t e d a l s o with such s t r u c t u r a l probes as p o s i t r o n l i f e t i m e s i n macromolecular s o l i d s . Extensive recent s t u d i e s of p o s i t r o n l i f e t i m e are based on positronium decay. In t h i s , the l i f e t i m e of o-positronium (bound p o s i t r o n - e l e c t r o n p a i r with t o t a l s p i n one) i s reduced from about 140 nanoseconds to a few nanoseconds by " p i c k - o f f a n n i h i l a t i o n " i n which some unpaired e l e c t r o n spins i n the medium cause conversion quenching of orthopositronium to para-positronium. The speed of the τ e f f e c t i s supposed, among other things, to represent by p i c k - o f f a n n i h i l a t i o n the presence of defects i n the c r y s t a l l i n e l a t t i c e . In any case, what amounts to empty space between molecules can then be occupied by orthopositronium.(14,15,16) I t i s now found in linear polyethylene, by T. T. Wang and h i s c o - w o r k e r s of Bell Laboratories(JL_7) that there i s marked s h i f t i n p o s i t r o n l i f e times over the temperature range of 80°K to 300°K. For


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= -=-L, f o r a 2 v a r i e t y of specimens, there i s a p a r a l l e l l i n e a r temperature dependence, except i n the region 160°K to 230°K. Indeed, outside of t h i s region the temperature dependence i s very l i k e the volume change, except with opposite slope. Further the change outside the t r a n s i t i o n region i s i n s e n s i t i v e to c r y s t a l l i n i t y of the specimen, and apparently t h e r e f o r e the λ / Τ curves r e l a t e to s t r u c t u r a l changes i n the d i s o r d e r e d regions only. It i s believed that molecular motion i n those regions, with a correlation of frequency v of 10 10 hertz or more, f a c i l i t a t e the d i f f u s i o n of e l e c t r o n density i n t o the f r e e volume occupied by the orthopositronium. S e l f - a n n i h i l a t i o n rate would then be reduced.(18) The disordered polyethylene shows a broader d i s t r i b u t i o n of orthopositronium annihilation irregularities than a more c r y s t a l l i n e low molecular weight sample. Above 230°C, which i s the Tg claimed f o r polyethylene,(19,20) positron annihilation e f f e c t s are uniform f o r a l l specimens of varying p e r f e c t i o n . Thus, o v e r a l l , i n the f u t u r e we should look f o r s p e c i f i c c o r r e l a t i o n s of the charge implantation, e l e c t r e t formation, charge transfer, and positron annihilation as methods of i d e n t i f y i n g s o l i d state q u a l i t i e s . These i n turn would lead to a d d i t i o n a l f u n c t i o n s of polymers f o r the transformation and storage of i n f o r m a t i o n . Someday one could hope that there would be a c o u p l i n g of t h i s i n f o r m a t i o n a l content with molecular mechanics of o r i e n t e d or otherwise configured polymer systems. A c c o r d i n g l y , a s t r u c t u r e could be programmed, by appropriate electromagnetic or o p t i c a l information i n s e r t i o n , then to a l t e r i t s p h y s i c a l s t a t e under h i g h l y c o n t r o l l e d and timed conditons. orthopositronium p i c k - o f f a n n i h i l a t i o n rate λ

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W i l l there be such polymeric machines, based on rather more intimate i n t e r a c t i o n s than even the ion-based, l a r g e l y long term e x e r c i s e s that analogs of muscle f u n c t i o n have already produced? Indeed the i n f l u e n c e of e x t e r n a l f i e l d s on n a t u r a l macromolecular processes remains a l s o a f a s c i n a t i n g arena. For instance, i t has been reported r e c e n t l y that the p o l y t e t r a f l u o r e t h y l e n e e l e c t r e t s described above were included i n bandages a p p l i e d to the h e a l i n g of f u l l - t h i c k n e s s s k i n i n c i s i o n s i n guinea p i g s . These charged f i l m s appeared to i n f l u e n c e the formation of c o l l a g e n f i b e r s . Compared to the presence of the same m a t e r i a l s uncharged, examples showed 128% improvement i n t e n s i l e strength of the i n c i s i o n a f t e r f i v e days and 55% increase a f t e r nine days. S i m i l a r i n f l u e n c e s on bone k n i t t i n g have a l s o been reported by Japanese workers.(21) Combinations of Polymers; Phases Indeed, i n the world of tomorrow we can expect new aspects of polymer s o l i d s to extend the conventional and successful s t r u c t u r e ideas of t h i s century. These, of course, were the r e c o g n i t i o n as molecular i d e n t i t i e s of the chains of repeating chemical monomers. The circumstances of those e n t i t i e s have r e s u l t e d i n i n t e r e s t i n g concepts of s o l u b i l i t i e s , v i s c o s i t y , and other mechanics, and e s p e c i a l l y thermodynamic l i m i t a t i o n s >n mutual s o l u b i l i t y or compatability of polymer mixtures. But we have known f o r decades that even homogeneous r e g u l a r chain polymers such as Carothers p o l y e s t e r s and polyamides formed s o l i d s with manifold imperfections and i r r e g u l a r i t i e s , such as order-disorder c r y s t a l configurations.(22,23) 1

Now as we discussed with respect to charge d i s t r i b u t i o n i n polymer f i l m s , we know that there are d i s l o c a t i o n s and d i s o r d e r s i n marvelous v a r i e t y . The technology of these imperfection systems w i l l i n c r e a s i n g l y take advantage of t h i s complexity of s t a t e s , just as i t has f o r decades i n polymer and rubber formulat i o n s and compounding, p l a s t i c i z e r m i s c i b i l i t y , e t c . But now we have a s p e c i a l stimulus f o r probing polymer mixtures, blends, composites and heterogeneous s t a t e s , i n which even the simplest mixtures are mostly found. For we know that somehow i n nature these l i m i t e d c o m p a t i b i l i t i e s are coupled probably with charge d i s t r i b u t i o n s from ions or other e l e c t r o l y t e phenomena. This a c t i o n must lead to such macroassemblies as t u b u l i n , of microtubules, of wondrous membranes f i b e r nets, and a host of other supermolecular s t r u c t u r e s , i n n a t u r a l t i s s u e . These segregations of matter presumably represent some surface or interfacial definitions. These may be rudimentary q u a l i t i e s of information content t h a t we a l s o b e l i e v e must be present in living structures.



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Thus, l e t us look toward i d e n t i f y i n g what we now can understand about mixtures and surfaces and i n t e r f a c e s of compatible and incompatible polymer systems. Perhaps then we s h a l l see a l i t t l e of a beginning p a t t e r n of how the sublime beauties of D'Arcy Thompson's "shape and form" must u l t i m a t e l y r e l a t e to macromolecules. We have seen that charges do d i s t r i b u t e , do provide t e c h n i c a l q u a l i t i e s of high value, do e x i s t f o r long times i n a polymer environ and thus could perhaps provide these f o r c e s at a distance that Coulombic ranges engender, and over which chemical bonding and d i s p e r s i o n f o r c e s f a l l s h o r t .


Polymer I n t e r f a c e s i n Composites Once more, too, as we seek to peer i n t o the f u t u r e , a l i v e l y technology seems to be p a r a l l e l i n g the deep challenges of scientific understanding of polymer composites and their components. So l e t us sample b r i e f l y some of the major trends i n these a p p l i c a t i o n s as a f u r t h e r preface to noting how simpler polymer systems combine or r e j e c t combination. In each case we s h a l l be mindful that we are looking f o r the f i l m , f i b e r or s u r f a c e q u a l i t i e s which i n v o l v e a c t i o n over some distance beyond the usual d i s p e r s i o n and d i p o l e forces (although these remain presumably the p r i n c i p a l i n t e r a c t i o n s ) . A p e r c e p t i v e survey by T. A l f r e y , J r . and W. J . Shrenk (24) covers the e x t r a o r d i n a r y qualities of multipolymer systems. These range from the commercial v i r t u e s of Noryl polystyrene/polyphenyleneoxide blends m i s c i b l e i n a l l proportions, to i n t e r p e n e t r a t i n g polymer networks having r e s t r a i n e d phase separation i n t o submicroscopic regions. Oriented forms of these systems can y i e l d m i c r o f i b r i l s , s p i r a l s and other morphologies suggestive of n a t u r a l plant and animal tissues. So once more, i n crude comparisons at l e a s t , the future needs to probe the f i n e d e t a i l s of mixed polymer behavior. S i m i l a r l y , where inorganic and organic matter are combined as i n composites, f i l l e d rubbers and laminates, the mechanics of phase, surface and f i l m i n t e r a c t i o n are often s t a r t l i n g . Epoxy composites c o n t a i n i n g around 65% by weight of polymer carbons f i b e r s are having a profound impact on the design of s t r u c t u r e s i n c l u d i n g a i r c r a f t , rockets, spaceships and automobile bodies. In a recent assessment of such engineered s t r u c t u r a l m a t e r i a l , J . J . Harwood and h i s a s s o c i a t e s (25) at the Ford S c i e n t i f i c Research Laboratory have shown how assembly of these polymer carbon/epoxy systems can y i e l d t e n s i l e strength of more than 200,000 pounds per square inch or 15,000 MPa with s t i f f nesses of m i l l i o n s of p s i or n e a r l y 200 GPa. The essence of these q u a l i t i e s seems c o n s i s t e n t with our comments about polymer s t r u c t u r e , f o r the carbon f i b e r s are generated by s e l e c t i v e decomposition of carbon chain systems which r e s u l t i n extensive network formation and e l e c t r o n i c e x c i t a t i o n as i n F i g . 7, F i g . 8. These lead to r i g i d , s t a b l e , s o l i d s , which show l i t t l e of the planar anisotropy or c r y s t a l l i n i t y of graphite.(26) The a c t u a l


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Figure 7.

Schematic conversion by heating, of dense network of vinyl benzene solids under oxidizing conditions.


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strength of such f i b e r s i s enhanced, however, by o r i e n t a t i o n of the l a y e r planes p a r a l l e l to the f i b e r a x i s . ( 2 7 ) Polymer carbon composites are f u l l y e s t a b l i s h e d as major parts of the new ways i n which designers and m a t e r i a l s engineers merge to generate novel p r o p e r t i e s and f u n c t i o n s . But as the understanding of polymer carbon systems spreads, the f e a t u r e s we have noted about the c o n f i g u r a t i o n and bonding of the progenitor polymer w i l l y i e l d enhanced performance. Fifty million psi modulus i s now c h a r a c t e r i s t i c of commercial products of carbon f i b e r s and u n i - d i r e c t i o n a l composites r e i n f o r c e d with i t go to more than h a l f of t h i s r i g i d i t y . Not only m i l i t a r y and rocket components, but most of the s t r u c t u r e of the business j e t aircraft called Lear Fan are based on the e x t r a o r d i n a r y p r o p e r t i e s of polymer carbon composites. Fourteen hundred pounds of such f i b e r s are used i n the t o t a l s t r u c t u r e of t h i s a i r p l a n e , which can c a r r y 1700 pounds of f u e l . Bonded carbon fiber s e c t i o n s of the plane are designed to withstand 8,000 pounds of t o r s i o n and 25,000 pounds of compression. The 20 to 30 percent r e d u c t i o n i n weight, t y p i c a l of many a i r c r a f t uses, i s even surpassed by 70 percent weight r e d u c t i o n achieved i n experiments noted, i n the Ford S c i e n t i f i c Laboratory, i n which a t o t a l carbon f i b e r r e i n f o r c e d body of a s i x passenger automobile has been created and t e s t e d . This i n c l u d e s high modulus polymer carbon f i b e r s of Hercules and Union Carbide types, with s t r e n g t h at breaking of about 2350 Mpa's (340 k s i ) with a modulus of about 350,000 Mpa (50 χ 10 p s i ) . The cured composites contained about 62 percent by volume of the polymer carbon f i b e r . (A d e t a i l e d account of the design and fabrication of this remarkable conceptual v e h i c l e was reported at the I n t e r n a t i o n a l Conference on Composites, P a r i s , J u l y , 1980, by E. J . Horton.) With respect to other polymer carbon composites, s t u d i e s by D. Gloge, B e l l L a b o r a t o r i e s , i n d i c a t e s that 10% polymer carbon f i b e r content of the cross s e c t i o n , i n our ongoing design of cable c a r r y i n g l i g h t g u i d e g l a s s f i b e r s f o r communications, can t r i p l e the duct run. This i s due to the higher s t r e n g t h , and i n f a c t w i l l completely r e l i e v e the g l a s s f i b e r s from s t r e s s e s on the c a b l e . A l s o , such carbon f i b e r reinforcement i s 4 times l i g h t e r than s t e e l . It f u r t h e r , of course, r e t a i n s the t o t a l i n s u l a t i n g q u a l i t i e s of the whole new photonics cable system. This stage of polymer science and technology thus betokens a p e r i o d of growth comparable to the surge i n e a r l i e r decades occasioned by s y n t h e t i c organic chemistry, with i t s v a r i e t y of new chemical monomers and novel bonding s t r u c t u r e s . In other words, we may see the f i e l d s of mixtures, blends, composites and i n t e r n a l s t r u c t u r e p e r f e c t i o n c o n t r o l s producing n o v e l t i e s of performance i n a d d i t i o n to those bestowed by the vast range of chemical variance.(28,29) 6


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A c c o r d i n g l y , i t i s i n t e r e s t i n g to observe the beginnings of these combinations of new science and already f a m i l i a r technology in such s t r u c t u r e s as block copolymers and blends of both drastically varied and c h e m i c a l l y s i m i l a r macromolecular structures. An example of the l a t t e r i s the v a r i o u s blends of m i c r o g e l molecules, three dimensional g l o b u l a r types, with the l i n e a r systems of a d i v e r s i t y of s y n t h e t i c rubbers and n a t u r a l rubber. The g l o b u l a r microgel network s t r u c t u r e indeed modifies both the rheology and u l t i m a t e mechanics of the rubber.(30) Improvement i n the processing and v u l c a n i z e d q u a l i t i e s of a range of systems have been reported over the past decades. M o d i f i c a t i o n of n a t u r a l rubber, due to work i n the B r i t i s h Rubber Producers Research A s s o c i a t i o n , y i e l d s some of the most s t r i k i n g a p p l i c a t i o n s of m i c r o g e l . A d e t a i l e d study at the MV Lomonosov I n s t i t u t e of Fine Chemical Technology, i n Moscow, on the e f f e c t of microgels on mechanical p r o p e r t i e s of c i s - p o l y i s o p r e n e and butadiene-styrene rubbers e x t e n s i v e l y i l l u s t r a t e s the p r o p e r t i e s of blends from l a t e x combination of microgel and c o n v e n t i o n a l or l i n e a r systems.(31) Regarding simpler mixtures of r e l a t e d but c h e m i c a l l y different polymers, the dimensions of f u t u r e a c t i v i t y are r e f l e c t e d i n recent monographs.(32,33) Polymer Blends:

L i n e a r but Varying i n Subunits

A recent i n v e s t i g a t i o n i n our l a b o r a t o r i e s i n v o l v e s the d e l i c a t e balances i n energy and entropy which determine various l e v e l s of c o m p a t i b i l i t y of even c l o s e l y r e l a t e d polymers. Thus, A. J . Lovinger has examined the t e n s i l e p r o p e r t i e s and morphology of blends of polyethylene and polypropylene, F i g . 9.(34) These blends are known commercially f o r high impact s t r e n g t h s . Various e a r l i e r workers have found a range of q u a l i t i e s y i e l d i n g a maximum i n s t r e n g t h and modulus i n a blend of about 90% polypropylene by weight.(35) Others had observed a maximum i n s t r e n g t h and modulus at 75% polypropylene.(36) Current f i n d i n g s are that over a wide range the presence of one regular microcrystalline polymer partly i n f l u e n c e d the morphology of the t o t a l blend and a f f e c t e d the n u c l e a t i o n and s p h e r u l i t e growth of the other component. So i n the present context, the conclusions are that surfaces and i n t e r f a c e s are r e a d i l y induced i n such mixtures such that, i n accord with our e a r l i e r f i n d i n g s , r e l a t i v e l y long range, and even macroscopic e f f e c t s are produced by r e l a t i v e l y intimate mixtures of c l o s e chemical s i m i l a r i t y .




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Figure 9. Percent elongation at rupture as a function of the composition of mixed polymers of polypropylene and polyethylene indicating influence of solid state phases on strength and extensibility.


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of Blends

In f u r t h e r search of q u a l i t i e s of mixtures which could bear on the ways that changing polymer i n t e r f a c e s regulate and take on c e r t a i n gross forms, Douglass and M c B r i e r t y have a p p l i e d many s t u d i e s of nuclear magnetic resonance to a p p r o p r i a t e hydrogens and other magnetically polar components of the systems.(37) They have examined i n our l a b o r a t o r i e s a s e r i e s of alkanes CgH through C H o a reference frame for relations of the magnetic spins to the host l a t t i c e v i s - a - v i s t h e i r c o u p l i n g , and thus to the exchange of energy between neighbors i n the s p i n system. In t h i s l a t t e r , the s p i n energy moves from a hot or e x c i t i n g , to c o l d , r e l a x i n g r e g i o n . The scale of volume involved (that i s , the r e l a x a t i o n time r e q u i r e d i n a specimen having i r r e g u l a r motions and hence inhomogeneity) can r e f l e c t on the distances and dimensions of domains when the diffusion c o e f f i c i e n t f o r the s p i n energy i s a l s o known. In the alkanes, the methyl group i n t e r m i n a l molecular planes apparently can r e o r i e n t r a p i d l y and thus provide an energy sink f o r the r e s t of the e x c i t e d proton system. 11+

a


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19

It i s found that the r e l a x a t i o n parameter as a f u n c t i o n of temperature does not f o l l o w an increase with chain length, as the square of the number of methylene carbons. Nor i s i t l i n e a r with N, the number of methylene carbons, which should be true i f r e l a x a t i o n to the l a t t i c e were rate c o n t r o l l i n g . Rather, i t shows a temperature-induced increase of the minimum value of with about the 1.6 of N. So, both s p i n d i f f u s i o n and s p i n l a t t i c e coupling are r e f l e c t e d . For a s p i n d i f f u s i o n c o e f f i c i e n t D of approximately 2 χ 10~ cm. /sec, the mean square d i s t a n c e f o r d i f f u s i o n of s p i n energy i n a time t i s the / r = 200/TjA, or about 15Â on a T p time s c a l e . When the a p p l i e d magnetic f i e l d H c o n s i d e r a b l y exceeds the l o c a l f i e l d of the proton d i p o l e s , the small s c a l e s t r u c t u r e of inhomogeneity determines shape of the T ^ decay. Models can be made of formalized s p h e r i c a l domains and the l i k e . They a f f i r m that a composite decay such as noted above, r e s u l t i n g from the combined spin c o u p l i n g and spin d i f f u s i o n e f f e c t s , does demonstrate inhomogeneities. In even so c l a s s i c a system as p l a s t i c i z e d p o l y v i n y l c h l o r i d e , recent heat c a p a c i t y measurements i n our l a b o r a t o r i e s by B a i r ( B a i r , Η., P r i v a t e Communications) i n d i c a t e at l e a s t two g l a s s t r a n s i t i o n s . Douglass f i n d s that p o l y v i n y l c h l o r i d e at 75°C c o n t a i n i n g 1.5% p l a s t i c i z e r (and h i g h e r ) gives composite s i g n a l s , one of which appears to be u n p l a s t i c i z e d PVC. Presumably the p l a s t i c i z e r s are not uniformly mixed, and f r e e i n d u c t i o n decay studies i n d i c a t e very small regions of low m o b i l i t y . 12

2

7

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1

In s t i l l other NMR studies of mixtures, Douglass and M c B r i e r t y have considered the homogeneity of polyvinylidene f l u o r i d e - poly methylmethacrylate blends.(38) Here the energy exchange between proton and f l u o r i n e magnetic spins i s e f f i c i e n t only i f the n u c l e i are adjacent. The r e s u l t s i n d i c a t e , when taken around 40°C, that e i t h e r the f l u o r i n e n u c l e i i n a 40 polyvinylidene f l u o r i d e / 6 0 poly methylmethacrylate blend are



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c l o s e to a large f r a c t i o n of methyl groups, or at l e a s t that the molecular motion of the p o l y v i n y l i d e n e f l u o r i d e molecules i s a l t e r e d by the presence of the poly methylmethacrylate molecules. Under both circumstances, the evidence i s that the blend seems to be homogeneous i n the amorphous regions. A c o n t r a s t i n g c o n d i t i o n s occurs as found by Douglass and M c B r i e r t y when polypropylene and polyethylene are blended. This i s to be expected from our e a r l i e r comments on c r y s t a l l i n e and mechanical properties. Here, films of h i g h molecular polyethylene and polypropylene were prepared from s o l u t i o n by c o p r e c i p i t a t i o n and f u s i o n , according to the technique of Coombs, Cannon and K e l l e r . ( 3 9 ) The general model derived from these s t u d i e s shows c o e x i s t i n g c r y s t a l l i n e aggregates of polyethylene and polypropylene, with v a r i o u s stages of interpénétration and molecular sharing. Thus i t i s evident again that polymer blends are h i g h l y s e n s i t i v e to l o c a l submolecular s t r u c t u r e . P a r t i c u l a r l y s t r i k i n g behavior of polymer separations i n t o c h a r a c t e r i s t i c domains such as spheres are found when f i l m s of binary or more polymer species are cast from s o l u t i o n . In the case of polystyrene and poly ( v i n y l methyl e t h e r ) , Davis and Kwei have studied e f f e c t s of subsequent heating of the heterogeneous f i l m , cast from t r i c h l o r e t h y l e n e . When such f i l m s were heated above the c r i t i c a l temperature, they became c l e a r and homogeneous i n appearance as long as the elevated temperature was below another temperature curve of between 140° and 160°C, over a compositional range 20 to 80% polystryene i n the mixture. The lower temperature curve which had t o be exceeded f o r homogenization was i n the 60° to 80°C range. When these two polymers were cast from toluene, the f i l m was initially homogeneous and showed only one g l a s s transition temperature T . ( 40) Thus, we see i n t h e s o l i d state significant redistribution of i n t e r f a c e s and domains can be achieved, i n some intermediate temperature range which was found to depend h e a v i l y on moledular weight. The domain s i z e s ranged from 4 to 140 micrometers i n a 50-50 polystyrene (molecular weight 37,000) f i l m blend. A f t e r the r e d i s t r i b u t i o n , single g l a s s t r a n s i t i o n temperatures equal those f o r the corresponding toluene-cast f i l m were determined. In r e l a t e d work, Kwei, F r i s c h , Radigan and Vogel have examined ternary polymer mixtures c o n t a i n i n g the incompatible pair polymethylmethacrylate and p o l y e t h y l m e t h a c r y l a t e . They found that a t h i r d component, p o l y v i n y l i d e n e f l u o r i d e , would lead to completely homogeneous mixtures. In the s i n g l e phases, Tg, at l e a s t over the range 40 to 70% by weight of p o l y v i n y l i d e n e f l u o r i d e , equals the volume f r a c t i o n average of the Tg of the component polymers. (This work followed determination of binary parameters of the polymethylmethacrylate/polyvinylidene f l u o r i d e and p o l y e t h y l m e t h a c r y l a t e / p o l y v i n y l i d e n e f l u o r i d e methacrylate/ p o l y v i n y l i d e n e f l u o r i d e . ) (41,42) g


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The primary i n c o m p a t i b i l i t y of the two polymethacrylates (43) is itself s t r i k i n g evidence of the s e n s i t i v i t y of the fluorine i n t e r a c t i o n parameters to subtle chemical and compositional effects.(44) In the intermediate ranges of p o l y v i n y l i d e n e f l u o r i d e concentration, when the ternary mixture becomes apparently homogeneous and Tg equals the average of Z-j^^Tg^ over the range of 40 to 70% polyvinylidene f l u o r i d e , i t appears that the free volumes are a d d i t i v e . Thus, the various segments of d i f f e r i n g s t r u c t u r e would seem i n t h i s case to be e x t e n s i v e l y mixed. Again, future studies are promising, i n r e v e a l i n g how e x t e n s i v e l y polymer blends can be controlled, and what the kinds and properties of the inhomogeneities are. Polymer I n t e r f a c e s and

Phases

I t also appears, as we s h a l l discuss p r e s e n t l y , that some macromolecules, such as p o l y v i n y l i d e n e f l u o r i d e noted above, have e x c e p t i o n a l i n t e r a c t i o n p r o p e r t i e s , i n which the segments may behave rather d i f f e r e n t l y than the chemical monomer u n i t s would imply. For these and many r e l a t e d reasons, the studies of E. Helfand at B e l l Laboratories on t h e o r e t i c a l concepts of i n t e r f a c e s i n polyphase systems of macromolecules give us a keen sense of the scope of future d i s c o v e r i e s that are p o s s i b l e i n this f i e l d . Once more, of course, we have i n mind the pervasive issue of how nature d i s t r i b u t e s complex polymer compounds and f u n c t i o n s i n the formation of s u b c e l l u l a r and c e l l u l a r and l i v i n g systems. Thus a theory has been derived for two immiscible polymers. ^45,4J3) The nature of unsymmetric polymer/polymer i n t e r f a c e i s assumed to a r i s e from balancing of the l o c a l and n o n l o c a l free energies. The nonlocal p o r t i o n does not tend to sharp boundaries, i n o p p o s i t i o n to the l o c a l p o r t i o n s . The n o n l o c a l f a c t o r s of f r e e energy come from the conformational entropy, which requires the u n i t s to be a s s o c i a t e d with each other through the chain bonds, and a l s o the corresponding i n t e r a c t i o n that those c o n d i t i o n s impose on the appropriate segments. Reasonably good consistency with known parameters of 15 polymer p a i r s are obtained. Specifically, interfacial tension calculated i s comparable with that observed. The s e r i e s has been extended to concentrated polymer s o l u t i o n / s o l v e n t i n t e r f a c e s by the same workers.(47) The e s s e n t i a l parameters of the i n t e r f a c e have been i d e n t i f i e d i n t h i s d e t a i l e d theory. In accord with e a r l i e r work, the density p r o f i l e at the i n t e r f a c e f o r both the l a t t i c e model and the Gaussian random walk s t a t i s t i c a l form (which agree very well) show t h a t a great v a r i e t y of configurations and i n t e r a c t i o n s could e x i s t , and thus might o f f e r options f o r novel t e c h n i c a l treatment. Another welcome outcome of the t h e o r e t i c a l studies i s a stimulus f o r more experimental information and the i d e n t i f i c a t i o n



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OVERVIEW

of parameters s u i t a b l e f o r sharpening measurements. A promising aspect of such matters i n our l a b o r a t o r i e s i s the expanding use and i n t e r p r e t a t i o n of B r i l l o u i n s c a t t e r i n g by G. D. Patterson and h i s associates.(48,49) Both the Rayleigh and B r i l l o u i n s c a t t e r i n g by s o l i d s are s e n s i t i v e to d e n s i t y f l u c t u a t i o n , i n p u r i t i e s , inhomogeneities of the sort that we are emphasizing. Inhomogen e i t i e s i n f i l m s of p o l y v i n y l c h l o r i d e and of c e l l u l o s e acetate are shown as peaks near the main l o n g i t u d i n a l B r i l l o u i n s p i k e s . For polyethylene terephthalate f i l m , the s c a t t e r i n g spectrum was complex and there seemed to be at l e a s t two w e l l defined l o n g i t u d i n a l peaks. This suggests heterogeneity of dimensions of about Ι,ΟΟΟΑ and i s presumably c o n s i s t e n t with p a r t i a l c r y s t a l l i n i t y of the p o l y e s t e r . It seems l i k e l y that the transverse phonon peaks, which appear r e l a t i v e l y s t r o n g l y compared to l o n g i t u d i n a l ones, arise from p r o p e r t i e s of the c r y s t a l l i n e regions.(50) The r e l a x a t i o n phenomena and s c a t t e r i n g i n d i c a t e no l a r g e e f f e c t on the moduls μ at hypersonic frequencies at Tg. However, at melting, there i s a large s h i f t i n μ. A study of the mixtures 40/60 and 75/25 i n d i c a t e s i n g l e p a i r s of p o l a r i z e d B r i l l o u i n peaks marking a homogeneous amorphous phase. Block Co

Polymers

Now again, a s t a t e of inhomogeneity i n polymers, so especially interesting i n films and interfaces, occur when discontinuities are b u i l t i n t o the main valence chains and networks. Block polymers are the c l a s s i c embodiments of t h i s . Many p e r i o d i c distances separating domains i n such a l t e r n a t i n g or rhymthic copolymers have been reported. These i n d i c a t e existence of phases i n laminar domains and, i n other cases, of s p h e r i c a l domains.(51) Cases are shown experimentally f o r styrene/isoprene copolymers and a l s o f o r styrene/butadiene.(52,53,54) Through Helfand's theory,(55) interface conditions are defined. T r a n s i t i o n s from n e a r l y pure component A to component Β are expected i n the i n t e r f a c e regions. Most i n t e r e s t i n g l y , the theory suggests an entropy decrease a s s o c i a t e d with p r e f e r r e d s e l e c t i o n of conformations necessary to keep the d e n s i t y uniform i n the interphase area. Thus, we may speculate that l o c a l i z e d but supermolecular c o n f i g u r a t i o n s e x i s t s i n forms which would allow i n f o r m a t i o n to be d i s t r i b u t e d i n such a f i l m , such as through selective diffusion, particular light absorption, d i e l e c t r i c c o n d i t i o n or other p h y s i c a l , o p t i c a l or electromag netic pecularity. The d i f f e r e n c e between simple polymers w i l l , of course, be concentrated i n the interphase area. Likewise, conformation entropy decreases as the microdomains enlarge, because the system rejects increasingly the many conformations l e a d i n g to density inhomogeneity. I t favors the s p e c i a l ones which f i l l the lamellae centers i n a c h i e v i n g d e n s i t y uniformity. M i n i m i z a t i o n of the f r e e energy ( F i g . 10) taking these things i n t o account gives a domain s i z e i n styrene/isoprene


13.

BAKER

Polymers

in the

World

of

Tomorrow

cases of around 40 manometers, quite c l o s e to the rather observed f i g u r e s , F i g . 11.

185

roughly


Polymer Films as Pattern Generators Another r o l e f o r polymer f i l m and surfaces i n the world to come i s already f i r m l y founded i n the notion of modern t h i n f i l m and i n t e g r a t e d e l e c t r o n i c c i r c u i t r y . The era of s o l i d s t a t e e l e c t r o n i c s determines nowadays our use of automata and other elements of highest p r o d u c t i v i t y i n i n t e r n a t i o n a l economy, as w e l l being i n c r e a s i n g f a c t o r s i n science, eduction, and n a t i o n a l security. These c a p a b i l i t i e s are now p r i m a r i l y embodied i n micro circuits, whose i n t e g r a t e d form i s made d i r e c t l y on s i n g l e c r y s t a l surfaces of s i l i c o n or s i m i l a r semiconductor. A forthcoming era of photonics c i r c u i t r y embodying laser generators and various photo detectors and storage systems, w i l l provide s i m i l a r u l t r a m i c r o s c o p i c c i r c u i t s f o r communications, l o g i c and memory. These elegant instances of the best we know of how to a t t a i n e l e c t r o m a g n e t i c a l l y the a c t i o n of d i g i t a l machines and of analog s i g n a l s and processes are produced by computer aided design (CAD). They then come out as t r u l y a r t i s t i c elements i n a combination of engineering and o p e r a t i o n a l support of knowledge and communication around the world. Now the r o l e of polymer f i l m s i s as the l i t h o g r a p h i c r e s i s t s on the semiconductor chip s u r f a c e . A c c o r d i n g l y , the various l a y e r patterns and d i f f u s i o n processes i n the semiconductor and other e l e c t r o n i c a l l y a c t i v e f i l m s that comprise e v e n t u a l l y the i n t e g r a t e d c i r c u i t can be regulated as to shape and depth. The present i d e a l i s to have continued down-sizing of the a c t i v e components, from the present 150,000 on a s i l i c o n chip of about a square centimeter s i z e , to a m i l l i o n or so w i t h i n t h i s decade. (Our a s p i r a t i o n s to be comparable to organic e f f i c i e n c i e s are still some distance o f f , since even the 150,000 corresponds roughly i n cubic form to an order of magnitude l e s s numbers of a c t i v e components than there are neurons i n a cubic centimeter of the b r a i n . And of course, the neuron arrays work v a s t l y beyond any f u n c t i o n s we can achieve on these c h i p s . ) However, the fabulous economy of t h e s e systems and t h e i r u n s u r p a s s e d e f f i c i e n c y (56,57) depend e s p e c i a l l y on the more than 500,000 interconnections which must be assured among the 150,000 component-bearing c h i p s . These mean f i n e l i n e s of conducting matter, p e r f e c t l y formed, so that metals and other i n g r e d i e n t s can be e i t h e r added or d i s s o l v e d away, according to the eventual c i r c u i t shape. Photography has performed t h i s with the use of p o s i t i v e r e s i s t s f o r decades. These are when the polymer becomes s o l u b l e because of some photo exposure i n c o n t r a s t , to negative r e s i s t s when the polymers i s c r o s s - l i n k e d and i t s removal i s decreased by i n s o l u b i l i t y , ( F i g . 12). The c l a s s i c positive r e s i s t s u s u a l l y have a weakly a c i d i c polymer such as phenol or



186


Figure 10. Illustration of influence of domain formation in block copolymers according to the models of H elf and and coworkers. The free energy is shown as a function of the size and separation of the domains of varying composition. (The spontaneous separations may be analogous to the way superstructure is formed in natural polymers of plants and animals.)

Figure 11. Schematic of the block copolymers domains with density and structure indicated by the H elfand concept and approximated by certain experiments.


13.

BAKER

Polymers

in the World

of

187

Tomorrow

DEGRADATION (BOND CLEAVAGE) BOND REARRANGEMENT

POSITIVE ORGANIC; RESISTS >

CROSS LINKING NEGATIVE


ION PAIRING INORGANIC RESISTS

NEGATIVE

DIFFUSION

Figure 12. Description of the functions of polymer films forming organic resists, acting as the information pattern in the design and fabrication of electronic integrated circuits.

ELECTRON BEAM

ELECTRON IRRADIATED

ELECTRON BEAM EXPOSURE

REGION ELECTRON RESIST MASK MATERIAL SUBSTRATE

DEVELOPING POSITIVE RESIST

/

\

NEGATIVE RESIST

7 RESIST

RESIST

ETCHING AND STRIPPING

Figure 13. Outline of the pattern generation for integrated circuits provided by electron beam writing on chemically suitable polymer films, which are thus sensitized for development.


188

P O L Y M E R SCIENCE

formaldehyde condensation systems, or sometimes a s t r o n g l y a c i d i c a c r y l i c a c i d c o n t a i n i n g element. E v i d e n t l y , a new area of polymer f i l m a c t i v i t y i s a r i s i n g from t h i s f u n c t i o n of information pattern production,(58) Our i n v e n t i o n i n recent years of r e l a t i v e l y high speed e l e c t r o n beam generators ( F i g . 13) f o r primary patterns (mask making) and a l s o d i r e c t w r i t i n g where the c i r c u i t design i s traced d i r e c t l y on the s e m i c o n d u c t o r c h i p has had a r e v o l u t i o n a r y i n f l u e n c e on compactness and quality of integrated circuitry.(59) Correspondingly, i t has depended on steady improvement of polymer resists. For t h i s f u n c t i o n such f i l m should be a f t e r d i s s o l u t i o n , or c r o s s - l i n k a g e to prevent s o l u b i l i t y , (negative r e s i s t ) capable of submicron r e s o l u t i o n with a s e n s i t i v i t y to 10 to 30 k i l o v o l t e l e c t r o n s of about 10"" C/cm . The removal processes or development may include plasma and s p u t t e r etching, ion milling and other supplements to wet etching. E v i d e n t l y , these f a c t o r s occasion new polymer science and technology, ranging from initial syntheses to the understanding of phase r e l a t i o n s , charge d i s t r i b u t i o n and absorption, and o v e r a l l chemical r e a c t i v i t y . With e l e c t r o n beams poly-methylmethacrylate has e x c e l l e n t r e s o l u t i o n , but d i s s o l v e s r e l a t i v e l y slowly, by a curious nonswelling mechanism long ago remarked,(60) S e n s i b i l i t y of the p o l y o l e f i n sulfone to e l e c t r o n r a d i a t i o n was e a r l i e r described to chain breaking at the CS bond«(61) Polybutene"" sulfone i s p a r t i c u l a r l y appropriate and i s now e x t e n s i v e l y used commercially ( F i g . 14). For negative r e s i s t , where c r o s s - l i n k a g e i s required to reduce s w e l l i n g and prevent s o l u b i l i t y , various balances between s o l u b i l i t y of the unexposed portions and c r o s s - l i n k a g e of the negative itself have been sought i n a v a r i e t y of polymer s t r u c t u r e s ( F i g . 15). A p a r t i c u l a r l y u s e f u l one developed by Thompson and coworkers i n our l a b o r a t o r i e s i s a copolymer of g l y c i d y l m e t h a c r y l a t e and chlorostyrene ( F i g . 16). I t i s capable of r e s o l v i n g one micrometer l i n e s and spaces, but s w e l l i n g s t i l l obscures submicron r e s o l u t i o n . In the world of tomorrow i t does seem that widespread commerce, technology and science w i l l proceed from these new information-based a p p l i c a t i o n s of polymer f i l m s . Obviously, v a r i e t i e s of p r i n t i n g p l a t e s are p r e s e n t l y using these methods f o r the conventional patterns of human language. The recording of d i g i t a l codes, now widely done by polymer f i l m s containing magnetic p a r t i c l e s , may turn toward d i r e c t polymer i n s c r i p t i o n . The processes involved extend to behavior of polymer f i l m s as p r o t e c t i o n f o r metals, woods, and other e s s e n t i a l elements of civilization's structure. The d e t a i l e d studies of chain s c i s s i o n , polymerization and of c r o s s - l i n k a g e are a l l fundamental to processes of curing, degradation, s t a b i l i z a t i o n and synthesis which have been studied i n other contexts f o r generations, but which are sure to acquire new a t t e n t i o n as t h i s era of information science and technology evolves. 6


OVERVIEW

2

1


13.

BAKER

Polymers in the World of Tomorrow

189

POLYMERS FROM SULFUR DIOXIDE AND OLEFINS

Î

1

?

c=c + I R

e.g.

I R

2

! I -hÇ—Ç—S0

SO?

2

+

4

CH =CH + SO I ?

?

-+CH — C H - S O - h 2

?

CH I CH,


2

BUTENE - 1

POLY(BUTENE-1 SULFONE)

Figure 14.

Example of polysulfones exhibiting special response to electron beam bond cleavage, yielding positive resist.

Figure 15.

Schematic of systems providing negative resists through precisely controlled cross-linking, such as in epoxy systems.


190


Economics industrial electronics science

derived

now

national

product

national

security

and

make of

from

contribute

information

this

the

processing

on

systems

use

t r a n s i s t o r and

solid

of

i n every

present

solid

Further, the

the

and

billions

directly.

for

circuitry

original

$100

depend

probable,

integrated

per

year

to

the

state state gross

many

elements

these

communication

phase of

command,

of

our and

control

weaponry.

Polymers


alone

applications

OVERVIEW

in

Photonics

I n d e e d , a f a s c i n a t i n g example o f t h e new wave o f s c i e n c e and engineering u s i n g the p r e c i s e f o r m a t i o n of polymer f i l m s f o r a f u n c t i o n c r u c i a l t o new r e s o u r c e s f o r h a n d l i n g i n f o r m a t i o n i s now in full activity. I t i s t h a t , as a c o n s e q u e n c e o f d i s c o v e r y o f t h e l a s e r by Townes and Schawlow, an e r a o f p h o t o n i c s i s coming i n t o p e r f o r m t h e f u n c t i o n s o f s i g n a l s , l o g i c and memory p r o v i d e d by e l e c t r o n i c s and m a g n e t i c s up t o now. The transmission of photons e f f i c i e n t l y i s an e s s e n t i a l e l e m e n t i n t h i s new arena. I n our l a b o r a t o r i e s and o t h e r s , h a i r - t h i n f i b e r s o f a p p r o p r i a t e l y chemically p u r e and doped s i l i c o n now d r a m a t i c a l l y exceed the e f f i c i e n c y of copper or o t h e r e l e c t r o n c o n d u c t o r s i n t r a n s m i t t i n g l i g h t waves. The p r o d u c t i o n o f t h e s e f i b e r s i s a n o t h e r s a g a o f modern s c i e n c e , i t s e l f d e r i v e d from our k n o w l e d g e o f s i l i c o n and its reactions developed in the origination of silicon s e m i c o n d u c t o r s t h r e e d e c a d e s ago and since.(62) the

W h i l e the t r a n s p a r e n c y l a s t d e c a d e as much as

of in

t h e s e f i b e r s has b e e n i m p r o v e d i n 3,000 y e a r s b e f o r e ( F i g . 17), the

fragility of glass remains a crucial limitation. It can, however, be drastically reduced by coatings, which fill the s u r f a c e d e f e c t s o r d i s t r i b u t e the s t r e s s e s so t h a t f r a c t u r e s a r e reduced. These coatings must be done c o n c u r r e n t l y with the drawing of of i t with

the f i b e r f r o m the p r e f o r m b e f o r e t h e r e i s any contact a solid surface. The a p p l i c a t i o n o f t h e c o a t i n g w h i c h

follows 2200°C h i g h purity environment of the fiber drawing furnace i s a l i q u i d c o a t i n g system a p p l i e d w i t h a pressureless r e s e r v o i r by a p p l i c a t o r . I t was d e v e l o p e d by L. L. B l y e r , J r . and for

h i s a s s o c i a t e s at B e l l L a b o r a t o r i e s . A compliant a p p l i c a t o r , monitoring of c o n c e n t r i c i t y by laser adjustment of the

applicator, (Fig. 18). required for For

hence relieves contact with the coating S o l u t i o n systems are a v o i d e d b e c a u s e o f the solvent vaporization.

highly

fluid

coatings

that

have

to

solidify

die time

rapidly,

o b v i o u s l y f a s t c r o s s - l i n k i n g s by t h e r m a l o r r a d i a t i o n a c t i v a t i o n are effective. A characteristic susceptibility of fibers to f r a c t u r e with i n c r e a s i n g l e n g t h , because of the statistics of f l a w d i s t r i b u t i o n and t h e many ways i n w h i c h t h e s e f l a w s c a n be i n d u c e d , s u c h as by c h a n c e p a r t i c l e s , inhomogeneous q u a l i t i e s o f t h e c o a t i n g , e t c . , demand u n p r e c e d e n t e d p r e c i s i o n i n p o l y m e r f i l m formation. However, there are additional f a c t o r s , such as



13.

BAKER

Polymers


Figure 16. GMC, an example of copolymer selected by Bowden and Thompson for optimal sensitivity in pattern generation, through negative resist formation.

Figure 17. Chronology of improvement in light transmission of glasses over periods of history leading to introduction of photonics technology in the information age. Polymer protection of glass surfaces is an essential present feature.


191

192

POLYMER

SCIENCE

OVERVIEW

s e n s i t i v i t y of glass to formation of c o l o r centers (F-center) as a r e s u l t of any kind of r a d i a t i o n , as a t t r a c t i v e as that may be i n forming the polymer layer ( F i g . 19).


Mechanical Factors

i n Polymer-Coated L i g h t Guides

Beyond that, i t i s also found that fiberlight guides engender apreciable attenuation from what i s called micro bending. This i s when micron-sized displacements of the f i b e r axis occur i n small periods of length, l i k e a m i l l i m e t e r . These a r i s e from casual perturbations of the f i b e r and i t s cable by nonuniform l a t e r a l stresses l i k e winding, handling, suspending, etc. These important o p t i c a l losses can be v a s t l y reduced or eliminated by cushioning the f i b e r , by means of the t h i n polymer p r o t e c t i v e l a y e r , from these s t r e s s e s . This introduces, however, a need f o r low modulus coating which may, of course, be covered by a hard secondary coating, i f necessary. The r e l a x a t i o n modulus should be below 10 Newtons per square meter to give appropriate p r o t e c t i o n ( F i g . 20). Thus, we see the immediate application of s o p h i s t i c a t e d polymer rheology in relating s t r u c t u r e to these extraordinary demands f o r a f l u i d system at 10 - 10^ cent i p o i s e when a p p l i e d , but which can be q u i c k l y converted to the s o l i d cushioning and, at the same time, flawh e a l i n g f i l m noted. Obviously, f o r such s i l i c a f i b e r p r o t e c t i o n , s i l i c o n e s f o r thermal cure are u s e f u l . The ones normally used are vinyl end blocked ρο 1 y d i m e t h y 1 s i 1 ο χ a n e or polymethylphenylsiloxane c r o s s - l i n k e d by m u l t i f u n c t i o n a l s i l a n e s . Cross-linkage at high temperatures i s s u f f i c i e n t l y rapid so that t o t a l f i b e r drawing rates of greater than one meter per second are p r a c t i c a l . But the abrasion r e s i s t a n c e of these s i l i c o n e s i s so poor that an extruded nylon jacket i s put over them. E t h y l e n e / v i n y l acetate polymers have also been applied from melt. Poly (ether-urethane a c r y l a t e ) polymers have t e n s i l e r e l a x a t i o n modulus over 30 minutes of about 7 x 1 0 dynes/cm and y i e l d 0.3db/kilometer excess micro bending l o s s , whereas even a modified epoxy a c r y l a t e coating with a t e n s i l e r e l a x a t i o n modulus in 30 m i n u t e s of about 4.5 x 10 dynes/cm yields 11.6db/kilometer excess micro bending l o s s , ( r e s u l t i n g from a 132 grams tenison on a 10" diameter drum). 7

3

7

8

2

2

As can be seen ( F i g . 21), the appropriate p r o t e c t i o n of these f i b e r s y i e l d s extraordinary strength, exceeding p r e v i o u s l y achieved q u a l i t i e s of f i b e r g l a s s . A p p l i c a t i o n of the f i n d i n g s and p r i n c i p l e s to the making of l a r g e - s c a l e composites, as well as to the use of polymers i n s t a b i l i z i n g glass contains and s t r u c t u r a l glass o f f e r new f r o n t i e r s f o r future and extensive progress.


BAKER

Polymers

in the World of

193

Tomorrow

PREFORM FEED MECHANISM

IRCONIA INDUCTION FURNACE


FIBER DIAMETER MONITOR

Figure 18.

Method of coating ultratransparent light guide fibers of silica with polymer films for strength and stability.

600

700 800 900 1000 WAVELENGTH (nm)

1100

Figure 19. Influence of UV radiation as polymerization agent on the subsequent total photon attenuation in silica fibers, as a function of wavelength in nanometers. When no absorption of the UV is arranged lowest losses are assured. (The loss expressed in decibels per kilometer is a modern figure of merit for light guide systems.)



194


OVERVIEW

RELAXATION MODULUS AT 30 min, 23 °C (N/m ) 2

Figure 20. Limitation of excess microbending loss of photon transmission through light guides, as a function of relaxation modules of the stabilizing polymer coating. As evidence of light guide fiber stabilization and control through processing refinement, plot of frequency of failure against the tensile strength (in hundreds of thousands pounds per square inch) shows extraordinary uniformity for the control system compared to wide distribution of failures from surface defects and other variations in a conventional fiber glass system.


BAKER

Polymers

in the World of

GN/m


99.9 99

-

40

-

•

-

30

3 Γ

Δ HIGH DRAW TENSION Ο LOW QUALITY STARTING TUBE DUST IN DRAWING • ENVIRONMENT WELL-CONTROLLED MATERIALS AND PROCESSING

95 90 80 70 60 50

2

2 1

1

195

Tomorrow

•

20,

10

t

100

200

300

J_ 400 500 600

800

-=l-5

KPSI Figure 21. Demonstration of high strength and sharp distribution of tenacity of silica fibers protected and controlled compared to those from conventional processing.



196

OVERVIEW


Macroscopic P o l a r i z a t i o n i n Polymer S o l i d s Our general c o n s i d e r a t i o n of domains and phases i n the polymer systems have u s u a l l y involved rather small regions of a given sample or surface. This q u a l i t y includes even the f a m i l i a r crystallite and s p e r u l i t e aspects of macromolecule solids, although conventional o r i e n t a t i o n i n f i b e r s or b i a x i a l sheets then does p r o j e c t these l o c a l s t r u c t u r e s i n t o dimensions that approximate the t o t a l sample. There are some i n t e r e s t i n g cases emerging, which w i l l doubtless be extended i n the future, where polymers are f u r t h e r serving as information and e l e c t r o n i c a l l y sensing elements, because of q u a l i t i e s which have been induced i n the t o t a l f i l m by cooperation of a l l the molecules. A good example i s p o l y v i n y l i d e n e f l u o r i d e , where the 3 form of i t s c r y s t a l and the c o n f i g u r a t i o n of the molecule i n that, was found to give a h i g h l y d i p o l a r c e l l . ( 6 3 ) Correspondingly suitably poled f i l m s , or those cold drawn at moderate temperature and then exposed to a high e l e c t r i c f i e l d at high temperatures, do give a p i e z o e l e c t r i c constant (induced charge per unit s t r e s s ) of d 3, about 16 x 10" C. (Ul t r a s o n i c e l e c t r o n i c transducers and other Ν sensing devices can well be constructed from these f i l m s and have already been widely explored.)(64) Consideration of the s t r u c t u r e of p o l y v i n y l i d e n e f l u o r i d e (6_5) assuming a b a r r i e r of 3 k i l o c a l per mole for r o t a t i o n a l minima of conformation of the chain by A. E. T o n e l l i (66) led to d e t a i l e d conformation and i t s i m p l i c a t i o n s for d i p o l e s t r u c t u r e (Fig. 22). Indeed, the m a t e r i a l can approximate a f e r r o electric. It i s thus of i n t e r e s t i n our expectations of the environments that polymers can provide for the c r e a t i o n of new phenomena. The t o t a l array of dipoles i n p o l y v i n y l i d e n e f l u o r i d e w i l l switch i n about 3 microseconds at 20°C with 200 megavolts per meter f i e l d . The system becomes much slower at lower temperatures and f i e l d s . But we do have a case of macroscopic polarization intrinsic to the polymer molecules, which thus supplements the extensive trapping and other charge of d i s t r i b u t i o n phenomena that we have discussed i n connection with electrets. 3

12

New

Polymers W i l l Serve New

Purposes

Now we have sampled new aspects of the p r o p e r t i e s and potentials of polymers for an era of information and communications. We should also ever be mindful that new chemical s t r u c t u r e s and unexpected q u a l i t i e s w i l l continue to appear. In terms of the surface features, we have remarked on charges i n f i l m s and i n electromagnetic p r o p e r t i e s for s i g n a l storage and processing. We s h a l l expect also to f i n d the r o l e of composites and adhesives, where surface i n t e r a c t i o n s are c r u c i a l , to be spreading widely i n mechanical design. In subtle ways, such as how hydroxyethylmethacrylates serve as s o f t contact lenses, the surface and bulk properties w i l l f u n c t i o n i n complex b i o l o g i c a l and p r o s t h e t i c replacements. Stahl; Polymer Science Overview ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


13.

BAKER

Polymers


Figure 22. Schematic of poly vinylidene fluoride showing polarity in the unit cell when suitably oriented, so that the system exhibits macroscopic polarity and piezoelectric properties.

Figure 23.

Spiral structure of the constituent fibers in collagen composed of segregated assemblies of peptide molecules.


197


198

POLYMER

SCIENCE

OVERVIEW

S t i l l other a p p l i c a t i o n s of surface and t h i n f i l m p r o p e r t i e s of polymers are as d i f f u s i o n and slow release agents for drug a d m i n i s t r a t i o n by capsules, for s p e c i f i c release agents i n j e c t e d l o c a l l y into tumors, and for various h e r b i c i d e s and p e s t i c i d e s . Thus, 2-4-dichlorophenoxy a c e t i c acid has been e s t e r i f i e d with poly (2-hydroxy e t h y l methacrylate) for f i e l d t e s t i n g of c o n t r o l of aquatic weed growth i n ditches and canals. Such polymeric d e l i v e r y systems, e s p e c i a l l y for drug therapy, would appear to have extensive a p p l i c a t i o n where e s s e n t i a l l y the information for dosages i s contained i n the s t r u c t u r e chemical composition, dimensions and aggregation of the polymer host. As i n d i c a t e d i n the d i s c u s s i o n of s i g n a l p r o p e r t i e s of polymers charged by implantation, these and other q u a l i t i e s of polymer films can presumably be modified by yet other implantations of charges, i r r a d i a t i o n and s e l e c t i v e heat conversion of small surfaces or volumes, such as are being produced i n metals and semiconductors by l a s e r fusion and annealing. It appears that these intense thermal impacts can produce chemically and p h y s i c a l l y modified surfaces. Indeed, with the use of very fine l a s e r beams, c e r t a i n microporous, heterogeneous systems can be created i n t h i s way, whereas l a r g e r scale i r r a d i a t i o n can modify f i l m p r o p e r t i e s and s t r u c t u r e as well as composition. Obviously, a l l of these p r i n c i p l e s applied to f i l m formation and m o d i f i c a t i o n w i l l be of s p e c i a l s i g n i f i c a n c e as when the f i l m s are used as coatings. Here too, we should expect a strong extension of an old and c l a s s i c r o l e of polymers. In the energy domain, new and e f f i c i e n t uses i n gas l i n e s , electric cable ducts and the like, will promote surface s t a b i l i z a t i o n and endurance as well as complex s t r e s s c a p a b i l i t y of various extruded or cast systems. Such reactants as acetylene terminated polymers have y i e l d e d c r o s s - l i n k e d cured, networks of exceptional density and durability. A diimide dianhydride combined with (3) e t h y n y l a n i l i n e y i e l d s an acetylene terminated t e t r a i m i d e . On f u r t h e r polymerization at 250°C, the c r o s s - l i n k e d s t r u c t u r e derived can be used continuously at about 230°C. When t h i s i s combined with polymer carbon f i b e r s or filaments, an exceedingly r e f r a c t o r y and tough binder i s produced. P y r o l y s i s analogous to polymer carbon formation has also been applied to m e t h y l c h l o r o d i s i l a n e . This i s converted to beta s i l i c o n carbide f i b e r s of high t e n a c i t y . O v e r a l l , the polymer of tomorrow w i l l reach into i n o r g a n i c , quasi m e t a l l i c combinations on one s i d e , and bio polymers of l i v i n g t i s s u e on the other. These w i l l provide the widest i n t e r f a c e i n the science and the technology of matter. Both the wonderful s p i r a l conformation of c o l l a g e n , F i g . 23, and the subtle information content of i t s peptide components i n muscle a c t i o n are q u a l i t i e s to be sought i n polymers made by people.


13. BAKER Polymers in the World of Tomorrow 199

LITERATURE CITED

1. See Advanced Technology, AAAS, Wahington, D.C. (1980) pp. vii-xi., Baker, W. O., Science, 1981, 211, 359. 2. Nature, 1980, 285, 287; Evan, W. Η., Nature, 1980, 283, 521.


3. Newmark, P., Nature, 1980, 284, 659. 4. Dickenson, Τ. Α., Electrical Manufacturing, August, 1948, 101. 5. Sessler, G. M. and West, J. E., J. Acoust. Soc. of America, 1973, 53, 1589. 6. Sessler, G. M. and West, J. Ε., Proc. Fifth Intl. Congr. Acoust. Liege, 1965, paper J42; J. Acoust. Soc. of America, 1962, 34, 1787; 1966, 40, 1433. 7. Baker, W. O. and Grisdale, R. O., U.S. Patent 2,697, 136, 1954; Baker, W. O. and Winslow, F. Η., Twelfth International Congress of Pure and Applied Chemistry, September, 1951; Winslow, F. Η., Baker, W. O., Pape, Ν. R. and Matreyek, W., J. Poly. Sci., 1955, 16, 101. 8. Gross, Β., Ann. Acad. Brasil, Cieng, 1945, 17, 219. 9. Perlman, M. M. and Unger, S., Electrets, Charges Storage and Transport in Dielectrics, 1973, Perlman, M. M. ed., 105, Electrochemical Society, Wintle, H. J., Jour. Appl. Phys., 1971, 42, 4724. 10. An expert review covering a range of insulating and semiconducting polymers and their charging behavior is by Mort, J., Science, 1980, 208, 819. Earlier extensive investigations of these effects were done by H. A. Pohl and co-workers, Pohl, H. A. Progress in Solid State Chemistry, H. Ruri, Ed MacMillan, New York 1964, 316. 11. Mort, J. and Lakatos, A. I., Jour, of Non-Crystal. Solids, 1970, 4, 117. 12. Gross, Β., West, J. E., Feffeira, G. F. L. and Faria, R., J. Appl. Phys., 1980.



200

13. Gross, Β., Sessler, G. Μ., Seggern, H. and West, J. Ε., Appl. Phys. Letters, 1979, 34, 555. 14. Stevens, J. R. and Mao, Α., Jour. Appl. Phys., 1970, 41, 4273. 15. Groseclose, G. and Loper, G. D., Phys. Rev., 1965, 137, 939. 16. Wilson, R. Κ., Johnson, P. O. and Stump, R., Phys. Rev., 1963, 129, 2091.


17. Chuang, S. Y., Tao, S. J. and Wang, T. T., J. Poly. Sci., 1976, 18. Tao, S. J., Appl. Phys., 1974, 3, 1. 19

Davis, G. T. and Eby, R., J. Appl. Phys., 1973, 44, 4274.

20. Change, S. S., Poly. Preparation, 1972, 322. 21. Konikoff, J. J. and West, J. Ε., "Annual Report of the Conference on Electrical Insulation and Dielectric Phenomenon," National Research Council, 1978. 22. Baker, W. O., Fuller, C. S. and Pape, Ν. R., J. Am. Chem. Soc., 1940, 62, 3275. 23. Baker, W. O. and Fuller, C. S., J. Am. Chem. Soc., 1942, 64, 2399. 24. Alfrey, T. and Shrenk, W. J., Science, 1980, 208, 813. 25. Beardmore, P., Harwood, J. J., Kinsman, K. R. and Robertson, R. E., Science, 1980, 208, 833. 26. Winslow, F. Η., Baker, W. O. and Yager W. Α., Proceedings of the Conferences on Carbon, 1956, 93, University of Buffalo, New York. 27. Watt, W., Proc. Roy. Soc. of London, 1970, A319, 5. 28. The continuing vitality of the latter resources is skillfully shown by Anderson, B. C., Bartron, L. R. and Collette, J. W., Science, 1980, 208, 807. 29. Abelson, P. and Dorfman, Μ., "Advanced Technology," Eds., AAAS, 3, Washington, D.C. 30. Baker, W. O., Ind. Eng. Chem., 1949, 41, 511.


201

13. BAKER Polymers in the World of Tomorrow

31. Kuleznev, V. M., Elkina, I. Α., Vankova, L. N. and Dogadkin, Β. Α., Kolloidzhurnal, 1970, 32, 381. 32. Paul, D. R. and Newman, S., "Polymer Blends," 1978, Academic Press, New York. 33. Manson, J. A. and Sperling, L. Η., Polymer Blends and Composites, 1976, Freedom Press, New York.


34. Lovinger, A. J. and Williams, M. L., J. Appl. Poly. Sci., 1980, 35. Noel, O. F. and Carley, J. F., Poly. Eng. Sci., 1975, 15, 117. 36. Deanin, R. D. and Sansone, J. F., Polymer Preprints, 1978, 19(1), 211. 37. Douglass, D. C., ACS Symposium Volume "Characterization of Macromolecules by ESR/NMR," 1980, Washington, D. C. 38. Douglass, D. C. and McBrierty, V. J . , Macromolecules, 1978, 11, 766. 39. Coombs, A. and Keller, Α., J. Poly. Sci., Polymer Phys. Ed., 1979, 40. Davis, D. D. and Kwei, T. K., J. Poly. Sci., 1980, 41. Nishi, T. and Wang, T. T., Macromolecules, 1975, 8, 909. 42. Kwei, Τ. Κ., Patterson, Macromolecules, 1976,

G. D., and Wang, T. T.,

43. Hughes, L. J. and Britt, G. E., J. Appl. Poly. Sci., 1961, 5, 337. 44. Flory, P. J . , "Principles of Polymer Chemistry," 1953, Cornell university Press, Ithaca, New York. 45. Helfand, E. and Tagami, Y., J. Poly. Sci., 1971, B-9, 741. 46. Helfand, E. and Tagami, Y., J. Chem. Phys., 1971, 56, 3592; 1972, 57, 1812. 47. Helfand, E. and Sapse, Ann Marie, J. Chem. Phys., 1975, 62, 1327. 48. Patterson, G. D., Macromolecules, 1974, 7, 220.



202

49. Patterson, G. D., J. Poly. Sci. Phys. Ed., 1975, 13,—. 50. Patterson, G. D., Nishi, T. T. and Wang, T. T., Macromolecules, 1975, 8—. 51. "Block and Graft Co-Polymers," Burke, J. J. and Weiss, V., Editors, 1973, Syracuse University Press, Syracuse, New York. 52. Meyer,

R.

R.,

Polymer,

15,

1974,

137.


53. Douy, Α., Meyer, R., Rossi, J., and Gallot, Β., Molecular Crystals and Liquid Crystals, 1969, 7, 103. 54. Duoy, A. and Gallot, Β., Makromol Chemistry, 1972, 156, 81. 55. Helfand, Ε., and Wasserman, Z., Macromolecules, 1977 and Polymer Preprints, American Chemical Society, March 1977. 56. Linvill, J. G. and Hogan, C. L., Science, 1977, 195, 1107; "Advanced Technology". 57. Abelson, P. H. and Dorfman, Mary, Editors, 1980, 110 117, 132, A.A.A.S., Washington, D. C. 58. Bowden, M. J. and Thompson, L. F., Solid State Technology, 1979, May, 72. 59. Herriott, D. P., Collier, R. J., Alles, D. S. and Stafford, J. W., EEG Trans, on Electron Devices, 1975, Ed. 22, 87. 60. Ueberreiter, Κ., "Diffusion in Polymers," Editors: Crank, J. and Park, G. S., Academic Press, New York, 1968. 61. Brown, J. R. and O'Donnell, J. Η., Macromolecules, 1972, 5, 109. 62. Miller, S. E. and Chynoweth, A. G., Editors, "Optical Fiber Telecommunications," 1979, Academic Press, New York. 63. Hayakawa, R. and Wada, Υ., "Advances in Polymer Science," 3, 1973, 1, Springer, Berlin. 64. Crane, G. R., J. of Appl. Phys., 1975,

.

65. Kawai, H., Jap. J. of Appl. Phys.,

1969, A, 975.

66. Tonelli, RECEIVED

A.

E . , Macromolecules,

1976,

August 4, 1981.


547.

Polymer Science Overview - American Chemical Society

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