Contributions of polymer Chemistry to the Plastics and Coating Industries C . S , FULLER Bell Telephone Laboratories, Murray Hill, N . J. zation by Reid and the classical work of Carothers on linear polymers. So in this period during which the Division of Paint, Varnish, and Plastics Chemistry has been in existence there has grown up what amounts t o a new chemistry, which we now know as polymer chemistry. Already wide appreciation of this new force is evident in industry itself, not only in plastics and coatings but in rubber, textiles, and allied industries. Figure 1 is an attempt t o portray this evolution. HE production of synthetic organic polymers today in the A brief tabulation of some of the major technological develUnited States amounts t o about 3 billion pounds annually opments in plastics and coatings is given in Table I. This table ( 9 7 ) . This is about 1570, when calculated on a volume basis, does not pretend to be complete, but is to be regarded as a list of of the total steel production of the country. It represents a suggested items illustrating the advance of these industries. truly huge chemical effort directed toward polymer synthesis. Two facts stand out: the complete invasion of synthetic Furthermore, the rate of growth of this synthetic industry exchemistry into the plastics and coatings fields during this period, ceeds t h a t of any other basic materials industry. and the competitive nature of the developments themselves. Many chemists and chemical engineers have had a part in this These 25 or so years have been a period of tremendous change. major expansion, the scope of which extends into the field of One cannot help but wonder what forces distillcd these particular textiles and rubber. This paper gives a review of recent polymer products out of our researches. The mere listing of developchemistry and the part it has played in industrial progress. I n ments as in Table I provides no measure of the very large amount order to see this in its proper perspective, it is useful to recall of effort put forth, not only by chemical engineers and industrial br icfly some tcchnological developments in the field of polymers as chemists but also by the synthetic chemists and later by polymer ~ c l as l some related contributions of synthetic organic chemistry. chemists, nor does it give a n adequate picture of the variety of form in which each product appears. PROGRESS IN COATINGS AND PLASTICS TECHNOLOGY Synthetic organic Chemistry, broadly interpreted, has been the underlying and pervading theme in all this technical develTwenty-five years ago it would have been difficult to identify opment. Furthermore, it has constituted the bulk of what has a plastics industry, Cellulose chemistry perhaps laid the earliest been called research in this field and forms the main trunk from claim in cciluloid. Hard rubber, too, satisfied the first demands which branch the newer fields of research in polymer chemistry. for rigid plastic moldings. But it was not until the advent of Table I1 summarizes some of these contributions of organic Bakclite and the perfection of the modern injection process that synthesis. what we regard now as the plastics industry really took form. Without doubt, the The idluloseand rubber most striking fact shown iridust.ries slowly arid inby Table I1 is that, many depondent,ly created ti cheinistry arid (eclinoiogy of t,he commercial polyor Ilieir own which form mers today have been unthe basis of present-day, der long and more or less sporadic developnient . Why should there be this lag between Iirst preparInat-ely also me.de imporation and first industrial tant cont,ribut,ions, paruse? Many. of the fact,ors ticu1arl.y t,o our underin this delay were outside standing of gela1,iun phethe chemists’ control. nomena, chiefly through The molding press, for theworlrof Kienle (74)and example, had not yet appeared in 1831 when polyBradley ( 2 7 ) . Synthetic thermoplastics, known styrene was discovered. from the earliest times, In fact, the modern metals began to assume real form industry itself was only after 1930 with the disraking its head. The incovery of internal plasticiFigure 1. Roots of Polymer Chemistry jection press, although T w o facts stand out-the complete invasion of synthetic chemistry into the plastics and coatings field and the competitive nature of the developments during the past 25 years. This paper reviews the contributions of polymer chemistry to the plastics and coating industries and Eabulates major technological developments. Polymer chemistry is of growing importance to industry and its future is bright.
T
259
INDUSTRIAL AND ENGINEERING CHEMISTRY
260 Table I.
Important Industrial Developments in Plastics and Coatings in Past 25 Years
Year" 1924 1926 1927 1928 1929 1930 1932
Development
Yeara 1939
Development Butvl rubber Saran-polyvinylidene chloride plastic? Xelaminc plastics Alkylated urea-formaldehyde coatings Allyl ester plastics Styrene-copolymer plastics Silicones High acetyl cellulose acetate plastics Pentaerythritol dryinv oils I o n exchange resins Buna N Buna S Styrene-polyester casting resin, Polyethylene
1940
Thiokols Cellulose acetate butyrate plastics Vinylite plastics Cyclorubber plastics
1941
h-eonrme
P o l < i t i G n e plastics Ethylcellulose plastics Koroseal Nylon 1936 Vistanex Methylmethacrylate plastics Rosin-maleic alkyds Polyvinyl acetals 1937 Higher polyalcohol alkyds Rubber hydrochloride plastics 1938 Dates are approximate only and refer t o introduction in U. 8 .
1943
1935
a
Vol. 41, No. 2
RISE O F POLYMER CHEMISTRY
The direct contributions of polymer chemistry have been many and the subject has vaPt possibilities for induqtry. For the most part they have bcen scientific contributions. Concepts as well ac: Facts have been laid down, and these are filtering into the industrial fabric a t an accelerating pace. Molecular Structure. At the beginning of the present century, speculation led to the suggestion that rubber and cellulose myere coniposcd of chainlike molecules, but It was not until the late nineteen twentiw that the English group of scientists, Haworth (69), Hirst (64, 68),Irvine (68), Purves (64), and others clinched the organic structure of cellobiose and therebv provided the clew to the real structure of cellulose. Sponsler and Dore (114) in 1926 first showed how the glucose ring units could form into a chain latticelike structure, although the details of their structure were not quite correct. About the same time, Meyer and Mark (95)came
Organosols Plastisols Melamine coatings Cellulose propionate plastics Polyacrylonitrile textiles Acrylonitrile cqpolyiiier plastics Styrenated drying oils
1946
References (26, $8, 7 1 , 7 8 , 89, 97, 184).
conceivedin 1878,reached its useful form only in recent times. The art of mold making had to be developed. Then, too, the chemist did not know how to control the polymerization of styrene adequately in 1831; only recently has h? learned the essential facts. In the earlv he knew nothing- of molecular weight distribu" davs " tion, its control, and its influence on the mcchanical and thermal properties. Coatings chemistry, plastics chemistry, cellulose chemistry, and rubber chemistry have all merged during the past quarter century. A biief chronology of this period, covering items more specifically related to polymer chemistrv, is offered in Table 111,which again makes no claim to completeness. The growth of polymer chemistry IS illustrated also in Figure 2 . Many of the workcrs included in Table I1 have contributed also i 1 Table I11 to the subject matter of polvmer science. Table I11 differs from Table I1 in its emphasis on structure and property determination rather than on synthesis.
-
Tpflnn _.._..
1944
to a similar conclusion. They finally propoyed a 1,4glucosidic structure which is today accepted. A s early as 1922 Staudinger and Fritqchi (118) adduced important evidence that rubber was composed of chain niolecules by converting it into derivatives which still retained their polymer properties. Later with Luthv
Table TI.
Progress in Organic Synthesis of Polymers'a
Derivatives of Ccllulose and Rubber
-4ddition Polymers
Condensation Polymers
Period 1800 t o 1880 Chlorinated rubber. Roxburgh, 1801 Vulcanization of rubber. Goodyear, 1839 Cellulose nitrate. Pelouze, 1838 Cellulose acetate. Schutzenbercer, 1866 Celluloid. Hyatts, Parkes, 1873
Polystyrene. S i n o n , 1831 Polyvinylidene chloride. Regnault 1838 Polyisoprene. Bouchardat, 1875 Polyethyl methacrylate. F i t tig and Paul. 1877 Po!&nyl halides. Baumann,
Polyglyceryl tartrate. Berzeliuc 1847 Hydrdlyaed ethyl silicate. Holrnann, 1860 Linear polyesters. Laurenco, 1863 Phenol-formaldehyde. Bayer. 1872
101"
Polyisobutylene. ButleroT* and Gorianow, 1873 Period 1880 to 1020 Primary acetate. Cross a n d Bevan, 1894 Rubber hydrochloride. Weber, 1900 Secondary acetate. Miles, 1904 Methyl cellulose. Suida, 1905 Ethylcclhilose. Leuchs, Lillienfeld, 1912 Cycloruhber. Harries, 1910 Cellulose- anetate process. Dreyfuss, 1914
Low ethylene polymers. Balsohn, 1880 Pulydimethylbutadicne. Courturier, 1892 Sodium polymerization. > l a t h e m , Harries, Lebedev, 1910 Emulsion polymerization. Bayer & C o . , 1912 Copolvmeriaation. Klatte, 1914 Polyvinyl halide process, Ostroiniden?ky, 1916
Cyclo r u b b e r catalysts. Fisher, !927 Trimethylcellulose. Freudenberg and Braun, 1928 Cellulose dibasic acid esters. Frank and Caro, I930 Cellulose mixed ester process. Clarke aqd Malm, 1932 Cellulose higher f a t t y acid esters. Sakurada et al., 1935
Polymerization inhibitors. Ostromiilensky and Shepard,
IJrea-formaldehvde. Holzer 1884 Linear polyamide. Xaass Polyglyceryl 1899 phthalatr. Smith 1901 Phenol-for.nialdeliyde process, Baekeland, 1906 Polypeptides. Fischrr, 1906 Silicones. Stock, Kipping, lhgen et aZ. 1509 Glyceryl p h h a l a t e (oil modified), Callahan, 1914
Period 1920 to D a t e
Rubber, phenol formaldehyde reartions. Farmer e t a l . , 1943
IYLL
Polvvinyl cliloroacetate. Reid, 1925 Polyvinyl alcohol, Herman a n d Ilaehnel 1927 Polyisohuiylene (high m.w.). Hofmann and Otto, 1928 Polvvinvl acetal. Matheson akd Skirrow, 1929 RIaleic copolymers. T h . Wagner-Jauregg, 1930 Polychloroprene. Carothers e l al. 1531 Styrbne-butadiene copolymer. Bock et al., 1933 Polymerization regulators. Bock et al., 1933 Polvethvlene. F a v c e t t et al., 1934 Polyethylene tetrafluoride. Plunkett, 1941
Urea-formaldehyde catalysb Pollack, 1922 Polyoxymethylenes. Staudinger et al., 1925 Polyethylenetetrasulfide. Patrick 1928 Siiioon'es, film forming. SulIivan, 1930 2- and 3-dimensional polyesters. Xienle and Hovey, 1930 Fiber-formin- polyesters and polyamide:. Carothers et al., 1931 Butylated urea-formaldehydem Ludwig, 1939 Polyurethanes. Bayer, 1940 Pol~~dimetholsiloxanerubber 1944
Examples are intended t o illustrate rather t h a n to serve ar 5 S o claim as t o pompleteness is made. accurate record. References (80,$ 2 , 5'6, 3 9 %68, 79, 87, 1 1 0 ) .
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1949
h\k. Ab,,
Figure
.
\. I
Branches of Polymer Chemistry
261
enon. This eventually led in turn to the concept of molecular networks and t o a n elucidation by Flory (49) of the statistics of gelation in polymers of this kind. Kienle and his eo-workers (76, 7 7 ) in particular have explored the 2,3 reaction and have recently supplied additional quantitat,ive data. Their work shows t h a t intra- as well as interesterification plays a part in these reactions. The condensation polymers did not give immediate clews to the structures of vinyl and diene polymerizations except in a general way. The work of Marvel (88) and his eo-workers went far towards establishing a predominant 1,3 arrangement of substituents for many vinyl polymers. Staudinger and Steinhofer (181) similarly concluded t h a t polystyrene has a 1,3 arrangement of phenyl groups from pyrolysis studies. I n diene polymers and copolymers, the application of ozonization methods, SO successfully used on natural rubber, has yielded useful results (63, 107), particularly in differentiating between 1,2 and 1,4 types of polymerization. Physical methods have also made their contributions. Diffraction methods confirm in general the 1,3 structure of most olefin polymers (19, 48, 99). Kenney (73) showed the similarity between polychloroprene and gutta-percha. X-ray studies furthermore indicate that many chain molecules in the solid are coiled or twisted (7, 19, 5 2 ) . Infrared absorption has provided a measure of the 1,2 and 1,4 types of polymerization in polybutadiene and GR-S (40) and promises t o be a powerful instrument for determining structure (108, 129). Refraction methods too have been useful in the study of GR-S copolymer structures (12).
(120) Staudinger found t h a t truly synthetic polymers like the polyoxymethylenes exhibited properties similar to natural high polymers and was one of the first t o advocate close study of synthetic polymers (217) as models. Simultaneously with the work on polymer synthesis in Germany and England research.of great significance was being done in this country. Publications began t o appear in 1929 by Carothera and his coworkers, who took u p the thread of early work on condensation polymers and Table 111. Important Contributions to Progress in Polymer Science Organic Reaction Kinetics Studies in carried it forward with great brilliance Investigations a n d Solutions Condeyed State (15, 86). It is safe to say that no comPeriod u p t o 1920 parable work has had a greater influence, Empirical formula for rubber. Proposed chain polymerization. Crystalline nature of cellulose, Faraday, 1826 Stobbe ,and Posnjak, ,1909 Nishikawa a n d Ono, 1913 either On the Of industry Or On Levulinic aldehyde from rubber. Degradation a n d solution visZigzag chain structure. Langpolymer science. For the first time a Harries, 1904 cosity. Biltz a n d Berl, 1913 muir, 1917 Urea-forma1dchyde Einhorn and Hamburger structures' 1908 Crystalline nature of silk. Herrational basis for linear polymer formal o g and Jancke, 1920 Glucose from cellulose. osk and Physical properties a n d solution laid down and an unlimited Wilkening, 1910 tion viscosity. Clibbens and series of high polymers of controllable Proposed chain molecule for Ridge, lp20 rubber. Pickles, 1910 Melting point a n d chain length. constitution was made available for study. Phenolic structures. Raschig, Garner et a!., 1926 The condensation kinetics, as Flory (41) Proposed 1912 chain structure for has shown, proved t o be helpfully simple cellulose. Freudenberg, 1921 Period 1920 to D a t e and equations were soon derived for Proof of chain structure of rubUltracentrifuge method. .SvedCrystallinity in stretched rubmolecular weight distributions (41). The ber. Staudinger, 1922 berg, 1925 ber. K s t z 1925 Hydroxyl positions in cellulose. Chain molecule a s a n entity. Chain s t r u c t h e in crystalline conceptsof reaction, based for the most Irvine a n d Hirst, 1928 Staudinger, 1926 cellulose. Sponsler a n d Dore, part on classical organic chemistry, were Mechanism of rubber vuloanizaStaudinger equation. 1930 1926 tion. Meyer and M a r k , 1928 Osmotic method. Herzog a n d Monoclinic cell for cellulose. also simple and easily comprehended. Functionality concept. CarothSpurlin, 1931 M a r k et al., 1927
a, Of work, were provided for extensive study of the properties of polymers in the solid state as dependent on chemical structure and ~onstitutioll~ These model systemsprovided fruitful structures for examining the x-ray structure of chain polymers 48,493 51, 5 2 ) - They also formed the inspiration for a host Of synthetic fiber developments, even contributing to the discovery Of polyethylene by Calling attention to its cold-drawing properties. Before Carothers undertook this basic work on synthetic polymers, Callahan and his co-workers at the General Electric Laboratories (3, 24) had interested themselves in condensation resins for varnish use. Continuing this work Kienle and Hovey (75) were led t o the role of trifunctional alcohols in gelation phenom-
ers, 1929 Copolymer structures. WagnerJauregg, 1930 Urea-formaldehyde structures. Walter and Gewing, 1931 Ring chain equilibria. Carothers et al., 1931 Mechanism of polymerization. Chambers, 1934 Mechanism. Sodium polymerisation. Ziegler et al., 1934 H-bonds in polymers. Huggins, 1937 Structure of vinyl polymers. A!arvel, 1938 Phenol-formaldehyde structures. Zincke et al., 1939 Theory of gelation. Flory, 1941 Proof of free radical initiation. Price a n d Kell, 1941 Hydroxyl reactivity i n cellulose. . Purves et al., 1942
Solubility theory. Br$nsted, 1931. Schuls, 1937 Isothermal distillation method. Ulmann and Hess, 1933 Kinetics of polymerization. Dostsl and Mark, 1935 Kinetics of condensation. Chain transfer theory. Flory, 1936 Solution viscosity equation. Mark 1938 E n t r o p i of mixing. Meyer, 1940. Huggins a n d Flory, 1941. Treloar and Gee, 1942 Copolymerization theory. Jenckel, 1941. Wall, 1941. AIfrey a n d Goldfinger, 1944. Mayo a n d Lewis 1944 Molecular weight ' from light scattering. Debye, 1943 Solution viscosity theory. Debye, 1946. Brinkman, 1947
References (8.9, 83, 66, 84-86,91,94, 10.4, 116).
Macromolecular lattice polyoxymethylenes. Henstengberg et al., 1927 Double orientation. Herzog, 1929 Fringed Micelle theory. Gerngross et al., 1930 Continuous structure theory. Pierce, 1930 Molecular folding in proteins. Astbury and Woods, 1930 Cis-trans structures. Meyer and M a r k , '1930 Kinetic theory of elasticity. Meyer et al. 1931 S ec o n d o r dkr t r a n sit i o n. Jenckeland Ueberreiter, 1938. Boyer a n d Spencer, 1944 Melt viscosity a n d chain length. Flory, 1940 Segment theory of flow. EYring et c l . , 1940. Segment rotation-degree of order. Baker a n d Fuller, 1940 Equation of s t a t e of rubber. G u t h , Flory, Treloar, Wall, 1942 Physical properties a n d chain length. Sookne a n d Harris, 1945 Cross-linking a n d properties. Flory, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
262
Figure 3.
Concepts of Properties of Solid Polvmers Stnudinger and Signer, 1929 K . H . Meyer, 1930 c. Gerngross, Hermann, a n d Ahitz, 1930 d. H. Mark, 1940 a.
b.
Reaction Kinetics and Mechanisms. JYhile the reaction kinetics in condensation polymerization turn out t o be essentially identical to that of ordinary esterification and amide formation (42,76), vinyl and diene polymerizations have been known for some time t o be considerably more complicated. T t is nonestablished that free radicals play the leading role. Considorabk information has becn acquired about t,he way in which chains are initiated and terminated (67, 84)106, 106). The concept of chain transfer, int’roduced by Flory (4W),explained the action of mercaptan “regulators” introduced in Germany t o cmtrol the plasticity of synthetic rubber, ae well as branching and crosslinking reactions. The theory of copolymerization has especially been pushed forward (2, 69, 90, 106: 126). Plausible mechanisms for both free radical and ion-caralyeed polymerizations have been advanced (84,106). Because of its industrial importance the mecha,nism of emulsion polymerization has been actively investigated and evidence adduced that the reaction starts mainly in micelles in the aqueous solution and completes it,self in the polymer particles so formed (68, 98). Considerable detailed work reniaiiis t o be done, however, before these fascinating reactions can be said t o bc understood and controlled. Solution Properties. Staudinger early advocated the idea t h a t chain molecules could exist as the ultimate particles in solution and although his “viscosity law” (119) byas rather crudely applied,
Figure 4.
Vol. 41, No. 2
it has been of very great’ value in stimulating research and in providing the first empirical relation between average rnolccular weight) and solution viscosity. Numerous other empirical equations have sirice been proposed (10, 80, 112) and both Huggins (66) and Debye (34) have attempted t o attack the problem directly. The nature of polymer solutions has also been advanced considerably by a study of the thermody-namics involved. Meyer and Boissonnas (93) were t.he first t o emphasize the large entropy contribution to solution based on the discrepancy in size between the solvent and polymer molecules. Othcr contributions were made by Huggins (65),Flory (44), Gee (63), Gee and Treloar (54),and Alfrey and Doty ( 1 ) . This work has already led to useful data on solubility, swelling, and miscibility (37, 45, 463. The basis of a new absolute method for det,ermining molecular weights of polymers in solutions has been developed by Dcbye (33) through the use of light scattering. h complete test on this niethod has still to be made, but its convenience and thc precision of measurement possible hold out corisiderablc promise. I t is to be expected that, the studies on solutions, besides furnishing useful information on plasticizer coinpalibiliLy and niolecular size distributions, will also furnish valuable data on molecule flexibility and degree of molecular coiling under various conditions (34). The problem of fractionation of polymers from solut.ion has been the subject of a n escellcnt rcview bl- Craig and and Hamnierschlag (29). Properties of Solid Polymers. Four main concepts of the solid state of polymers, all fairly closely related, developed about 1930 and one of these, the continuous structure theory, has evolrcd into what we now regard today as perhaps the most useful picture. Figure 3 reproduces some of these concepts. The idea of polymer solids comprising a macromolecular lattice in \vliich the erid groups form imperfections in the lattice as showri in a grew out, of Hengstengberg’s x-ray work on the polyosymethylenes ( 6 1 ) . Ifeyer (92) and Meyer and Mark (96) advocated the block micelle idea, h, in which they first assumed that t’hc molecules were the length of the niicelles. This picture was proposed for cotton and silk and hleyer intimated that amorphous, presumably noricellulosic or norifibroin, components might occupy the inserinicellar spaces. The fringed micelle (56) of Gerngross, Herrnann, and I b i t e , c, \vas suggested to explain the behavior of grlatin. I t portrayed the ends of the molecules protruding so as to form secondary valence unions with those from neighboring micelles Finally in d is shovn the concept of continuous chairis traversing organized as well as disorganized portions of a fiber. This concept was originally suggested bv Pierce (106) as “patchy crystallization,” but later modified by “Keale (101), Mark (@), Kata (70j, Astbury (4)) and others. This picture probably comes closest t o our present-day ideas of the state of polymer solids. We still do not h a m a complete picture of t’he chain structure
X-Ray Fiber Patterns Taken with Fiber Axis Vertical
L e f t to r i g h t . Polytetrafluoroethylene, polyvinylidene chloride, and polyisobutylene
February 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
organization in solid polymers under different conditions, nor do we have too good an idea of how the chains form into the crystalline regions or how these transform on stretching into fibers. It appears that crystallization proceeds laterally with respect to the chains as in low molecular chain compounds (122). We may imagine spherulitic structures in which the chain molecules weave courses through successive columns of radial growth ($0). Once the idea of the long molecule was established, it became logical to ask how such molecules behave in the solid and how the properties of the solid are related to the size, shape, and chemical nature of the molecules that compose it. Quantitative answers to these questions must obviously wait, but several very important concepts provide helpful guides. One principle which seems more or less obvious is supported by all the work on synthetic polymers-namely, that the properties of high elongation which make plastics “tough” are acquired only after the average chain length of the polymer reaches a certain threshold range (28, 109, 119, 2 1 6 ) . Below that range the properties rapidly approach those characteristic of substances of low molecular weight. Another important tenet is that the electrical and chemical properties are dependent chiefly on the chemical structure of the repeating group alone (111, 127) and are relatively independent of chain length. They are of course dependent on viscosity. To understand the origin of the physical properties of solid polymers, it is necessary to consider the kind of bonding between the various atoms in all directions in space. I n chain polymers, the chain direction provides a continuous line of primary valence bonding representing high rigidity and strength. The other directions are ruled by van der Waals’, dipole and polarization forces which are considerably weaker and operate over a longer range of interatomic distance. These forces also act between substituent atoms along the chains, thus influencing chain flexibility. It is Lhese forces both between and along the chains which are chiefly responsible for the mechanical properties such as modulus, hardness, tensile strength, and elongation of chain polymers (7, 9, 81). The magnitude and the nature of the forces obviously are uniquely determined by the nature of the atoms and the atomic groupings constituting the polymer and the distance they are from each other. If the surfaces of the chains are nonpolar as in polyisobutylene, i,he intermolecular forces are low, so that there is little difficulty for sections of the chain molecules to slide rather easily over one another. Stress a t room temperature causes an unfolding (against some intrachain rcsistance) of the chain molceule. Flow of the entire chain is resisted by the high viscosity or, if cross links are present, by chemical forces. R7e say such a material is “rubberlike.” If instead of methyl groups on the main chain we have chlorine atoms, thus producing polyvinylidene chloride, a totally different situation is brought about. Along the chain r e apparently have yonsiderable repulsion which effectively stiffens the chain. Between the chains, however, there seem to be rather low forces, although because of the C-C1 dipoles they are higher than in polyisobutylene. Both sets of forces and the good regularity which apparently exists in this chain cause polyvinylidene chloride to crystallize readily at temperatures below its melting point. The relatively high value of the melting point (approximately 200” C.) in spite of the moderate interchain forces indicates a rather high amount of rotational entropy in the solid (11,50),. In polyvinylidene chloride as in polyethylene (6) and polyethylenetetrafluoride (57) x-ray studies also favor a high degree of rotational freedom in the solid state (16). The lattices in general transform to hexagonal near the melting point (polyethylenetetrafluoride is hexagonal apparently even a t room temperature). Figure 4 illustrates x-ray fiber patterns of polytetrafluoroethylene, polyvinylidene chloride, and polyisobutylene. I n all the above cases the heat effects are small compared to polymers in which strong intermolecular forces exist such as in the polyamides. Here, although the rotational energy of the
Figure 5.
263
Constant Temperature Bath, Viscometers, and Timers
molecules increases, effecting ultimately a transformation to a hexagonal lattice, layers of dipoles continue to persist up to the melting point when their breakdown causes considerablc absorption of heat (8). Thus in the polyamides the chains, which isolated can be regarded as flexible perhaps at the amide link, are forced by high intermolecular attractions (H-bonding) t o straighten out in the crystallites and thus lose their potentialities for rubberlike behavior in the room temperature range. I n fact, the dipole forces act to quench the chains in disordered configurations if cooling is carried out sufficiently rapidly. Polymers disordered in this way exhibit different mechanical properties than when annealing is allowed to occur (11, 50). The examples treated so far are of polymers capable of crystallizing spontaneously or under stretch. Polystyrene, polymethylmethacrylate, and many other polymers do not form crystallites under any circumstances but nevertxeless .represent chain systems which have a rather high intermolecular attraction a t room temperature. This not only operates t o freeze out the flexibility of the chains, but also limits radically the interchain movements. Consequently these materials are like glass in their room temperature behavior. We see now how two types of texture arise in plastics: the partially microcrystalline and the completely amorphous. T h e n the latter are rubberlike and in addition possess sufficient regularity and chain flexibility, stretching will often bring about crystallite formation. The common origin of all high polymer properties whether like rubber, glass, or plastics is thus revealed. Finally, because the secondary forces are greatly dependent on temperature, it is clear too why the properties of all chain polymers can be made roughly to correspond by altcring temperature. In a recent paper, Mark (85) has given an excellent review bearing on this topic. In closing this inadequate account of solid state properties, more particular emphasis should be laid on the role of segments of molecules in both the crystalline and amorphous types of polymers. Kauzmann and Eyring (7W) were led to the segment concept in order to explain the flow properties. I t is necessary too to account for the convergence of the melting point in polymer series. Finally, segment rotation in crystalline polymers (6, 60), analogous to the rotation of long-chain molecules in low molecular compounds (13, 16, 60, loo), seems to be a characteristic of many chain polymers. This segment behavior, particularly the rotational entropy induced by temperature rise, is of considerable moment in connection with the deformation properties of polymer solids (15).
264
Figure 6.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 41, No. 2
Apparatus for Measuring Percentage Gel, Swelling Volume, and Dilute Solution Viscosity on Single Sample
Rapid strides in the field of polymer science are being made in many directions, so much so that it will press the plastics and coatings chemists hard if they are to make adequate use of the findings. TECHKICAL APPLICATlONS OF POLYMER CHEMISTRY
The proof that' many simple polymer systems can be dealt with quantitatively has stimulat,ed the application to industry of the methods evolved by polymer science. Knovledge of the structure of polymers and of the relation of structure to properties has had a signal influence in guiding new developments in bot,h coatings and plastics. It is becoming encouragingly common to refer to such terms as chain length, degree of crosslinking, molecular weight distribution, intrinsic viscosity, swelling volume, percentage cryst,allinity, and degree of orientation in discussing commercial applications of plastics and coatings materials. It is usual practice also to control the degree of polymerization, the degree of branching, arid the molecular Tteight distribution of many commercial polymers. In most cases only relative measurements are possible but these often serve adequately for control. The future will undoubtedly bring precise methods for the determination of the truly fundamental polymer characteristics. The polymer manufacturer is in the business of producing mixtures of long-chain molecules and it ii just as important that they be controlled with respect to chain length and chain shape as that t,hey be of controlled composition. Because of its sim-. plicitg, dilute solution viscosity a t a fixed low concentration is frequently employed to characterize polymers consisting of linear molecules. Figure 5 shows a setup with constant temperature bath, viscometers, and timers employed a t the Bell Telephone Laboratories to measure relative chain. lengths of polymers (47). Changes resulting from degradative p:.ocesses are readily followed. Very often changes in the chain length of polymers are accompanied by gelat,ion. I t is important therefore that the percentage gel and its swelling volume be determined as well as t,hP dilute solution viscosity of the extracted sol polymer. Figure 6 shows an apparatus developed in connection with the government synthetic rubber research program in which these three measurements can be carried out on a single sample (47). These quantities have a direct relationship to important physical properties
(126). This method is useful also as a means for following polymerization reactions. Figure 7 shows the change of dilute solution viscosity for samples of a styrene-b:itadiene copolymer removed a t various conversions during the course of reaction. The gel point is indicated by ihe vertical line on the curve. To the right of this line the values of the sol show a decided drop because of the preferent,ialremoval of the longer chains by the gel. The interaction of plasticizers and solvents with polymers is now much closer to quantitative treatment as a result of recent research advances. This can be done through application of viscosity, osmotic pressure, or swelling mct,hoda. So far, however, direct application in industry has been limited. The method of light scattering has been successfully applied t o the deterininatiori of t,he particle sixes of latices and relative molecular weights (33) and offers promise of broad use as a tool for polymer charactcrization. Polymcrizat,ion and condensation are the most important chemical processes carried out in the plastica and coatings indurtries. The application of the lunctionality coricept in t h t w reactions is a well known and highly useful practice. The control of terminal viscosity (viscosity stabilization') and of gelation in alkyd resin and nylon manufact,ure are familiar examples. The role of catalysts, promoters, and modifiers in vinyl and diene polymerization likewise is becoming better understood. Co: polymerization in particular is nom a mort important industrial process. The underlying theory for it has been laid down only in the past few years but has already been of great assistance in the determination of the specific rates of reaction of the individual comonomers ($7, 90). The field of application of physical methuds to plast,ios arid coatings is so active that only the briefest mention can be made. X-rays, infrared absorption, ultraviolet absorption, sound absorption, and velocity measurements find daily use in detcrmining a variety of polymer features. Molecular oricntation and strain in molded plastics have yielded t o detection and measurement (6, 14). The percentage crystallinity can likewise be estimated t,o advantage, as it plays a role in fixing physical properties. Elastic modulus and viscosity data are provided b> the ingenious application of modern sound generation and measuring techniques (35). Finally, ult,raviolet absorption has been of great utility in determining the degree of c,onjuy:ition of raw materials for coatings.
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1949
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Figure 7.
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Change of Intrinsic Viscosity of GR-S with Per Cent Conversion
With the further development of the methods of polymer chemistry, it seems certain that still more notable progress will be made in dealing with plastics and coatings materials. Nowhere could one find more complicated organic products t o organize. Yet we only have t o look back t o see what can be accomplished. The evaluation of the performance of these products has always been a controversial topic and much effort has gone into it. Unfortunately much “testing” in the past has been of little use because too little knowledge of these complicated systems existed. We know today that identical compositions can exist in different physical states as a result of fabricating processes and have learned t o make due allowance for it. Our evaluation programs can be greatly simplified and improved in the light of present knowledge.
265
ment of polymers from diisocyanates and hydroxyl-containing compounds t o provide fiber-forming plastics (polyurethanes) and adhesives (Desmodurs) has so faryeceived little notice in this country. It seems only a matter of time, however, before the excellent properties of these substances are made use of. Their low water absorption in particular as compared to the polyamides makes them of interest in electrical applications. The continued development of styrene-polyester liquid casting materials in the molding, laminating, adhesives, and finishing fields since the war (97)is another example of the vitality of the synthetic approach. In this instance the basic reactions have been known for some time but adaptation and control of the materials to industrial use remain t o be completed. The ability of synthetic chemistry to continue to bring forth new and interesting substances is therefore by no means exhausted. Many more examples including the silicones and acrylonitrile copolymers could be mentioned. The broad principles of structure, however, have now been laid down and future work will consist largely of variations of existing types. CONCLUSION
Polymer chemistry is of growing importance to industry. Future products will be better controlled and better in performance. They will be sold on the basis of sound technical representations. Already many companies have established reputations in this respect by publishing reliable bulletins about their products. The chemists who have contributed to this rationalization in industries, as complex from the chemical standpoint as are the coatings and plastics industries, deserve the highest commendation. LITERATURE CITED
(1) Alfrey and Doty, J . Chem. Phys., 13, 77 (1945). (2) Alfrev and Goldfinrzer. Ibid.. 12. 205- (1944). (35 Arsek, W. C., U. Patent 1,098,777(1914). (4) Astbury, W. T., Trans. Faraday Soc., 29, 204 (1933). (5) Baker, W. O., “Advancing Fronts in Chemistry,” ed. by Twiss, I
FUTURE OF POLYMER SYNTHESIS
One cannot help but wonder on looking over our progress in synthetic polymer chemistry, as illustrated in part by Table 11, whether we have not exhausted most of the existing possibilities. T h a t this is not true is evidenced by the recent appearance of several novel polymer-forming substances both in this country and abroad. A recent treatment of new polymers has been provided by Mark (83). In Germany a n interesting development is the use of ethyleneimine in conjunction with diisocyanates to give compounds capable of coupling under heat (108). Hexamethylene diisocyanate and ethyleneimine, for example, react to give a compound melting at 96’ C. which readily polymerizes to a tough transparent plastic in thin layers.
0
E
HzC H 1)N - - N - (CH2)e H,C/ tough, infusible polymer
0
- E - !! - N-& Sons, 1943. Hanford and Joyce, J . Am. Chem. SOC.,68, 2082 (1946). Harkins, W. D., J . Chem. Phys., 13, 381 (1945); 14, 47 (1946). Haworth, W.N., H e h . Chim.Acta, 11, 534 (1928). Hendricks, S. B., N u t w e , 126, 167 (1930). Henstengberg, J., Ann. Phys., 84, 245 (1927); Z . phus. Chem., 126,425 (1927). lieuser, Emil, “Chemistry of Cellulose,” New York, John Wiley &Sons, 1944. Hill, Lewis, and Sinionsen, Trans. Furadag SOC.,35, 1067, 1073, (1939). Hirst and Purves, J . Chem. Soc., 123, 1352 (1923). Huggins, & L., I. Ann. .\7.Y. Acad. Sci., 43, 1 (1942). Huggins, M. L., J . Phys. Chem., 42,911 (1938) : 43,439 (1939). Hulburt, Harman, Tobolsky, and Eyring, Ann. N . Y . Acad. Sci., 44, 371 (1943). Irvine and Hirst, J . Chem. Soc., 123, 518 (1923). Jenckel, E., 2.phys. Chem., 190A, 24 (1941). Katz, J. R., Trans. Faraday Soc., 26, 236 (1933). Kausch, Oskar, “Handbuch der kunstlichen plastischen Massnn.” Miinich. 6 . F. Lehmann. 1931. - - - .., . -- . (72) Kauzmann and Ejrlng, J . Am. Chem SOC.,62, 3113 (1940). (73) Kenney, A. W., I b i d , 53, 4207 (1931). (74) Kienle, R. H., J . SOC. Chem. Znd., 55, 2291‘ (1936). (75) Kienle and Hovey, J . Am. Chem. Soc., 51, 509 (1929); 52, 3636 (1930). (76) Kienle, van der Meulen, and Petke, Ihid., 61, 2258, 2268 (1939). (77) Kienle and Petke, Ibid , 62, 1053 (1940); 63, 481 (1941). (78) Krumbhaai, William, “Coating and Ink Resins,” Xew York, Reinhold Publishing Corp., 1947. I__
~
Vol. 41, No. 2
Marchionna, Frederick, “Butalastio Polymers,” New York, Reinhold Publishing Corp., 1946. Mark, H., “Der feste KBrper,” p. 103, Hirzel, Leipaig, 1938. Mark, H., IXD.ENG.C m n . , 34, 1343 (1942). Mark, H., Trans. Faraday SOC.,26, 234 (1933). lhid., 43, 447 (1947). Mark and Raff, “High Polynieric Reactions,” Sew York, Interscience Publishers, 1941. Mark, H., and Whitby, G. S., “bdvances in Colloid Sc,iences,” Vols. I and 11,Interscience Publishers, 1942, 1946 Mark, H., and Whitby, G. S., “Collected Works of W. H. Carothers,” New York, Interscience Publishers, 1940. Marsh, J. T., and Wood, F. C., “Introduction t o Chemistry of Cellulose,” London, Chapman & Hall, 194Q. Marvel, C. S., “Frontiers in Chemistry,” T‘ol. I, p. 219, New York, Interscience Publishers, 1943. Mattiello, J. J., “Protective and Decorative Coatings,” Vol. 111, New York, John Wiley & Sons, 1943. Mayo and Lewis, J . Am. Ch.e?n.Soc., 66, 1594 (1944). Meyer, K. H., “High Polymeric Substances,” Interscience Publishers, 1942. e n ,736 (1928) ; Kolloid-Z., Meyer, K. H.. i ~ . a t u r ~ i s s e n s c h a ~ ~17, 53, 13 (1930). Meyer and Boissonnas, Helv. Chim. Acta, 23, 430 (1940). hleyer, K. H., and Mark, H., “Aufbau der hochpolymereii,“ 1930. RIeyer and Mark, Ber., 61, 593 (1928). Ibid.. 62,1933 (1928). Modern Plastics Encyclopedia, Yol. I, Plastics Catalogue C‘01.p.. 1947. Montroll, E. W., J . Chem. Phys., 13, 337 (1945). 63,2828 (1941). Mooney, R. C. L., J . Am. Chem. SOC., Mtiller, A . , Proc. Roy. SOC.(London), 127A, 417 (1930). Neale, S. hf., Trans. Faraday SOC.,29, 233 (1933). Sorrish and Brookman, Proc. Roy. SOC.(London), 171A, 147 (1939). Office of Publication Board P. B. Rept. 46961, Sci. Ind. Iteports, 1947. Ott, Emil, “Cellulose and Cellulose Derivatives,” Vol. V, New York, Interscience Publishers, 1943. Pieroe, F. T., Trans. Faraday SOC.,26,809 (1930),29,50 (1933) Price, C. C., Ann. N. Y .Acad. Sci., 44, 351 (1943). Rabjohn, Bryan, Inskeep, Johnson, and Lawson, J . Am. Chem. Soc., 69,314 (1947). Richards and Thompson, J . Chenr. Soc., 1947, 1260. Rocha, KoZZoid-Beihefte, 30, 230 (1930). Rohrs, W., Staudinger, H., and Vieweg, R., “Fortschritte der Chemie, Physik, und Technik der makromolecularen Stoffe, Vols. I and 11, Munich, J. F. Lehmann, 1939. Sakurada and Lee, Kolloid-Z., 82, 67 (1938). Schulz and Blaschke, J . p r a k t . Chem., 158, 130 (1941). Sockne and Harris, IKD.EKG.CHEN.,37, 478 (1945). Sponsler and Dore, Cotloid S ~ j m p o s i w nMonograph, 4, 174 (1926) Spurlin, H. M., IND. ENGICHEM.,30, 538 (1938). Staudinger, H., “Aufbau der hochmolekularen organischen Verbindungen, Kautschuk und Cellulose, in Sinne der Kekule’schen Strukturlehre,” Berlin, Hirschwaldsche Buchhandlung, 1932. (117) Staudinger, H.. Ber., 59, 3019 (1926). (118) Staudinger and Fritschi, Helv. Chim. Acta. 5, 785 (i922). (119) Staudinger and Heuer, Ber., 59, 3031 (1926). (120) Staudinger and Ltlthy, Hela. Chim. Acta, 8, 41 (1925). (121) Staudinger and Steinhofer, Ann., 517,35 (1935). (122) Thiessen and Spychalski, Z. phys. Chem., ( A ) 156, 309, 405 (1931). (123) Thompson and Torkington, Proc. Roy SOC. (London), 174A, 3, 21 (1945); Trans. Faraday SOC.,41, 246 (1945). (124) Wakeman, R. L.,“Chemistry of Commercial Plastics,” New York, Reinhold Publishing Corp., 1947. (125) Wall, F. T., J . Am. Chem. Soc., 63, 186% (1941): 66, 2050 (1944). (126) White, L. hf., et al., IND.ENC.CHEM.,37, 770 (1945). (127) Yager and Baker, J. Am. Chem. SOC.,64,2164, 2171 (1942). a
RECEIVED May 24, 1948.
COURTESY THE PORT
OF NEW YORK
AUTHORITY
Application of Alkyd Resin on Exposed Equipment Provides Long-Term Protection against Weather
