1 Introduction: Polymer Modification—Some Problems and Possibilities—Areas in Need of Research CHARLES E. CARRAHER, JR. Department of Chemistry, Wright State University, Dayton, O H 45435
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MINORU TSUDA Laboratory of Physical Chemistry, Chiba University, 1-33, Yayoi, Chiba (280) Japan
The modification of polymers has been practiced since the dawn of mankind with the working of animal hides and natural fibers. In spite of this ancient beginning significant advances are occurring almost daily. The "black art" of polymer modification is increasingly yielding to scientific investigation and as new insights become available, new applications are found for this information - the advances in knowledge and applications coupled. The modification of polymers is interdisciplinary in nature cutting across traditional boundaries of chemistry, biochemistry, medicine, physics, biology and materials science and engineering. Because of this interdisciplinary nature, persons involved with polymer modification should be broadly trained to permit the best application of revealed information. Polymer modifications are intended to impute different, typically desired properties to the new modified material-properties such as enhanced thermal stability; multiphase physical responses; biological resistance, compatibility or degradability; impact response; flexibility; rigidity; etc. Today modifications can be roughly grouped into two categories - a. physical modifications including entanglement and entrapment and radiation induced changes and b. chemical modifications where chemical reactions on the polymer are emphasized. This distinction is often unclear at best. Following is a brief summary of only some of the areas in need of study in the broad area of polymer modification. As signaled within this book, modification through exposure to radiation, (thermal, light and particle) continues to be at the forefront of many areas of polymer modification. A major problem involves use of industrial radiation curing of 0-8412-0540-X/80/47-121-001$05.00/0 © 1980 American Chemical Society In Modification of Polymers; Carraher, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
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c o a t i n g s s u r f a c e s because o f the present p r a c t i c a l l i m i t a t i o n o f depth o f cure p e n e t r a t i o n . T h i s problem was c i t e d i n the 1978 Workshop on Organic Coatings held a t Kent S t a t e U n i v e r s i t y . The problem i s common t o the a p p l i c a t i o n o f a l l i n d u s t r i a l c o a t i n g s . P o t e n t i a l s o l u t i o n s are numerous i n c l u d i n g a. repeatable c o a t i n g s a p p l i c a t i o n (negative f e a t u r e s i n c l u d e time, adhesion o f the separate c o a t s , and i n c r e a s e d energy requirements and equipment housing and c o m p l e x i t y ) ; b. i n c r e a s e d energy o f r a d i a t i o n ( c u r r e n t l y l a r g e l y r u l e d out due to energy, s a f e t y and c o s t c o n s i d e r a t i o n s ) ; c. f o r m u l a t i o n o f polymer mixtures t h a t can be " s e t " with r a d i a t i o n , but which continue to cure on standing by a slower mechanism; and d. a d d i t i o n o f species which can t r a n s f e r "captured" r a d i a t i o n to g r e a t e r depths. Regarding the l a t t e r , polydyes have been s y n t h e s i z e d using Group IVB C p M C l compounds condensed with dyes such as xanthene and 2
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s u l f o n p h t h a l e i n dyes.
The Group IVB C p M C l compounds are known 2
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" u l t r a v i o l e t s i n k s " . By proper c o u p l i n g o f the metal, dye and r a d i a t i o n i t i s p o s s i b l e impact m a t e r i a l impregnated with a polydye with the polydye a c c e p t i n g and r e e m i t t i n g the r a d i a t i o n p e r m i t t i n g g r e a t e r depth o f p e n e t r a t i o n by the e f f e c t s o f r a d i a tion.
A remaining problem a n d o n e where no r e a l widespread s o l u t i o n has even been ( e x p e r i m e n t a l l y ) proposed i s the adequate d e s c r i p t i o n o f molecular weight o f c r o s s l i n k e d m a t e r i a l s and the i n n e r r e l a t i o n s h i p ( s ) o f amount and type o f c r o s s l i n k i n g , polymer molecular weight and p h y s i c a l and chemical c h a r a c t e r i s t i c s . Related to t h i s i s the need t o b e t t e r c o n t r o l extent and l o c a t i o n ( i . e . random, homogeneous, e t c . ) o f m o d i f i c a t i o n s on polymers. Some o f the good NMR work concerning i d e n t i f i c a t i o n o f sequence with copolymers can be u t i l i z e d i n the d e s c r i p t i o n o f many graph and block copolymers. Mass spectrophotometry u t i l i z i n g l a s e r e x c i t a t i o n o f modified polymers may enable a b e t t e r d e s c r i p t i o n o f the a c t u a l framework o f many c r o s s l i n k e d modified m a t e r i a l s s i n c e l a s e r e x c i t a t i o n allows the examination o f both small and l a r g e (to g r e a t e r than 1000 amu) fragments. The c o n s t r u c t i o n o f a powerful, c o n t i n u o u s l y v a r i a b l e wavelength l a s e r i s approaching r e a l i t y . Such a l a s e r could be o f g r e a t use i n t a i l o r i n g polymer m o d i f i c a t i o n s through a c t i v a t i o n o f only s e l e c t e d s i t e s f o r r e a c t i o n . A number o f groups are c u r r e n t l y conducting s e l e c t e d r e a c t i o n s u t i l i z i n g l a s e r
In Modification of Polymers; Carraher, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
1.
CARRAHER
Introduction
to Polymer
Modification
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energy so the needed technology i s becoming a v a i l a b l e .
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While much o f the c u r r e n t and near past research has emphasized m o d i f i c a t i o n o f s y n t h e t i c polymers, i n c r e a s i n g e f f o r t s w i l l undoubtedly focus on the m o d i f i c a t i o n o f regenerable polymers and the blending o f n a t u r a l polymers and n a t u r a l polymers with s y n t h e t i c polymers through b l o c k , g r a f t , e t c . approaches. The need f o r replacements o f o b j e c t s c u r r e n t l y d e r i v e d from nonregenerable m a t e r i a l s (most p l a s t i c s , rubbers, elastomers, metals) with o b j e c t s d e r i v e d from regenerable m a t e r i a l s i s c r i t i c a l and must be c o n t i n u a l l y emphasized i n our research e f f o r t s . I t i s the e d i t o r ' s o p i n i o n t h a t t h i s 1s one o f the f u t u r e areas o f s c i e n c e which o f f e r s the g r e a t e s t l a s t i n g benef i t s to s o c i e t y . T h i s book presents s e v e r a l chapters r e l a t i n g recent advances i n the m o d i f i c a t i o n o f regenerable m a t e r i a l s and many other r e c e n t books and symposia have p o r t i o n s devoted to t h i s t o p i c . Some o f the work r e l a t e d to t o t a l m o d i f i c a t i o n s may be i n time extended to the m o d i f i c a t i o n o f c u r r e n t l y wasted m a t e r i a l s such as l e a v e s , sea weed, flower and weed s t o c k s , corn s t o c k s , g r a s s , e t c . a l l o f which t y p i c a l l y c o n t a i n high degrees o f c e l l u l o s i c m a t e r i a l which when s u i t a b l y s o l u b i l i z e d should r a p i d l y permit s u i t a b l e m o d i f i c a t i o n s to ensue. As an I n t e r e s t i n g s i d e note, paper m i l l workers have been a b l e to i n c r e a s e the amount o f usable " c e l l u l o s i c " m a t e r i a l through e l e c t r o n bombardment or other s u i t a b l e r a d i a t i o n treatment o f the "raw" ground wood presumably through i n i t i a t i o n o f c r o s s l i n k i n g r e a c t i o n s between the c e l l u l o s i c p o r t i o n s and other m a t e r i a l s such as the l i g n i n . I t should be p o s s i b l e to r o u t i n e l y g r a f t onto raw ground wood g i v i n g m a t e r i a l s which can d i r e c t l y be pressed to g i v e a product s u p e r i o r i n thermal s t a b i l i t y , hardness, e t c . to "simple" pressed board, with the g r a f t e d p o r t i o n s c o n t a i n i n g u n i t s to enhance c o l o r , flame retardance, adhesion, e t c . The advent o f computer c h i p s and l a s e r s i g n a l and c o n t r o l l i n g devices w i l l permit more complex m o d i f i c a t i o n s to be c a r r i e d out on an i n d u s t r i a l s c a l e . Another area i n need o f work i s the o n - s i t e g r a f t i n g , attachment o f polymeric m a t e r i a l s on b i o l o g i c a l s i t e s such as p a r t i c u l a r l y badly broken bones where the l e g i s s u r g i c a l l y opened and a polymeric m a t e r i a l c h e m i c a l l y attached a f t e r s u i t able bone a c t i v a t i o n with the polymeric m a t e r i a l degrading a f t e r i t s use p e r i o d i s up. T h i s area i s mentioned only to r e i n f o r c e the n o t i o n t h a t i n t e r d i s c i p l i n a r y team e f f o r t s and polymer chemists with broad t r a i n i n g are needed to make the best use o f
In Modification of Polymers; Carraher, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
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a p p l i c a t i o n s o f polymer m o d i f i c a t i o n s . The area o f d e l i v e r y o f b i o l o g i c a l l y a c t i v e m a t e r i a l s a l s o w i l l i n v o l v e i n great p a r t polymer m o d i f i c a t i o n s . For i n s t a n c e , Gebeleln d e s c r i b e s the i d e a l polymer - f o r good drug d e l i v e r y as being composed o f three parts - one to g i v e the o v e r a l l polymer the d e s i r e d s o l u b i l i t y , the second p a r t c o n t a i n i n g the drug to be d e l i v e r e d and the t h i r d p a r t c o n t a i n i n g chemical u n i t s which w i l l d i r e c t the o v e r a l l m a t e r i a l only to the s i t e where the drug i s to be d e l i v e r e d . I t may be p o s s i b l e to combine s e v e r a l o f these aspects by a j u d i c i o u s c h o i c e o f polymeric u n i t s but p r e s e n t l y more f r u i t f u l approaches Include g r a f t i n g o f d e s i r e d components together forming the needed o v e r a l l polymeric p r o p e r t i e s . As a s i d e comment, r e l a t i v e l y l i t t l e work has been done with the generation o f " d i r e c t i n g groups" and t h i s i s an area where much work i s needed i f the advantages o f polymeric drugs are to be recognized. In summary, much has been done and much remains to be done i n the area o f polymer m o d i f i c a t i o n . S i g n i f i c a n t problems await s o l u t i o n . RECEIVED July 12,
1979.
In Modification of Polymers; Carraher, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
