Applied Polymer Science - American Chemical Society

21

Engineering Thermoplastics: Chemistry a n d Technology DANIEL W. FOX and EDWARD N. PETERS

Downloaded by TUFTS UNIV on November 22, 2016 | http://pubs.acs.org Publication Date: September 25, 1985 | doi: 10.1021/bk-1985-0285.ch021

General Electric Company, Pittsfield, MA 01201

Nylon Polyacetals Polycarbonates Other Polycarbonates and Related Polymers Polyestercarbonates Polyarylates Tetramethylbisphenol A Polycarbonate Phenylene Ether-Based Resins Polysulfones Thermoplastic Polyesters Poly(phenylene sulfide) Polyetherimide Blends and Alloys Conclusion

Engineering polymers comprise a special, high-performance segment of synthetic plastic materials that offer premium properties. When properly formulated, they may be shaped into mechanically functional, semiprecision parts or structural components. The term "mechanically functional" implies that the parts will continue to function even i f they are subjected to factors such as mechanical stress, impact, flexure, vibration, sliding friction, temperature extremes, and hostile environments. As substitutes for metal in the construction of mechanical apparatus, engineering plastics offer advantages such as corrosion resistance, transparency, lightness, self-lubrication, and economy in fabricating and decorating. Replacement of metals by plastic is favored as the physical properties and operating temperature ranges of plastics improve and the cost of metals and their fabrication increases. Plastics applications in transportation, a major growth opportunity, have been greatly accelerated by the current awareness of the interplay of vehicle weight and fuel requirements. 0097 6156/85/0285^0495$06.00/0 © 1985 American Chemical Society

Tess and Poehlein; Applied Polymer Science ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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applied polymer science

The ability to replace metal in many areas has resulted in tremendous growth in engineering thermoplastics. The consumption of engineering plastics increased from 10 million to more than 1 billion lbs from 1953 to 1982. Engineering polymers are the fastest growing segment of the plastics industry with an anticipated growth rate ranging from 12 to 15%. This chapter focuses on the development of engineering thermoplastics during the past 30 years.


Nylon Nylon, the first commercial thermoplastic engineering polymer, is the prototype for the whole family of polyamides. Nylon 6,6 began at Du Pont with the polymer experiments of Wallace Carothers in 1928, and made its commercial debut as a fiber in 1938 and as a molding compound in 1941. By 1953, 10 million lbs of nylon 6,6 molding compound represented the entire annual engineering plastic sales. Nylon was a new concept in plastics for several reasons (_1). Because it was crystalline, nylon underwent a sharp transition from solid to melt, thus it had a relatively high service temperature. A combination of toughness, r i g i d i t y , and "lubrication-free" performance peculiarly suited it to mechanical bearing and gear applications. Nylon acquired the reputation of a quality material by showing that a thermoplastic could be tough, as well as stiff, and do jobs better than metals in some cases. This performance gave nylon the label "an engineering thermoplastic." Nylon 6,6, derived from the condensation of a six-carbon diamine and a six-carbon dibasic acid and normally chain terminated with monofunctional reactants, presented some unusual characteristics (Figure 1) (2). The crystallinity and polarity of the molecule permitted dipole association that conveyed on relatively low molecular weight polymers the properties normally associated with much higher molecular weight amorphous polymers. At its crystalline melting point the polymer collapsed into a rather low-viscosity fluid in a manner resembling the melting of paraffin wax. It lacked the typical familiar broad thermal plastic range that is normally encountered in going from a glassy solid to a softer solid to a very viscous taffy stage. This factor led to some complications in molding because very close tolerances were required in mold construction, and very precise temperature and pressure monitoring was necessary to prevent flash or inadvertent leaking of the mobile melt. Early molders of nylon were highly skilled—they had to be because the industry was young. Nylons based on ω-aminocarboxylie acids, although briefly investigated by Carothers, were commercialized first in Germany around 1939 (Figure 1). Of particular interest to the plastic industry is nylon 6 (based on caprolactam), which became available in 1946 in Europe. It was initially introduced to the United States in 1954 by A l l i e d Chemical Company for fiber purposes. Polycaprolactam is crystalline, has a lower melting point than nylon 6,6, and has been successfully applied as a molding compound. The key features of nylon are fast crystallization, which means fast mold cycling; high degree of solvent resistance; toughness;


21.

FOX AND PETERS

Engineering Thermoplastics

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l u b r i c i t y ; f a t i g u e r e s i s t a n c e ; and e x c e l l e n t flexural-mechanical p r o p e r t i e s t h a t vary w i t h degree of water p l a s t i c i z a t i o n . Deficiencies include a tendency to creep under applied load. The most important t e c h n o l o g i c a l breakthroughs of the past decade are m i n e r a l - f i l l i n g technology, which r e s u l t s i n high modulus and high-temperature d i m e n s i o n a l s t a b i l i t y , f i r e r e t a r d a n c y , and impact modification as exemplified by Du Pont's ST technology (super tough n y l o n compounds d e r i v e d from patented impact m o d i f i c a t i o n technology). Many d i f f e r e n t v a r i e t i e s of polyamides have been produced by v a r y i n g the monomer c o m p o s i t i o n . V a r i a t i o n s i n c l u d e n y l o n 6,9; n y l o n 6,10; and n y l o n 6,12 (made from the 9 - , 10-, and 12-carbon d i c a r b o x y l i c acids, r e s p e c t i v e l y ) ; and nylon 11 and nylon 12 ( v i a the self-condensation of 11-aminoundecanoic acid and l a u r y l l a c t a m , respectively). These s p e c i a l t y n y l o n s e x h i b i t lower moisture absorption—only one-third or one-fourth that of nylon 6 or nylon 6,6. When unsymmetrical monomers are used, the normal a b i l i t y of the polymer to c r y s t a l l i z e can be d i s r u p t e d ; amorphous ( t r a n s p a r e n t ) nylons can then be formed. For example, the polyamide prepared from the condensation of terephthalic acid with a mixture of 2,2,4- and 2,4,4-trimethylhexamethylenediamines (Figure 2) was developed at W. R. Grace and Company, and l a t e r produced under l i c e n s e by Dynamit Nobel AG. This polyamide i s s o l d under the tradename Trogamid T. Another amorphous nylon was developed at Emser Werke AG and i s based on a l i p h a t i c , as w e l l as c y c l o a l i p h a t i c , amines and t e r e p h t h a l i c a c i d . I t i s marketed i n Europe under the tradename Grilamid 55 and u n t i l r e c e n t l y was d i s t r i b u t e d i n the United States by Union Carbide under the tradename Amidel. These amorphous nylons are not as tough as n y l o n 6 or 6,6, but they do o f f e r transparency and good chemical resistance i n some environments. Nylons prepared from aromatic diamines and diacids (aramids) can l e a d to very h i g h - h e a t amorphous n y l o n s such as Du P o n t s Nomex materials [polyOn-phenyleneisophthalamide)], or the h i g h l y oriented c r y s t a l l i n e K e v l a r f i b e r s [poly(p-phenyleneterephthalamide)] derived from l i q u i d - c r y s t a l l i n e technology. Both of these aramids are s o l d as f i b e r s . They have e x c e l l e n t inherent flame-retardant properties, and K e v l a r e x h i b i t s a very high modulus. f

Polyacetals A f t e r n y l o n , the next e n g i n e e r i n g polymers to be c o m m e r c i a l l y i n t r o d u c e d were p o l y a c e t a l s (_3). The b a s i c polyformaldehyde s t r u c t u r e was e x p l o r e d r a t h e r t h o r o u g h l y by H. Staudinger i n the l a t e 1920s and e a r l y 1930s, but he f a i l e d to produce a s u f f i c i e n t l y high molecular weight polymer with r e q u i s i t e thermal s t a b i l i t y to permit p r o c e s s i n g (4). P u r e f o r m a l d e h y d e c o u l d be r e a d i l y p o l y m e r i z e d , but the polymer e q u a l l y , r e a d i l y , spontaneously depolymerized—unzipped. In 1947, Du Pont began a development program on the p o l y m e r i zation and s t a b i l i z a t i o n of formaldehyde and i t s polymer. Twelve years l a t e r , Du Pont brought the u n z i p p i n g tendency under c o n t r o l w i t h p r o p r i e t a r y s t a b i l i z e r s and c o m m e r c i a l l y announced D e l r i n p o l y a c e t a l polymer ( F i g u r e 3). The key to the s t a b i l i z a t i o n of polyformaldehyde r e s i n s appears to be a b l o c k i n g of the t e r m i n a l



FOX AND PETERS

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hydroxyl (OH) groups that p a r t i c i p a t e i n , or t r i g g e r , an unzipping a c t i o n . The h y d r o x y l groups may a p p a r e n t l y be b l o c k e d by p o s t e t h e r i f i c a t i o n or e s t e r i f i c a t i o n . Celanese j o i n e d Du Pont i n the market w i t h t h e i r p r o p r i e t a r y C e l c o n p o l y a c e t a l polymer w i t h i n a year ( F i g u r e 3). Celanese managed to o b t a i n b a s i c patent coverage, d e s p i t e Du Pont's p r i o r f i l i n g , on the b a s i s of a copolymer v a r i a t i o n t h a t l e d to an enhanced s t a b i l i z a t i o n against thermal depolymerization Both Celanese and Du Pont aimed t h e i r products d i r e c t l y at metal replacement. Items such as plumbing hardware, pumps, gears, and b e a r i n g s were immediate t a r g e t s . In many r e s p e c t s , the a c e t a l s resemble nylons. They are h i g h l y c r y s t a l l i n e , r i g i d , and c o l d - f l o w r e s i s t a n t , solvent r e s i s t a n t , fatigue r e s i s t a n t , mechanically tough and s t r o n g , and s e l f - l u b r i c a t i n g . They a l s o tend to absorb l e s s water and are not p l a s t i c i z e d by water to the same degree as the polyamides. Rapid c r y s t a l l i z a t i o n of a c e t a l s from the melt contributes to fast mold c y c l e s . C r y s t a l l i z a t i o n a l s o causes a s i g n i f i c a n t amount of mold s h r i n k a g e . Thus, i t i s necessary to compensate i n mold design for dimensional changes that occur during the transformation from a hot, low-density, amorphous melt to a more dense, c r y s t a l l i n e solid. P o l y a c e t a l s are used m a i n l y i n l i q u i d h a n d l i n g (plumbing) equipment and m i s c e l l a n e o u s hardware. With the e x c e p t i o n of an enhanced a b i l i t y to m e t a l l i z e for hardware appearance, few t e c h n i c a l advancements have been announced. Key deficiencies of p o l y a c e t a l s are a tendency to thermally unzip and an e s s e n t i a l l y unmodifiable flammability. Polycarbonates The aromatic polycarbonates were the next engineering polymers to be i n t r o d u c e d (5, 6^). Researchers at Bayer AG (Germany) and G e n e r a l E l e c t r i c Company i n d e p e n d e n t l y discovered the same unique, supertough, heat-resistant, transparent, and amorphous polymer i n 1953. When t h e companies became aware o f each o t h e r s a c t i v i t i e s , agreements were reached t h a t enabled both p a r t i e s to c o n t i n u e independent c o m m e r c i a l i z a t i o n a c t i v i t i e s without concern f o r possible subsequent adverse patent findings. The General E l e c t r i c Company's p o l y c a r b o n a t e c a l l e d Lexan was introduced i n the United S t a t e s i n 1959 at about the same time as the p o l y a c e t a l s , and a commercial plant was brought on stream i n 1960. P o l y c a r b o n a t e s of numerous b i s p h e n o l s have been e x t e n s i v e l y studied. However, most commercial polycarbonates are derived from b i s p h e n o l A. At f i r s t , b o t h d i r e c t - r e a c t i o n and m e l t t r a n s e s t e r i f i c a t i o n processes were employed (Figure 4). In d i r e c t r e a c t i o n processes, phosgene r e a c t s d i r e c t l y w i t h b i s p h e n o l A to produce a polymer i n a s o l u t i o n . In t r a n s e s t e r i f i c a t i o n , phosgene i s f i r s t reacted with phenol to produce diphenyl carbonate, which i n t u r n r e a c t s w i t h b i s p h e n o l A to regenerate phenol f o r r e c y c l e and molten, s o l v e n t - f r e e polymer. T r a n s e s t e r i f i c a t i o n i s reported to be the l e a s t expensive route. I t was phased out, however, because of i t s u n s u i t a b i l i t y to produce a wide range of products.



Figure 4 . Polycarbonates


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Today, most p o l y c a r b o n a t e i s produced by an i n t e r f a c i a l adapt a t i o n of the r e a c t i o n i n e q u a t i o n 4 (_7). The b i s p h e n o l p l u s 1-3 mol% monofunctional p h e n o l , which c o n t r o l s m o l e c u l a r weight, i s d i s s o l v e d or s l u r r i e d i n aqueous sodium h y d r o x i d e ; methylene c h l o r i d e i s added as a polymer s o l v e n t , a t e r t i a r y amine i s added as a c a t a l y s t , and phosgene gas i s d i s p e r s e d i n the r a p i d l y s t i r r e d mixture. A d d i t i o n a l caustic s o l u t i o n i s added as needed to maintain b a s i c i t y . The growing polymer d i s s o l v e s i n the methylene c h l o r i d e , and the phenolic content of the aqueous phase diminishes. The p o l y c a r b o n a t e s do not c r y s t a l l i z e r e a d i l y . They are e s s e n t i a l l y glassy or amorphous with unusually high softening points f o r g l a s s y amorphous polymers. The g l a s s t r a n s i t i o n temperature (T ) of these polymers approaches 150 °C, and they have some mechanical s t r e n g t h or i n t e g r i t y up to t h i s temperature. At temperatures below 100 °C they e x h i b i t very l i t t l e creep. Thermaluse properties of amorphous polymers are r e l a t e d to t h e i r T values, whereas thermal-use properties of c r y s t a l l i n e polymers t§nd to be more r e l a t e d to c r y s t a l melting points. The polycarbonates, l i k e the nylons and a c e t a l s , were directed toward metal replacement a p p l i c a t i o n s . Transparency gave them another dimension—an e a r l y a p p l i c a t i o n was wing l i g h t s f o r supersonic m i l i t a r y a i r c r a f t . Skin temperatures were becoming hot enough to c u r l the a c r y l i c s they were r e p l a c i n g . T h e i r toughness over a very wide temperature range l e d to a p p l i c a t i o n s from nonbreakable windows and auto t a i l l i g h t s to boat and pump i m p e l l e r s , food m a c h i n e r y p a r t s , and a s t r o n a u t h e l m e t s . Inasmuch as polycarbonates are polyesters, they do have some s u s c e p t i b i l i t y to attack by bases and high-temperature moisture. They are s o l u b l e i n a v a r i e t y of organic s o l v e n t s . G l a s s f i b e r - f i l l e d versions of polycarbonates are a v a i l a b l e , and t h i s combination i s p a r t i c u l a r l y w e l l suited to compete with metal parts. As i n the case of other semiamorphous polymers, g l a s s acts as a s t i f f e n i n g and strengthening agent but does not r a i s e operating temperatures s i g n i f i c a n t l y . In c r y s t a l l i n e polymers, f i l l e r s tend to a c t as a pseudo c r o s s - l i n k or c r u t c h to b r i d g e the s o f t , amorphous r e g i o n s t h a t have T -dependent p r o p e r t i e s , thereby permitting the p l a s t i c to maintain s t r u c t u r a l i n t e g r i t y up to i t s c r y s t a l l i n e m e l t i n g p o i n t . Without f i l l e r , c r y s t a l l i n e polymers tend to creep under s t a t i c l o a d at r e l a t i v e l y low temperatures because t h e i r T values are g e n e r a l l y comparatively low. Recent advances i n polycarbonates include further enhancement of n o r m a l l y good f i r e r e s i s t a n c e ; c o l o r e l i m i n a t i o n (an improvement approaching glass) and development of scratch-resistant coatings for g l a z i n g a p p l i c a t i o n s ; branched material for blow-molding b o t t l e s ; optimization of s t r u c t u r a l foam molding and compounds; s e l e c t i v e c o p o l y m e r i z a t i o n ; and development of many d i f f e r e n t commercial polyblends. Other Polycarbonates and Related Polymers The e a r l y polycarbonate syntheses that were practiced enabled f a c i l e i n c o r p o r a t i o n of aromatic c a r b o x y l i c a c i d s i n the polymers to produce c o p o l y e s t e r c a r b o n a t e s . Subsequently, a wide range of polymers v a r y i n g from 100% p o l y c a r b o n a t e to 100% p o l y e s t e r was produced. The trouble with most of these e a r l y product v a r i a t i o n s ,


21.

FOX AND PETERS


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e s p e c i a l l y those comprised of a l l - a r o m a t i c polyesters, was the very high melt v i s c o s i t y that n e c e s s i t a t e d very h i g h p r o c e s s i n g temperatures. The p l a s t i c f a b r i c a t o r s were not prepared to cope w i t h p o l y c a r b o n a t e p r o c e s s i n g when t h e p o l y c a r b o n a t e s were introduced, and they c e r t a i n l y did not need even tougher problems. S i n c e then advances i n t e c h n o l o g y and equipment have made the p r o c e s s i n g of such higher temperature polymers f e a s i b l e . Recent a c t i v i t y i n t h i s area has ranged from the copolyestercarbonates to aromatic polyesters. Polyestercarbonates. G e n e r a l E l e c t r i c Company c o m m e r c i a l l y introduced copolyestercarbonates i n 1981. These copolymers provide the outstanding balance of t e n s i l e , f l e x u r a l , and impact properties inherent i n bisphenol A polycarbonate resins while increasing the heat-deflection temperature to greater than 160 °C. These polymers were designed to b r i d g e the thermal performance gap between p o l y c a r b o n a t e and o t h e r h i g h - p e r f o r m a n c e m a t e r i a l s such as polysulfone and a l l - a r o m a t i c p o l y e s t e r s . Potential applications include s t r u c t u r a l and o p t i c a l components i n l i g h t i n g , appliances, housewares, and s p e c i a l t y a p p l i c a t i o n s r e q u i r i n g higher heat resistance or a combination of c l a r i t y and heat resistance. P o l y a r y l a t e s . The s o - c a l l e d p o l y a r y l a t e s are a c l a s s of aromatic p o l y e s t e r s . They are prepared from b i s p h e n o l s and d i c a r b o x y l i c a c i d s . The f i r s t c o m m e r c i a l l y a v a i l a b l e p o l y a r y l a t e was the U polymer of U n i t i k a L t d . (Japan). T h i s m a t e r i a l i s marketed i n the U n i t e d S t a t e s by Union Carbide as A r d e l . Bayer AG l i k e w i s e has introduced a bisphenol-A based p o l y a r y l a t e designated APE polymer. The basic U-polymer i s derived from the reaction of bisphenol A and a mixture of terephthaloyl and i s o p h t h a l o y l d i c h l o r i d e s i n the molar r a t i o 2:1:1 (Figure 5). Hooker Chemical and P l a s t i c s introduced and l a t e r withdrew a s i m i l a r p o l y a r y l a t e Durel that was prepared by the t r a n s e s t e r i f i c a t i o n r e a c t i o n o f d i p h e n y l i s o p h t h a l a t e s and terephthalates with bisphenol A. The p o l y a r y l a t e s are transparent and, l i k e polycarbonates, have high toughness and s i m i l a r mechanical properties. Being amorphous polymers l i k e p o l y c a r b o n a t e s , the p o l y a r y l a t e s are susceptible to stress cracking, p a r t i c u l a r l y from aromatic hydrocarbons, ketones, and e s t e r s . However, the thermal properties, p a r t i c u l a r l y continuous-use temperature range and heatd e f l e c t i o n temperature, are h i g h e r . The UV r e s i s t a n c e o f p o l y a r y l a t e s i s reported to be e x c e l l e n t . Ardel molding conditions are s i m i l a r to those employed f o r p o l y s u l f o n e , except t h a t p o l y a r y l a t e s r e q u i r e a 25-30 °F higher temperature. Suggested a p p l i c a t i o n s are i n e l e c t r o n i c and e l e c t r i c a l hardware, t i n t e d g l a z i n g , s o l a r energy, mine-safety d e v i c e s , and t r a n s p o r t a t i o n components. Tetramethylbisphenol A Polycarbonate. A new polycarbonate has been i n t r o d u c e d i n Europe by Bayer AG ( F i g u r e 6). I t i s based on t e t r a m e t h y l b i s p h e n o l A (TMBPA). The monomer i s produced by c o n densing two molecules of 2,6-dimethylphenol, which i s the monomer f o r General E l e c t r i c ' s p o l y ( 2 , 6 - d i m e t h y 1 - 1 , A - p h e n y l e n e e t h e r ) polymers, with acetone. The polycarbonate from tetramethylbisphenol A resembles the dimethylphenylene ether polymers i n t h e i r unusually h i g h T :207 °C f o r the p o l y c a r b o n a t e and 215 °C for the p o l y e t h e r .


504


Both polymers have e x c e l l e n t h y d r o l y t i c s t a b i l i t y — o n e because i t i s a polyether and the other because i t s t e r i c a l l y hinders h y d r o l y t i c a c t i o n . The p o l y c a r b o n a t e , l i k e the p o l y e t h e r , i s r e p o r t e d to be compatible with polystyrene. The high T would suggest dimensional s t a b i l i t y and u t i l i t y at very h i g h temperatures, but t h e r m a l o x i d a t i v e l i m i t a t i o n s w i l l p r o b a b l y f a v o r b l e n d a p p l i c a t i o n s at moderately high continuous-use temperatures. g

Phenylene Ether-Based Resins In 1956, A. Hay of G e n e r a l E l e c t r i c d i s c o v e r e d a c o n v e n i e n t c a t a l y t i c o x i d a t i v e coupling route to high molecular weight aromatic e t h e r s (8 9). These polymers c o u l d be made by b u b b l i n g oxygen through a copper-amine c a t a l y z e d s o l u t i o n of p h e n o l i c monomer a t room temperature (Figure 7). A wide v a r i e t y of phenolic compounds were explored, but the cleanest reactions resulted from those that c o n t a i n e d s m a l l , e l e c t r o n - d o n o r s u b s t i t u e n t s i n the two ortho positions. Work q u i c k l y focused on 2 , 6 - d i m e t h y I p h e n o l because i t was the most r e a d i l y synthesized. The poly (phenylene oxide) (PPO) ether d e r i v e d from 2 , 6 - d i m e t h y I p h e n o l had e x c e l l e n t h y d r o l y t i c r e s i s t a n c e , an extremely h i g h T (215 °C), a h i g h m e l t i n g range (260-275 °C), a very high melt v i s c o s i t y , and a pronounced tendency to o x i d i z e and g e l at process temperatures. The polymer was c a l l e d PPO r e s i n i n a n t i c i p a t i o n of d e v e l o p i n g the c o u p l i n g process to produce unsubstituted poly(phenylene oxide) from phenol. When t h i s objective and the program was r e d i r e c t e d to 2,6-dimethy I p h e n o l , a p a r a l l e l effort was i n i t i a t e d to develop a synthetic route to t h i s monomer. Thus, both monomer and polymer commercialization proceeded s i m u l t a n e o u s l y . They went on stream i n 1964. The v e r y h i g h m e l t v i s c o s i t y and required high processing temperature, coupled with a high degree of o x i d a t i v e s u s c e p t i b i l i t y , resulted i n a polymer that e s s e n t i a l l y defied thermal processing. That i s , i f the temperature were raised s u f f i c i e n t l y to induce a useful degree of flow, a trace of oxygen could lead to c r o s s - l i n k i n g and g e l a t i o n . The phenylene ether-based polymers might never have achieved commercial success i f t h e i r t o t a l c o m p a t i b i l i t y w i t h s t y r e n i c polymers had not been discovered at an e a r l y stage of development. This fortuitous and rather rare c o m p a t i b i l i t y provided the basis for what i s now known as the Noryl family of polymers. Noryl resins became the world's most successful and best known polymer blends or a l l o y s because combinations of PPO r e s i n s and styrene polymers tend to assume the best features of each:


9

1.

2. 3. 4.

PPO resins with very high heat d i s t o r t i o n temperatures (HDTs) can r e a d i l y r a i s e the HDT of styrenics to over 100 °C, which i s a s i g n i f i c a n t temperature because t h i s q u a l i f i e s the product for a l l b o i l i n g water a p p l i c a t i o n s . Styrene polymers, with ease of processing and w e l l - e s t a b l i s h e d impact m o d i f i c a t i o n , b a l a n c e the r e f r a c t o r y n a t u r e of PPO resins. PPO resins bring f i r e retardance to the system. Both PPO r e s i n s and s t y r e n e polymers have e x c e l l e n t water resistance and outstanding e l e c t r i c a l properties.



FOX AND PETERS


Figure 5. Polyarylate

Figure 6. Tetramethyl bisphenol A polycarbonate

+ nH 0 2

Figure 7. Phenylene ether based r e s i n



506


The f i r s t a p p l i c a t i o n s were those r e q u i r i n g a u t o c l a v i n g ( m e d i c a l equipment) or o u t s t a n d i n g e l e c t r i c a l p r o p e r t i e s at elevated temp e r a t u r e s . As compounding, s t a b i l i z a t i o n , and p r o c e s s i n g s k i l l s improved, markets f o r N o r y l expanded to include o f f i c e equipment, e l e c t r o n i c components, automotive parts, water d i s t r i b u t i o n systems, and general metal replacement. Noryl phenylene ether-based resins are r e l a t i v e l y r e s i s t a n t to b u r n i n g , and t h e i r burn r e s i s t a n c e can be i n c r e a s e d by j u d i c i o u s compounding. They may be m o d i f i e d w i t h g l a s s and other m i n e r a l f i l l e r s . Because of low moisture absorption, dimensional s t a b i l i t y , and a b i l i t y to be used o v e r a wide temperature range, N o r y l phenylene e t h e r - b a s e d r e s i n s are e s p e c i a l l y a d a p t a b l e to m e t a l l i z i n g . However, l i k e most amorphous polymers, they show poor s o l v e n t resistance. Polysulfones P o l y a r y l s u l f o n e s are a c l a s s of high-use temperature thermoplastics that c h a r a c t e r i s t i c a l l y e x h i b i t e x c e l l e n t thermal-oxidative resistance, good solvent resistance, h y d r o l y t i c s t a b i l i t y , and creep resistance (10). In 1965, Union Carbide announced a thermoplastic polysulfone based on dichlorodiphenylsulfone and bisphenol A (11). T h i s p o l y s u l f o n e became c o m m e r c i a l l y a v a i l a b l e i n 1966 and was designated as Udel p o l y s u l f o n e . S i n c e 1966, I m p e r i a l Chemical Industry (ICI), Minnesota Mining and Manufacturing (3-M), and Union Carbide have c o m m e r c i a l i z e d p o l y a r y l s u l f o n e s t h a t c o n t a i n o n l y aromatic moieties i n the polymer s t r u c t u r e . These m a t e r i a l s have been designated V i c t r e x p o l y e t h e r s u l f o n e (ICI), A s t r e l 360 (3-M), and Radel polyphenylsulfone (Union Carbide). There are two primary methods f o r the s y n t h e s i s of p o l y a r y l sulfones: n u c l e o p h i l i c displacement r e a c t i o n s and F r i e d e l - C r a f t s processes. U d e l p o l y s u l f o n e i s made by the n u c l e o p h i l i c displacement of the c h l o r i d e on bis(p_-chlorophenyl) sulfone by the anhydrous disodium s a l t of bisphenol A (Figure 8). The reaction i s conducted i n a d i p o l a r a p r o t i c s o l v e n t r e p o r t e d to be d i m e t h y l sulfoxide. The process i s s a i d to be a l i t t l e demanding, and considerable attention i s required i n the various unit operations. V i c t r e x and Radel are a l s o made v i a n u c l e o p h i l i c s u b s t i t u t i o n (Figure 9). The F r i e d e l - C r a f t s r e a c t i o n t h a t uses dipheny l e t h e r 4 , 4 - d i s u l f o n y l c h l o r i d e , biphenyl, and a Lewis-acid c a t a l y s t such as FeCl3 i s employed to produce A s t r e l 360 (Figure 10). The prices of Udel and V i c t r e x are h i g h i n comparison to other e n g i n e e r i n g t h e r m o p l a s t i c s ; the p r i c e s of Radel and A s t r e l are very high as a consequence of l i m i t e d a v a i l a b i l i t y . P o l y a r y l s u l f o n e s are somewhat p o l a r aromatic e t h e r s w i t h o u t s t a n d i n g o x i d a t i o n r e s i s t a n c e , h y d r o l y t i c s t a b i l i t y , and h i g h h e a t - d i s t o r t i o n temperature. L i k e p o l y c a r b o n a t e s , the amorphous character, high h e a t - d i s t o r t i o n temperatures, high melting points, and very high melt v i s c o s i t i e s of p o l y a r y l s u l f o n e s present severe processing problems. The p r o c e s s a b i l i t y of Udel polysulfone resin has been s i g n i f i c a n t l y improved since the e a r l i e r offering, but i t i s s t i l l not very easy to f a b r i c a t e . P o l y e t h e r s u l f o n e i s even higher m e l t i n g than p o l y s u l f o n e , and i t i s more d i f f i c u l t to process. T



FOX AND PETERS


CH

o

3

Figure 8. Polysulfone

O

O Polyethersulfone

O

O Polyphenylsulfone

Figure 9. Victrex and Radel

O

O

Figure 10. A s t r e l polysulfone


507

508


The h y d r o l y t i c s t a b i l i t y and very high thermal endurance of t h i s p l a s t i c i n conjunction with a good balance of mechanical properties s u i t i t for hot water and food handling equipment, range components, TV a p p l i c a t i o n s , a l k a l i n e b a t t e r y c a s e s , and f i l m f o r hot transparencies. The unmodified product i s t r a n s p a r e n t w i t h a s l i g h t l y y e l l o w t i n t . Low flammability and low smoke suite i t for a i r c r a f t and t r a n s p o r t a t i o n a p p l i c a t i o n s . As w i t h the other amorphous polymers, s u s c e p t i b i l i t y to attack by organic s o l v e n t s i s a deficiency.


Thermoplastic Polyesters T h e r m o p l a s t i c p o l y e s t e r s are c u r r e n t l y the h o t t e s t t o p i c i n the e n g i n e e r i n g polymer f i e l d (12). They had t h e i r b e g i n n i n g i n 1941 when J . R. W h i n f i e l d and J . T. Dickson d i s c o v e r e d t e r e p h t h a l a t e based p o l y e s t e r s . E a r l i e r , J . W. H i l l and W. R. C a r o t h e r s had examined a l i p h a t i c p o l y e s t e r s and found them inadequate as f i b e r p r e c u r s o r s because of t h e i r low m e l t i n g p o i n t s . The a l i p h a t i c polyesters were bypassed by polyamides with much higher c r y s t a l l i n e melting points. W h i n f i e l d and D i c k s o n , i n a s u b s e q u e n t i n v e s t i g a t i o n of p o l y e s t e r s as f i b e r p r e c u r s o r s , substituted terephthalic acid for the p r e v i o u s l y investigated a l i p h a t i c dibasic a c i d s and d i s c o v e r e d h i g h m e l t i n g c r y s t a l l i n e polymers. These polymers were developed by I C I , Du Pont, and o t h e r s i n t o the f a m i l i a r polyester f i b e r s and f i l m s . Whinfield and Dickson q u i c k l y r e a l i z e d that the polymer based on ethylene g l y c o l and terephthalic acid was the best suited for f i b e r s ( F i g u r e 11). They d i d , however, make and d e s c r i b e s e v e r a l other polyesters i n c l u d i n g p o l y ( b u t a n e d i o l t e r e p h t h a l a t e ) (PBT). Many years l a t e r a number of polyester f i b e r producers became interested i n PBT. One producer e x p l a i n e d t h a t he was i n t e r e s t e d i n PBT because i t made a f i b e r t h a t resembled n y l o n . Because n y l o n was becoming p o p u l a r as a c a r p e t y a r n , and because he was not i n the n y l o n b u s i n e s s , he c o n s i d e r e d PBT a means of competing i n c a r p e t yarns. W h i l e the f i b e r producers were b u s i l y expanding t h e i r f i b e r a c t i v i t i e s , a number of companies were s i m u l t a n e o u s l y t r y i n g to adapt poly(ethylene terephthalate) (PET) to molding i n much the same way as the n y l o n s had been made to double i n brass as m o l d i n g compound and f i b e r . This objective has been p a r t i c u l a r l y a t t r a c t i v e because the manufacturing capacity for PET i n the United States has surpassed 5 b i l l i o n l b s per year, and a l l the economy of s c a l e has been obtained to y i e l d high-performance polymers at commodity prices. A number of companies have t r i e d to promote PET as a m o l d i n g compound. In 1966, the f i r s t i n j e c t i o n molding grades of PET were introduced; however, these e a r l y materials were not very successful. The primary problem was that PET does not c r y s t a l l i z e very r a p i d l y ; a molded object composed of a c r y s t a l l i z a b l e polymer caught i n an amorphous or p a r t i a l l y c r y s t a l l i z e d state would be rather useless. In s e r v i c e such a part could c r y s t a l l i z e , shrink, d i s t o r t , crack, or f a i l . The obvious s o l u t i o n was to use hot molds and hold the parts i n the mold u n t i l the c r y s t a l l i z a t i o n process was completed. P o s t a n n e a l i n g a l s o permits continued c r y s t a l l i z a t i o n . These approaches, e s p e c i a l l y w i t h g l a s s f i b e r i n c o r p o r a t i o n , l e d to



"

n HO-C—((J)/ 0

H

+

n

H 2

Ethylene Glycol

2

0"CH CH -OH-

L

C—/O/

O " O

PET

c

O C

H

2

2 C H 2

J

- 0 2

3

+ 2nH 0

1,4 Butanediol Figure 11. Polygycol terephthalates

Dimethyl terephthalate

2

PBT

Terephthalic Acid + n H O - ( - C H - ^ - O H — • - C - / 0 ) — C - 0 - ( C H ) - 0 — + 2nCH OH or n

Terephthalic Acid

C

o

o




510

a c c e p t a b l e p a r t s at e c o n o m i c a l l y u n a c c e p t a b l e m o l d i n g c y c l e s . A l t e r n a t e l y , some developers t r i e d to use very low molecular weight PET-glass products that c r y s t a l l i z e d more r a p i d l y ; however, because of t h e i r low m o l e c u l a r w e i g h t s , these products l a c k e d e s s e n t i a l properties. A very broad search has been conducted for such things as nucleating agents and c r y s t a l l i z a t i o n accelerators. An improved PET i n j e c t i o n m o l d i n g compound was i n t r o d u c e d by Du Pont i n 1978 under the tradename R y n i t e . A number of other companies have followed Du Pont i n t o the market. The PET-based molding compounds are gaining acceptance at a s u b s t a n t i a l rate, but a c t u a l volume i s r e l a t i v e l y s m a l l because of the recent b e g i n n i n g . W h i l e other companies sought means of increasing the rate of c r y s t a l l i z a t i o n of PET, Celanese chemists turned t h e i r attention to PBT and found that i t met a l l the requirements for a molding compound. The basic composition of matter patents had long since expired when Celanese sampled the market i n 1970 w i t h a g l a s s f i b e r r e i n f o r c e d PBT product d e s i g n a t e d X - 9 1 7 . T h i s p r o d u c t was subsequently c a l l e d Celanex p o l y e s t e r molding compound. Eastman Kodak followed Celanese e a r l y i n 1971, and General E l e c t r i c followed Eastman Kodak l a t e r i n the same year with Valox PBT polyester r e s i n . S i n c e t h a t time a dozen or more a d d i t i o n a l companies around the world have entered (and some have subsequently exited) the business. B a s i c a l l y , PBT seems to have a unique and favorable balance of properties between nylons and a c e t a l resins. I t has r e l a t i v e l y low moisture a b s o r p t i o n , e x t r e m e l y good s e l f - l u b r i c a t i o n , f a t i g u e resistance, s o l v e n t resistance, and good maintenance of mechanical properties at elevated temperatures. Maintenance of properties up to i t s c r y s t a l melting point i s e x c e l l e n t i f i t i s reinforced with g l a s s f i b e r . Very f a s t m o l d i n g c y c l e s w i t h c o l d to moderately heated molds complete the picture. Key markets include "under the hood" automotive a p p l i c a t i o n s s u c h as i g n i t i o n s y s t e m s and c a r b u r e t i o n , w h i c h r e q u i r e t h e r m a l and s o l v e n t r e s i s t a n c e ; e l e c t r i c a l and e l e c t r o n i c a p p l i c a t i o n s ; power t o o l s ; s m a l l and large appliance components; and a t h l e t i c goods. Poly(phenylene s u l f i d e ) The f i r s t poly(phenylene s u l f i d e s ) were made i n 1897 by the F r i e d e l Craf t s r e a c t i o n of s u l f u r and benzene (13). Researchers at Dow Chemical, i n the e a r l y 1950s, succeeded i n producing high molecular weight l i n e a r p o l y ( p h e n y l e n e s u l f i d e ) by means of the Ullmann condensation of a l k a l i m e t a l s a l t s of p-bromothiophenol (14). V a r i o u s other e a r l y attempts have been r e p o r t e d , a l l of which r e s u l t e d i n amorphous r e s i n o u s m a t e r i a l s t h a t decomposed between 200-300 °C. These m a t e r i a l s were p r o b a b l y h i g h l y branched and p a r t i a l l y cross-linked. In 1973, P h i l l i p s P e t r o l e u m i n t r o d u c e d l i n e a r and branched products under the tradename Ryton (15). The m a t e r i a l s were prepared by r e a c t i n g 1,4-dichlorobenzene with sodium s u l f i d e i n a d i p o l a r aprotic s o l v e n t (Figure 12). The polymer p r e c i p i t a t e s out of s o l u t i o n as a c r y s t a l l i n e white powder. The polymer e x h i b i t s a T at 85 °C and m e l t s at 285 °C. Continued h e a t i n g i n a i r l e a d s to cross-linking. g



21. FOX AND PETERS


511

Ryton i s c h a r a c t e r i z e d by h i g h heat r e s i s t a n c e , e x c e l l e n t c h e m i c a l r e s i s t a n c e , low f r i c t i o n c o e f f i c i e n t , good a b r a s i o n r e s i s t a n c e , and good e l e c t r i c a l p r o p e r t i e s . P h y s i c a l c h a r a c t e r i s t i c s i n c l u d e h i g h f l e x u r a l modulus, very low e l o n g a t i o n , and g e n e r a l l y poor impact strength. Glass, g l a s s - m i n e r a l , and carbon f i b e r r e i n f o r c e d grades t h a t have h i g h s t r e n g t h and r i g i d i t y are a v a i l a b l e . The u n r e i n f o r c e d r e s i n i s used o n l y i n c o a t i n g s . The r e i n f o r c e d m a t e r i a l s are f i n d i n g a p p l i c a t i o n s i n a e r o s p a c e t e c h n o l o g y , pump systems, e l e c t r i c a l and e l e c t r o n i c equipment, appliances, and automotive v e h i c l e s and machines. Poly(phenylene s u l f i d e s ) are reported to be somewhat d i f f i c u l t to process because of t h e i r very high m e l t i n g temperatures and r e l a t i v e l y poor f l o w c h a r a c t e r i s t i c s , and because some chemistry appears to continue during the f a b r i c a t i o n step. Molded pieces have limited regrindability. A n n e a l i n g of molded p a r t s enhances mechanical p r o p e r t i e s but l e a d s to almost t o t a l l o s s of t h e r m a l p l a s t i c character. Polyetherimide The newest e n g i n e e r i n g t h e r m o p l a s t i c i s a polyetherimide that was formally announced by General E l e c t r i c Company i n 1982 (16). This amorphous polymer i s designated Ultem r e s i n and r e s u l t e d from the r e s e a r c h work of a team headed by J . G. W i r t h i n the e a r l y 1970s (9). The e a r l y laboratory process i n v o l v e d a c o s t l y and d i f f i c u l t synthesis. F u r t h e r d e v e l o p m e n t r e s u l t e d i n a number o f breakthroughs t h a t l e d to a s i m p l i f i e d , c o s t - e f f e c t i v e production process. The f i n a l step of the process i n v o l v e s the i m i d i z a t i o n of a d i a c i d anhydride with m-phenylene diamine (Figure 13). Polyetherimide offers an i m p r e s s i v e c o l l e c t i o n of a t t r i b u t e s s u c h as h i g h h e a t r e s i s t a n c e , s t i f f n e s s , i m p a c t s t r e n g t h , transparency, high mechanical strength, good e l e c t r i c a l properties, h i g h flame r e s i s t a n c e , low smoke g e n e r a t i o n , and broad c h e m i c a l resistance. In a d d i t i o n to i t s unique combination of p r o p e r t i e s matching those of h i g h - p r i c e d s p e c i a l t y p l a s t i c s , polyetherimide e x h i b i t s the p r o c e s s a b i l i t y o f t r a d i t i o n a l engineering thermoplastics, although higher melt temperatures are required. The e x c e l l e n t thermal s t a b i l i t y i s demonstrated by the maintenance of s t a b l e melt v i s c o s i t y after m u l t i p l e regrinds and remolding. The p r o c e s s i n g window i s n e a r l y 100 °C, and p o l y e t h e r i m i d e can be processed on most e x i s t i n g equipment. Furthermore, t h i s e x c e l l e n t flow r e s i n can be used for the molding of complicated parts and t h i n sections (as t h i n as 5 m i l ) . Polyetherimide i s s u i t a b l e for use i n i n t e r n a l components of microwave ovens; e l e c t r i c a l and e l e c t r o n i c p r o d u c t s ; and a u t o m o t i v e , a p p l i a n c e , and a e r o s p a c e , and transportation a p p l i c a t i o n s . Blends and A l l o y s An i n t e r e s t i n g trend that appears to presage the wave of the future i n e n g i n e e r i n g t h e r m o p l a s t i c s i s the c u r r e n t focus on polymer blending and a l l o y i n g . Metals and t h e i r a l l o y s have been c o e v a l with the spread of c i v i l i z a t i o n . E a r l y man used a v a i l a b l e metals i n t h e i r n a t u r a l l y occurring state. The progress of c i v i l i z a t i o n was l i t e r a l l y determined by man's a b i l i t y to modify n a t u r a l m e t a l s




512

Figure 13.

Polyetherimide



21.

FOX AND PETERS


513

through a l l o y i n g to induce the properties necessary for i n c r e a s i n g l y s o p h i s t i c a t e d t o o l s . Indeed, s o c i e t i e s t h a t l e a r n e d to e x p l o i t b l e n d s o f m e t a l s d e v e l o p e d d i s t i n c t advantages o v e r t h e i r monometallic neighbors; t h i s was exemplified by the advent of bronze and l a t e r s t e e l . M e t a l a l l o y i n g has p r o b a b l y made the t r a n s i t i o n from a r t to science i n the past century. The basic ingredients are e s s e n t i a l l y known and f i x e d i n number. The p l a s t i c age began i n 1909 w i t h the discovery by Leo Baekeland of synthetic phenol-formaldehyde r e s i n . As p o i n t e d out i n the b e g i n n i n g of t h i s c h a p t e r , the e n g i n e e r i n g p l a s t i c age began 30 years ago. W h i l e metal a l l o y components are e s s e n t i a l l y f i x e d , polymer a l l o y components are u n l i m i t e d from a t e c h n i c a l standpoint, but somewhat fixed from an economic point of view. I t i s s t i l l possible to make t o t a l l y new and useful polymers i f t h e i r value w i l l support the cost of synthesizing new monomers and polymers. However, i t i s much more economically a t t r a c t i v e to t r y to combine a v a i l a b l e polymers to produce d e s i r a b l e and novel a l l o y s . The a v a i l a b l e degrees of freedom make the o p p o r t u n i t y c h a l l e n g i n g and provide almost i n f i n i t e p o s s i b i l i t i e s . V a r i a b l e s include base polymers (20 or more), impact modifiers, a d d i t i v e s , and fillers. I t i s hard to say where or when the concept of polymer a l l o y s was born, but w i t h i n G e n e r a l E l e c t r i c Company, Robert F i n h o l d was w r i t i n g and t a l k i n g about a l l o y s of PPO r e s i n with styrene polymers i n the very e a r l y 1960s. S i n c e then other b l e n d s have been i n t r o d u c e d . Union Carbide has i t s p o l y s u l f o n e - p o l y e s t e r b l e n d s (Mindel) that e x h i b i t improved processing and reduced cost v i s - a - v i s p o l y s u l f o n e by i t s e l f . U n i t i k a has a broad l i n e of p o l y a r y l a t e blends. Bayer offers polycarbonate-acrylonitrile-butadiene-styrene and tetramethylbisphenol A polycarbonate-polystyrene blends. Most r e c e n t l y , General E l e c t r i c Company introduced a new polymer blend, Xenoy, i n t o the European market. T h i s b l e n d i s composed of two polymers, p l u s impact m o d i f i c a t i o n , to be used f o r a f r o n t - e n d , rear-end e x t e r i o r bumper system for automobiles (17). I t combines the key mechanical p r o p e r t i e s of impact s t r e n g t h , d i m e n s i o n a l s t a b i l i t y , and high modulus with chemical resistance. C l e a r l y , the trend toward a l l o y s and blends i s gaining momentum.

Conclusion The future of engineering p l a s t i c s looks bright. Those i n d u s t r i e s s e r v e d by these p l a s t i c s , and many o t h e r s who use t r a d i t i o n a l m a t e r i a l s such as m e t a l s , g l a s s , and c e r a m i c s , w i l l l o o k to the benefits of engineering polymers to provide them with c o s t - e f f e c t i v e materials to help overcome the pressures of s p i r a l l i n g costs. The w o r l d economy w i l l c o n t i n u e to i n f l u e n c e t e c h n i c a l t r e n d s . The c o m m e r c i a l i z a t i o n of any new e n g i n e e r i n g polymer based on a new monomer, a l t h o u g h not i m p o s s i b l e , i s u n l i k e l y . Rather, the major t h r u s t w i l l take p l a c e i n m o l e c u l a r s h u f f l i n g w i t h e x i s t i n g monomers, blend a c t i v i t y , and processing improvements.


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Literature Cited 1. 2. 3. 4.


5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

Kohan, M. I. "Nylon Plastics"; SPE Monograph, Wiley: 1973; p. 2. Welgos, R. J. "Kirk-Othmer Encyclopedia of Chemical Tech nology," 3rd ed.; Interscience: New York, 1982; Vol. 18, pp. 406-25. Persak, K. J . ; Blair, L. M. "Kirk-Othmer Encyclopedia of Chemical Technology," 3rd ed.; Interscience: New York, 1978; Vol. 1, pp. 112-23. Staudinger, H. "Die Hochmolekularen Organischen Verbindungen Kautschuk und Cellulose"; Springer-Verlag: Berlin, 1932. Fox, D. W. "Kirk-Othmer Encyclopedia of Chemical Technology," 3rd ed.; Interscience: New York, 1982; Vol. 18, pp. 479-94. Schnell, H. "Chemistry and Physics of Polycarbonates"; WileyInterscience: New York, 1964. Vernaleken, H. in "Interfacial Synthesis"; M i l l i c h , F. and Carraher, C., Jr., Eds.; Dekker: New York, 1977; Vol. II, Chap. 13. Hay, A. S. J. Polym. Sci. 1962, 58, 581. White, D. M.; Cooper, G. D. "Kirk-Othmer Encyclopedia of Chemical Technology," 3rd ed.; Interscience: New York, 1982; Vol. 18, pp. 595-615. Ballintyn, N. J. "Kirk-Othmer Encyclopedia of Chemical Technology," 3rd ed.; Interscience: New York, 1982; Vol. 18, pp. 832-48. Johnson, R. N.; Farnham, A. G.; Clendinning, R. Α.; Hale, W. F.; Merriam, C. N. J. Polym. Sci., Part A-1 1967, 5, 2375. Jaquiss, D. B. G.; Borman, W. F. H.; Campbell, R. W. "KirkOthmer Encyclopedia of Chemical Technology," 3rd ed.; Interscience: New York, 1982; Vol. 18, pp. 549-74. Genvresse, P. Bull. Soc. Chim. Fr. 1897, 17, 599. Lenz, R. W.; Handlovits, C. E.; Smith, H. A. J. Polym. Sci. 1962, 58, 351. Short, J . M.; Hill, H. W. CHEMTECH 1972, 2, 481. Floryan, D. E.; Serfaty, I. W. "Modern Plastics"; 1982; p. 146. "Plastics World"; 1982; p. 8.


Applied Polymer Science - American Chemical Society

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