Copolyesters

Copolyesters with molecular weights of several thousands could be produced by polymerizing macrolides in the presence of aliphatic polyesters. Random copolyesters containing both units were obtained, showing that the lipase had catalyzed not only the polymerization of macrolide but also the intermolecular transesterification reaction of the starting and resulting polyesters [68]. Random copolyesters were also obtained by the copolymerization of 8-octanoUde with DDL [69]. Highly crystalline random copolyesters of PDL and CL have been prepared via a Novo-zyme 435-catalyzed copolymerization at 70°C in toluene [70]. 

The enzyme-catalyzed synthesis of diblock polyesters has been reported by Kumar et al. [71]. Here, monohydroxyl-terminated polybutadiene with M of 2.6, 

Resorbable microblock copolymers based on DXO and CL and elastomeric hydrolyzable porous scaffolds based on copolymers of DXO, L-lactide and CL have recently been reported [72, 73]. 

FuUy biobased poly(L-lactide)-b-poly(ricinoleic acid)-b-poly(L-lac-tide) triblock copolyesters have been described (31). Methyl ri-cinoleate, produced from castor oil, is condensed in the presence of a small amount of 1,3-propanediol. This results in a a, (D-hydroxy-terminated poly(ricinoleic acid) with a molar mass 

In molding techniques, the crystallization rate and crystallinity of PLA are relatively low due to its slow nucleation (32,33). This causes long molding cycles for the production of products, c.f. Table 3.4. 

The crystallization behavior of amorphous PLA was investigated by exposing to vapor of acetone (34). Acetone vapor effectively induced the crystallization of the amorphous PLA. The crystallization of a 10 X 20 X 0.55 mm specimen at 25°C is completed within 24 min. 

The crystallization rate is increased with temperature. A high crystallinity about 40% can be obtained. The specimens crystallized by the acetone vapor exhibit a higher transparency than those prepared by annealing or immersion methods. 

The crystallization is induced by the diffusion of the acetone into the amorphous phase of PLA. The diffusion obeys a Pick type diffusion, as suggested by polarized optical photomicrograph measurements. The crystallization behavior is shown in Table 3.4. 

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PCTA Copolyester. Poly(l,4-cyclohexanedimethylene terephthalic acid) (PCTA) copolyester is a polymer of cyclohexanedimethanol and terephthalic acid, with another acid substituted for a portion of the terephthalic acid otherwise required. It has the following formula ... 

Polyesters. The hard portion consists of copolyester, and the soft portion is composed of polyol segments. 

In the late 1980s, new fully aromatic polyester fibers were iatroduced for use ia composites and stmctural materials (18,19). In general, these materials are thermotropic Hquid crystal polymers that are melt-processible to give fibers with tensile properties and temperature resistance considerably higher than conventional polyester textile fibers. Vectran (Hoechst-Celanese and Kuraray) is a thermotropic Hquid crystal aromatic copolyester fiber composed of -hydroxyben2oic acid [99-96-7] and 6-hydroxy-2-naphthoic acid. Other fully aromatic polyester fiber composites have been iatroduced under various tradenames (19). 

Standard polyester fibers contain no reactive dye sites. PET fibers are typically dyed by diffusiag dispersed dyestuffs iato the amorphous regions ia the fibers. Copolyesters from a variety of copolymeri2able glycol or diacid comonomers open the fiber stmcture to achieve deep dyeabiHty (7,28—30). This approach is useful when the attendant effects on the copolyester thermal or physical properties are not of concern (31,32). The addition of anionic sites to polyester usiag sodium dimethyl 5-sulfoisophthalate [3965-55-7] has been practiced to make fibers receptive to cationic dyes (33). Yams and fabrics made from mixtures of disperse and cationicaHy dyeable PET show a visual range from subde heather tones to striking contrasts (see Dyes, application and evaluation). 

Chemical Properties. The hydrolysis of PET is acid- or base-catalyzed and is highly temperature dependent and relatively rapid at polymer melt temperatures. Treatment for several weeks in 70°C water results in no significant fiber strength loss. However, at 100°C, approximately 20% of the PET tenacity is lost in one week and about 60% is lost in three weeks (47). In general, the hydrolysis and chemical resistance of copolyester materials is less than that for PET and depends on both the type and amount of comonomer. 

The glass-transition temperature, T, of dry polyester is approximately 70°C and is slightly reduced ia water. The glass-transitioa temperatures of copolyesters are affected by both the amouat and chemical nature of the comonomer (32,47). Other thermal properties, including heat capacity and thermal conductivity, depend on the state of the polymer and are summarized ia Table 2. 

Also in 1972 (6), Carbomdum researchers described a family of aromatic copolyesters which were recognized later to form Hquid crystalline melts. The polymers are based on a bisphenol monomer. In 1976, in a patent assigned to Carbomndum, a hydroxybenzoic acid—terephthaHc acid—bisphenol system, modified and softened with isophthaHc acid, was reported to be melt spinnable to produce fiber. 

First,/)-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) are acetylated to produce the low melting acetate esters which are molten at 200°C. In an inert gas, the two monomers are melted together at 200°C. The temperature is raised to 250—280°C and acetic acid is coUected for 0.5 to 3 h. The temperature is raised to 280—340°C and additional acetic acid is removed in vacuum for a period of 10 to 60 min. The opalescent polymer melt produced is extmded through a spinning jet, foUowed by melt drawdown. The use of the paraUel offset monomer, acetylated HNA, results in the formation of a series of random copolyesters of different compositions, many of which faU within the commercially acceptable melting range of... 

The open hoUow fiber shape shown ia Figure 13 is made by a unique process requiring bicomponent yam technology (145). A yam is spun with a water-soluble copolyester core and nylon sheath where the core is dissolved out with an alkaH treatment ia fabric dyeiag. 

Thermoplastic copolyester elastomers are generally block copolymers produced from short-chain aUphatic diols, aromatic diacids, and polyalkjlene ether-diols. They are often called polyesterether or polyester elastomers. The most significant commercial product is the copolymer from butane-l,4-diol, dimethyl terephthalate, and polytetramethylene ether glycol [25190-06-1J, which produces a segmented block copolyesterether with the following stmcture. 

PC—copolyester better processibihty, hydrolytic, and gamma radiation resistance than PC sterilizable apphcations 43,109... 

Uses. Approximately 70% of the U.S. production is used to make poly(tetramethylene ether glycol) [25190-06-1] (PTMEG), also known as poly-THE, which is used in the production of urethane elastomers, polyurethane fibers (ether-based spandex), and copolyester—ether elastomers. PTMEG is also the fastest growing use (see PoLYETPiERS, TETRAHYDROFURAn). The remaining production is used as a solvent for the manufacture of poly(vinyl chloride) cements and coating, precision magnetic tape, a reaction solvent in the production of pharmaceuticals, and other miscellaneous uses. 

Blends of PBT with polycarbonates have been widely used for car bumpers. Interest in PBT/PET blends and PBT/ASA has arisen because of the good surface finish possible even with glass-reinforced grades. Copolyesters based on PBT but with some longer chain diol or acid are also now produced. 

The copolyester was first marketed as Tenite Polyterephthalate 7DRO but is now sold as Kodar PETG. 

Table 25.9 Typical properties of the copolyester Kodai PETG...

One such material is the copolymer first marketed by the Japanese company Unitika in 1974 as U-Polymer and more recently by the Belgian company Solvay as Arylef and Union Carbide as Ardel. (Around 1986 the Union Carbide interest in Ardel, as well as in polysulphones, was taken over by Amoco.) Similar polyarylates have since been marketed by Hooker (Durel), Bayer (APE) and DuPont (Arylon). This is a copolyester of terephthalic acid, isophthalic acid and bis-phenol A in the ratio 1 1 2 Figure 25.23). 

The y relaxation appears around - 120°C (Fig. 19). PTEB and the copolyesters show the y maximum at a temperature that is practically constant, slightly lower than the one for P8MB. The low activation energy values (Table 3) are the usual ones for this relaxation. 

One may now ask whether natural systems have the necessary structural evolution needed to incorporate high-performance properties. An attempt is made here to compare the structure of some of the advanced polymers with a few natural polymers. Figure 1 gives the cross-sectional microstructure of a liquid crystalline (LC) copolyester, an advanced polymer with high-performance applications [33]. A hierarchically ordered arrangement of fibrils can be seen. This is compared with the microstructure of a tendon [5] (Fig. 2). The complexity and higher order of molecular arrangement of natural materi-... 

Figure 1 Schematic representation of the microstructure and cross-sectional view of a liquid crystEilline copolyester fiber [33].

Figure 17 Differential scanning colorimetric trace of the liquid crystalline copolyester of 8-(3-phenyl hydroxy) octanoic acid and paro-hydroxy benzoic acid.

Plasticization Polycaprolactone, polyurethanes, nitrile rubber, ethylene-vinyl acetate, copolyester, chlorinated polyoxymethylenes (acetals)... 

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