Thermoplastic copolyesters terephthalate

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. 

Kodar PETG PETG, a thermoplastic copolyester of 1,4 cyclohexylene glycol and mixture of iso- and terephthalic acids Eastman Chem. 

The segmented block copoly(ether ester)s, based on poly(butylene terephthalate) (PBT) and on polyoxytetramethylene (POTM) are typical examples for this class of thermoplastic elastomers . They can be described as random copolyesters of tereph-thalic acid with 1,4-butanediol and a-hydro-hard phase whereas the remaining ester segments mix with the ether segments and build up the soft matrix. 

The next two decades saw the development of new polymers such as thermoplastic PU (1961), aromatic polyamides, polyimides (1962) polyaminimides (1965), thermoplastic elastomers (styrene-butadiene block copolymers in 1965), ethylene-vinyl acetate copolymer, ionomers (1964), polysulfone (1965), phenoxy resins, polyphenylene oxide, thermoplastic elastomers based on copolyesters, poly butyl terephthalate (1971) and polyarylates (1974). 

Ecoflex (poly(butylene adipate-co-terephthalate)), a commercialized aliphahc-aromatic copolyester from BASF, was characterized to be an ideal random copofymer with 44 mol% of BT units. The glass transition occurs at 30°C, and the melting point is 110-115°C [86]. The physical and mechanical properties of this soft thermoplastic are similar to those of LDPE, and it can be processed on convenhonal equipment for LDPE. 

Other thermoplastic polyesters have been reported, including copolyesters based on 1,4-cyclohexylenedimethylene glycol and terephthalic acid and polymers and copolymers of p-hydroxybenzoic acid. Little is known about established applications. Hot melt adhesives, based on polyesters made from adipic or phthalic acids with mono- or di-ethylene glycols or 1,4-butane diol, find use in shoe manufacture. 

These thermotropic liquid-crystalhne polymers have high melting points but can be melt-processed like other thermoplastics. The macroscopic orientation of the extended-chain crystals depends on the orientation imparted by flow during processing (molding, extrusion, etc.). Because of the fibrous nature of the extended-chain crystals, these plastics behave as self-reinforced composites, with excellent mechanical properties, at least in the chain direction. This is illustrated in Table 4.3 for molded specimens of a hquid-crystalline copolyester of ethylene glycol, terephthalic acid, and / -hydroxybenzoic acid [14]. In the direction parallel to the flow, the properties listed in Table 4.3 favorably compare with ordinary crystalline thermoplastics (nylons, polyesters) reinforced with up to 30% glass fibers. 

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