Copolyesters, segmented

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

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. 

Polyether-based thermoplastic copolyesters show a tendency toward oxidative degradation and hydrolysis at elevated temperature, which makes the use of stabilizer necessary. The problem could be overcome by incorporation of polyolehnic soft segments in PBT-based copolyesters [31,32]. Schmalz et al. [33] have proposed recently a more useful technique to incorporate nonpolar segments in PBT-based copolyesters. This involves a conventional two-step melt polycondensation of hydroxyl-terminated PEO-PEB-PEO (synthesized by chain extension of hydroxyl-terminated hydrogenated polybutadienes with ethylene oxide) and PBT-based copolyesters. 

Deak G. and Kennedy J.P., Copolyesters containing polyisobutylene soft segments and polybutylene terephthalate as crystalline segments, MacrolmoL Rep., A33(Suppls 7 8), 439, 1996. 

Schmalz H., Abetz V., Lange R., and Soliman, M. New thermoplastic elastomers by incorporation of nonpolar soft segments in pbt-based copolyesters, Macromolecules, 34, 775, 2001. 

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. 

Mechanical studies have also been performed on another non-LCP system -copolyesters of PET and PEN, where both copolymer units having flexible chain segments and lack a liquid-crystalline behaviour (Santa Cruz et al, 1992). The whole range of PET/PEN copolymers can therefore be prepared in the amorphous state. 

Figure 6.7. Model of the PEE block copolyester structure with hard (- - - -) PBT segments and soft (-0-0-0-) PEO segments in equimolar amounts. Basically four phases are possible because both the PBT and PEO are crystallizable. (From Fakirov et al., 1990.)...

The example given in Equation 5(39) is a special kind copolyester of alternating sequence. Since the" two monomers, 4-hydroxyben-zoic acid and 6-hydroxy-2-naphthoic acid, can undergo homopolymerization, one first has to synthesize the starting dyad monomer and then polymerize it to obtain the final, alternating copolyester. Otherwise, the copolyester chains will consist of random chain segments consisting of the two monomer units(40,41). 

The copolyesters may be considered as having been derived by randomly joining, head-to-tail, soft and hard segments. A generalized structure is ... 

Figure 13. Variation of tensile stress (300%) with hard-segment melting point in PTMEG-T copolyesters A = 2GT A = 3GT Q = 4GT =...

The results presented here show that there are two distinct motional environments for the "central" deuterons of poly (butylene terephthalate) in the segmented copolyesters containing poly (butylene terephthalate) as the hard segment. One of the motional environments is identical to that observed in the poly (butylene terephthalate) homopolymer, in which Helfand-type motions (6) about three bonds occur with a correlation time of 7 x 10-6 s at 20 °C. The Tj for these deuterons is ca. 60 ms at 20 °C. Approximately 90% of the hard segments reside in these organized lamellar environments in the segmented copolymer with 0.87 mole fraction hard segments. 

One significant result of the nonuniform distribution of PET and HBA segments in the copolyester chains is the low HDT as shown in Table 5.10. The HDT for the copolymer containing 60 mol-% HBA (PET/60-HBA) was only 64 °C which was about the same as that of PET. Obviously this low value was attributed to the presence of PET-rich phase. Another result is the presence of highly melting particles which may come out unmelted during process leading to structural defects and lower properties. 

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