Copolyesters crystallization-induced

However, interchange reactions appear to be rather slow at temperatures below Tm(15). We(50) observed that thermal treatment of some of liquid crystalline, aromatic copolyesters at the temperatures substantially lower than Tm did not lead to any changes in the comonomer sequence even after a prolonged period of time. A copolyester especially of 4-hydroxybenzoic acid, however, can undergo a special type of sequence changes below Tm, which is called the crystallization induced reaction(51). 

Youk J H and Jo W H (2001) Origin of miscibility-induced sequential reordering and crystallization-induced sequential reordering in binary copolyesters A Monte Carlo simulation, J Polym Sci Part... 

In a previous paper (1), phase segregation by spinodal decomposition in mixtures of polyethylene terephthalate and polyhydroxybenzoic acid copolymer (PET-PHB) and polycarbonate (PC) has been investigated. It was shown that thermally induced phase segregation takes place above the Tg of PC and exhibits a lower critical solution temperature (LCST). However, the phase separated domains do not grow until the temperature exceeds 255°C. Some disclinations developed within the liquid crystal rich regions. Even in the pure PET-PHB component, four dark brushes with negative sense of disclinations form around 240°C, indicating the presence of nematic liquid crystals. Paci and coworkers (2) claimed that a smectic-nematic transition exists near 270°C in this liquid crystalline copolyester. 

Quintana et al. (95) prepared two types of PECT copolyesters with 25 and 30% of CHDM units and containing small amounts of pen-taerithrytol branching agent. Then, they studied the rheological features and flow-induced crystallization of PECT copolymers by capillary extrusion experiments at 180 °C. They observed that copolymers with the lower content in CHDM were able to crystallize in these conditions whereas linear or branched PECT with 30 %-mole of CHDM units did not crystallize. 

Shabana HM, Olley RH, Bassett DC, Zachmann H-G (1996) On crystallization and phase separation phenomena in PEN/PHBA copolyesters. J Macromol Sci Phys B35 691-708 Shabana HM, Olley RH, Bassett DC, Jungnickel BJ (2000) Phase separation induced by crystallization in blends of polycaprolactone and polystyrene an investigation by etching and electron microscopy. Polymer 41 5513-5523... 

Nicholson TM, Mackley MR, Windle AH (1992) Shear-induced crystallization in a liquid oys-talline random copolyester. Polymer 33 434—435 Onogi S, Asada T (1980) Rheology. In Astanta G, Marrucci G, Nicolais L (eds) vol 1. Plenum, New York... 

The presence of a mesomorphic component dispersed in a crystallizable polymer matrix, can induce noteable changes of the crystallization behavior, crystallinity degree, and crystal morphology of the matrix. For blends of PET with liquid-crystalline copolyesters the crystallization rate of PET matrix was found to increase with increasing the LCP content, indicating a nucleating effect of the LCP component [139]. Similar effects have been reported for blends with polyolefin matrix for blends of iPP with a smectic polyester (PTEB) compati-... 

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