Copolyesters thermal behavior

In this research, commercially available PHB/PET copolyester LCP, PEN and PET were mechanically blended to form the LC phase of the blends. The critical composition of PHB in the PEN and PET forming an LC ternary blend was investigated, and the miscibility and thermal behavior were studied using thermal analysis. The PHB content in the ternary blend was controlled by the amount of PHB/PET copolyester, as a high-molecular-weight PHB homopolyester does... 

A type of aromatic-aliphatic liquid crystalline copolyesters has been synthesized from 2-chlorohydroquinone, 1,4-CHDM and terephthaloyl chloride (Figure 6.14). The CHDM units act in these copolyesters as flexible spacers providing the necessary chain mobility to be thermotropic. The structure and thermal behavior of these copolyesters were characterized by hot-stage polarized light microscopy, SEM, FTIR, NMR, DSC and TGA (57). It has been reported that they are insoluble in common solvents and may form mesophases at temperatures near the melting temperature of PET (58). 

A similar thermal behavior dependence on the alkylene unit has been observed for the CHDM containing poly(n-alkylen naphthal-ate)s copolyesters (55). PECN behaves similarly to PECT copolymers showing a window of intermediate compositions were the copolymers are amorphous. On the contrary, copolyesters of PBCN crystallize for all compositions with an eutectic point at about 41% of 1,4-CHDM. On the other hand, in the case of PHCN copolymers, it was observed a continuous increase in the melting temperature with the content in 1,4-CHDM, indicating the occurrence of unlimited isomorphic crystallization. 

Leblanc J-P, Tessier M, Judas D, Friedrich C, Noel C and Marechal E (1995) Aromatic copolyesters with stilbene mesogenic groups, 2. Synthesis and thermal behavior, Macromolecules 28 4837-4850. 

Smith et al. [64] prepared a series of PET/PTT copolyesters, and found that addition of the other component suppressed the melting point of the respective homopolymer. Between 37 and 60 % PTT content, the copolymers became amorphous and did not show any melting endotherms in the differential thermal analyzer scans. A similar behavior was observed by Balakrishnan and coworkers [102] in PET/PTT copolyesters prepared by the transesterification of PET with PDO, and by the copolymerization of EG and PDO with DMT [103, 104], The non-crystallizing behavior of copolymers with intermediate contents of the respective component is similar to that of a eutectic mixture, indicating formation of random copolyesters. The 7 g and solubility temperature of the copolyesters were, however, continuous and went through minima with increasing PTT content [64],... 

Chlorinated polymers/Copolyester-aniides Recent studies (5) of blends of chlorinated polyeAylenes with caprolactam(LA)-caprolactone(LO) copolymers have been able to establish a correlation between miscibiUty and chemical structure within the framework of a binary interaction model. In some of the blends, both components have the ability to crystallize. When one or both of the components can crystallize, the situation becomes rather more complicated. Miscible, cystallizable blends may also undergo segregation as a result of the crystallization with the formation of two separate amorphous phases. Accordingly, it is preferable to investigate thermal properties of vitrified blends. Subsequent thermal analysis also produces exothermic crystallization processes that can obscure transitions and interfere with determination of phase behavior. In these instances T-m.d.s.c has the ability to separate the individual processes and establish phase behavior. 

Poly(butylene-co-l,4-cyclohexylenedimethylene terephthalate) copolyesters (PBCT) (Figure 6.9) with a random microstructure have been synthesized by melt polycondensation for a range of BD/1,4-CHDM ratios between 94/8 and 23/77 (47,48). PBCT are crystalline for all compositions and display an eutectic behavior. Copolyesters with less than 25 %mol of CHDM units crystallize in a PBT like lattice whereas above 38 %mol they adopt a PCT-like lattice. PBCT copolyesters were found to be more stable than PCT and PBT at the initial stage of the thermal decomposition (49). 

Some liquid ciystalline copolyesters (LCP) derived from dihydroxydiphenylacetate, acetobenzoic acid, isophthtalic and terephthtalic acids with various proportions of the latter two comonomers were investigated. The LCP thermal stability and the degradation behavior under processing temperatures were studied. The kinetics of loss in weight, the oxygen uptake as well as the oxidation product evolution were studied. On the basis of the data obtained a mechanism for the LCP high-temperamre thermal oxidation, relative to such for other polyheteroaiylenes was proposed. 

Owing to the strong dependence of the rheological behavior of TLCP on thermal and deformation histories, the transient shear flow data for 73/27 HBA7HNA copolyester reported by two laboratories have been found to be quite different (Cocchini et al. 1991 Guskey and Winter 1991). As we have already pointed out, it is extremely important for one to control the initial morphology (i.e., initial conditions) of test specimens in order to obtain reproducible transient shear flow data for TLCPs. 

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