Copolyesters, melting point

Copolyesters of poly(3HB-co-3HV) have approximately the same degree of crystallinity as the homopolymer PHB and all copolymers show similar conformation characteristics as those observed for PHB [24,26,65]. They show a minimum in their melting point versus composition curve at a 3HV content of approximately 40 mol%. The apparent ability of the two different monomeric units to cocrystallize might result from the fact that the copolymers are prone to show isodimorphic behavior [21, 26, 66-70]. However, the considerable reduction of the heat of fusion upon 3HV inclusion, as reported by Bluhm et al. 

Figure 7.7 Effect of CHDM concentration on the melting point of the copolyester prepared from TPA, EG and CHDM...

Low-level incorporation of IPA (5-10 mol %) widens the processing window by lowering the melting point of the polyester while also retaining the crystallinity, Tg and toughness of the PCT homopolymer. At higher IPA incorporation levels, chain crystallization is severely restricted so that at 35 mol % of IPA and higher, the amorphous copolyesters do not crystallize without the addition of an added nucleator [55-59],... 

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],... 

The modification of PET with naphthalene-2,6-dicarboxylic acid and other additional comonomers is a common measure in bottle manufacturing. Copolyesters based on this compound show excellent barrier properties. Such materials can be produced by addition of the desired amount of comonomer during polymer processing or by blending PET with poly(ethylene naphthalate) (PEN). Additionally, PEN can also be modified by other comonomers such as isophthalic acid (IPA) to improve the flow properties and reduce the melting point. The high price of naphthalene dicarboxylic acid is the reason for its limited application. The overall cost may be reduced by using TPA or IPA as comonomers. 

We report here that polyethylene adipate (PEA) and polycaprolactone (PCL) were degraded by Penicillium spp., and aliphatic and alicyclic polyesters,ester type polyurethanes, copolyesters composed of aliphatic and aromatic polyester (CPE) and copolyamide-esters (CPAE) were hydrolyzed by several lipases and an esterase. Concerning these water-insoluble condensation polymers, we noted that the melting points (Tm) had a effect on biodegradability. 

On the other hand, as opposed to the randomizing reactions which occur in the nematic melt if one anneals these copolyesters near their crystal nematic transition a completely different process appears to be operative. Thus several workers [11, 14], have reported that heating the HBA/HNA system near its melting point results in a dramatic increase in Tcn by approximately 50 °C. As... 

Table 2. Melting Points of Copolyesters of Ethylene Glycol and Terephthalic and Sebacic Acids...

The agreement between heats of fusion of the same polymer is excellent in some cases, but very poor in others. Obviously, in the case of polypropylene more work needs to be done before the heat of fusion of this substance will be known with any certainty. Heats of fusion calculated from the copolymer equation, Eq. (6), are uniformly low, except in the case of Rybnikar s data. As pointed out by Dole and Wunderlich (1957) this is probably due to the failure to measure the maximum melting of carefully annealed samples. Thus, Dole and Wunderlich (1959) found that the calorimetrically estimated melting point in the case of the carefully annealed copolyester, the 80/20 polyethylene terephthalate and sebacate, was 240° C, whereas the value calculated from Eq. (6) using the heat of fusion estimated from the calorimetric data of Smith and Dole (1956) was 245° C. The unannealed sample had a melting point of ca. 210°. 

Fig. 11. Specific heat of annealed80/20 copolyester of polyethylene terephthalate-sebacate in the neighborhood of the melting point. Dotted line, calculated values from adaptation of theory of Feory...

The kinetics of crystallization of polyethylene-naphthalene-2,6-dicarboxylate (PEN) and of copolyesters of this material with p-hydroxybenzoic acid (PHB) was studied by Wiswe, Gehrke, and Zachmann. PEN crystallizes in two different crystal modifications. One modification is obtained by crystallization at comparatively low temperatures, the other one is obtained sometimes when the material is crystallized near the melting point. Fig. 55 shows the change in the wide angle scattering during isothermal crystallization at 167 °C and 245 °C. 

Copolymerization of two monomers with different substituents was used as another approach for depressing the transition temperatures of the polymers For example, a copolyester prepared from an equimolar mixture of cyano- and methoxyhydro-quinone and l,10-decane-h(x(p-chloroformylbenzoyloxy)decane had a melting point of 133 °C and a clearing temperature of 177 °C, while the corresponding temperatures of the cyano-substituted homopolymer were 157 and 219 °C. 

Figure 8. Effect of 4GT weight fraction on the melting points (DSC) of various copolyesters calculated from Figure 7 A = 4GT/PTMEG-T B = 4GT/4G10...

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

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