Copolyesters random

First,/)-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) are acetylated to produce the low melting acetate esters which are molten at 200°C. In an inert gas, the two monomers are melted together at 200°C. The temperature is raised to 250—280°C and acetic acid is coUected for 0.5 to 3 h. The temperature is raised to 280—340°C and additional acetic acid is removed in vacuum for a period of 10 to 60 min. The opalescent polymer melt produced is extmded through a spinning jet, foUowed by melt drawdown. The use of the paraUel offset monomer, acetylated HNA, results in the formation of a series of random copolyesters of different compositions, many of which faU within the commercially acceptable melting range of... 

Aromatic polyesters that do not contain any flexible structural units are often nonmeltable or extremely high melting polymers that cannot be processed. Copolymerization is a way to obtain processable wholly aromatic polyesters The Tm versus copolyester composition curve is a U-shaped curve exhibiting a minimum that is generally well below the Tm of corresponding homopolymers. Liquid crystalline aromatic polyesters, for instance, are usually copolymers.72 An example is Ticona s Vectra, a random copolyester containing 4-oxybenzoyl and 6-oxy-2-naphthoyl units in ca. 70 30 mol ratio. This copolymer melts at ca. 

As already discussed (Section 2.2.1.3), interchange reactions are also implicated in the formation of random copolyesters exhibiting the most probable molar mass distribution when polyester blends are melt mixed. They are also involved in the randomization of block copolyesters taking place in the melt upon heating.2,m 211... 

The polymerization of terephthaldehyde in the presence of triethoxyalu-minum391 or Uialkylaluminum392 (Tischchenko-Claisen reaction) yields random copolyesters containing ca. 1 1 mol ratio of p-methylenebenzoate and / -xyleneterephthalate units (Scheme 2.43). The reaction does not take place with sterically hindered aldehydes.392... 

Many random copolyesters and polyester-polycarbonates have also been prepared by ester interchange reactions in the molten state. Thus, poly(ethylene terephthalate-co -isophthalates) can be obtained by simple melt blending of PET and poly(ethylene isophthalate) (PEI) homopolyesters at 270°C. The copolymer changes gradually from a block type at the beginning of reaction to a random-type... 

The copolymerization of lactones took place through enzyme catalysis [92]. The copolymerization of e-CL with d-VL catalyzed by lipase PF affords the corresponding copolymer having a molecular weight of several thousand. From 13C NMR analysis, the copolymer was found to be of random structure having both units, suggesting the frequent occurrence of transesterifications between the polyesters. In the copolymerization of 8-OL with e-CL or DDL, random copolyesters were also formed [84], whereas the copolymer from e-CL and PDL was not statistically random [88]. 

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],... 

Fig. 12. PHBA dyad sequences for PHBA/PET copolyesters - experimental values, O -calculated values for totally random copolyesters...

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. 

Another point to be noted is the fact that the mesophase temperature ranges, i.e., ATlq= Ti - Tm, are broader for the random copolyesters than for the ordered sequence ones. This phenomenon is particularly evident when a copolyester is composed of linear and nonlinear units, as shown for the copolymers of Equations 20 and 22. 

The interchange reactions between two homopolyesters have been studied by many different groups(45-49). For example, Yamadera and Murano(46) observed that a random copolyester was obtained after 3 hours when poly(ethylene terephthalate) and poly(ethylene sebacate) were allowed to react at 276 °C. A similar observation was made by Zachmann et al.(47) for a mixture of deuteriated and nondeuteriated PET. 

Random copolyesters based on bromoterephthalic acid, methyl hydroquinone, and hexane diol have been synthesized. Their mesophase properties were studied by differential scanning calorimetry, optical microscopy, realtime X-ray diffraction and melt rheology. At low molecular weight these copolymers exhibit triphasic behavior, where two mesomorphic phases coexist with an isotropic phase. Fractionation based on solubility in THF enables the identification of two components. Simple statistical arguments are employed to model the polymerization reaction and account for the observed phase behavior. 

The groups of Windle (1) and Blackwell (2) have demonstrated that particular sequences of monomers in thermotropic LC random copolyesters lead to very small crystalline regions in the solid state. Based on a statistical treatment of random copolymerization one concludes that the probability of sequences matching in two different chains, and hence the degree of crystallinity, increases as the chain length is lowered (1). 

The lipase-catalyzed copolymerization of lactones often afforded random copolyesters, despite the different enzymatic polymerizability of lactones in some cases.165 167g-174 So far, the random copolymers were enzymatically obtained from combinations of d-VL-e-CL, e-CL-OL, e-CL-PDL, and OL-DDL. The formation of the random copolymers suggests that the intermolecular transesterifications of the polyesters frequently took place during the copolymerization. By utilizing this specific lipase catalysis, random ester copolymers were synthesized by the lipase-catalyzed polymerization of macrolides in the presence of poly-(e-CL).175... 

While the first efforts [11, 12] of the biotechnological generation of aliphatic homopolyesters and random copolyesters have been restricted essentially on monomers from 3-hydroxybutyric acid (3HB) and 3-hydroxypentanic acid (3HV), newer investigations concentrate on mraiomers with branches in the range of medium chain length, the so-called thermoplastic elastomers [13—15]. Steinbiichel et al. [3] catalogued more than 100 hydroxyalkanoic acids as craistituents of biosynthetic PHAs. 

Abe, H. and Doi, Y B/oraacwmo/e. 2002, 3/7/, 33- 3i. Side-Chain Effect of Second Monomer Units on Crystalline Morphology, Thermal Properties, and Enzymatic Degradability for Random Copolyesters of (R)-3-Hydroxybutyric Acid with (R)-3-Hy-droxyalkanoic Acids. 

CH2 carbons have shown the existence of two components with different Ti values for each carbon. This Ti result is in accord with the previous Ti results for poly[(R)-3-hydroxybutyric acid] [P(3HB)] homopolymer and other P(3HB)-type random copolyesters. In previous papers, however, the assignment of the two components with different Ti values have been remained unsolved. By performing variable-temperature experiments and by comparing with the results... 

Integral lines have been observed in the threaded texture [25] of a random copolyester prepared by the Eastman Kodak Company from 40 mol% poly(ethylene tereph-thalate) and 60 mol% jt -acetoxybenzoic acid and commercially known as X-7G ... 

Thin microtomed sections of these random copolyesters were... 

There is a further very important class of main-chain liquid-crystal polymers that differ from those discussed above by being random copolyesters based on polymers such as poly(hydroxybenzoic acid) -fO— —C=0), where — — represents a para-disubstituted benzene ring (para-phenylene unit). The random copolymers include units of various other forms containing phenylene or naphthylene rings and their introduction reduces the crystallinity and melting point considerably without necessarily lowering the value of Polymers of these types have... 

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