Fractionated random copolyester

Table 5.2 Light scattering, photon correlation spectroscopy, viscosity and size-exclusion chromatography data of a fractionated random copolyester (for structure and composition see text) in BTFMP at 60 C [8]... 

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. 

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. 

In 1990, 3,5-bis(trifluoromethyl)phenol (BTFMP) was found to be a solvent for aromatic polyesters [6-9]. This discovery made it possible to perform for the first time the fractionation and molecular characterization of a thermotropic MCLC copolyester. Table 5.2 reports results for a typical random copolyester consisting of 70mol% of p-hydroxybenzoic acid and 30mol% of 2-hydroxy-6-naphtho acid moieties. 

Montaudo and co-workers [8] reported on a SEC/MALDI study of molar mass distribution in two random copolyesters polybutylene adipate - polybutylene sebacate (PBA - PBSe) and polybutylene sebacate - polybutylene sccinate (PBSe - PBSu). MALDI allows desorption and when polydisperse polymer samples are fractionated by size exclusion chromatography, they yield fractions with very narrow distributions which, when analysed by MALDI give mass spectra with molar mass values in excellent agreement with those obtained by conventional techniques. These workers derived the following equation for the molar mass of the copolymer molecule ... 

Copolyesters of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) were produced by Burkholderia cepacia D1 at 30 °C in nitrogen-free culture media containing n-butyric acid and/or n-valeric acid [115]. When n-valeric acid was used as the sole carbon source, the 3HV fraction in copolyester increased from 36 to 90 mol% as the concentration of n-valeric acid in the culture medium was increased from 1 to 20 g/1. The addition of n-butyric acid to the culture solution resulted in a decrease in the 3HV fraction in copolyester. The copolymers biosynthesized by this method were mixtures of random copolymers having a wide variety of composition of the 3HV component. The melting points of the fractionated copolymers show a concave curve with the minimum at the 3HV content of approximately 40 mol%. The alpha-parameter of lattice indices of the PHB crystal for the fractionated copolymers largely increased as the 3HV composition increased. Biodegradability of the copolymer increased with the lower content of 3HV composition and/or the lower crystallinity. 

Fig. 1. Melting temperature (—and enthalpy (—, AH) of poly(8CL-co-6VL) random copolymers at different compositions, as synthesized by coordination-insertion ROP initiated with Al(OzPr)3 in toluene at 0 °C. is the molar fraction of eCL in the copolyester. (Tjjj and AH were determined by DSC at a heating rate of 10 °C/min)...

To understand the nature of the microstructures that are present in these systems it is important to start by examining the role of the synthetic route in preparing these copolyesters. In the case of the PHBA/PET copolyester, this system presents a degree of complexity which is unusual. In the mid seventies, Jackson and Kuhfus reported that this system was random, but they did not comment on the possibility of compositional variations [2]. Fortunately, because of the modest solubility of this system, most of the confusion has recently been eliminated through detailed NMR studies [9]. Thus, it has been shown that the 60/40 PHBA/PET copolymers originally available from Tennessee Eastman actually consisted of two distinct compositions, namely 44/56 and 62/38 PHBA/PET (see Fig. 11). Furthermore, the soluble PET rich fraction ( 20%) was shown to be blocky while the insoluble PHBA rich fraction (80%) was more random (see Fig. 12). These observations can be explained from a... 

To check the influence of the length of the aliphatic and aromatic sequences in the chains, we synthesised copolyesters of different structure, such as (blends), block copolymers, random copolymers and alternating BTA copolyester, all with the same fraction of terephthalic acid (50 mol % of the total acid components) (Fig 5). 

Crystallization provides the driving force for phase separation in these materials as well. These materials have especially low chemical permeability and can offer good properties at low temperatures. A commercial example of a copolyamide is PEBAX [7] marketed by Atofina. Copolyamides compete with polyurethanes and copolyesters for market share. lonomers are the final material that will be discussed. lonomers are materials where a small mole fraction of monomers, usually less than 10%, contain an ionic functionality. These materials are not segmented like most of the other materials discussed in this chapter, rather the ionic groups are distributed randomly along the polymer backbone. Incompatibility between the ionic groups and the nonpolar polymer backbone leads to the formation of ionic-rich domains. A commercial example of an ionomer is Surlyn [8] manufactured by DuPont, shown in Fig. 2. 

Studies on the melt behaviour of the aromatic copolyesters of poly(ethylene terephthalate) and / -acetoxybenzoic acid have been reported previously. Baird and co-workers have examined the rheological properties of the 40/60 and 20/80 (PET/PHBA) copolyester compositions over a wide temperature range and observed that the melt viscosity of both copolyester compositions was significantly lower than that of poly(ethylene terephthalate) and dependent on the composition of the copolyester. Wissbrun has also studied the flow properties of liquid-crystalline behaving polymers and observed that the flow curves of the 40/60 (PET/PHBA) copolyester composition are very sensitive to the temperature of the melt and its thermal history. In our studies " we observed that the 20/80 (PET/PHBA) copolyester is a block copolymer in which the PHBA blocks aggregate in crystalline domains in contrast to PET/PHBA copolyesters with lower fractions of PHBA which are reported to be random copolymers. 

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