Copolyesters microstructure

One may now ask whether natural systems have the necessary structural evolution needed to incorporate high-performance properties. An attempt is made here to compare the structure of some of the advanced polymers with a few natural polymers. Figure 1 gives the cross-sectional microstructure of a liquid crystalline (LC) copolyester, an advanced polymer with high-performance applications [33]. A hierarchically ordered arrangement of fibrils can be seen. This is compared with the microstructure of a tendon [5] (Fig. 2). The complexity and higher order of molecular arrangement of natural materi-... 

Figure 1 Schematic representation of the microstructure and cross-sectional view of a liquid crystEilline copolyester fiber [33].

This topic has been the subject of considerable debate over the past decade. In fact, with respect to the three best known structures indicated in Fig. 1, there are almost as many reports indicating that the sequence distributions are blocky as there are claiming that they are random [7-13]. A similar confusion has surrounded possible changes in the microstructure on heating these copolyesters in the nematic melt. In this latter case, some workers have argued that these systems are stable in the melt [7], while others claim that they undergo ordering... 

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... 

The complex viscosity of BB1 was measured at 290°C in both cone and plate and parallel plates geometry and showed no significant differences. The general trend that systems containing some kind of microstructures in the melt (suspensions) show complex viscosities higher than the steady shear viscosities, was also true in this case. A similar observation was made with an Eastman copolyester (31). 

A comprehensive interpretation of the microstructure of the liquid crystalline aromatic copolyesters is presented. The role of the synthetic route and of high temperature processing on the microstructure are clearly defined. As a result of this study a predictive model now exists which permits interpretation of the very subtle chemical processes which can occur at elevated temperatures leading to either randomization or ordering of the microstructure. 

ECONOMY ETAL. Synthesis and Microstructure of Aromatic Copolyesters 135... 

Windle and coworkers [51, 54, 56] have then interpreted some discrepancies between optical microstructures and X-ray diffraction patterns of nematic domains in copolyesters 3 and 6 in terms of biaxiality. 

Montaudo, G., Montaudo, M.S., Scamporrino, E., and Vitalini, D., Composition and Microstructure of a copolyester Formed in the Melt-Mixing of Poly(ethylene terephthalate) and Poly(ethylene truxillate), DieMakromoL Chem, 194,993 (1993). 

Montaudo, G., Montaudo, M.S, Scamporrino, E., and Vitalini, D., Composition and microstructure of copolyesters formed in the melt mixing of poly(ethylene terephthalate) and poly(ethylene truxillate), Makromol. Chem., 194, 993, 1993. Montaudo, G., Puglisi, C., and Samperi, E, Copolymer Composition a Key to the Mechanism of Exchange in Reactive Polymer Blending, in Transreactions in Condensation Polymers, Kakirov, S., Ed., Wiley-VCH, Weinheim, 1999. Bloembergen, S., Holden, D.A., Hamer, G.K., Bluhm, T.L., and Marchessault, R.H., Studies of Composition and Crystallinity of Bacterial Poly()3-hydroxybu-tyrate-co-jS-hydroxyvalerate), Macromolecules, 19, 2865,1986. 

Sequence distribution and chemical structure of mass-selected macromolecules of macroinitiators derived from selected biopolyesters were accomplished recently with the aid of ESI-Mtechnique. The NMR and ESI-MS evaluation of the chemical structure of macroinitiators obtained by partial depolymerization of natural PHB, PHBV and PHO revealed that due to the elimination reaction they contain olefinic and carboxylic end groups. Based on the ESI-MS" studies of PHBV macroinitiator obtained by partial alkaline depolymerization of natural PHBV (containing 5 mole % of hydroxyvalerate units) the microstructure of this bacterial copolyester was assessed, starting from dimer up to the oligomer containing 22 repeat units. ... 

Gan ZH, Abe H, Kurokawa H, Doi Y (2001) Solid-state microstructures, thermal properties, and crystallization of biodegradable poly(butylene succinate) (PBS) and its copolyesters. Biomacromolecules 2 605-613... 

Du C, Lin SKC, Koutinas A, Wang R, Webb C (2007) Succinic acid production from wheat using a biorefining strategy. Appl Microbiol Biotechnol 76 1263-1270 Fujimaki T (1998) Processability and properties of aliphatic polyesters, BIONOLLE , synthesized by polycondensation reaction. Polym Degrad Stab 59 209-214 Gan ZH, Abe H, Kurokawa H, Doi Y (2001) Solid-state microstructures, thermal properties, and crystallization of biodegradable poly(butylene succinate) (PBS) and its copolyesters. Biomacromolecules 2 605-613... 

Tjong, S. C. and Meng, Y. Z. 1999. Microstructural and mechanical characteristics of compatibilized polypropylene hybrid composites containing potassium titanate whisker and liquid crystalline copolyester. Polymer 40 7275-7281. 

Flores, A., Ania, F., Balta Calleja, F. J. (1997). Novel aspects of microstructure of liquid crystalline copolyesters as studied by microhardness Influence of composition and temperature, 38(21), 5447-5453. 

Microstructure of block copolyester with crystalline domains. 

Fig. 27. Microstructures of liquid crystal copolyesters obtained in polarized light showing the variation of orientation with position in (a) polymer X of a degree of polymerization greater than 100. (Photograph courtesy of T. J. Lemmon, Department of Materials Science and Metallurgy, Pembroke Street, Cambridge.) (b) polymer XI with a degree of polymerization of approximately 50. ...

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