Aliphatic polyesters and copolyesters

3 and 1,4-cyclohexanedimethanol, or mixtures of them, have been used for the synthesis of biodegradable aliphatic polyesters and copolyesters or segmented copolyesters with potential biomedical applications. Polycondensation in the melt has been usually the method chosen for the preparation of these polyesters. Enzymatic polymerizations of 1,4-CHDM with succinic, adipic, suberic and sebacic acids using a cutinase from Humicola insolens have been recently reported (17), but the resulting polyesters had moderate molecular weights. 

Riande et al. (21,22) synthesized the cis and tmns isomers of PCDS as well as the trans isomer of poly(l,4-cyclohexylenedimethylene adipate) (PCDA), and studied their polarity by measurements of dielectric constants and dipole moments. They observed that the trans isomer exhibited lower polarity than the cis one, and that the dipole moment decreased with the number of methylene groups of the diacid unit. The configurational properties of the two PCDS isomers were comparatively examined, both experimentally and theoretically, using the rotational isomeric state model. 

An unsaturated polyester with = 140 °C and T = 20 °C has been prepared from 1,4-CHDM and diethyl fumarate by melt poly-condensation. The polyester was then crosslinked using N-vinyl pyrrolidone in the presence of variable amounts of inorganic fillers. The hydrolytic stability of these composites with different compositions was then examined for their potential use as bioresorbable boned cements (27). 

When bicyclic rigid units are copolymerized with CHDM, as for instance bicyclo[2.2.2]octane-l,4-dicarboxylate, a notable increase in takes place in the polyesters (33). Such a behavior was claimed to be a clear advantage to spread the applications of these materials. 

1 Poly(e-caprolactone)/PLA Blends Poly( -caprolactone) (PCL) is a water-insoluble biodegradable, petroleum-based aliphatic polyester synthesized by ringopening polymerization of -caprolactone (e-CL) [81, 82]. PCL blends are widely used in many applications such as compostable bags for yard waste or other organics collection, disposable food service items, food packaging, health care products, mulch films in agriculture, and adhesives [81, 82, 101-103]. The nontoxicity, biocompatibility. 

FIGURE 16.10 Ternary phase diagrams obtained by turbidity measurements at room temperature (a) PVP/PDLLA/CH2CI2 and (b) PVP/PLLA/CH2CI2. The solid symbols show the compositions of the solutions used for electrospinning, and the hollow squares mark the phase boundary. The concentrations are given in wt%. Reprinted from Ref 100. Copyright 2001, with permission from John Wiley Sons, Inc. 

FIGURE 16.11 Cloud point curve for PDLA/PCL system at three heating rates 2.0, 1.0, and 0.5°C/min. The uncertainty in temperature is 0.5°C an in composition if 0.5 wt%. Reprinted from Ref. 121. Copyright 2000, with permission from John Wiley Sons, Inc. 

The phase morphology and/or phase inversion of immiscible PLA/PCL blends have been investigated by a number of researchers using SEM. A dispersed particle-matrix structure was found with higher weight fractions of PLA (0.7-0.9), where PCL was a dispersed phase and PLA was a continuous phase. With lower weight fractions of PLA (0.4-0.7), PLA was the dispersed phase and PCL was the matrix [117, 120, 127]. A fibrous domain structure and also 

Zhang et al. [133] reported that PHB/PDLLA blends prepared by solvent casting were immiscible. However, greater miscibility was observed for 60% PLA and 40% PHB samples prepared by melt blending. The blend solution was magnetically stirred and evaporated at 190°C for 30 min. The miscibility was ascribed to possible small-scale trans-esterification. The rate of crystallization of PHB decreased with an increase in the PLA content in the blends, and the final blends showed improvement in mechanical properties compared to the neat polymers. 

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Several review articles on biodegradable polymers and polyesters have appeared in the literature [12-22]. Extensive studies have been carried out by Al-bertsson and coworkers developing biodegradable polymers such as polyesters, polyanhydrides, polycarbonates, etc., and relating the structure and properties of aliphatic polyesters prepared by ROP and polycondensation techniques. In the present paper, the current status of aliphatic polyesters and copolyesters (block, random, and star-shaped), their synthesis and characterization, properties, degradation, and applications are described. Emphasis is placed primarily on aliphatic polyesters derived by condensation of diols with dicarboxylic acids (or their derivatives) or by the ROP of cyclic monoesters. Polyesters derived from cyclic diesters or microbial polyesters are beyond the scope of this review. 

Aliphatic polyesters and copolyesters (e.g. poly(butylene succinate) - PBS poly (butylene snccinate adipate) - PBSA). 

Poly(ethylene succinate adipate) PESA Figure 2-17 Aliphatic polyesters and copolyesters. 

Commercially available aliphatic polyesters and copolyesters are given in Table 2.11. 

Table 2.11. Aliphatic polyesters and copolyesters commercially available...

Aliphatic polyesters and copolyesters Aromatic polyesters and copolyesters Poly(caprolactone) - PCL Poly(esteramide)s - PEA Poly(vinyl alcohol) - PVA... 

Commercial aliphatic polyesters and copolyesters under the tradename Bionolle (Showa Highpolymer, Japan) are white crystalline thermoplastics, have melting points ranging from... 

Aliphatic polyesters and copolyesters based on sncdnic add and commercialized under the name Bionolle are biodegradable in compost, in moist soil, in fresh water with activated sludge and in sea water [67]. 

The large variety of polyesters or copolyesters that can be obtained with 1,4-CHDM make these products usable in a broad range of applications. Thus aliphatic polyesters and copolyesters are produced to generate biodegradable or biocompatible objects, as it is the case of poly(l,4-cyclohexylenedimethylene fumarate), with application in the manufacture of bioresorbable bone cement composites (27). Polyoxaesters of 1,4-CHDM are a new class of synthetic absorbable polyesters with potential surgical applications as suture coatings, or adhesion prevention barriers (28). 

The results obtained in the field of thermoplastic starch in combination with polymers or copolymers of vinyl alcohol with aliphatic polyesters and copolyesters in terms of biodegradation kinetics, mechanical properties and reduced sensitivity to humidity make these materials ready for a real industrial development starting from film and foam applications. The present global market is around 12000 tons/year. Main producers are Novamont with Mater-Bi trade-mark, ENPAC and National Starch. The tensile properties of films made of two Novamont s Mater-Bi grades are reported in Table 3, in comparison to these of low density polyethylene (LDPE). Figs. 6-7 show applications of Mater-Bi starch-based materials now on the market. 

Pure P(3HB) has poor physical properties for commercial use, as it is stiff, brittle and has a very small window of processing conditions. This has led to an increased interest in the production of other microbial aliphatic polyesters and copolyesters with improved properties, characterised by different functional groups [17]. 

Products are available based on thermoplastic starch in combination with polymers or copolymers of vinyl alcohol and with aliphatic polyesters and copolyesters. Their biodegradation kinetics, mechanical properties and reduced sensitivity to humidity make these materials suitable for industrial development beginning with film and foam applications. 

Biodegradable polymers can also be produced from petroleum sources and are comprised of aliphatic polyesters and copolyesters (e.g., PBS, and poly(butylene succinate adipate)—PBSA), aromatic copolyesters (e.g., poly(butylene adipate terephthalate)—PBAT), poly(e-caprolactone) PCL, polyesteramides (PEA), and poly(vinyl alcohol) (PVA). Further details concerning the synthesis of these polymers can be found in the book by Rudnik (2008). In this section we summarize some of the key properties of these materials... 

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