Aliphatic polyesters polymers

A variety of low-molecular-weight artificial synthetic compounds are biodegradable, whereas only few synthetic polymers are biodegradable. Among synthetic polymers, aliphatic polyesters are generally known to be susceptible to biological attack (1-5) ... 

Determination of B for a series of blends made it possible to establish empirical rules for the observed miscibilities. Thus, for example, Prud homme [1982] reported systematic variation of miscibility in a series of halogenated polymer/ aliphatic polyester blends. The highest miscibility was observed for the chlorinated polymer, e.g., PVC, and the lowest for the fluorinated, PVF, with the brominated, PVB, having an intermediate behavior. Furthermore, when the chlorinated polymer was mixed with a series of polyesters, the highest miscibility was found when the ratio of the -CH - to -COO- groups reached an optimum value. This optimum value depended on the chemical nature of the halogenated polymer — as shown in Figure 2.7, for PVDC blends with aliphatic polyesters this value is 5 to 6. 

Key words bioresorbable medical polymers, aliphatic polyesters, polyanhydrides, poly(ortho esters), polyphosphazenes, poly(amino acids), polyalkylcyanoacrylates, poly(propylene fumarate), poloxamers, poly(p-dioxanone), polyvinyl alcohol. 

Aldiough they were the first step-growth polymers fully characterized, it is interesting to note that die first commercial applications of aliphatic polyesters appeared only in the late 1950s and the 1960s, widi die development of polyurediane foams and elastomers (see Chapter 5). 

Aliphatic polyesters are low-melting (40-80°C) semicrystalline polymers or viscous fluids and present inferior mechanical properties. Notable exceptions are poly (a-hydroxy acid)s and poly (ft -hydroxy acid)s. 

PET, PTT, and PBT have similar molecular structure and general properties and find similar applications as engineering thermoplastic polymers in fibers, films, and solid-state molding resins. PEN is significantly superior in terms of thermal and mechanical resistance and barrier properties. The thermal properties of aromatic-aliphatic polyesters are summarized in Table 2.6 and are discussed above (Section 2.2.1.1). 

Although low-molar-mass aliphatic polyesters and unsaturated polyesters can be synthesized without added catalyst (see Sections 2.4.1.1.1 and 2.4.2.1), the presence of a catalyst is generally required for the preparation of high-molar-mass polyesters. Strong acids are very efficient polyesterification catalysts but also catalyze a number of side reactions at elevated temperature (>160°C), leading to polymers of inferior quality. Acid catalysts are, therefore, not much used. An exception is the bulk synthesis of hyperbranched polyesters reported in Section 2.4.5.1, which is carried out at moderate temperature (140°C) under vacuum in the presence of p-toluene sulfonic acid catalyst. The use of strongly acidic oil-soluble catalysts has also been reported for the low-temperature synthesis of polyester oligomers in water-in-oil emulsions.216... 

Phthalazinone, 355 synthesis of, 356 Phthalic anhydride, 101 Phthalic anhydride-glycerol reaction, 19 Physical properties. See also Barrier properties Dielectric properties Mechanical properties Molecular weight Optical properties Structure-property relationships Thermal properties of aliphatic polyesters, 40-44 of aromatic-aliphatic polyesters, 44-47 of aromatic polyesters, 47-53 of aromatic polymers, 273-274 of epoxy-phenol networks, 413-416 molecular weight and, 3 of PBT, PEN, and PTT, 44-46 of polyester-ether thermoplastic elastomers, 54 of polyesters, 32-60 of polyimides, 273-287 of polymers, 3... 

Nagata M, Kiyotsukuri T, Ibuki H, Tsutsumi N, and Sakai W. Synthesis and enzymatic degradation of regular network aliphatic polyesters. React Fund Polym, 1996, 30, 165-171. 

Chu, C. C., Degradation phenomena of two linear aliphatic polyester fibers used in medicine and surgery. Polymer. 26,... 

Schindler, A., Hibionada, Y. M., and Pitt, C. G., Aliphatic polyesters III. Molecular weight and molecular weight distribution in alcohol-initiated polymerization of e-caprolactone, J. Polym. Sci., Part A Polym. Chem., 20. 319-326, 1982. 

Aliphatic polyesters based on monomers other than a-hydroxyalkanoic acids have also been developed and evaluated as drug delivery matrices. These include the polyhydroxybutyrate and polyhydroxy valerate homo- and copolymers developed by Imperial Chemical Industries (ICI) from a fermentation process and the polycaprolactones extensively studied by Pitt and Schindler (14,15). The homopolymers in these series of aliphatic polyesters are hydrophobic and crystalline in structure. Because of these properties, these polyesters normally have long degradation times in vivo of 1-2 years. However, the use of copolymers and in the case of polycaprolactone even polymer blends have led to materials with useful degradation times as a result of changes in the crystallinity and hydrophobicity of these polymers. An even larger family of polymers based upon hydroxyaliphatic acids has recently been prepared by bacteria fermentation processes, and it is anticipated that some of these materials may be evaluated for drug delivery as soon as they become commercially available. 

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