Polyanhydrides melt polycondensation

Leong, K. W., Simonte, V., and Danger, R., Synthesis of polyanhydrides Melt-polycondensation, dehydrochlorination, and dehydrative coupling. Macromolecules, 20. 705-712, 1987. 

Several approaches were examined for synthesizing polyanhydrides melt polycondensation, dehydrochlorination, and dehydrative coupling. A report of polyanhydride synthesis techniques and polymerization conditions for polyanhydrides appears in Leong et al. (22). 

We examined several approaches for synthesizing polyanhydrides, including melt polycondensation, dehydrochlorination, and dehydrative coupling. Extensive details of these new polymer synthesis techniques and numerous polymerization conditions for a wide variety of polyanhydrides were previously described (1). 

Synthesis of polyanhydrides from the aromatic dicarboxylic acids (isophthalic and terephthalic acids) by melt polycondensation was first... 

Scheme 2. Polyanhydride synthesis via melt polycondensation involves first the formation of oligomeric acetylated prepolymers, followed by condensation under vacuum. Acetic acid is formed as a byproduct of the second reaction.

Polyanhydrides based on unsaturated and fatty acid-derived monomers are shown in Table III. Poly(fumaric acid) (PFA) was fist synthesized by Domb et al. (1991) by both melt polycondensation and solution polymerization. The copolymer of fumaric acid and sebacic acid (P(FA-SA)) has been synthesized and characterized (Domb et al., 1991 Mathiowitz et al., 1990b). The mucoadhesive properties of this polymer... 

Fatty acids have also been converted to difunctional monomers for polyanhydride synthesis by dimerizing the unsaturated erucic or oleic acid to form branched monomers. These monomers are collectively referred to as fatty acid dimers and the polymers are referred to as poly(fatty acid dimer) (PFAD). PFAD (erucic acid dimer) was synthesized by Domb and Maniar (1993) via melt polycondensation and was a liquid at room temperature. Desiring to increase the hydrophobicity of aliphatic polyanhydrides such as PSA without adding aromaticity to the monomers (and thereby increasing the melting point), Teomim and Domb (1999) and Krasko et al. (2002) have synthesized fatty acid terminated PSA. Octanoic, lauric, myristic, stearic, ricinoleic, oleic, linoleic, and lithocholic acid acetate anhydrides were added to the melt polycondensation reactions to obtain the desired terminations. As desired, a dramatic reduction in the erosion rate was obtained (Krasko et al., 2002 Teomim and Domb, 1999). 

Synthesis of polyanhydrides is carried out through generalized methods such as melt polycondensation, solution polymerization, use of coupling agents, and ring-opening polymerization. 

Polyanhydrides hydrolyse to their constituent dicarboxylic acids in aqueous media. They have been used and investigated as an important biomaterial for short-term release of drugs for more than two decades. " They are produced by melt polycondensation of diacids and have glass transition temperatures in the range of 50-100 °C. Owing to their highly hydrophilic... 

Polyanhydrides have been synthesized by various techniques such as melt polycondensation, ring-opening polymerization, interfacial polycondensation, dehydrochlorination, and dehydrative coupling (13,14). The most widely used technique for polyanhydride synthesis is melt polycondensation, which occurs in two steps. In the first step, dicarboxylic acid monomers react with excess acetic anhydride to form acetyl-terminated anhydride prepolymers (1) with a degree of polymerization (DP) ranging from 1 to 20 (eq. 1). 

Because melt polycondensation often requires a high temperature, it is not suitable for making heat sensitive polymers. A variety of solution pol5mierizations at ambient temperature have been reported (18,22). Polyanhydride formation can be effected at room temperature by a dehydrochlorination between a diacid chloride and a dicarboxylic acid (eq. 3). 

Polyanhydrides are biodegradable polymers with backbone composed of repeat units linked by anhydride bonds (Figure 16.15). They have been synthesized by several techniques, including melt-polycondensation, dehydrochlorination and dehydrative coupling. Melt-polycondensation is the method which allows the obtainment of POA with higher molecular weights [56]. 

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