Polyanhydrides solution polymerization

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... 

The development of unsaturated polyanhydrides responded to the necessity of improving the mechanical properties of the polymers in applications such as the temporary replacement of bone. " Unsaturated polyanhydrides, prepared by melt or solution polymerization, include homopolymers of fumaric acid (FA), acetylene-dicarboxylic acid (ACDA), and 4,4 -stilbenzenedi-carboxylic acid (STDA). The chemical structures of poly(FA) and poly(ACDA) are shown in Table 1. These polymers are highly crystalline and insoluble in common organic solvents. The double bonds of these monomers make them suitable for further crosslinking to improve mechanical properties of polyanhydrides. When copolymerized with aliphatic diacids, less crystalline polymers with enhanced solubility in chlorinated solvents result. 

The Schotten-Bauman condensation produces polyanhydrides with moderate molecular weights by a dehydrochlorination reaction between a diacid chloride and a dicarboxylic acid. The polymerization takes place by reacting the monomers for 1 hr at room temperature, and it can be conducted via solution or interfacial methods. Solvents that are used in solution polymerization include dichloromethane, chloroform, benzene, and ethyl ether. The degree of polymerization obtained with this method is approximately 20-30. Lower molecular weight products are obtained for less reactive monomers such as isophthaloyl chloride. 

A series of unsaturated polyanhydrides were prepared either by melt or solution polymerization of fumaric acid (FA), acetylenedicarboxylic acid (ACDA), and 4,4 -stilbenedicarboxylic acid (STDA) [39,40]. The properties of several of these polymers are listed in Table 3. 

Polyanhydrides of diacid monomers containing aliphatic and aromatic moieties, poly[p-carboxyphenoxyalkanoic anhydride], were synthesized by either melt or solution polymerization with molecular weights of up to 44600 (Table 8) [52]. 

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

The solution polymerization is carried out by Schotten-Baumann technique. In this method, the solution of diacid chloride is added dropwise into an ice-cooled solution of a dicarboxylic acid. The reaction is facilitated by using an acid acceptor such as triethylamine. Polymerization takes place instantly on contact of the monomers and is essentially complete within 1 h. The solvents employed can be a single solvent or a mixture of solvents like dichlorometh-ane, chloroform, benzene, and ethyl ether. It was found that the order of addition is very important in obtaining relatively high-molecular-weight polyanhydrides. Addition of... 

Polyanhydrides have been synthesized by melt condensation of activated diacids (Domb et al, 1987), ring opening pol) merization, dehydrochlorination, and dehy-drative coupling agents (Leong et al, 1987 Domb et al, 1988). Solution polymerization yielded in general low molecular weight pol miers. The most widely used method is the melt condensation of dicarboxylic acids treated with acetic anhydride ... 

---