Polyanhydrides unsaturated

The second type of polymer, unsaturated polyanhydrides of the structure [-(OOC-CH=CH-CO)x-(OOC-R-CO)y-]n, have the advantage of being able to undergo a secondary polymerization of the double bonds to create a crosslinked matrix. This is important for polymers requiring great strength, for instance. These polymers were prepared from the corresponding diacids polymerized either by... 

Pharmaceutical research has to date been focused on polyanhydrides derived from sebacic acid (SA) and its copolymers with bis(p-carboxyphenoxy)propane (CPP) [75,113,115,119]. More recently, a new class of polyanhydrides was presented, containing fatty acid dimers (FAD) [ 116,118,258]. Erosion characteristics, microsphere preparation, pH-dependence, release rates, morphology, and in vivo performance of polyanhydrides from SA, CPP, and FAD have been intensely studied [75, 111-115,117, 119, 258-260]. Other unsaturated polyanhydrides have been derived from ricinoleic acid [261] and ricinoleic acid half-es-... 

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. 

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. 

Unsaturated polyanhydrides exhibiting unsaturated bonds along the chain and thus being suitable for the synthesis of a crosslinked matrix. Unsaturated bonds remain intact during polymerization. 

Unsaturated homopolymers are crystalline and insoluble in common organic solvents, whereas copolymers with aliphatic diacids are less crystalline and soluble in chlorinated hydrocarbons. The unsaturated polyanhydrides also provide a means for cross-linking through the double bonds that remain intact during the polymerisation process, and thus their mechanical properties can be improved (Domb et al., 1991). 

Polyanhydrides from Unsaturated and Fatty Acid-derived Monomers... 

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). 

Fig. 11 In situ formation of amine nucleophiles and a,/S-unsaturated carboxamides that react further in thermosetting of hyperbranched dendrimer-polyanhydride nanocomposite thin films...

Fatty acids have been used previously in the development of polymers for biomedical applications as they are considered to be inert, inexpensive and biocompatible. The main fatty acids which are used as a base for synthesis of biomedical polymers (polyanhydrides) are stearic acid (/), erucic acid (C22 unsaturated fatty acid) dimer (2), bile acid dimer (i), ricinoleic acid 4) and other fatty acids (5), middle long carbon chain (C12 - 15) dibasic acids, such as dodecanedioic, brassylic acid, tetradecandioic acid and pentadecandioic acid (/). 

There are three major classes of polyanhydrides aliphatic, unsaturated, and aromatic. The chemical structures are shown in Table 1. 

Polyanhydrides were synthesized from dimer and trimer of unsaturated fatty acids. The dimers of oleic acid and erucic acid, prepared by radical coupling via... 

Domb, A.J., Mathiowitz, E., Ron, E., Giannos, S., Danger, R., 1991. Polyanhydrides. IV. Unsaturated and crosshnked polyanhydrides. Journal of Polymer Science Part A Polymer Chemistry 29, 571-579. 

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