Branched polyanhydrides

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). 

Sanders et al. (1999) attempted to lower the melting points of aromatic polyanhydrides by substituting branched alkyl groups in place of the linear alkyls of P(CPP-SA). They synthesized poly[l,2-bis(/ -carboxyphenoxy)-propane-co-sebacic acid] (P(1,2-CPP-SA)), poly[l,3-bis(/ -carboxyphenoxy)-2-methyl propane-co-sebacic anhydride] (P(CPMP-SA)), and poly[l,3-bis (/ -carboxyphenoxy)-2,2-dimethyl propane-co-sebacic anhydride] (P(CPDP SA)), all of which had melting points below 165°C. 

The branched aromatic polyanhydrides synthesized by Sanders et al. (1999 Mathiowitz et al., 1990b) demonstrated lower Tgs than the corresponding P(PCPP-SA) copolymers. The para-xylyl polymers synthesized by Anastasiou and Uhrich (2000a) (Pp-o-CPX and Pp-m-CPX) had systematically higher Tgs than the ortho-isomers (Po-o-CPX, Pm-o-CPX, P/uo-CPX). 

The physical and mechanical properties of polyanhydrides can be altered by modification of the polymer structure with a minor change in the polymer composition. Several such modifications include the formation of polymer blends, branched and crosslinked polymers, partial hydrogenation and reaction with epoxides. 

Fig. 5. Molecular weight of branched polyanhydrides effect of the concentration of poly(acrylic add) (PAA) branching agent on gei time, and molecular weight ( ) 0% (o) 0l5% ( ) 1.0% (A) 1.5% , (A) 2.0%. (from Ref [60])...

Polyanhydrides were effective as diacid substrate for enzjunatic synthesis of polyesters (136). The reaction of poly(azelaic anhydride) and 1,8-octanediol took place by lipase CA catalyst to give the corresponding polyester with molecular weight of several thousands. In the reaction of poly(azelaic anhydride) and glycerol, a highly branched polyester was obtained. 

Bhardwaj and Mohanty [8] proposed and demonstrated a new industrially relevant methodology to develop a polylactide (PLA)-based nano blend having outstanding stiffness-toughness balance. In this approach, a hydroxyl functional hyper branched polymer (HBP) was in situ cross-linked with a polyanhydride (PA) in the PLA matrix during melt processing. There was formation of new HBP-based cross-linked particles in the PLA matrix. TEM and AFM revealed the sea-island morphology of... 

Lutolf, M. P., J. L. Lauer-Fields, H. G. Schmoekel et al. 2003. Synthetic matrix metalloproteinase-sensitive hydrogels for the conduction of tissue regeneration Engineering cell-invasion characteristics. Proceedings of the National Academy of Sciences of the United States of America. 100 5413-18. Maniar, M., X. D. Xie, and A. J. Domb 1990. Polyanhydrides. 5. Branched polyanhydrides. Biomateriak. 11 690-94. 

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