GREEN CHEMISTRY Structure of PHA films The poly(hydroxyalkanoic acids) are bacterial polymers with remarkable biodegradability characteristics. N. Koyama and Y. Doi reported on how the structure of polyhydroxyalkanoate films influenced their enzymatic degradation. Several homopolymers and copolymers were studied, and polymer films crystallized from the melt. Crystallinity ranged from 53% to 80% for the homopolymers and from 39% to 71% for the copolymers. The rates of enzymatic degradation decreased with increases in crystallinity. The copolymer films were degraded several times faster than homopolymer films with the same degree of crystallinitv The authors sueeested that degradation rate is rr J l i J r IT • dllcLLcU Vy LIlc U c g r c c Ul L-I ybldlilllity
droxyaiKanoate mm. {ivicicroniole-
Biodegradable polymers Amino acid linkages can be inserted into the backbone of synthetic polymers to provide sites for cleavage by enzymes widely distributed in the environment. Such polymers could have enhanced biodegradability. S. Jin and colleagues report synthesis of two monomers containing the leucine-tyrosine linkage and two different length spacers: hexamethylenediamine and Jeffamine®-D400. Three polyureas, a polyamide, and a polyesteramide were synthesized from combinations of the monomers The polyureas had higher molecular weights and greater polydispersities than the polyamides The authors conclude that their techniques can be used in synthesizinff polymers containing amino acid linkages with a varietv anri that thpv havp thp notential for hinHppradahilitv (T Pnlvm SW : Part A- Pnlvm Chem 1997 It 49
