Graft Copolymers of Amino Acids onto Natural and Synthetic Polymers

Abstract

By analogy with natural chitin-protein complexes, grafting of amino acids to natural polymers produces biodegradable biocomposites. The literature on grafting amino acid N-carboxyanhydrides (NCAs) to proteins, natural polymers and vinyl polymers is reviewed. Macroinitiators with primary amino substituents were synthesized by one of the following techniques: (a) cyanoethylation of cellulose followed by reduction to produce aminopropylcellulose [1], and (b) phthalimidation followed by hydrazinolysis to yield amino-methyl poly(arylene ether sulfone) [3]. Heterogeneous grafting of γ-benzyl-L-glutamate-N-carboxyanhydride (BLG-NCA) [8] to polymer [1] resulted in non-random distribution of amino acid residues; a-helical conformations were detected at low BLG-NCA/NH2 ratios ( 80%) were achieved. Polypeptides grafted to polymer [3] appeared to adopt the expected conformation for the chain length predicted by the BLG-NCA/NH2 ratio. The benzyl ester functions on the BLG grafts are subject to direct modification with amine nucleophiles; studies with butylamine correlate reaction conditions with extent of ester vs. peptide cleavage. In the presence of 1-hydroxybenzotriazole, aminolysis of the ester is favored and conversions to γ-amides up to 75% are achieved.