Grafting of polypeptides on polyhydroxy polymers

The homogeneous graft polymerization of γ-benzyl-l-glutamate NCA (N-carboxy anhydride) and ε-carbobenzoxy-l-lysine NCA on cellulose acetate alkoxide was studied to discover the mechanism of the graft polymerization. It was found that the initiation reaction was that of a direct addition of the alkoxide to carbonyl no. 5 of the NCA, and proof was obtained for the existence of an ester linkage between the polypeptide side chain and the cellulose acetate backbone. The polypeptide side chains had the amino group as the characteristic end group, as determined from titration and Van Slyke determination, and their DP_n was equal to [NCA]_o/[alkoxide]_o(A/I). A linear relationship was found between log [η] of graft polymer vs. log A/I, showing that DP{down triangle, filled} of the polypeptide side chains was proportional to A/I. The DP_w found on the cleaved polypeptide side chains was higher than A/I, and the ratio DP_w/DP_n was between 9 and 23. This high ratio was due to the fact that only 4-9 per cent of the alkoxide used initiated graft polymerization of the high molecular weight polypeptide side chains, the rest of the initiator leading to grafting of amino-acid units instead of the high polypeptide chains. The effects of the solvent, the alkali metal counterion and the concentrations of reactants on the intrinsic viscosity of the graft polymers was explained by the existence of propagation through a dissociated carbamate ion-pair as postulated by Idelson and Blout. The effect of both the polymeric backbone and the grafted side chains on the viscosity of the graft polymers was investigated and correlated with the conformation of the polypeptide side chains.