Kinetics of γ-benzyl-L-glutamate NCA's polymerizations and molecular-weight distributions on corresponding polymers

The kinetics of γ-benzyl-L -glutamate NCA's polymerizations in dioxane as solvent are discussed. The partial orders respective to A], the NCA concentration and I₀], the initial initiator concentration are given; the rate constants are deduced and a mechanism is proposed to justify a rate of polymerization V_p = kA]I₀]². The dependence of the rate constants on the conformation of the growing chains is demonstrated; the acceleration is attributed to the ordered structures favorable to hydrogen bonding. The kinetics of aging have also been examined and discussed; it is shown that they cannot modify the kinetics of polymerization. The DP _n were obtained on the same samples before and after debenzylation; it is proved that at any concentration, DP _n ? A₀]/I₀]. The molecular-weight distributions were obtained by chromatography and a polydispersity lower than 1.3 was deduced for each sample. The trimodal distribution, appearing as soon as A₀]/I₀] is larger than 3, is attributed to the existence of the three structures σ, β, and α. The weight fraction of each of the structures was correlated to the kinetics of polymerization.