| Abstract: | The temperature dependence of the polymerization rate is investigated using the NCA's of β-benzyl L-aspartate and γ -benzyl L-glutamate. Activation energies for polymerizing the above NCA's are 13 and 9 Kcal per mole, respectively. Entropies of activation and Arrhenius constants, A, are also calculated and discussed in terms of the polymerization mechanism. The significance of the proton-transfer reaction in the “active monomer” mechanism is recognized through a kinetic isotope effect and also by comparing the polymerization rates of L-alanine NCA and its structural analog L-alanine N-thiocarboxyanydride. It is theorized that a changing position of equilibrium of the neutralization step decreases the concentration of “active monomer”, thereby slowing the polymerization rate. |
