Abstract
DL-β-Phenylalanine N-carboxyanhydride(NCA) was polymerized by poly(N-n-propylglycine) diethylamide (DEA) at a much faster rate than by low molecular weight amines having a similar base strength. This phenomenon (the chain effect) had been observed also with other polypeptides such as polysarcosine DEA and poly(N-ethylglycine) DEA. The chain effect was found to diminish in the order: polysarcosine DEA > poly(N-ethylglycine) DEA > poly(N-n-propylglycine) DEA. In order to compare these polymer catalysts, the equilibrium constant for the NCA adsorption on to the polymer chain by hydrogen bonding was determined. It was found to be almost the same for the three polymer catalysts. The intrinsic reactivity of the terminal base group of the polymer catalyst was also determined. It was found to decrease as the N-alkyl substituent became bulkier (that is, methyl > ethyl > n-propyl). As a consequence, the difference in the chain effect was ascribed mostly to the latter effect. However there still remains some difference in the reactivity of polymer catalysts, which can be explained in terms of the flexibility of the polymer chain.
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