Highly Radical-Polymerizable Methacrylamide Having Dipeptide Structure. Synthesis and Radical Polymerization of N-Methacryloyl- l -leucyl- l -alanine Methyl Ester

Synthesis and radical polymerization of methacrylamide having an l -leucyl- l -alanine methyl ester structure, N -methacryloyl- l -leucyl- l -alanine methyl ester (MA-LA-M), were carried out. Radical polymerization of MA-LA-M in the presence of AIBN (1 mol %) in chlorobenzene (1.0 mol/L) afforded the corresponding polymer (poly(MA-LA-M)) with M̄ n 196 000. The 10% weight loss temperature of poly(MA-LA-M) under nitrogen was 300 °C. Increase of the absolute value of specific rotation in the transformation from MA-LA-M (−48.0°) to poly(MA-LA-M) (−76.5°) could be observed. The rate of radical polymerization of MA-LA-M was 4−6 times larger than that of N -methacryloyl- l -leucine methyl ester (MA-L-M) in benzene- d 6 (1.0 mol/L), whereas the activation energy ( E a ) of MA-LA-M (51.4 kJ/mol) was larger than that of MA-L-M (29.7 kJ/mol). The absolute value of the activation entropy (Δ S ⧧ ) in the radical polymerization of MA-LA-M (−144 J/(K·mol)) was smaller than that of MA-L-M (−221 J/(K·mol)). These parameters for the both monomers were nearly equal in the polymerizations in DMSO- d 6 . From the IR and 1 H NMR analyses, MA-LA-M in benzene might be suggested to be more strongly aggregated each other by intermolecular hydrogen bonds than MA-L-M.