Effect of solvents on polymerization of N-propargylamide monomer and secondary structure of polymer

Abstract

Polymerization of M1, a chiral N-propargylamide monomer, was carried out with (nbd)Rh⁺B⁻(C₆H₅)₄ as the catalyst in five solvents to explore the effect of solvents on polymerization. All the polymerizations occurred smoothly and provided polymers in high yield, however the number-average molecular weights of the polymers differ largely, which is attributed to the different solubility of the polymers in solvents. The helical structure and the optical activity of the polymer prepared in THF was examined by CD and UV-Vis spectroscopy measurements in the five solvents and in solvent mixtures consisting of CH₂Cl₂ (a relatively good solvent) and THF (a relatively not-so-good solvent) in varied ratios. The polymer could adopt helical conformations in all the solvents, but different CD intensities and UV-Vis absorptions were observed. In CH₂Cl₂, the polymer exhibited lower intensity in both CD effect and UV-Vis absorption, while they were higher when the polymer was examined in THF, demonstrating that solvophobic effects made large contribution for the polymer chains to adopt helical conformations.