Living Anionic Polymerization of <i>N</i>-Methacryloylazetidine: Anionic Polymerizability of <i><i>N,N</i></i>-Dialkylmethacrylamides

Abstract

Anionic polymerization of a series of N,N -dialkylmethacrylamides such as N -methacryloylazetidine ( M4 ), N -methacryloylpyrrolidine ( M5 ), and N -methacryloylpiperidine ( M6 ) was carried out with diphenylmethyllithium (Ph 2 CHLi) or diphenylmethylpotassium (Ph 2 CHK) in the presence of LiCl or Et 2 Zn in THF to clarify the relationship between polymerizability and monomer structure. Poly( M4 )s possessing predicted molecular weights and very narrow molecular weight distributions ( M w / M n < 1.1) were obtained quantitatively with Ph 2 CHLi/LiCl or Ph 2 CHK/Et 2 Zn at −40 to 0 °C within 24 h. From the polymerizations of M4 at the various temperatures ranging from −40 to −20 °C, the apparent rate constant and the activation energy of the anionic polymerization were determined as follows: ln k p ap = −6.17 × 10 3 / T + 22.4 L mol −1 s −1 and 51 ± 5 kJ mol −1, respectively. Compared to the previous report on the anionic polymerization of N -methacryloyl-2-methylaziridine ( M3 ), the polymerization rate of M4 was significantly slower and the activation energy was slightly larger, indicating the lower polymerizability of M4 . The acryloyl counterpart, N -acryloylazetidine ( A4 ), also underwent the anionic polymerization to afford the well-defined polymer quantitatively. The polymerizations of M5 gave the polymers in 30−77% yields but did not complete even after 1 week at 0 °C. By contrast, no polymer was obtained from the anionic polymerization system of M6 similar to the case of N,N -dimethylmethacrylamide (DMMA). From the experimental results, it was demonstrated that the polymerizability of a series of N,N -dialkylmethacrylamides with cyclic substituents decreased drastically with increasing the ring size from three to six ( M3 > M4 > M5 ≫ M6 = DMMA). The observed relative polymerizability was well correlated with the chemical shifts of vinyl β-carbons for monomers in the 13 C NMR spectra. The NMR data suggested that the polymerizable M3 and M4 attained effective conjugation between C═C and C═O double bonds, while M5, M6, and DMMA had negligible conjugation effects.