Anionic polymerization of monomers containing functional groups, 11 - Anionic polymerizations of alkynyl methacrylates

Anionic polymerization of 2-propynyl methacrylate (1), 3-trimethylsilyl-2-propynyl methacrylate (2), 2-butynyl methacrylate (3), and 3-pentynyl methacrylate (4) was carried out in tetrahydrofuran at -78 degrees C for 1 h. The employed initiator systems were (diphenylmethyl)potassium/diethylzinc (Et2Zn) and 1,1-bis(4'-trimethylsilylphenyl)-3-methylpentyllithium/lithium chloride (LiCl). Although poly(1) was obtained quantitatively with each initiator system, the observed molecular weights were always higher than the predicted values and the molecular weight distributions were rather broad ((M) over bar(w)/(M) over bar(n) > 1.3), indicating a side reaction at the acidic acetylenic proton. On the other hand, the polymerization of 2-4, i.e., methacrylate monomers having no terminal acetylenic protons in the ester moieties, proceeded quantitatively under similar conditions. The resulting poly(2-4)s were found to possess the predicted molecular weights and narrow molecular weight distributions ((M) over bar(w)/(M) over bar(n) < 1.1), indicating the living character of the polymerization systems. The trimethylsilyl protecting group of poly(2) was completely removed to form a poly(1) having well-defined chain structures by treating it with potassium carbonate in a mixed solvent of THF and methanol at room temperature for 1 h.