Metal-free anionic polymerization of methyl methacrylate.

In the metal-free anionic polymn. of MMA with tetrabutylammonium di-Et 2-ethylmalonate or tetrabutylammonium 2-nitropropanate as initiators an inhibition period is caused by traces of initiator precursor mols., undergoing a transfer reaction with the active species. Induction periods in time conversion curves point to an initiation reaction, being slower than the propagation reaction. All polymns. of MMA are usually going to complete conversion. Surprisingly. the well-known intramol. cyclization reaction was not obsd. in the MMA system. However, a Hofmann elimination reaction terminates growing chains. This is due to the Bu ligands of the ammonium cation. A b-hydrogen atom can be transferred to the growing chain under the formation of tri-Bu amine and 1-butene. To eliminate this termination step, tetramethylammonium di-Et 2-ethylmalonate has to be used as initiator. But now a transalkylation under the formation of a Me group terminated satd. chain end and tri-Me amine arises as further termination reaction. However, since the termination reactions are not very fast, the metal-free anionic polymn. of MMA exhibits some kind of living character.