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Abstract�Results on the metal-free anionic polymerization of methyl methacrylate (MMA) are presented. MMA was polymerized in tetrahydrofuran, using tetrabutylammonium diethyl 2-ethylmalonate and tetrabutylammonium 2-nitropropanate as initiators. Immediate polymerization was observed only in cases where the initators did not contain traces of their precursor molecules, the presence of which causes an appreciable inhibition period. This is attributed to the transfer reaction between active species and the precursor molecules. Only after their consumption can the major polymerization start. Using very pure initiators, no inhibition period was observed. Curves from dilatometric measurements showed the existence of an induction period. As usual, this is attributed to an initiation reaction which is slower than the propagation reaction. It is more clearly marked for tetrabutylammonium diethyl 2-ethylmalonate than for tetrabutylammonium 2-nitropropanate as initiator. All polymerizations of MMA usually go to complete consumption of the monomer. However, termination reactions have to be taken into account as well. The well-known intramolecular cyclization reaction was not observed in the MMA system. Here, a Hofmann elimination reaction terminates the growing of chains, which is due to the butyl ligands of the ammonium cation, where a β-hydrogen atom can be transferred to the growing chain under the formation of tri-n-butylamine and 1-butene. To eliminate this termination step, tetramethylammonium diethyl 2-ethylmalonate was synthesized and used as the initiator for the polymerization of MMA. Now transalkylation under the formation of a methyl group terminated the saturated chain end and trimethyl amine could be detected as a second termination reaction. Neither of the termination reactions seems to be very fast. The molecular weight distributions of the synthesized polymers are relatively broad.

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