New aspects of tetramethylene initiation in polymer chemistry.

Abstract

Hall's Bond Forming Initiation Theory, derived for [2 + 2] systems, was applied to [4 + 2] systems. Polymerizable electron-rich and electron-poor olefins were reacted to obtain evidence for reactive intermediates using polymerization as a trap. A diradical intermediate was successfully trapped in reactions of 1-methoxy-1,3-butadiene with methyl 2,2-dicyanoacrylate, dimethyl cyanofumarate, trimethyl ethylenetricarboxylate, maleic anhydride and acrylonitrile. Diradical intermediates were also trapped in reactions of isoprene, 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, cis and trans-piperylene and 2,5-dimethyl-2,4-hexadiene with acrylonitrile. Copolymers were obtained in all cases. Copolymerization was accompanied by [4 + 2] cycloaddition. A zwitterionic intermediate was successfully trapped in the reactions of p-anisyl-1,3-butadiene and 1-phenyl-1,3-butadiene with various leaving groups in the β-position. Homopolymer of the arylbutadiene was obtained in all cases. Polymerization was initiated from a cationic species which arose from the elimination of the leaving group from a zwitterionic hexamethylene species. Polymerization was accompanied by [4 + 2] cycloaddition. Reactions of p-anisyl-1,3-butadiene and 1-phenyl-1,3-butadiene with methyl 2,2-dicyanoacrylate, dimethyl cyanofumarate, trimethyl ethylenetricarboxylate gave only the [4 + 2] cycloadduct. No polymer was formed in this reaction and no evidence for a reactive intermediate was obtained. The BFI theory was also applied to Group Transfer Polymerization reactions to determine whether the reaction mechanism involved a tetramethylene diradical intermediate. No styrene was incorporated into the methyl acrylate polymer, and so no evidence for a radical intermediate was obtained. LUMO energies calculated by AM1 were compared to reduction potential and UV data for tetrasubstituted and trisubstituted electrophilic olefins. The trends exhibited by the calculated LUMO energies agreed well with the experimental data, implying that calculations may be a reasonable method of predicting reactivity.