Vinyl monomer complexes in copolymerization processes. Studies on the complexes of acrylonitrile and methyl methacrylate with lewis acids

Complexes of acrylonitrile and of methyl methacrylate with various Lewis acids, 1 and 2 , were studied by means of IR, NMR, and UV spectroscopy. The influence of the Lewis acid strength on the induction effect and on the delocalization of π-electrons in the complexed monomer molecule was established. As the relative acidity of the complexing agent is increased, the inductive effect of the nitrile or of the carbonyl group in the complex molecule rises, whereby the electron density on the carbon atom in β-position in the vinyl group diminishes. Complexation of the monomer also results in increased delocalization of π-electrons in the molecule. In the complexes with moderately strong Lewis acids like CH₃AlCl₂ and C₂H₅AlCl₂, delocalization of π-electrons seems to reach its maximum. The methyl methacrylate-C₂H₅AlCl₂ complex was found to give a charge-transfer complex with 1,5-cyclooctadiene. On the basis of the present spectroscopic studies and of earlier studies on copolymerization of acryl monomers with butadiene, the delocalization of π-electrons in the complexed monomer molecule is believed to be one of the major factors controlling the rate of copolymerization.