Methylaluminoxane (MAO) was used as a catalyst for the polymerization of several vinyl monomers. Polymer yields were found to decrease in the order styrene > isobutyl vinyl ether > methyl methacrylate approximate to acrylonitrile > alpha-methylstyrene > vinyl acetate = 0. The polymers exhibit low to moderate molar mass with broad distributions. NMR analysis were used to determine the polymers steric microstructure and the end groups. MAO was also able to produce styrene-methyl methacrylate, styrene-isobutyl vinyl ether and methyl methacrylate-isobutyl vinyl ether copolymers. Experimental evidences are against ionic polymerization mechanisms, whereas proofs for a radical mechanism are more controversial, but altogether against of it.