The cationic homopolymerization of the isocyanate monomer 3-isopropenyl-alpha,alpha＇-dimethylbenzyl isocyanate (1a) as well as its copolymerization with styrene (1b) and alpha-methylstyrene (1c) were studied. The syntheses involved the use of titanium tetrachloride in methylene chloride at low temperature. Apart from showing that it is possible to homopolymerize 1a, copolymers with less than 30 mol% of 1a were prepared and thoroughly characterized. They had a very wide molecular weight distribution (I-p similar to 4) and their T-g＇s followed Fox＇s equation. These highly reactive copolymers were synthetized in view of coupling them with cellulosic fibres.