A number of methyl-substituted phenylphosphetanes have been synthesised for an investigation of the stereoselective synthesis of polyphosphines by free-radical polymerization. Methyl substitution at the 1,3 positions of the phosphetane compared to the parent monomer, but the 2-methyl compound displays a reasonable rate of polymerization in hot benzene and copolymerization with oleferic monomers is being investigated. We showed computationally that these small phosphorus heterocycles would undergo facile ring-opening polymerisation via substitution of a carbon-centred radical at phosphorus, and that free-radical copolymerisation with normal polyolefins should also be possible.