The structure of the polymer of o-vinylphenol was studied. o-Vinylphenol(o-VP) was prepared by thermal decarbonization of o-cumaric acid which was obtained by hydrolysis of cumarin with sodium ethylate. Free radical and cationic polymerization of o-VP were carried out in bulk or in CH2Cl2 solution by using BPO, AIBN, BF3･OEt2, AlCl3, and TiCl4 as initiator. The polymers were reprecipitated by water from methanol solution and residual monomer was removed with dilute aqueous alkaline solution. The resulting polymers were white powder or viscous materials. The structure of the polymers were investigated by UV, IR, and NMR spectral measurement. UV spectra showed that the polymers have similar structures except for the one prepared by using BF3･OEt2. IR spectra showed the presence of methyl group and 1,2,4-trisubstituted benzene structure which are not expected from ordinary vinyl polymerization mechanism. The relative intensities of -CH3 and -CH2 group differ among polymers and suggested only the polymer prepared by using AIBN had relatively few -CH3 group. NMR spectral study supportedthe results obtained from IR spectra. The presence of -CH3 group was confirmed by C-methyl determination method (chromic acid oxidizing method) and the the amounts of C-CH3 groups were determined. From these results it was concluded that o-VP polymerizes through two different propagation steps, one is ordinary vinyl polymerization mechanism and the other the addition of vinyl group to pheno1ic nuclei
