Some aspects on the polymerization of N-vinylpyrrolidone in the presence of poly(methacrylic acid) templates

N-Vinylpyrrolidone (NVP) was polymerized in dimethylformamide (DMF) at 60°C in the presence of poly(methacrylic acids) (PMAA) of different tacticities and molecular weights. The rate enhancement, which was ascribed to chain growth of the poly(vinylpyrrolidone) (PVP) radical along the polyacid template, became more pronounced with increasing chain length and syndiotacticity of the PMAA template. The results can be expressed by v_R = aP _vⁿ, where v_R is the polymerization rate relative to that of the blank experiment, P _v is the viscosity-average degree of polymerization of PMAA, and a and n are constants depending on the reaction conditions and tacticity of PMAA. In the presence of excess monomer the rate enhancement decreased when the quantity of PVP produced corresponded to a stoichiometric ratio of 1:1 with the available PMAA. It is proposed that the template effect is caused mainly by delay of the bimolecular termination step of growing PVP radicals associated with PMAA. Diffusion of polymer radicals, and consequently termination, will be more impaired if the attached PMAA has a greater length (size) and if the binding forces between PVP radical and PMAA template are stronger. The latter implies that PVP forms the strongest complexes with syndiotactic PMAA. This is supported by experiments concerning complex stability.