Radical Copolymerization of Vinylimidazole and Vinylphosphonic Acid: Sequence Distribution-Glass Transition Temperature Relationship in Copolymers

Hypothesis:

 Copolymerization is the most successful and powerful method for making systematic changes in polymer properties. The utility of copolymerization is exemplified on the one hand by fundamental investigations of structure-property relations and on the other hand by the wide range of commercial applications. The elucidation of copolymer structure (copolymer composition, monomer sequence distribution) is the major concerns for the prediction of copolymer properties and the correlation between structure and properties.

Homopolymers of poly(1-vinylimidazole) and poly(vinylphosphonic acid) were synthesized in presence of α,´α-azobisisobutyronitrile (AIBN) initiator for the former, and in presence of α,´α-azodiisobutyramidine dihydrochloride (AIBA) initiator for the latter. Poly(1-vinylimidazole/vinylphosphonic acid) copolymers at various molar ratios of monomers in initial feed were obtained by precipitation free radical polymerization in dimethyl formamide (DMF) as solvent at 80°C. The structure and microstructure of the polymers were investigated by spectroscopy methods. Afterwards, the glass transition temperatures of the homo- and copolymers were measured by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA).

The reactivity ratio of 1-vinylimidazole and vinylphosphonic acid comonomers was obtained using extended Kelen-Todus method and the results of 1H-NMR were 0.078 and 0.870, respectively. The reactivity ratio of the comonomers indicated their tendency to form an alternative copolymer. The microstructure of the copolymers, i.e. the diad sequence of monomers, was determined using the reactivity ratio of the comonomers and the theoretical relationships. Then, the glass transition temperature of the copolymers was predicted utilizing calculated sequences and Barton's relation that showed good agreement with the experimental values, and it was found that the microstructure of the copolymers had a significant effect on their glass transition temperature.