A differential scanning calorimetric study of the radical polymerization of N-vinylpyrrolidone in dimethylformamide

Polymerization of N-vinylpyrrolidone (NVP) in dimethylformamide was studied by differential scanning calorimetry (DSC). The concentration of NVP was 0.75 M, that of the radical initiator (azobisisobutyronitrile) 0.01 or 0.02 M. For proper evaluation of scanning thermograms, it was necessary to correct for incomplete monomer conversion due to premature initiator exhaustion and to consider the instantaneous initiator concentration. If these points were allowed for in the computations, activation parameters agree well with those obtained from isothermal thermograms. The values for the overall activation energy were E_a = 82 and 84 kJ/mol, and those for the pre-exponential factor $\text{Z = 6 × 10}{}^{\mathrm{?9}}\text{and}\text{13 × 10}{}^{\mathrm{?9}}\text{(}\text{mol/l}\text{)}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}\text{.}\text{sec}{}^{\mathrm{?1}}$, obtained from the scanning (dynamic) and the isothermal method, respectively.