Abstract
As part of our continuing studies concerned with the elucidation of three-dimensional network formation mechanism in the free-radical crosslinking polymerization of multivinyl compounds, this article deals with the pursuit of network formation processes beyond the gel point in the copolymerization of methyl methacrylate (MMA) with ethylene dimethacrylate by ESR spectroscopy, especially focusing on the microheterogenization of network structure. Thus, poly (MMA-co-CuMAOTPP) s were prepared by the copolymerization of MMA with copper (II) methacryloyloxyphenyl tetraphenylporphyrin (CuMAOTPP) and their usefulness as polymer spin probes was examined as compared with its low-molecular-weight counterpart or copper (II) tetraphenylporphyrin (CuTPP). Poly (MMA-co-CuMAOTPP) of moderate molecular weight, i.e. about 20,000 was more useful than CuTPP for ESR spectroscopic investigation, but the polymer spin probe having 95,000 of molecular weight decreased its effectivity reversely. Then, the correlation between ESR spectra and microheterogeneity of networks formed under various polymerization conditions was examined by changing the factors influencing resultant network structures, including monomer concentration, crosslinker content and flexibility of network segments. Clearly, the mobility restriction of polymer spin probe by network formation was reduced under the conditions introducing inhomogeneous networks as a reflection of the exclusion of polymer spin probe into void part of a gelled system. Finally, the quantitative discussion on the microheterogeneity of network structure was attempted by simulating the observed ESR spectra.
