Free-radical crosslinking polymerization and copolymerization of multivinyl compounds

The network formation in the free-radical crosslinking polymerization and copolymerization of multivinyl compounds, especially including diallyl esters and dimethacrylates, was dealt with by focusing our attention on the mechanistic discussion on deviation from Flory-Stockmayer's (F-S) theory. First, the reasons for the greatly delayed gelation in diallyl polymerizations were discussed mechanistically in detail and the following conclusion was reached: The primary factor is the significance of the thermodynamic excluded volume effect on the intermolecular crosslinking reaction between the growing polymer radical and prepolymer, especially at high molecular weight. Beyond the theoretical gel point, a secondary factor is related to the intramolecular crosslinking which becomes progressively important with conversion. The latter leads to the restriction of segmental motion of the prepolymer and, moreover, imposes steric hindrance, inducing the significance of the reduced reactivity of prepolymer as a tertiary factor. This discussion was satisfactorily extended to the network formation in common multivinyl polymerizations and some problems involved are described in detail such as the validity of F-S theory, intramolecular cyclization, intramolecular crosslinking, microgelation, and the solvent effect on gelation. Finally, our preliminary attempts to control the network formation are introduced on the basis of the above mechanistic elucidation.