Mechanistic discussion on deviation from ideal network formation in radical polymerization of multivinyl monomers

The network formation in the radical polymerization of multivinyl monomers, especially including diallyl esters and dimethacrylates, is dealt by focusing our attention on the mechanistic discussion on deviation from ideal network formation. Thus, in the bulk polymerization of diallyl phthalate, the actual gel point was obtained to be 6.9 times higher compared with the theoretical one. In common multivinyl polymerization systems, the discrepancy was more than 10 times and sometimes, more than 102. Moreover, the extent of deviation was enhanced with increasing primary chain length, the content of pendant vinyl groups in the prepolymer, and dilution. In order to interpret reasonably the greatly delayed gelation different structural factors were considered. The primary factor concerns the significance of the thermodynamic excluded volume effect on the intermolecular crosslinking reaction between growing 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 prepolymer and, moreover, imposes the steric hindrance, inducing the significance of the reduced reactivity of prepolymer as a tertiary factor. Solvent effect was observed as much delayed gelation in a good solvent as opposed to Walling's results, although this is expected by considering the significance of excluded volume effect.