Nonidealities exhibited by cross-linking free-radical copolymerization

The predictions of ideal network theory for crosslinking free-radical polymerizations can be quite complicated because of the drifts which can occur in both primary chain length and composition. To compare properly theory and experiment in these systems, one has either to characterize the effects of conversion on instantaneous chain length and composition, or to avoid these difficulties altogether by working in very short pregel regimes. If one takes the latter route, four key predictions can be made for equally reactive monomers and long primary chains. We have tested these simple predictions on a system often considered equally reactive (but which is only nearly so⁵): methyl methacrylate (MMA)/ethylene glycol dimethacrylate (EGDMA). Short pregel regimes were ensured by working at volume fractions EGDMA, V_EGDMA, between 0.10 and 0.80 (0.111 ≤ a₄ ≤ 0.819) and under (required) conditions for which the primary chains are long.