Electron spin resonance spectroscopic studies on microheterogeneity of crosslinked polymers. IV. Correlation between void evaluation of crosslinked resin and microgelation in monomethacrylate/dimethacrylate copolymerizations

Abstract

ABSTRACT:Electron spin resonance spectroscopic studies on the microheterogeneity of crosslinked polymers were performed to ascertain the correlation of the void evaluation of monomethacrylate/dimethacrylate (DMA) cured resins with the microgel formation before gelation in their crosslinking copolymerizations. Lauryl methacrylate (LMA) was added to methyl MA (MMA)/ethylene DMA (EDMA) copolymerization because the addition of LMA reduces the occurrence of intramolecular crosslinking by the steric hindrance of bulky long-chain alkyl groups, leading to the formation of a less densely crosslinked microgel core and a less microheterogeneously crosslinked resin. Then MMA/vinyl laurate (VL)/EDMA terpolymerization was performed because the polymerizability of conjugated methacryloyl groups belonging to MMA and EDMA is markedly high compared with the unconjugated vinyloxycarbonyl group of VL. Thus, enhanced microheterogeneity for MMA/VL/EDMA terpolymerization would be induced as compared with MMA/EDMA copolymerization. Finally, allyl MA (AMA) and vinyl MA (VMA) crosslinkers were used in place of EDMA because in the polymerizations of AMA and VMA having two types of carbon-carbon double bonds of different reactivities there was no microgelation observed up to the gel-point conversion.

Effect of primary polymer chain rigidity on intramolecular cyclization and intramolecular crosslinking in free‐radical crosslinking monomethacrylate/dimethacrylate copolymerizations

“…Moreover, the occurrence of intramolecular crosslinking should be preceded by intermolecular crosslinking, whereas intramolecular cyclization would occur during the growth of a propagating radical, regardless of the occurrence of intermolecular crosslinking, and it always competes with intermolecular propagation with two monomer types as a lengthening reaction of the primary polymer chain. In addition, the locally extensive occurrence of intramolecular crosslinking would induce microgelation, leading not only to delayed gelation4–17 but also to the inhomogeneity of the network structures of three‐dimensional crosslinked polymers, being closely related to their properties 18–28…”