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ESR spectroscopic studies on the microheterogeneity of crosslinked polymers were extended to the attempt on a detailed void evaluation of microheterogeneously crosslinked monomethacrylate/dimethacrylate resins by measuring ESR spectra at lower temperatures, utilizing the interactions between spin probes and side chains. That is, the mobility of copper(II) tetraphenylporphyrin (CuTPP), a spin probe useful for the evaluation of void parts in crosslinked resins, excluded from densely crosslinked network parts to void ones was found to be much restricted at lower temperatures; this provides a useful tool to allow a detailed evaluation of the void parts. Thus, methyl methacrylate (MMA)/ethylene dimethacrylate (EDMA) (mole ratio 70/30) solution copolymerization in toluene at a dilution of 2/3 was chosen as a standard copolymerization system to provide the cured resin with void parts. The effect of introducing polar poly(oxyethylene) units was explored to clarify their interaction with the polar central part of the CuTPP molecule leading to the restricted mobility of CuTPP. The detailed evaluation of void sizes was done by changing the crosslinker content. The polar interaction was prevented by changing the CuTPP spin probe to a nonpolar one; the nonpolar interaction was verified by adding docosyl methacrylate having a long‐chain alkyl group to the MMA/EDMA copolymerization.

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.

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