ESR spectroscopic studies on the microheterogeneity of crosslinked polymers, 3 - Attempt to a detailed evaluation of void parts in monomethacrylate/dimethacrylate resins by ESR measurements at lower temperatures

ESR spectroscopic studies on the microheterogeneity of crosslinked polymers were extended to the attempt on a detailed void evaluation of microheterog eneously crosslinked momethacylate/diamethacrylate resins by measuring ESR spectra at lower temperatures, utilizing the interactions between spin prob es and side chains. That is, the mobility of copper(II) tetraphenylporphyri n (CuTPP), a spin probe useful for the evaluation of void parts in crosslin ked resins, excluded from densely crosslinked network parts to void ones wa s one found to be much restricted at lower temperatures; this provides a us eful tool to allow a detailed evaluation of the void parts. Thus, methyl me thacylate (MMA)/ethylene dimethacrylate (EDMA) (mole ratio 70/30) solution copolymerization in toluene at dilution of 2/3 was chosen as a standard cop olymerization system to provide the cured resin with void parts. The effect of introducing polar(oxy-ethylene) units was explored to clarify their int eraction with the polar central part of th CuTPP their interaction with the polar central part of the CuTPP molecule leading to the restricted mobilit y of CuTPP. The detailed evaluation of void sizes was done by changing the crosslinker content. The polar interaction was prevented by changing the Cu TPP spin probe to a nonpolar one; the nonpolar interaction was verified by adding docosyl methylacrylate having a long-chain alkyl group to the MMA/ED MA copolymerization.