2020 Volume 56 Issue 1 Pages 4-11
Butyl acrylate - acrylic acid copolymers with different molecular weights / molecular weight distributions（PDI） were synthesized, and the effect of the degree of crosslinking on the gel fraction, the degree of swelling,and the molecular weight distribution of the sol fraction, were studied. It was revealed that the PDI greatlycontributed to the onset of gel formation at low concentration of the crosslinking agent. PDI also related to thesaturation of the gel fraction at high concentration of the crosslinking agent. The gel fraction and the degree ofswelling could be evaluated from the identical specimen. The degree of swelling largely depended on the PDIof the raw material copolymer, even if the gel fraction was about the same. In addition, it was clarified that thedistribution of a molecular weight of 1,000,000 or more increased in the sol of the low equivalent compositionof crosslinking agent（ ie. 0.001 eq and 0.002 eq.）. In the same time, the distribution in the low molecularweight region decreased. It means that the copolymer and the crosslinking agent dimerized first to give a highmolecular weight polymer, and then the formation of a crosslink（ gel formation） occurred.
