Photocrosslinking of polymers containing cinnamoyl groups: The effect of molecular weight of copolymers on the reaction in solutions

Abstract

The rate and the change in polymer coil dimension during the competitive intra- and intermolecular photocrosslinking reactions were studied for copolymers of 2-cinnamoyl-oxyethyl methacrylate with methyl methacrylate having various degrees of polymerization ( N n = 650–5600 ) in tetrahydrofuran solution under u.v. irradiation at 30°. The rate parameter, K D inter, for intermolecular reaction is proportional to N n −0.46 and the quantum yield, Φ D intra, decreases linearly with a slope of 2 × 10 −7 per N n of copolymers. The number of cinnamoyl groups for intramolecular crosslinking increases with increasing the molecular weight. The magnitude of the contraction of polymer coils due to intramolecular crosslinking increases as the molecular weight decreases. The contraction ratio, g = 〈s 2〉 cr 〈s 2〉 1 , becomes 0.02–0.05 at the gel point in a dilute solution, showing that the volume of the crosslinked polymer coil shrinks up to 1 350 - 1 100 of the volume of the corresponding linear polymer with the same molecular weight. The gel formed contains many intramolecular cross-links.