Photocrosslinking of polymers containing cinnamoyl groups: the effects of cinnamoyl contents in copolymers on the reaction in solutions

Abstract

The effects of cinnamoyl contents in copolymers of 2-cinnamoyloxyethyl methacrylate with methyl methacrylate on the competitive intra- and intermolecular photocrosslinking were studied in THF solutions irradiated with a high-pressure Hg lamp at 30. The kinetic parameters for intra- and intermolecular crosslinking in degassed and aerated THF solutions were calculated from the initial concentration dependence of the rate of cyclodimer formation of cinnamoyl groups in copolymers by spectrophotometric measurements or from the data of the change in weight-average molecular weight by light-scattering measurements at various concentrations of copolymers. The quantum yields for intramolecular crosslink formation, Φ D intra, increase linearly with increasing CEMA mol% in a copolymer with a slope of 1 × 10 −4 per CEMA mol% in a copolymer. The parameters for intermolecular crosslink formation, K D inter, on the contrary, decrease with the extent of reaction, because the increase of intramolecular crosslinks prevents the interpenetration of polymer coils. The second virial coefficient becomes progressively smaller as the cyclodimerization proceeds; at the onset of gelation it reaches almost zero. The magnitudes of 〈 s 2 〉 1 2 and M w are related to the degree of the competition between intra- and intermolecular crosslinking. The contraction of polymer coils proceeds by predominant intramolecular crosslinking in dilute solution, and the contraction ratio, g = 〈 s 2 〉 cr/ 〈 s 2 〉 1, becomes 0.3–0.02 at the gel point, showing that the volume of the crosslinked polymer coil shrinks to 1 6 – 1 350 of the volume of corresponding linear polymer with the same molecular weight.