Design and Synthesis of New Thermally Reversible Photoresponsive Polymers

A novel photoresponsive polymer system involving the photocyclization of pendant 2, 4, 6-triisopropylbenzophenone groups into the corresponding benzocyclobutenols was investigated as a potential imaging material. Two monomers containing the photoactive 2,4,6-triisopropylbenzophenone moiety were prepared and their polymerizabilities investigated: A vinyl ether type monomer did not polymerize well either cationically or radically, though a copolymer with maleic anhydride could be obtained. A styrenic monomer containing 2,4,6-triisopropylbenzophenone pendant groups was also successfully copolymerized with styrene. In this way, new photoresponsive polymers that function both in solution and in the solid state were synthesized. Interestingly, the photoproducts, benzocyclobutenol-functionalized polymers, were found to be thermally sensitive such that the Norrish type II photocyclization was reversed on heating the styrene copolymers. The combination of photocyclization and thermal ring opening was found to constitute a reproducible process for polymer interconversion.