(521c) Photo-Responsive Monomer for Light Mediated ROMP

Ishan Fursule, Qunfei Zhou, Matthew Beck and Bradley Berron.

Department of Chemical and Materials Engineering, University of Kentucky.

Stimuli-responsive polymers are changing the landscape of actuated materials in optoelectronics, molecular machines, and biomedical materials. Here, we combine the concept of Ring Opening Metathesis Polymerization (ROMP) with azobenzene photoactuation to achieve a new monomer with photo-mediated ROMP kinetics. This novel approach allows photoactuation of both a polymerization reaction and of the formed polymer. This will allow us to precisely control the thickness of thin photo-responsive polymer coatings and hence the penetration intensity of radiations in the film.

Internal ring strain of monomer is a prerequisite for ROMP to minimize the reversibility of polymerization and carbon-carbon double bond for catalyst to initiate the polymerization reaction and then also for propagation. To optically-control the ring strain to the molecule, we synthesized a family of cyclic molecules with a photo responsive azobenzene group. We fine-tuned the light-induced ring strain through computational molecular design, and we synthesized saturated closed ring monomers with photo-tunable ring strain. Photoresponse of these molecules is confirmed by UV-Vis and NMR. Molecules are stable in the cis and trans state, but can be photoswitched with appropriate light sources. We are now synthesizing the analogous family of unsaturated closed rings where mean ring strain is contingent upon both the ring size and the isomerization of the azobenzene group. The ROMP kinetics of the alkene containing monomers will be analyzed under UV or visible light.