Photoresponsive Behavior of Methyl Methacrylate/Trans-4-Stilbene Methacrylate Statistical Copolymers in Solution and the Solid State

Photoresponsive copolymers of methyl methacrylate (MMA) with trans-4-stilbene methacrylate (TSMA) of different compositions were synthesized by free-radical copolymerization. Upon irradiation with light of 313-nm wavelength, the trans-to-cis isomerization of the stilbenyl pendant groups in the copolymer can be induced. Both fluorescence and UV absorption spectroscopy show that the reversible photocontrolled isomerization of the copolymer system is limited due to the irreversible side reaction from the cis-stilbenyl pendant groups to the phenanthrenyl pendant moieties. Photoinduced changes in physical properties including solubility, relative viscosity, and glass transition temperature were studied. Upon irradiation with light of 313-nm wavelength, a 5 °C increase in demixing temperature was observed for a 36.5 mol % TSMA copolymer in toluene solution whereas an increase in demixing temperature greater than 20 °C was observed for a TSMA homopolymer. Similarly, photoinduced changes in relative viscosity become increasingly negative with increasing TSMA content in the copolymer, with the pure TSMA homopolymer exhibiting a 4.5% decrease in relative viscosity after photoirradiation. The photoinduced change in glass transition temperature from 423 down to 414 Κ was also observed for a 36.5 mol % TSMA copolymer upon irradiation. The effects of both concentration and environment on the extent of isomerization in solution and the solid state were also examined.