Dual stimuli-responsive homopolymers: Thermo- and photo-responsive properties of coumarin-containing polymers in organic solvents

Abstract

Thermoresponsive properties of poly(7-methacryloyloxycoumarin) (P1a) and its derivatives as homopolymers containing a photoreactive coumarin unit were systematically investigated. P1a showed a lower critical solution temperature (LCST)-type phase separation in dichloromethane, chloroform, and 1,1,2-trichloroethane. The temperature producing a 50% transmittance (Tc) of 0.1wt% P1a in distilled chloroform was 26°C, while the Tc value decreased to 21°C in deuterated chloroform i.e., the deuterium isotope effect. The Tc values in chloroform were adjustable from 28 to 57°C by the introduction of the ethyleneoxy spacer and the substitution of α-methyl group by hydrogen. While the polymers containing 4-substituted coumarins were soluble in chloroform and dichloromethane from 0°C to their boiling points. In the distilled chloroform solution, the coumarin units in P1a underwent a [2+2] cycloaddition and the transmittance at 500nm decreased from 98% to 29% at 25°C by a 180-s photoirradiation (326mJ/cm2, emission band at 365nm).