Synthesis of Azobenzene-Based Polymers and the in-Situ Characterization of Their Photoviscosity Effects

Abstract

A new in-situ technique for the measurement of photoviscosity effects in polymer solutions has been developed using a custom-modified, cone-and-plate rheometer. The new technique permits simultaneous irradiation of the polymer solution and continuous measurement of its viscosity in a temperature-controlled environment. An additional benefit of the technique is the greatly reduced sample volume compared to traditional capillary viscometers. However, adequate measures have to be taken to minimize the evaporation of the sample solution and to maintain the required temperature. Copolymers of methyl methacrylate and azobenzene monomers with a chromophore in the side chain have been synthesized and characterized using the new technique. This polymer exhibits a photoviscosity effect when exposed to UV irradiation (λ = 365 nm), with the reduced specific viscosity (ηsp/c) of the polymer being up to 77% lower than in the dark. However, the magnitude of the photoinduced change in ηsp/c was found to increase with the...