Synthesis and optical characterization of photoactive poly(2-phenoxyethyl acrylate) copolymers containing azobenzene units, prepared by frontal polymerization using novel ionic liquids as initiators

2-Phenoxyethyl acrylate (2-PEA) was polymerized alone and in the presence of an azobenzene comonomer derived from Disperse Red-1, N-ethyl-N-(2-hydroxyethyl)-4-(4-nitrophenylazo)aniline (MDR-1), by using the frontal polymerization technique. Two novel ionic liquids, recently synthesized by us, were used as initiators: tetrabutylphosphonium persulfate (TBPPS) and trihexyltetradecylphosphonium persulfate (TETDPPS). Even if their concentrations were smaller than those found when benzoyl peroxide and terbutylperoxy neodecanoate were used, these compounds gave rise to stable propagating polymerization fronts characterized by relatively low maximum temperatures and good velocities. Moreover, at variance to these latter, TBPPS and TETDPPS prevent bubble formation, thus allowing the use of the obtained materials in optical applications. The obtained polymers were characterized by infrared spectroscopy (FTIR), their thermal properties were determined by differential scanning calorimetry, and their optical properties were studied by absorption spectroscopy in the UVvis region. Finally, the nonlinear optical (NLO) properties of the 2-PEA/MDR-1 copolymers obtained with TBPPS and TETDPPS were performed according to the Z-Scan technique with prepared film samples. It has been proven that samples with higher MDR-1 content (0.05 mol %) exhibited outstanding cubic NLO activity with negative NLO refractive coefficients around n(2) = -1.7 x 10(-3) esu. (c) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 821-830, 2012