Preparation and optical characterization of two photoactive poly(bisphenol A ethoxylate diacrylate) copolymers containing designed amino-nitro-substituted azobenzene units, obtained via classical and frontal polymerization, using novel ionic liquids as initiators

Abstract

The frontal polymerization (FP) of bisphenol A ethoxylate diacrylate (BPAEDA) was carried with and without the presence of two different azobenzene comonomers by means of an external heating source. The first azomonomer (MDR-1) is a derivative of disperse red-1, N-ethyl-N-(2-hydroxyethyl)-4-(4-nitrophenylazo)aniline, whereas the second (E)-2-(4-((4-nitrophenyl)diazenyl)phenyl)-5,8,11-trioxa-2-azatridecan-13-yl methacrylate (4PEGMAN) comes from the azo-dye Nmethyl- N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(11-hydroxy-3,6,9-trioxaundecas-1-yl) amine. In this work, an ionic liquid trihexyltetradecylphosphonium persulfate was used as initiator. This compound produced stable propagating polymerization fronts with good velocities and moderate maximum temperature values. Moreover, this initiator prevented bubble formation and was found to be the most efficient when it was used in lower amounts with respect to other initiators, such as benzoyl peroxide, 2,20-azobisisobutyronitrile, aliquat persulfate®, and tetrabutylphosphonium persulfate. The thermal properties of the obtained polymers and copolymers were determined by thermogravimetric analysis and differential scanning calorimetry. The nonlinear optical (NLO) characterizations of the developed BPAEDA/MDR-1 and BPAEDA/4PEGMAN copolymers were performed according to the Z-Scan technique in film samples prepared by classical polymerization. It has been proven that samples with higher 4PEGMAN content (0.26 mol %) exhibited outstanding cubic NLO-activity with positive NLO-refractive coefficients in the promising range of n2 = +3.2 x 10-4 esu