Influence of supramolecular interactions on photoresponsive behavior of azobenzene poly(amide imide)s

Abstract

Abstract This study presents the comparison between the photoresponsive behavior of a series of six poly(amide imide)s bearing azobenzene-derivative chromophores as side groups. The solubility, molecular weight, glass transition temperature and thermal stability of the polymers are reported. The chosen azopolymers contain one or two azochromophores in the repeating units attached to the main chain at different locations, i.e., one of the aromatic cores of azobenzene is a part of backbone connected in the 2 and 4 position with either the amide or/and imide groups. UV–vis spectroscopy shows that the chromophore position affects the polymer absorption band. The photoinduced birefringence measurements reveal large differences in the photoresponsive behavior of the materials. The birefringence of order of 0.02 and 0.05 is achieved for the polymers of moderate molecular weight containing one azo-dye per structural unit attached between the amide groups or for the polymers with two chromophores per structural unit placed between both the amide and imide groups, respectively. The lack of optical anisotropy is observed for the polymers of a low molecular weight containing the azochromophores located between the imide groups, indicating a very low efficiency of the trans–cis isomerization process in these materials. The explanation of the observed relationship based on H-bond formation is confirmed by FTIR and 1H NMR analysis.