In this paper, we have examined the effect of temperature on the interactions between imidazolium and ammonium based ionic liquids (ILs) and the low bandgap polymer (poly(2-heptadecyl-4-vinylthieno[3,4-d]thiazole) (PHVTT)). With the aim of exploring the utility of low bandgap polymers, we have carried out the interaction studies of the polymer with the ILs and investigated the behavior of polymer in the presence of ILs as the function of temperature. Recently, ILs have attracted extensive attention in polymer sciences. In this work, we have studied the temperature dependent interactions between the protic IL (1-methylimidazolium chloride ([Mim]CI) from imidazolium family) and aprotic ILs (tributylmethylammonium methyl sulfate ([N-1444][MeSO4])from ammonium family and 1-butyl-3-methylimidazolium chloride ([Bmim]CI) from imidazolium family) with a low bandgap polymer. Our experimental data of UV-vis spectroscopy, photoluminescence (PL) spectroscopy, FT-IR spectroscopy, density (rho) and speed of sound (u) as a function of temperature from 25 to 40 degrees C with the interval of 5 degrees C, clearly reveal that even at high temperature, [Bmim]CI interacts strongly with the polymer as compared to other studied ILs. (C) 2014 Elsevier B.V. All rights reserved.