The miscibility of poly(3-carboxypropylmethylsiloxane) (PSI100) and poly(3-carboxypropylmethylsiloxane-co-dimethylsiloxane) (PSIX, X = 76, 60, 41, 23 or 9, denoting the mole percentage of 3-carboxypropylmethylsiloxane unit in the copolymer) with poly(1-vinylimidazole) (PVI) was studied. PSI9 is miscible with PVI when the blend contains 80 wt% PVI. However, the other PSIX samples are miscible with PVI over the entire composition range. Most of the miscible PSIX/PVI blends show positive deviations in their glass transition temperature values. None of the miscible blends shows a lower critical solution temperature behavior prior to degradation. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy show that some of the imidazole nitrogens are protonated by the carboxylic acid,groups, leading to ionic interactions. (C) 2001 Elsevier Science Ltd. All rights reserved.