Copolymers of 1-vinylimidazole and (meth)acrylic acid: Synthesis and polyelectrolyte properties V.V. Annenkov a, * , E.N. Danilovtseva a , H. Tenhu b , V. Aseyev b , S.-P. Hirvonen b , A.I. Mikhaleva a a Laboratory of Unsaturated Heteroatomic Compounds, A.E. Favorsky Irkutsk Institute of Chemistry, 1 Favorsky St., Irkutsk 664033, Russia b Department of Chemistry, Helsinki University, A.I.Virtasen Aukio 1, PB-55, FIN-00014 Helsinki, Finland Received 15 December 2003; received in revised form 15 December 2003; accepted 17 December 2003 Available online 29 January 2004 Abstract New hydrophilic polyampholytes have been synthesized by copolymerization of 1-vinylimidazole with sodium salts of acrylic and methacrylic acids. Copolymerization reactivity ratios of the monomers are equal to: 0.54±0.06 and 1.3±0.3 for 1-vinylimidazole–sodium acrylate, 0.23±0.01 and 2.6±0.2 for 1-vinylimidazole–sodium methac- rylate systems, correspondingly. Isoelectric point of the copolymers changes continuously from 2.8 to 6.7 with increasing the 1-vinylimidazole content in contrast to polyampholytes with amino instead of imidazole side groups, whose isoelectric point changes discontinuously with changing composition. Static and dynamic light scattering data point to tendency of polyampholyte macromolecules to aggregation, even at pH values far from isoelectric point. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Polyelectrolyte; Vinylimidazole; Acrylic acid; Polyampholyte; Copolymer; Reactivity ratios; Light scattering; Aggregation 1. Introduction Combination of acidic and basic units in a polymer chain imparts the macromolecules highly interesting acid–base and complexing properties [1]. The behavior of such macromolecules is much more pH-dependent than that of the conventional polyelectrolytes, so poly- ampholytes can be employed in the design of the ‘‘intelligent’’ polymeric systems [2,3]. The use of imid- azole moieties in new polyampholytes is very promising because imidazole rings occur in nature, in particular as a part of such important aminoacid as histidine. The basicity of polymeric imidazoles (pK BH þ ¼ 5–6) lies be- tween that of stronger bases such as amines and that of very weakly basic amides and ethers [4]. Unlike amines, imidazole units are not completely protonated at low pH, being very active in hydrogen and donor–acceptor binding [5–7]. Thus, imidazole-containing polyampho- lytes may exhibit specific properties in the physiological pH range, which is important for the design of biologi- cally active compounds and methods for bioseparation. Esterolytic activity of imidazole-containing copolymers has been found by Overberger et al. [8–10]. Unfortu- nately, there is little information about copolymers of 1-vinylimidazole (VI) with unsaturated acids, and moreover, the copolymerization of acrylic acid (AA) with vinylimidazoles was reported to be complicated by side reactions [11]. The objective of this study was to synthesize new polyampholytes starting from 1-vinylimidazole (VI), acrylic (AA) and methacrylic (MAA) acids, and to investigate their polyelectrolyte properties. * Corresponding author. Tel.: +7-395-251-0056; fax: +7-395- 241-9346. E-mail addresses: annenkov@home.isu.ru, annenkov@ irioch.irk.ru (V.V. Annenkov). 0014-3057/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2003.12.014 European Polymer Journal 40 (2004) 1027–1032 www.elsevier.com/locate/europolj EUROPEAN POLYMER JOURNAL