Polymer Testing 21 (2002) 247–251 www.elsevier.com/locate/polytest Material Behaviour Viscometric study of complexes of poly(vinyl pyrrolidone) with Co 2+ Esperanza Dı ´az * , Rosa Valenciano, Purificacio ´n Landa, Jose ´ Luis Arana, Javier Gonza ´lez Departamento Ingenierı ´a Minera, Metalu ´rgica y Ciencia de Materiales, Escuela Superior de la Marina Civil de Bilbao, Universidad de Paı ´s Vasco, C/Mª Dı ´az de Haro, 68, 48920 Portugalete, Spain Received 13 April 2001; accepted 9 July 2001 Abstract A polymer–metal complex is a metal complex containing a polymer ligand presenting a remarkably specific structure in which central metal ions are surrounded by an enormous polymer chain. Based on this polymeric ligand, the polymer– metal complex shows interesting and important characteristics, especially catalytic activities different from the corre- sponding ordinary metal complex of low molecular weight. In this work we have studied the synthesis in solution of different polyvinyl pyrrolidone/cobalt complexes (PVP/Co), using distillate water as solvent. The study has been focused on the interactions established between the polyvinyl pyrrolidone and the metallic cation Co 2+ at 298 and 338 K with different cobalt concentration using four PVP molar mass samples. We have employed viscometry as the experimental technique.  2002 Elsevier Science Ltd. All rights reserved. Keywords: Polymer–metal complex; Viscometry; Change conformational 1. Experimental 1.1. Materials The samples of polyvinyl pyrrolidone (PVP) used in this work were provided by Janssen Chimica, Serva and Fluka Chemie respectively (see Table 1). The sample provided by Fluka Chemie is found in emulsion, and to obtain it in solid form, it was necessary for it first to be freeze dried. To characterise the different samples, size exclusion chromatography (SEC) was initially used. The chromato- graphic system employed to characterise the polymers used tetrahydrofurane as mobile phase, which does not dissolve the PVP, so it was necessary to replace it by chloroform (a good PVP solvent and used by liquid * Corresponding author. C/Mugakoa No. 23, 1º drcha, 48920 Portugalete, Vizcaya, Spain. E-mail address: iipditae@lg.ehu.es (E. Dı ´az). 0142-9418/02/$ - see front matter  2002 Elsevier Science Ltd. All rights reserved. PII:S0142-9418(01)00077-0 Table 1 Molar masses for PVP samples Polymer Molar mass (G mol -1 ) PVP-1 154,000 PVP-2 222,000 PVP-3 625,000 PVP-4 3,070,000 chromatography). However, the results were not as we expected, since the polymer was retained in the columns. That is why it was necessary to characterise the different PVP samples by viscometry. The intrinsic viscosity of the different PVP samples was obtained at 298 K using distilled water as solvent. The MHS (Mark–Houwink–Sakurada constants) used were a=0.55 and k=67.6×10 3 dl g -1 [1,2]. We have also used different metallic transition element salts, which