Miscibility and interactions of polystyrene/polyolefine and polystyrene/poly(n-alkyl methacrylate) mixtures in dilute xylene solutions Ante Jukic ´, Marko Rogos ˇic ´, Zvonimir Janovic ´ * Faculty of Chemical Engineering and Technology, University of Zagreb, Marulic ´ev trg 19, P.O. Box 177, HR-10000 Zagreb, Croatia Received 4 July 2005; received in revised form 4 October 2005; accepted 4 November 2005 Available online 20 December 2005 Abstract The miscibility and intermolecular interactions between polystyrene (PS) and poly(ethylene-co-propylene) (EPC), as well as between PS and long-chain poly(alkyl methacrylates) (PAMA), namely, poly(dodecyl methacrylate) (PDDMA) and poly(octadecyl methacrylate) (PODMA), in dilute xylene solutions at 30 °C were studied. Investigated polymers are widely used as rheology modifiers, i.e. viscosity index improvers and pour point depressants for lubricating mineral oils. The specific and reduced viscosities of two- and three-component polymer solutions as well as intrinsic viscosities and Hug- gins’ parameter values were determined as functions of the polymer mixture composition and overall polymer concentra- tion. The reduced viscosity was found to be linearly dependent on the overall polymer concentration. The observed viscosities of polymer mixtures were intermediate to those of the mixture constituents; the values decrease in the order: EPC > PS > PAMA. The specific viscosities of all the polymer mixtures obtained as the experimental results and calculated applying the Catsiff–Hewett and Krigbaum–Wall theoretical equations were considered. Since all the polymer/polymer pairs showed the negative viscometric interaction parameter values (Db 12 < 0), the PS/EPC and EPC/PAMA mixtures were found to be immiscible. The observed repulsive molecular interactions originate from the differences in polymer compo- sition and molar masses. This conclusion was supported by calculations employing the group contribution approach of Coleman, Graf and Painter. The calculated values of interaction parameters for (co)polymer blends, K 12 , were 5.47, 6.42 and 13.1 J cm 3 for PS/PDDMA, PS/PODMA and PS/EPC, respectively. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Polystyrene; Poly(ethylene-co-propylene); Poly(alkyl methacrylate); Polymer blends; Intermolecular interactions; Miscibility; Dilute solution viscometry 1. Introduction It is well known that the addition of minor quan- tities of appropriate polymeric additives may signif- icantly affect the rheological properties of liquids. A dissolved, flexible polymeric molecule will reach the conformation of an isolated statistical coil in dilute 0014-3057/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2005.11.003 * Corresponding author. Tel.: +385 1 4597 125; fax: +385 1 4597 142. E-mail address: zjanov@fkit.hr (Z. Janovic ´). European Polymer Journal 42 (2006) 1105–1112 www.elsevier.com/locate/europolj EUROPEAN POLYMER JOURNAL