Melt processed blends of poly(styrene-co-acrylonitrile) and poly(phenylene ether) compatibilized with polystyrene-b-polybutadiene- b-poly(methyl methacrylate) triblock terpolymers Thorsten Kirschnick a , Axel Gottschalk b , Harald Ott c , Volker Abetz d , Judit Puskas e , Volker Altsta ¨dt f, * a Kaldewei GmbH and Co., 59229 Ahlen, Germany b BASF-AG, Styrenic Polymers Europe, 67056 Ludwigshafen, Germany c Romira GmbH, 25421 Pinneberg, Germany d Macromolecular Chemistry II, University of Bayreuth, 95447 Bayreuth, Germany e The University of Western Ontario, London, Canada, N6A 5B9 f Polymer Engineering, University of Bayreuth, 95447 Bayreuth, Germany Received 4 September 2003; received in revised form 19 March 2004; accepted 23 March 2004 Available online 19 June 2004 Abstract Polystyrene-b-polybutadiene-b-poly(methyl methacrylate) triblock terpolymers (SBM) with equal (symmetric) and different (asymmetric) block lengths were used to compatibilize polymer blends based on poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(styrene-co- acrylonitrile) (SAN). First, the rheological behavior of the individual components and their binary mixtures was investigated. Based on the results, samples of PPE, SAN and SBM in weight ratios of 32/48/20 were melt blended and the morphology development during melt processing was investigated. It was found that a raspberry morphology, i.e. dispersion of PPE in SAN with rubbery PB domains at the PPE/SAN interface, could be achieved with a symmetric SBM with M n < 100 kg=mol under sufficiently high shear rate, while a symmetric SBM with M n ¼ 170 kg=mol did not yield the desired morphology. Asymmetric SBMs with long PS blocks dissolved in the PPE phase did not display the expected compatibilization effect. In order to obtain a raspberry morphology with asymmetric copolymers it is suggested to pre-blend the SBM with SAN before adding the PPE. Finally it is shown that a commercial PPE containing High Impact Polystyrene (HIPS) as a toughness modifier can be compatibilized with SAN by melt processing using a symmetric SBM triblock terpolymer with M n < 100 kg=mol: q 2004 Published by Elsevier Ltd. Keywords: Raspberry morphology; Poly(2,6-dimethyl-1,4-phenylene ether); Poly(styrene-co-acrylonitrile) 1. Introduction The addition of a third polymeric component to two immiscible polymers is a well-known method of compati- bilization. Effective compatibilizing agents should mini- mize the interfacial tension and reduce the size of the dispersed phase [1]. Control of the phase morphology during melt processing is of key importance in developing new blends with improved properties (i.e. strength, stiffness and toughness). The shape, size and spatial distribution of the phases result from a complex interaction between the dynamic viscosity of the components, interfacial properties, blend composition and processing conditions (mixing time, temperature) [2–6]. Block copolymers with covalently connected immiscible blocks can be very effective compa- tibilizing agents. Diblock copolymers have extensively been used and studied as compatibilizing agents [7]. Linear triblock copolymers have also been utilized and in some cases performed better than diblocks. For example, in high impact polystyrene (HIPS)/polypropylene (PP) blends, polystyrene-b-polybutadiene-b-polystyrene triblock copo- lymer was more effective than polystyrene-b-polybutadiene diblock copolymer as a compatibilizer, leading to better mechanical properties [8]. Recently polystyrene-b-polyiso- butylene-b-polystyrene was successfully used for rubber toughening of PS [9]. These block copolymers are phase separated at the nanometer-scale level, with microphase 0032-3861/$ - see front matter q 2004 Published by Elsevier Ltd. doi:10.1016/j.polymer.2004.03.106 Polymer 45 (2004) 5653–5660 www.elsevier.com/locate/polymer * Corresponding author. Tel.: þ 49-921-55-7470; fax: þ49-921-55-7473. E-mail address: altstaedt@uni-bayreuth.de .