Anionic dispersion copolymerization of styrene and 1,3-butadiene q I. Tausendfreund a , F. Bandermann a, * , H.W. Siesler b , M. Kleimann b a Institut fu ¨r Technische Chemie, Universita ¨t Essen, 45117 Essen, Germany b Institut fu ¨r Physikalische und Theoretische Chemie, Universita ¨t Essen, 45117 Essen, Germany Received 16 November 2001; received in revised form 9 May 2002; accepted 21 May 2002 Abstract The anionic dispersion copolymerization of styrene and butadiene was investigated. The suitability of the lower alkanes butane and pentane as dispersing media was tested. Only pentane turned out to be suited for the synthesis of non-aggregated polymer particles. Following block copolymerization experiments, the active chain ends were found to be homogeneously distributed over the whole particle volume by TEM analysis of OsO 4 treated polymer probes. This result contradicts the opinion of Kim et al. [Korea Polym J 7 (1999) 64] who suppose a location of the active centers only at the surface of the polymer particles. Polymer particle aggregation in the synthesis of poly(styrene-b-butadiene) and poly(styrene-b-butadiene-b-styrene) di- and triblock copolymers can be attributed during the early part of butadiene polymerization to the well known association of growing lithium chain ends from separated polymer. Later on, at higher butadiene conversions, an entanglement of longer polymer chains causes agglomeration, too. The most important parameter to obtain a stable poly(styrene-b-butadiene)lithium dispersion is the molecular mass of the poly(butadiene) block. The upper limit was evaluated to be 8000 g/mol. For technical applications, this means a maximum of 5 wt% of poly(butadiene) for a total molecular mass of 150,000 g/mol. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Anionic copolymerization; Butadiene; Styrene 1. Introduction Anionic dispersion polymerization (ADP) in hydro- carbons, which combines the advantages of anionic and suspension polymerization, has been a subject of research during the last few decades [1–3]. It delivers high solid contents in the polymerization reactor at low viscosity of the reaction medium and allows a mechanical separation of the polymers. The further interest arises from the need of uniform size polymer particles combined with the option of particle surface functionality due to the potential for many applications in biomedicine, catalysis, surface coating etc. [4]. Usually block copolymers are used as dispersants in ADP. In one type of process they are synthesized prior to their use. Here, two papers describe the possibility of controlling the particle size and size distribution of poly(styrene) by poly(styrene)/poly(butadiene) di- and triblock copolymers as dispersing agents, and the influence of reaction parameters like dispersing agent concentration, monomer concentration, initiator concentration, monomer multi-addition and reaction temperature on the time for onset of nucleation [5,6]. Quirk et al. [7] investigated the suitability of the poly(t-butylstyrene) moiety as part of poly(t-butylstyrene-b-styrene) as a dispersant for the formation of a stable dispersion in the anionic homo- polymerization of styrene and in the block copolymerization of t-butylstyrene and styrene. Another type of process is the so-called living dispersion polymerization (LDP). Here an ADP is performed using a mixture of a simple organo- lithium compound and a preformed polymeric organo- lithium compound as initiators for polymerization of vinyl monomers in alkane. Thus, homopoly(styrene) as the core phase and poly(t-butylstyryl-b-styrene) copolymer as steric stabilizer can be simultaneously produced when styrene is added to a mixture of sec-BuLi and poly(t-butylstyryl)- lithium as initiators [7,8]. Companies like BASF AG and Mobil Oil Corporation protected their results of research in ADP by patents. These patents describe among other topics the production of poly(styrene) as well as block and random copolymers of styrene and butadiene [9–16]. A problem of ADP is the separation of the polymer particles from the dispersing medium. The major part can be 0032-3861/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0032-3861(02)00448-2 Polymer 43 (2002) 7085–7091 www.elsevier.com/locate/polymer q Part of this article was presented at the Europolymer Congress held in Eindhoven, The Netherlands, 15–20 July 2001. * Corresponding author. E-mail address: friedhelm.bandermann@uni-essen.de (F. Bandermann).