Cross-linked latex particles grafted with polyisoprene as model rubber-compatible ﬁllers Mario Gauthier * , Abdul Munam Department of Chemistry, Institute for Polymer Research, University of Waterloo, 200 University Ave. West, Waterloo, ON N2L 3G1, Canada article info Article history: Received 15 May 2009 Received in revised form 2 October 2009 Accepted 7 October 2009 Available online 28 October 2009 Keywords: Fillers Rubber Core-shell polymers abstract Model ﬁller particles were obtained by grafting polyisoprene (PIP) chains onto spherical latex particles of polystyrene cross-linked with 12 mol% divinylbenzene. These particles, with a narrow size distribution and a diameter of ca. 400 nm, were synthesized by emulsiﬁer-free starved-feed emulsion polymerization. Acetyl coupling sites were introduced randomly at either low (5 mol%) or high (30 mol%) target substitution levels on the latex particles by Friedel–Crafts acylation with acetyl chloride and AlCl 3 in nitrobenzene. ‘Living’ polyisoprenyllithium chains, generated from isoprene and sec-butyllithium (sec-BuLi), were then coupled with the acetylated particles. The PIP side chains had a high 1,4-poly- isoprene microstructure content and a number-average molecular weight (M n ) of either 1.5  10 3 (1.5 K), 5  10 3 (5 K), or 3  10 4 (30 K). The PIP content of the grafted particles was determined from the yield of isolated particles and by 1 H NMR spectroscopy analysis. The grafted latex particles were blended in solution with linear polyisoprene (M n ¼ 3.95  10 5 , 395 K). The inﬂuence of the ﬁller–matrix interactions on the rheological behavior of the blends was determined by dynamic mechanical analysis for the different ﬁller blends. Increases in complex viscosity and storage modulus, and decreased damping factors were observed in all cases relatively to the pure matrix polymer. The enhancements, decreasing in the order 30 mol% > 5 mol% acetylation, and with the grafted PIP chain length as 30 K > 5K z 1.5 K, are deemed to reﬂect the extent of interactions between the ﬁller particles and the polymer matrix. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Commercial plastics and rubbers are often ﬁlled with solid particles, either to enhance their mechanical properties or to reduce cost [1]. The properties of these materials depend primarily on the interactions between the matrix and the ﬁller particles, although interparticle interactions are also important [2]. Conse- quently, the inﬂuence of physical interactions on the rheology of ﬁlled polymers can be very complex [3,4]. Strong interactions between the matrix polymer and the ﬁller particles can increase the viscosity and the dynamic moduli, for example through adsorption of the polymer on the ﬁller surface restricting chain mobility within the matrix. The nature and surface composition of the particles, as well as matrix properties such as the polarity and the molecular weight inﬂuence the rheology of the mixtures [3]. While much effort has been devoted to investigating the inﬂuence of ﬁller surface treatment on the rheological behavior of ﬁlled polymers, most studies have used commercial ﬁllers such as carbon black, calcium carbonate, mica, and talc [5–7]. These ﬁllers often have a complex structure and generally form aggregated suspensions with poorly characterized particle–matrix interactions impeding the interpretation of the rheological results. The inﬂuence on melt rheology of model cross-linked ﬁllers has been investigated by simple dispersion of the particles in different matrices [8–11], by incorporation of the particles into the matrix network through covalent bonding [12], and by adding a shell to enhance ﬁller compatibility with the matrix [13–21]. In the current investigation, we sought to elucidate the rheo- logical implications of particle–matrix interactions in a poly- isoprene rubber matrix ﬁlled with low-density rubber-compatible model core-shell particles synthesized by a new method. The particles have a core derived from cross-linked polystyrene (PS) latex particles of uniform size, and a shell of terminally grafted PIP chains of uniform size. The new grafting path proposed is derived from an anionic grafting onto scheme we developed for the synthesis of arborescent polymers [22]. A signiﬁcant disadvantage of the commonly used grafting from schemes – whereby the chains are grown from the surface of the particles – is that it is impossible to characterize the grafted chains unless they can be cleaved from the substrate. Under these conditions, the molecular weight of the side chains is typically approximated from linear chains grown in solution (e.g. due to residual initiator). The reactivity of initiating * Corresponding author. Tel.: þ1 519 888 4567; fax: þ1 519 746 0435. E-mail address: gauthier@uwaterloo.ca (M. Gauthier). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2009.10.050 Polymer 50 (2009) 6032–6042