Retardative chain transfer in free radical free-radical polymerisations of vinyl neo-decanoate in low molecular weight polyisoprene and toluene M.J. Monteiro 1 , N. Subramaniam 2 , J.R. Taylor, B.T.T. Pham, M.P. Tonge, R.G. Gilbert * Key Centre for Polymer Colloids, School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia Received 10 July 2000; received in revised form 10 October 2000; accepted 24 October 2000 Abstract The kinetics of free-radical polymerisation of vinyl neo-decanoate (VneoD) and the molecular weight distributions (MWDs) of the polymers formed in the presence and absence of low molecular weight polyisoprene at 50°C under a variety of conditions were investigated. The bulk reaction was successfully modelled using conventional free-radical polymerisation with termination rate coefficients calculated from diffusion theory. The reaction was strongly retarded by the presence of toluene or low-molecular-weight polyisoprene. This retardation behaviour was consistent with a mechanism comprising chain transfer of the radical activity to a double bond on the polyisoprene backbone to form a radical centre of low reactivity, which may subsequently terminate with other propagating radicals (“transfer-induced retardation”). Analysis of the rate and of the MWDs of the polymer formed yielded an estimation of the rate coefficient for transfer of the radical activity from the propagating VneoD radical to toluene and to polyisoprene. The rate coefficients for transfer to toluene determined by both methods were similar (7.5 dm 3 mol -1 s -1 from the conversion-time data, and 10.8 dm 3 mol -1 s -1 from the molecular weight distribution). The rate coefficient for transfer to toluene was similar for both vinyl acetate (9.9 dm 3 mol -1 s -1 ) and VneoD, as expected given the similar radical reactivity of these monomers. The rate coefficient for transfer to polyisoprene was found by the conversion-time method to be 150 dm 3 mol -1 s -1 , suggesting that the polymerisation of VneoD in the presence of polyisoprene would be a useful method for inducing grafts onto the polyisoprene backbone. The rate coefficients and inferred mechanism are similar to those found previously for a VneoD/ polybutadiene system [Macromolecules, 33 (2000) 2383].  2000 Elsevier Science Ltd. All rights reserved. Keywords: Grafting; Polyisoprene; Retardative chain transfer 1. Introduction There are currently two methods by which grafting may be induced in polyalkenylenes such as polyisoprene. The first is through graft-site initiation [1], where the initiator- derived radicals either add across the double bond or abstract hydrogens from the polyisoprene backbone [2]. High levels of grafting with cis-polyisoprene have been found to be induced with benzoyl peroxide [3] and other oxyl radicals [4], whilst azobisisobutyronitrile (AIBN) was shown to have little effect [5]. The second method is through hydrogen abstraction from polyisoprene by polymeric radi- cals [6]. Scanlan et al. [6,7] found that the rate was retarded in the polymerisation of vinyl acetate (VAc) in the presence of either natural rubber, high molecular weight synthetic polyisoprene or a model compound of polyisoprene (2,6- dimethylocta-2,6-diene). However, the authors could not distinguish between retardation due to chain transfer and retardation due to copolymerisation (i.e. addition across the double bonds of polyisoprene). The chain-transfer mechanism for the observed retardation was tested by Scan- lan et al. by polymerising VAc in the presence of a model compound, isopropylbenzene [7]; chain transfer is the only possible reaction in this system. Retardative chain transfer was found to occur, where the polyVAc radicals readily abstract hydrogens from isopropylbenzene, and these inci- pient isopropylbenzyl radicals are very unreactive towards VAc and consequently may act as primary radical termina- tors for polymeric radicals. This result supports the hypoth- esis that retardative chain transfer frequently occurs for the VAc/polyisoprene system, and therefore will invariably lead to grafting of polyVAc onto the backbone of poly- isoprene. Lehrle and Willis [8] proposed that VAc could facilitate grafting of methyl methacrylate (MMA) onto natural rubber Polymer 42 (2001) 2403–2411 0032-3861/01/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S0032-3861(00)00647-9 www.elsevier.nl/locate/polymer * Corresponding author. Fax: +61-2-9351-8651. E-mail address: gilbert@chem.usyd.edu.au (R.G. Gilbert). 1 Present address: Department of Polymer Chemistry and Coating Tech- nology, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands. 2 Present address: BASF AG, Business Unit Paper Chemicals Europe, EDP/M - H201, 67056 Ludwigshafen, Germany.