Kinetics and mechanism of grafting styrene onto natural rubber in emulsion polymerization using cumene hydroperoxide-tetraethylenepentamine as redox initiator

Styrene-natural rubber (NR) graft copolymerization using emulsion polymerization with cumene hydroperoxide (CHPO)-tetraethylenepentamine (TEPA) as redox initiator was investigated. Instead of an equimolar ratio, the optimal molar ratio of CHPO and TEPA was 1:4, probably due to the compensation for TEPA loss in chain transfer reactions. The rate of copolymerization in terms of initiator and emulsifier concentrations, derived from reviewing of the mechanism of the copolymerization covering reactions in both rubber particles and micelles, agreed well with experimental data. Its greater dependences on initiator and emulsifier than those in the Smith-Ewart theory were contributed from the NR addition, which was confirmed by performing styrene polymerization (keeping all ingredients' amounts constant, but without NR). The rate of homopolymerization was dependent on the initiator and emulsifier to the powers of 0.43 and 0.61, respectively, which was in good agreement with the theory. (C) 2013 Elsevier Ltd. All rights reserved.