FUNDAMENTAL-STUDIES OF GRAFTING REACTIONS IN FREE-RADICAL COPOLYMERIZATION .2. GRAFTING OF STYRENE, ACRYLATE, AND METHACRYLATE MONOMERS ONTO CIS-POLYBUTADIENE USING AIBN INITIATOR IN SOLUTION POLYMERIZATION

Grafting can be initiated by primary and/or polymer radical attack on the backbone polymer and it is well known that AIBN does not readily p romote grafting, even when using polybutadiene. We have studied the gr afting of several different monomers onto cis-polybutadiene using AIBN initiator and find dramatically different results among the monomers. As expected, styrene grafts at very low levels due to the inactivity of the initiator radicals and the polystyryl radicals. Methacrylate mo nomer grafts at a slightly higher level due to its more reactive polym er radical, while acrylate monomer readily grafts onto the polybutadie ne because polyacrylate radicals are quite reactive. The use of a kine tic model allowed the evaluation of rate coefficients for graft site i nitiation to be in the relative order of 0.1 : 1.0 : 10.0 (L/mol/s) fo r styrene:methacrylate:acrylate monomers. The model also provided succ essful interpretations of the grafting data and its dependence upon th e concentrations of monomer, initiator, and backbone polymer. Due to t he relatively higher reactivity of the polyacrylate radicals, the benz ene solvent acted as a chain transfer agent in this system. This affec ted the molecular weight of both free and grafted acrylate polymer and also surpressed the graft level. Polyacrylate radicals attack the cis -polybutadiene backbone by abstracting an allylic hydrogen and also ad ding across the residual double bond. The latter mechanism is responsi ble for the majority of the grafting; the hydrogen abstraction leads t o relatively inactive radicals which cause a retardation in the overal l reaction rate. (C) 1995 John Wiley & Sons, Inc.