FUNDAMENTAL-STUDIES OF GRAFTING REACTIONS IN FREE-RADICAL COPOLYMERIZATION .3. GRAFTING OF STYRENE, ACRYLATE, AND METHACRYLATE MONOMERS ONTO CIS-POLYBUTADIENE USING BENZOYL PEROXIDE INITIATOR IN SOLUTION POLYMERIZATION

Benzoyl peroxide (BPO), due to its higher radical reactivity as compar ed to AIBN, is known to promote grafting onto cis-polybutadiene. Switc hing from AIBN to BPO initiator made a dramatic difference in the exte nt of grafting for styrene and methacrylate monomers, but only a modes t difference for acrylate monomer. For styrene and methacrylate monome rs, graft site formation is due to BPO initiator radical attack onto t he backbone via allylic hydrogen abstraction. Significant levels of gr afting are achieved and depend upon the relative concentrations of mon omer and backbone polymer but not upon the level of initiator. For acr ylic monomer, graft site formation was found tb be due to polymer radi cal attack at the double bond in the backbone. Abstraction of allylic hydrogen also occurs but results in retardation of the overall reactio n rate. Graft level was dependent upon initiator and backbone polymer concentrations but not upon monomer concentration. The effective role of the initiator is only to produce polymer radicals; the BPO has no d irect role in the formation of effective graft sites. (C) 1995 John Wi ley & Sons, Inc.