MELT GRAFTING OF A BASIC MONOMER ON TO POLYETHYLENE IN A TWIN-SCREW EXTRUDER - REACTION-KINETICS

The grafting of 2-(dimethylamino) ethyl methacrylate (DMAEMA) on to li near low-density polyethylene (LLDPE) using peroxide initiators was st udied in an intermeshing co-rotating twin-screw extruder. The grafting reactions were carried out above the apparent ceiling temperature of the DMAEMA monomer. It was observed that above this ceiling temperatur e homopolymer propagation reactions are no longer occurring. The homop olymer initiation step was seen, however, to consume significant quant ities of monomer, thus resulting in low grafting efficiencies (GE). Re ducing the monomer concentration was shown to suppress the homopolymer initiation reaction and provide high grafting efficiencies with littl e loss in graft levels. It was also observed that initiator concentrat ion controls the overall conversion and degree of grafting (DG) as wel l as crosslinking. Graft levels are therefore limited by the amount of crosslinking that can be tolerated in the final graft product.