GRAFTING OF POLYETHYLENES BY REACTIVE EXTRUSION - I - INFLUENCE ON THE MOLECULAR-STRUCTURE

Grafting of polyethylenes is an important method used in the modificat ion of polyolefins with functional groups. Lately, the use of extruder s as polymerization reactors has increased considerably. However, know ledge of the details of the reaction in the extruder is still limited. In this investigation, the grafting of various commercial polyethylen es, high-density polyethylenes (HDPEs), and linear low-density polyeth ylenes (LLDPEs) with diethyl maleate (DEM) was carried out in two coro tating twin-screw extruders with different screw configurations and ex trusion conditions. Two initiators at different concentrations were us ed. It was found that when the initiator level was raised in the LLDPE s the grafting degree increased and the molecular weight distribution of the grafted LLDPE2 did not show appreciable differences when they w ere compared to the virgin resin. On the other hand, the terminal viny l group concentrations decreased at the expense of increasing the tran s unsaturation concentrations. This last result is consistent with the formation of long-chain branching. Additionally, the weight-average m olecular weight of grafted high-density polyethylene (HDPE1-g-DEM) dec reased. The grafting efficiencies were consistent with the attained re sidence times and also with the kinetics of the decomposition of the p eroxides. (C) 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 161-17 6, 1998.