Modification of maleic anhydride grafted polyethylene with 1,4-diaminobutane in near critical propane

Granules of high density polyethylene grafted with 0.17 wt.% maleic anhydride (PEMA) were modified with an excess of 1,4-diaminobutane (DAB) by impregnation from near critical propane. After formation of amic acid groups, the excess of diaminobutane was extracted with a near critical propane-ethanol mixture (95/5 wt.%). Finally, the obtained PEMA-DAB was imidised quantitatively to the corresponding imide (PEMI) in the melt. The obtained PEMI showed no increased gel content with respect to the PEMA. The presence of primary amine groups was indirectly proven by selective extraction experiments. It appeared that PEMI samples had reacted with the anhydride groups of styrene-MA copolymer (SMA) during melt blending of SMA with PEMI, while the PEMA had not reacted. SMA/PEMI 80/20 blends consisted of a continuous SMA phase and PEMI droplets with a diameter of less than I pm. SMA/PEMA 80/20 blends showed a course morphology of PEMA strings in a continuous SMA phase. With this article we have shown that this new technique for the chemical modification of swollen HDPE particles in near critical propane has proven to be much better than the conventional modification in the melt, when it comes to avoiding crosslinking. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.