AbstractThe reaction of molten HDPE with MAH at 215 and 250°C using di‐t‐amyl peroxide andt‐butyl cumyl peroxide as catalysts yielded HDPE‐g‐MAH accompanied by crosslinked polymer. The formation of the latter, increased by the presence of MAH and insoluble in refluxing xylene, was prevented by the presence of electron donor additives, i.e., dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), and tri(nonylphenyl) phosphite (TNPP). A charge containing 0.0625–0.125 catalyst, 5 MAH and 0.5 additive, all based on HDPE and added to the molten HDPE in four portions, resulted in gel‐free polymer with an MAH content of 0.7–1.7. HDPE‐g‐MAH with the least color was obtained with TNPP, followed by DMAC and DMSO. Notwithstanding the absence of gel in the HDPE‐g‐MAH prepared from HDPE with a melt flow of 17 g/10 min, the carboxylated HDPE had a melt flow of 0.0–1 g/10 min, indicative of an increase in the molecular weight of the product. This is attributed to a coupling reaction between MAH radicals appended to the HDPE backbone (HDPE–MAH·) and HDPE radicals formed as a result of hydrogen abstraction from HDPE by radicals from th
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