SynopsisThe reaction of molten HDPE with MAH at 215 and 250°C using di-t-amyl peroxide and t-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(nonylpheny1)phosphite (TNPP). A charge containing 0.0625-0.1258 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 HDPEg-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 the catalyst and/or excited MAH.

SYNOPSISThe reaction of maleic anhydride (MAH) with molten 2 MI poly( ethylene-co-butene-1) (LLDPE) a t 160°C in the presence of peroxyesters ( tllz < 10 s ) as catalysts resulted in the formation of a mixture of cross-linked and trichlorobenzene-soluble LLDPE-g-MAH.The soluble fraction constituted more than 50% of the mixture and had an MI of 0.0 and an MAH content ranging from 0.3 to 1.8 wt %. The presence of tri (nonylphenyl) phosphite (TNPP) in the LLDPE-MAH-t-butyl peroctoate ( tBPO) reaction at 160°C increased the MI of the soluble product to 0.7-2. The amount of soluble polymer increased at higher TNPP concentrations while its MAH content ranged from 0.05 to 0.54 wt %, with most contents in the 0.2-0.3 wt % range. The color development that usually occurs in polyolefin-MAH reactions was reduced by the presence of TNPP. However, the reaction of TNPP with the peroxide and with the products from the thermal decomposition thereof reduced the availability of the excited species necessary for the appendage of MAH units onto the polyolefin. I NTRODUCTIO NThe reaction of maleic anhydride (MAH) with molten polyolefins in the presence of a peroxide catalyst proceeds as a heterogeneous reaction due to the insolubility of molten MAH and results in the appendage of individual MAH units onto the polyolefin backbone, accompanied by cross-linking in the case of low-density polyethylene (LDPE) and highdensity polyethylene ( HDPE) 2 , degradation in the case of polypropylene ( P P ) , 3 and both cross-linking and degradation in the case of ethylene-propylene copolymer rubber (EPR) . 4 The cross-linking and/or degradation reactions result from the generation of radical sites on the polymer backbone, followed by coupling or disproportionation, respectively. Such sites, which arise from hydrogen abstraction, are generated in the presence of a peroxide due to the attack of radicals derived therefrom. When MAH is present, the number of such sites, and, therefore, the extent of cross-linking and/or degradation, is increased. The appendage of MAH to a polyolefin backbone occurs under the conditions that are necessary to promote MAH homopolymerization, i.e., using a peroxide catalyst at a temperature where it has a short half-life. Consequently, the cross-linking and/ or degradation that accompanies the appendage of MAH units is considered to be due to radical generation on the polymer backbone by some intermediate in the homopolymerization of MAH. The presence of electron donors that inhibit the homopolymerization of MAH reduces or prevents these undesirable side reaction^.^ Colored products are generated during the homopolymerization of MAH, i.e., in the presence of a free radical catalyst undergoing rapid decomposition, as well as during the graft copolymerization of MAH onto a molten polyolefin, under the same conditions. The interaction of MAH, a strong electron acceptor, and an electron donor compound results in the formation of colored complexes. When an electron donor is present during the peroxide-catalyzed reaction of MAH...

pH regulates the transmembrane transport of Cl− ions by bis(iminourea) derivatives.