Maleation of linear low‐density polyethylene by reactive processing

Abstract

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...

Functionalization of polyolefins by reactive processing

“…In recent years, there has been considerable progress in the modi¯cation of polyole¯ns by the methods of graft copolymerization with polar monomers [1][2][3][4]. The solid state graft copolymerization of PE and PP with maleic anhydride (MAH), maleic acid (MA) or its salts is a promising method capable of retaining the mechanical properties of the initial polymers [5][6][7].…”

Bulk modification of styrene–butadiene–styrene triblock copolymer with maleic anhydride

“…5,6,19,20 The higher the [peroxide]/[MAH] ratio, the higher the MAH excited species concentration and, consequently, the higher the grafting and crosslinking degree obtained. The highest grafting degree was obtained at 150°C.…”

Maleic anhydride‐grafted linear low‐density polyethylene with low gel content

“…Then, the GD of LLDPE-g-MAH was chemically titrated by potassium hydroxide (KOH) solution in isopropyl alcohol as reported in the literature [8,9], and was calculated by the following equation:…”

“…Many efforts have been made to enhance the grafting degree (GD) and reduce the gel content (GC). Gaylord and coworkers [7][8][9] proposed that the addition of nitrogen-, phosphorous-, and sulfur-containing organic electron donors could prevent the crosslinking of PE and homopolymerization of MAH. Yao et al [10] also found that p-benzoquinone, triphenyl phosphate, and tetrachlomethane are good inhibitors for crosslinking of linear low-density polyethylene (LLDPE) during free radical graft polymerization.…”