Process for the grafting of monomers onto polyolefins

Claim 1

A continuous process for the grafting onto a polyolefin of an ethylenically unsaturated monomer that is capable of reacting with said polyolefin in a molten condition, said polyolefin being selected from the group consisting of homopolymers of ethylene and copolymers of ethylene and C 4 -C 10 higher alpha-olefins, and mixtures thereof, said process comprising: (i) feeding a physical admixture to an extruder equipped with a mixing screw, said physical admixture being comprised of (a) a major portion of particles of a polyolefin, (b) a minor portion of particles of a second polymer, (c) said monomer and (d) 125-400 ppm of an organic peroxide having a half life of from about one minute to about 120 minutes at 150° C., said polyolefin being the polyolefin defined above and said second polymer being a normally solid thermoplastic polymer selected from the group consisting of: (A). homopolymers and copolymers consisting of unsaturated hydrocarbons; (B). copolymers of an alpha-olefin having the formula R--CH═CH 2 , wherein R is a radical selected from the class consisting of hydrogen and alkyl radicals having from 1 to 8 carbon atoms, with alpha,beta-ethylenically unsaturated acids having from 3 to 8 carbon atoms, and esters and anhydrides thereof, such acids being mono-, or di- or polycarboxylic acids, the moieties being randomly or non-randomly distributed in the polymer chain and being 0.5-50% by weight of the copolymer, any other copolymerized monomer being monoethylenically unsaturated; (C). ionomeric polymers derived from the copolymers of (B); (D). graft copolymers obtained by grafting 0.1 to 5 percent by weight of alpha-beta unsaturated carboxylic acids having 3 to 8 carbon atoms or an unsaturated carboxylic acid anhydride onto a preformed backbone derived from ethylene or ethylene and C 3 to C 8 alpha-olefin, in which polyolefin backbone any other optionally copolymerized monomer component is mono-ethylenically unsaturated; (E). homopolymers of R'--CH═CH--R' were each R' is independently selected from the group consisting of H, Cl and F, with the proviso that at least one R' is other than H, copolymers of ethylene with R'--CH═CH--R' and chlorinated homopolymers and copolymers of C 2 -C 10 hydrocarbon alpha-olefins; (F). saturated polyamides and polyesters; (G). homopolymers of vinyl esters of aliphatic carboxylic acids having 3 to 8 carbon atoms, copolymers of ethylene with such esters, and partially saponified polymers thereof; and (H). copolymers of (B) in which all or part of the alpha-olefin has been replaced with styrene or alkyl styrene, where the alkyl group has 1 or 2 carbon atoms, and having a meltin point of less than 185° C/ and a shear viscosity that is not more than 50% of that of said polyolefin when measured at 200° C. and a shear rate of 400 sec -1 , said organic peroxide being in the form of a composition with the second polymer, (ii) mixing said admixture in the extruder at a temperature in the range of from the melting point of said polyolefin to 195° C. for a period of time such that the amount of decomposition of the organic peroxide is less than about 25%, said period of time being at least ten seconds, (iii) mixing the resultant admixture in a second zone of the extruder at a temperature above the melting point of the polyolefin and second polymer for a period of time that is at least four times the half-life of the peroxide, and (iv) extruding the grafted polymer so obtained into a shaped article.