| 摘要 |
A graft blend polymer is prepared by polymerizing an ethylenically unsaturated monomer consisting of at least 80% by weight of vinyl halide in the presence of either (i) a copolymer of ethylene and another olefin, the copolymer comprising from 40 to 75% by weight of polymerized ethylene, or (ii) a copolymer of an olefin and an alkyl acrylate or methacrylate; the polymerization product being a mixture of graft polymer, polymer of said ethylenically unsaturated monomer and, possibly, a minor proportion of ungrafted (unchanged) copolymer. Said other olefin of copolymer (i) or olefin of copolymer (ii) preferably contains up to 8 carbon atoms, and in the latter copolymer the alkyl group of the ester component preferably has up to 12 carbon atoms. Monomers which can be used together with the vinyl halide for grafting include vinylidene halides, vinyl esters, acrylonitrile, acrylates, methacrylates, maleates and fumarates; vinyl chloride is the preferred vinyl halide. Polymerization can be effected in bulk, solution or emulsion. The preferred procedure comprises dispersing the copolymer in the monomer, adding the mixture in the absence of oxygen to water which contains a suspending agent (e.g. methyl cellulose or polyvinyl alcohol) and has been heated to 20-100 DEG C, and agitating the resultant mixture at 10-80 DEG C. until polymerization is complete; this procedure being generally effected under pressure. Suitable catalyst which may be used include peroxides, hydroperoxides, percarbonates, perborates and azo compounds; polymerization can also be effected using irradiation. Chain regulators such as chlorinated hydrocarbons, alcohols and aldehydes may also be present. To the graft blends may be added additional components, e.g. stabilizers such as Ba/Cd soaps, fillers, colourants, processing aids, lubricants and coplasticizers; such components include other polymers, e.g. vinyl halide homopolymers and copolymers, polyvinylidene halide, polymethyl methacrylate, styrene-acrylonitrile copolymers, methylstyrene - acrylonitrile copolymers, methylstyrene - styrene - acrylonitrile copolymers, styrene-methyl methacrylate copolymers and butadiene - acrylonitrile copolymers, and also epoxy and chlorinated paraffin components. The graft blends are suitable for preparing rigid and semi-rigid sheets, tubes, pipes, wire coatings and moulded objects, and can be reinforced with asbestos fibres. |
