| 摘要 |
<p>In a process for polymerizing vinyl chloride, optionally with up to 20 weight per cent of at least one other ethylenically unsaturated monomer, in an aqueous medium in the presence of a polymerization catalyst and separating the polymer from the aqueous medium, a stabilizing component is added to the aqueous medium before or during the separation step, which stabilizing component comprises at least one lead salt insoluble in both water and vinyl chloride and capable of absorbing hydrochloric acid, optionally together with up to 50 weight per cent of at least one other lead salt. Specified comonomers are vinyl acetate, vinylidene chloride, alkyl esters of acrylic, methacrylic, maleic and fumaric acids, acrylonitrile, methacrylonitrile and maleic anhydride. Specified insoluble lead salts are lead carbonate, lead silicate, lead chlorosilicate, lead phosphite, triboric lead sulphate and basic lead carbonate. Optional lead salts specified are lead stearate and dibasic lead stearate. Other additives such as lubricants, e.g. calcium and magnesium stearates, stearic acid, glyceryl monoerucate, glyceryl monostearate, cetyl palmitate, stearyl alcohol and cetyl alcohol; secondary stabilizers, e.g. cadmium stearate and laurate; plasticizers; pigments, e.g. titanium dioxide and carbon black; processing aids, e.g. methyl methacrylate/ethyl acrylate copolymers, styrene/acrylonitrile copolymers and chlorinated polyethylene; and impact strength improvers, e.g. calcium carbonate which may be coated with stearic acid, acrylonitrile/butadiene/styrene copolymers and ethylene/vinyl acetate copolymers. Specified polymerization catalysts are hydrogen, benzoyl and lauroyl peroxides, alkali metal and ammonium persulphates, percarbonates and peracetates, peroxydicarbonates and azo compounds. Polymerization may be effected in the presence of emulsifying and dispersing agents, e.g. sodium dioctyl sulphosuccinate, sulphonated diesel oil, sodium lauryl sulphate, stearamidopropyl dimethyl - b -hydroxyethyl ammonium nitrate, cetyl pyridinium bromide, cetyl trimethyl ammonium bromide and polyethylene oxides, and gelatin, methyl cellulose and hydrolysed polyvinyl acetate. In examples vinyl chloride is polymerized in aqueous media in the presence of: tribasic lead sulphate, lead stearate, calcium stearate, wax, hydrolysed polyvinylacetate and (1) lauroyl peroxide and (2) azodiisobutyronitrile; azodiisobutyronitrile, hydrolysed polyvinyl acetate and (3 and 6) tribasic lead sulphate, (7) tribasic lead sulphate and lead stearate, (8) tribasic lead sulphate, lead stearate and dibasic lead stearate, (9) tribasic lead sulphate, lead stearate, dibasic lead stearate and calcium stearate and (10) tribasic lead sulphate, cetyl alcohol and stearyl alcohol; and diisopropyl peroxydicarbonate, hydrolysed polyvinyl acetate and (4) dibasic lead phosphate and (5) dibasic lead phthalate.</p> |
