GB791851A - Elastomeric latices derived from diisocyanates and substances containing active hydrogen atoms - Google Patents

Abstract

An elastomeric latex is made by reacting an organic compound having a molecular weight of at least 750 and containing at least two groups bearing active hydrogen atoms with a stoichiometric excess of an organic diisocyanate and thereafter effecting chain extension of the reaction product by emulsifying it in aqueous medium and in the presence of an emulsifying agent. The aqueous medium may contain a diamine (e.g. phenylene-, tolylene-, cyclohexylene-, propylene- or ethylene-diamine) which reacts, with the isocyanate terminated polymer preferentially to the water. The organic compound with a molecular weight of at least 750 may be a linear or branched polyester, a polyesteramide, a polyalkylene glycol, a polyalkylene ether-thioether glycol having terminal hydroxyl groups or an ester of a hydroxy fatty acid with a polyhydric alcohol (e.g. castor oil or glyceryl ricinoleate). A mixture of castor oil and polyethylene glycol may be used. In addition to these organic compounds smaller amounts of low molecular weight diols (e.g.2-butene-1,4-diol) may be used. The Specification lists suitable starting materials of the type referred to above. Suitable emulsifying agents are the polyethylene glycol ethers of long-chain alcohols, quaternary ammonium salts, the tertiary amine or alkylol amine salts of long-chain alkyl acid sulphate esters, alkyl sulphonic acids or alkyl aryl sulphonic acids, the sodium salt of long-chain sulphated alcohols, casein, and alkali metal salts of high molecular weight organic acids (e.g. rosin or tall oil). The last named may be formed in situ by adding the acid to the isocyanate terminated polymer and adding alkali to the aqueous bath. The isocyanate terminated polymer may be added to the aqueous medium while dissolved in an organic solvent (e.g. heptanes, octanes, nonanes, kerosenes, synthetic hydrocarbons, methylcyclohexane, benzene or toluene). Coagulation of the latex may be effected by adding an acid (e.g. acetic) and/or an inorganic salt (e.g. sodium or calcium chloride) or by freezing. In an example, a film of elastomer is formed by dipping a cylindrical glass mould first into a coagulating solution and then into a latex, the coagulating solution comprising methanol, acetone, calcium nitrate and calcium chloride. The coagulated polymer may then be dried and cured by milling it with a diisocyanate. Films of the dried polymer may be cured either by dipping into a liquid diisocyanate or a solution thereof or by exposure to the vapours of a diisocyanate. In Example 21, toluene is added to the reaction product of castor oil, polyethylene glycol and 2,4-tolylenediisocyanate and the mixture added to a solution containing water, the sodium salt of sulphated long-chain alcohols, casein and an anti-foaming agent comprising pine oil and tributyl phosphate. An emulsion suitable for gluing wood results. In Example 25, tall oil is added to the reaction product of polytetramethylene ether glycol and 2,4-tolylene diisocyanate and the mixture added to sodium hydroxide solution to produce a latex. A curing agent is then dispersed in the latex comprising the dimer of 2,4-tolylene diisocyanate, the sodium salt of polymerized formaldehyde napthalene sulphonic acids, water and casein. A dip film is then made, coagulated and dried. The elastomers may be made fireproof by adding antimony or zinc oxide and electrically conductive by adding carbon black or powdered metals. Compounding agents such as carbon black, clay, silica, talc, zinc and magnesium oxides, calcium and magnesium carbonate, titanium dioxide, plasticizers and inorganic or organic colouring agents may be added. The Specification lists a large number of uses for the elastomers. Specifications 731,071, 753,712, [Group IV (b)], 791,852 and 791,854 are referred to.