Patent GB-796043-A (GB)
Title: Improvements in or relating to the preparation of polyurethane elastomers
IPC: C08G18/70
Filed: 1956-05-18
Abstract: A process for the production of elastomeric products from curable polyether urethanes and diisocyanates is characterized in that a mixture of a plsyurethane polymer substantially free from isocyanate groups and consisting essentially of structural units having the formula <FORM:0796043/IV (a)/1> (wherein O-G-O- is a bivalent radical resulting from removal of the terminal hydrogen atoms of a high molecular polymeric glycol, B is a bivalent organic radical inert to isocyanate groups, Q is a carbonyl group or a nonpolymeric diacyl radical, n is an integer greater than zero and m is an integer including zero, each of the said structural units being connected by a radical Q as aforesaid) with 3 to 40 per cent by weight of a polytetramethyleneether glycol/2:4-toluylene diisocyanate reaction product of the formula <FORM:0796043/IV (a)/2> (wherein n is an integer corresponding to polytetramethyleneether glycol molecular weights of about 750 to about 3000 and x is an integer from 1 to 19 corresponding to a polytetramethyleneether glycol/2:4-tolylene diisocyanate molar ratio range of 2:1 to 20:19), is reacted with 1 to 20 per cent by weight of a polyisocyanate and the mixture is heated to produce a cured elastomer, said percentage weights being calculated on the weight of said polyurethane polymer.  "Acyl" defines the radical which results after the imino radical is removed from the radical obtained by reacting the active hydrogen compound or chain-extending agent with an isocyanate group.  The curable elastomer may be one obtained by reacting a polyalkylene ether glycol of molecular weight at least 750, a molecular excess of a diisocyanate and a chain-extending agent, for example as described in Specification 796,041.  Polyalkylene glycols useful in the preparation of the elastomer may contain a mixture of radicals, although polytetramethylene-ether glycol is preferred.  Water and organic amines are preferred chain-extending agents.  Others which may be used are hydrogen sulphide, ethylene glycol, adipamide, p-aminobenzoic acid, ethanolamine, 1,4-cyclohexanedisulphonamide, succinic acid and hydroxypropionic acid.  In preparing the uncured elastomer an excess of diisocyanate over the polyalkylene ether glycol is reacted, and if the resulting product contains free isocyanate groups these may be reacted with added primary or secondary nitrogen bases as in a Specification 791,853.  The polyalkylene glycols employed can also contain arylene or cycloalkylene groups in the molecule.  Polyetherpolythioether glycols can also be used.  Elastomers prepared by the method of Specification 796,042 can also be cured by this method.  As compounding agents there can be used carbon black, clay, silica, esterified silica particles (obtained by esterifying -SiOH groups of silica particles with a monohydric alcohol), talc, zinc, calcium and magnesium oxides, titanium oxide, plasticizers and inorganic and organic colouring agents.  In a typical example, a plasticizer is prepared by reacting polytetramethyleneether glycol of molecular weight 930 and 2,4-tolylene diisocyanate in the molar ratio of about 20:19.  An elastomer is prepared by reacting a polytetramethyleneether glycol and 2,4-tolylene diisocyanate and reacting the product firstly with water, then with further 2,4-tolylene diisocyanate and then with more water, being then stabilized by adding piperidine.  A mixture of the plasticizer, elastomer, conductive channel black and 1,3 - bis - (3 - isocyanato - 4-methylphenyl) urea (curing agent) is then compounded on a rubber mill.