Patent GB-976902-A (GB)
Title: Polyurethane material
Inventor: WATSON JOHN WILLIAM
IPC: C08G18/75
Filed: 1960-07-07
Abstract: A process for producing a polyurethane comprises mixing under anhydrous or substantially anhydrous conditions a reaction product of a diol and a stoichiometric excess of an aliphatic (including alicyclic) diisocyanate each molecule of the reaction product having at least two terminal or substantially terminal aliphatic radicals each containing an isocyanate substituent with a polyol containing more than two -OH or -SH groups in the molecule and a catalyst to accelerate cross-linking between said reaction product and said polyol. (Isothiocyanates, thioethers and thiols are included).  The diol is preferably a linear polymer with M.W. in excess of 750. Suitable are those containing polymethylene oxide units or polyesters, preferably based on dihydric alcohols containing a gem dimethyl group. Specified catalysts are (a) triethylenediamine, its homologues and analogues, for example the corresponding compound in which phosphorus replaces nitrogen or (b) esters, alkyl esters and salts of metals of groups 4, 5 and 6 of the Mendel<\>aeeff Periodic System, e.g. dibutyl tin dilaurate, dibutoxy tin dilaurate or stannous octoate or oleate. Preferably the molar ratio of polymeric diol to diisocyanate is 1:N where n is in the range 2 to 3 inclusive and the molar ratio of polyol cross-linking agent to the diisocyanate is less than 2(n-1)/3n:1 and preferably less than (n-1)/3n:1. To prevent the products acquiring a permanent set in the stretched condition, this ratio is usually greater than (n-1)/30n:1 and preferably greater than (n-1)/20n:1. The polyol preferably has a molecular weight not exceeding 500. Examples are trimethylol propane, hexane triol and a polyester diol from neopentyl glycol and a dicarboxylic acid. There may also be included a minor proportion of a diol. Threads and films of the product are formed In examples (1) a prepolymer from polypropylene ether glycol (M.W.2000) and dicyclohexylmethane diisocyanate is mixed with trimethylol propane and dibutyl tin dilaurate is added. Layers of the mixture are cured at 100 DEG C. to form films; (2) hexane triol is the polyol in a similar process; (3) a prepolymer from polypropylene ether glycol and hexamethylene diisocyanate is treated similarly to (1) and (2); (5) the prepolymer from polytetramethylene glycol (M.W.3000) and hexamethylene diisocyanate (reacted in two portions) is mixed with trimethylolpropane and dibutyl tin dilaurate and cured to a film; (9) a prepolymer from polytetramethylene glycol, trimethylol propane and dicyclohexylmethane diisocyanate is mixed with 1,4-butane diol, trimethylol propane and dibutyl tin dilaurate; (11) prepolymer from neopentyl glycol adipic acid polyester and dicyclohexylmethane diisocyanate is dissolved in acetone, methylene chloride or butyl acetate, and trimethylol propane and dibutyl tin dilaurate are added, giving a lacquer; (12) a film is prepared from a polytetramethylene ether glycol/hexamethylene diisocyanate prepolymer, anhydrous trimethylol propane and dibutyl tin dilaurate (both latter in acetone solution) and methylene-bis-dibutyl dithio-carbamate antioxidant. Specification 976,901 is referred to.