GB922946A - Process for preparing polyurethane compositions - Google Patents

Abstract

A method for the preparation of a liquid, curable polyurethane composition comprises heating at a temperature between about 60 DEG and about 160 DEG C. for a period of about 1 to about 24 hours (a) 1,0 molar proportion of a polypropylene ether glycol having a molecular weight of from about 1,000 to 2,500; (b) 0,2 to 10 molar proportions of a diol having a molecular weight in the range between about 76 to about 750 and having the general formula HO(GO)nH wherein G is a divalent hydrocarbon radical selected from saturated aliphatic hydrocarbon radicals having 3 to 4 carbon atoms and isopropylidene-bis-cyclohexyl radical, n is 1 when G is isopropylidene-bis-cyclohexyl and n is from 1 to 13 when G is a divalent saturated aliphatic hydrocarbon radical having 3 to 4 carbon atoms, and (c) 2,4 to 24 molar proportions of an organic diisocyanate, with the proviso that the ratio of the molecular weight of (a) to the molecular weight of (b) is at least 2,5, the average molecular weight of (a) and (b) combined is in the range between about 500 to about 1750 and the NCO/OH ratio is in the ratio between 2 to 2,5, components (a), (b) and (c) being reacted simultaneously or components (a) and (b) being reacted p separately with portions of component (c), the reaction products being thereafter combined. The liquid product is converted to a cured cast polyurethane by heating at a temperature from about 70% to about 160 DEG C. with a curing composition which is selected from aromatic primary diamines having a melting point below 136 DEG C. and mixtures of such amines with aliphatic polyhydroxy compounds having an equivalent weight below about 350, the mixtures being further characterized in that they contain at least 30 weight per cent of the aromatic primary diamines, quantity of the curing composition being sufficient to provide a ratio of NCO/active functional groups in the range between about 1,0 and 1,3. When the average molecular weight of the polyol mixture is around 500 the NCO/OH ratio in the first stage preferably does not exceed about 2,05. As curing agents in the second stage there are specified 4,41-methylene bis-(2-chloroaniline) and dichlorobenzidine and as polydroxy compounds castor oil, trimethylolpropane, pentaerythritol and the propylene oxide adducts of trimethylolpropane and of pentaerythritol, of M.W. 450 and 600 respectively. In the curing the mixture may be allowed to solidify in the mould before being subjected to heat and pressure. The products can be used in producing seals or laminants. They can be compounded with carbon black, silica or plasticizers. In the examples the polyols were stripped of water and reacted at 80 DEG C. with tolylene diisocyante. The liquid product was stirred with 4,41-methylene-bis-(2-chloro-aniline) curing agent and the mixture heated at 100 DEG C. for three hours. Comparative examples using a single polyol in place of a blend are given. Polyol blends employed consisted of (1) polypropylene ether glycols of M.W. 2000 and 400, the M.W. of the mixture being 1500; (2) either polypropylene ether glycols as in (1), the average molecular weight being 1250, or a mixture of polypropylene ether glycol of M.W. 2000 and fully hydrogenated bisphenol A. In Example (4) the curable mixture comprised (A) a reaction product of polypropylene glycol (M.W. 2000) with 2 molar proportions of tolylene diisocyanate and (B) a reaction product of polypropylene glycol (M.W. 400) with 2 molar proportions of tolylene diisocyanate, (A) and (B) being blended in such proportions as to provide an average molecular weight of polyol 775. The curing agent consisted of a blend of 4,41-methylene bis(2-chloroaniline) and a polyoxypropylene ether adduct of trimethylolpropane of average M.W. 445, the quantity of curing agent providing an NCO/(NH2+OH) ratio of about 1,1.