Polysiloxane-polyoxyalkylene block copolymers as stabilizers in the production of urethane foam

A process for preparing flexible polyether polyurethane foam, said process comprising reacting and foaming a mixture comprising (a) a polyether containing at least two hydroxyl groups per molecule, (b) an organic polyisocyanate, (c) a catalyst for the reaction of (a) and (b) to produce the polyurethane, (d) a blowing agent and (e) as the foam stabilizer a polysiloxane-poly(oxyethylene-oxypropylene) block copolymer consisting essentially of from about 15 to about 35 percent by weight of polysiloxane blocks and from about 85 to about 65 percent by weight of polyoxyalkylene blocks, and further consisting essentially of siloxy units of the formula R.sub.2 SiO, siloxy units selected from the group consisting of those of the formulas (R)(Q)SiO and RSiO3/2 and terminal siloxy units selected from the class consisting of those of the formulas R.sub.3 SiO1/2 and (R.sub.2) (Q)SiO1/2, wherein the average number of total siloxy units per molecule of the polysiloxane-polyoxyalkylene block copolymer ranges from about 20 to about 200, wherein from about 6 to about 15 percent of said total siloxy units are selected from the group consisting of (R)(Q)SiO and (R.sub.2) (Q)SiO1/2 and wherein there are no more than about four RSiO3/2 siloxy units per average polysiloxane molecule, wherein each R individually represents a monovalent hydrocarbon radical or a substituted monovalent hydrocarbon radical, said radicals being free from aliphatic multiple carbon to carbon bonds, and wherein each Q individually represents a polyoxyalkylene polyether block having the formula --MX wherein each M is a bridging group individually selected from the class consisting of --O-- and --C.sub.n H.sub.2n O-- wherein n has a value of 2 or 3, and X is a polyoxyalkylene radical consisting essentially of an admixture of Units A and B of the formula (C.sub.2 H.sub.4 O).sub.x (C.sub.3 H.sub.6 O).sub.y Z wherein Z is a terminal group selected from the class consisting of alkyl, aryl and aralkyl radicals, with the proviso that when M is --C.sub.n H.sub.2n O-- as defined above, Z can also be a terminal acyl radical, the values of x and y being determined by the following conditions prevailing for Units A and B;

• Unit A representing from about 20 to about 80 percent by weight of low molecular weight polyoxyalkylene polyether based on the total weight of Units A and B in said admixture;
• said polyether being selected from the class consisting of (i) a polyoxyalkylene copolymer having an average molecular weight in the range of from about 800 to about 2300 wherein about 20 to about 60 weight percent of the oxyalkylene groups of said copolymer are oxyethylene, the remainder of the oxyalkylene groups being oxypropylene, and (ii) a blend of at least two polyoxyalkylene copolymers having different average molecular weights in the range of from about 500 to about 2900 and wherein about 20 to about 60 weight percent of the oxyalkylene groups of the copolymers in said blend are oxyethylene, the remainder of the oxyalkylene groups being oxypropylene, with the proviso that said blend has an average molecular weight in the range of from about 800 to about 2300;
• and
• Unit B representing from about 80 to about 20 percent by weight of high molecular weight polyoxyalkylene polyether based on the total weight of Units A and B in said admixture said polyether being selected from the class consisting of (i) a polyoxyalkylene copolymer having an average molecular weight in the range of from about 3400 to about 5500 wherein about 20 to about 60 weight percent of the oxyalkylene groups of said copolymer are oxyethylene, the remainder of the oxyalkylene groups being oxypropylene, and (ii) a blend of at least two polyoxyalkylene copolymers having different average molecular weights in the range of from about 3000 to about 5500 and wherein about 20 to about 60 weight percent of the oxyalkylene groups of the copolymers in said blend are oxyethylene, the remainder of the oxyalkylene groups being oxypropylene, with the proviso that said blend has an average molecular weight in the range of from about 3400 to about 5500;
• and with the added proviso that said admixture of Units A and B has an average molecular weight in the range of from about 1600 to about 2900.