Silicone surfactants for rigid polyurethane foam made with hydrocarbon blowing agents
A method for making a rigid polyurethane foam employing a C4 or C5 hydrocarbon blowing agent, or mixtures thereof, and a silicone surfactant comprising a polyether-polysiloxane copolymer represented by the following formula: (CH3)3-Si-O-(Si(CH3)2-O)x-(Si(CH3)(R)O)y-Si(CH3)3 where R= (CH2)3-O-(-CH2-CH2-O)a-(CH2-CH(CH3)-O)b-R", and where R" is H, (CH2)zCH3, or C(O)CH3; x + y +2 is 60-130; x/y is 5 - 14; z is 0-4; the total surfactant molecular weight, based on the formula, is 7000 - 30,000 g/mole, the wt% siloxane in the surfactant is 32 - 70 wt%, the blend average molecular weight (BAMW) of the polyether portion is 450 - 1000 g/mole, and the mole% of ethylene oxide in the polyether portion is 70 - 100 mole%.