Silicone surfactants for rigid polyurethane foam made with hydrocarbon blowing agents

摘要

A method for making a rigid polyurethane foam by reacting a polyisocyanate and a polyol in the presence of a urethane catalyst, a blowing agent and a silicone surfactant characterized by employing a blowing agent comprising a C4 or C5 hydrocarbon, or mixtures thereof, with an average molecular weight of ≦72 g/mole and a boiling point in the range of 27.8 to 50° C., 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 whereR=(CH₂)₃—O—(—CH₂—CH₂—O)_a—(CH₂—CH(CH₃)—O)_b—R″, andwhere 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 %.