Polymer polyol and preformed stabilizer systems

A process for the preparation of polymer polyol composition which process comprises providing a composition comprising:

• (a) a polyol;
• (b) a preformed stabilizer comprising the reaction product of (i) a polyol;
• (ii) a precursor stabilizer obtainable by reacting a silicon atom containing compound of formula R.sub.n SiX.sub.4-n or R.sub.n Si((--OSi(R.sup.1).sub.2).sub.p X).sub.4-n wherein the R groups are independently saturated or unsaturated hydrocarbyl groups, at least one R group being an olefinically unsaturated hydrocarbyl group;
• R.sup.1 is a hydrocarbyl group, X is a C.sub.1 to C.sub.10 alkoxy group, n is an integer from 1 to 3 and p is an integer greater than zero, with a polyether polyol having an average molecular weight in excess of 400 and a hydroxyl number in the range 20 to 280;
• (iii) at least one ethylenically unsaturated monomer which is copolymerizable with the precursor stabilizer;
• and (iv) a free radical polymerization initiator;
• (c) at least one ethylenically unsaturated monomer;
• (d) a free radical polymerization initiator;
• and, optionally,
• (e) a chain transfer agent
• in a reaction zone maintained at a temperature sufficient to initiate a free radical polymerization, and under sufficient pressure to maintain only liquid phases in the reaction zone, for a period of time sufficient to react essentially at least major portion of the at least one ethylenically unsaturated monomer and recovering the polymer polyol.