Synthesis of polymer polyols in unsaturated polyols, polymer polyols and their use

A process for making a polymer polyol, the process comprising:

• mixing at least one melted thermoplastic styrene-acrylonitrile-copolymer (TP) with at least one polyol (P) in the presence of at least one stabilizer (S),
• wherein the polyol (P) comprises at least one unsaturated carbon-carbon bond per molecule, and
• wherein the stabilizer (S) comprises:
• (i) from 10 to 70% by weight, based on the total weight of the stabilizer (S), of at least one saturated polyol (P2);
• and
• (ii) at least one polyol (CSP) which comprises a reaction product of at least one macromer (M), styrene, and acrylonitrile in the saturated polyol (P2), optionally with an initiator and/ or a chain transfer agent,
• wherein the content of macromer (M) in the stabilizer (S) is between 30-70 wt %, based on the total weight of the stabilizer (S), and
• wherein the macromere M is defined as a molecule which comprises one or more polymerizable double bonds able to copolymerize with vinylic monomers and which comprises one or more hydroxyl-terminated polyether chains.