Method for preparing stable (co) polymers dispersions in a polyol

A process for preparing stable dispersions of (co)polymers in a polyol by in situ polymerization of an ethylenically unsaturated monomer or mixture of monomers in the presence of an initiator comprising an azocarboxylic acid ester of formula (II) or a mixture of azocarboxylic acid esters of formula (II)

• wherein R1, R2, R3 and R4, which may be identical or different, are independently selected from the group consisting of
• linear or branched alkyls comprising from 1 to 9 carbon atoms optionally substituted with one or more substituents selected from hydroxyl, C1 to C6 alkoxy and halogen substituents;
• C3 to C12 cycloalkyls, optionally substituted with one or more substituents selected from C1 to C6 alkyl, C1 to C6 alkoxy, hydroxyl and halo groups;
• aralkyls optionally substituted with one or more C1 to C6 alkyl, C1 to C6 alkoxy, hydroxyl and halo groups;
• aryls optionally substituted with one or more substituents selected from C1 to C6 alkyl, C1 to C6 alkoxy, hydroxyl and halo groups;
• with at least one of the combinations R1-R2 and R3-R4 possibly forming an aliphatic ring;
• R″ and R′ are identical or different and are independently selected from the group consisting of linear or branched C1 to C10 aliphatic radicals.