Method for obtaining polybutadiene based aqueous dispersions

A process for obtaining aqueous dispersions of copolymers, which consists in polymerizing a blend of monomers containing at least 60% by weight of butadiene and at least one monomer chosen from styrene, acrylic esters, vinyl nitrites with optionally up to 40% by weight of one or more other copolymerizable unsaturated monomers, as an aqueous emulsion in the presence of one or more free-radical initiator(s), is characterized in that at least one of the initiators or the initiator is an azocarboxylic acid ester of formula (I):

• 2
• in which:
• R1, R2, R3 and R4, which may be identical or different, are independently selected from the group consisting of
• linear or branched alkyls containing from 1 to 9 carbon atoms and preferably from 1 to 4 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 halogenated groups;
• aralkyls optionally substituted with one or more C1 to C6 alkyl, C1 to C6 alkoxy, hydroxyl and halogenated groups;
• aryls optionally substituted with one or more substituents selected from C1 to C6 alkyl, C1 to C6 alkoxy, hydroxyl and halogenated 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 and preferably C1 to C4 aliphatic radicals.