Patent ID: 7345121

Claim:
A method for the homopolymerisation of acrylic acid or of its salts, or copolymerisation of acrylic acid or of its salts with one or more water-soluble monomers, in solution, for obtaining non cross-linked polymers, comprising polymerizing acrylic acid and optionally one or more water-soluble monomers in the presence of a transfer agent or agents of the following formula: R—X—C(S)—S—R′ in which: X═O or S, R represents a group for stabilising the function R—X by a covalent bond of the C—X type, R′ represents a group such that the R′—S bond is a bond of the C—S type, whereby reaction parameters and the transfer agent or agents are selected so that the following four criteria are simultaneously achieved: a) an IP exp <2 for molar masses M n greater than 1000 without physical or physico-chemical separation and determined according to the IP called method, and b) absence of gel on polymerisation at conversion rates greater than 90%, c) >90% conversion rate after 4 hours at 100° C. and at atmospheric pressure, and d) the amount of transfer agent or agents is between 0.001% to 20% (molar) and 0.01% to 50% (by weight).