This work has been made in a company named DERYPOL SA for the purpose of obtaining narrow polydispersity index and high molecular weight MAAc/Na-AMPS copolymers. As the molecular weight is a very important parameter for this product, some aqueous free radical polymerization reactions were carried out at different temperatures using different thermal azo initiators. This copolymer synthesis was then modified using a dithiobenzoate as a RAFT agent with different [M]/[RAFT] and [RAFT]/[I] ratios. In order to obtain a higher molecular weight another RAFT copolymer was performed with double [M]/[RAFT] ratio. During polymerizations conducting to these copolymers samples were taken over time and analyzed by GPC and HPLC. The obtained results were compared and discussed. As the GPC equipment and parameters initially assayed in Derypol did not provide curves having a good resolution with these new copolymers, another column was selected and a new analytical GPC method was developed.