Thickening behavior of thermo-associative water soluble multiblock copolymers under redox RAFT polymerization

In this study, the synthesis of thermo-associative water soluble multiblock copolymers is reported. A trithiocarbonate functionalized polyacrylamide (PAM) was prepared and subsequently utilized in the preparation of three series of thermo-associative copolymers by addition of N-isopropylacrylamide (NIPAM) and acrylamide (AM) until reaching a nonablock copolymer with four thermo-associative blocks distributed into the backbone of polymer. Reactions were performed at 25 degrees C using a tertbutyl hydroperoxyde (TBHP) and ascorbic acid (As.Ac.) as redox initiator, and S,S '-Bis (alpha,alpha'-dimethyl-alpha"-acetic acid)-trithiocarbonate (DMAT) as chain transfer agent. The targeted molecular weight (M-nTheo) of PAM was maintained constant (10,000 g/mol) while the expected M-ntheo of polyN-isopropylacrylamide (PNIPAM) was varied from 10,000, 15,000, and 20,000 g/mol, respectively. The synthesized copolymers were characterized by infrared (IR), nuclear magnetic resonance (NMR), size exclusion chromatography (SEC) for determining the structure of materials, whereas ultraviolet (UV) analysis allowed to get access to the cloud point temperature (T-cp) of polymers. Rheological analyses were carried out for examining the effect of thermo-responsive block on the thickening behavior of aqueous polymer solutions. These analyses were performed at different concentration from 1 to 20 wt. % varying the temperature of measurements from 25, 30, 40, 50, 60, and 70 degrees C. Results confirmed the influence of the size of thermo-responsive blocks on the viscosity of these copolymers.