Controlled synthesis of starch-based branched polymers

In this research, waxy potato starch, a high-molecular-weight natural polysaccharide with a highly branched structure, was used to homogeneously synthesize macroinitiator for controlled radical polymerization. With the starch-based macroinitiator, controlled grafting of acrylamide/N-isopropylacrylamide/sodium 2-acrylamido-2-methyl-1-propanesulfonate (AM/NIPAM/SAMPS) was studied via aqueous copper-mediated living radical polymerization (Cu0-mediated LRP) with tris[2-(dimethylamino)ethyl]amine (Me6Tren) as catalysis at room temperature. Compared with copper that generated from the disproportionation of CuBr in water, direct addition of copper powder to the system was proved to be more efficient for the synthesis of long-chain (co)polymers. The degree of polymerization was then set to 5000 and ratio of AM/NIPAM/SAMPS was varied to investigate the influence of chain composition on the rheological properties of copolymer water solution. Results suggest that 25 mol% is the optimum NIPAM intake for starch-g-poly(AM-co-NIPAM) to display both thermo-thickening property and stable viscosity in saline solution. This is preferable for potential applications like enhance oil recovery (EOR). However, this two-component copolymer dissolves slowly in water due to the strong intramolecular hydrogen bond between AM units. To overcome this problem, SAMPS was introduced to the copolymer. 25 mol% of SAMPS was proved to be the optimum intake for balanced performance in viscosity and saline-resistance. The intake of 25 mol% NIPAM, just contrary to what expected, although endow the starch-g-poly(AM-co-NIPAM-co-SAMPS) copolymer with thermo-thickening property at low shear rate (≤ 3 s-1) in saline solution, the viscosity is lower than starch-g-poly(AM-co-SAMPS) possibly due to the intramolecular association between NIPAM units.