Impact of Solvent Selection on Graft Co-polymerization of Acrylamide Onto Starch

The impact on polymer properties [molecular weight, monomer conversion, graft content, graft efficiency and anhydroglucose units between grafts (AGU/graft)] that result from changing the solvent for the graft co-polymerization of acrylamide onto starch from water to dimethylsulfoxide (DMSO) was evaluated. Other reaction conditions were varied to determine their impact on properties, including solution solids (2.8–10.5 %), acrylamide (0.18–0.89 M), initiator (0.91–3.78 mM), and temperature (40–90 °C). Changing the solvent from water to DMSO had a large impact on the properties of the starch graft co-polymer at all reaction conditions. The most important difference was observed in the architecture of the resulting starch graft co-polymer. The number average molecular weight (Mn) of the polyacrylamide grafts as well as the number of AGU/graft was much lower when the reaction was performed in DMSO; the polymer was more comb-like. When conducted in water the Mn of the polyacrylamide grafts could be as high as 450,000 with over 6,500 AGU/graft. When DMSO was the solvent the Mn could be as low as 7,500 with 200 AGU/graft. The ability to control and generate starch graft co-polymers with dramatically different architecture may allow starch to be tuned to deliver improved properties for current or new applications.