Anionic graft polymerization of propylene oxide on starch

The anionic graft polymerization of propylene oxide on starch alkoxide in dimethyl sulphoxide has been studied. All the starch was incorporated into the graft polymers even at relatively low monomer concentrations. The yields of pure graft polymers decreased with increasing monomer concentration, due to increased homopolymerization caused by chain transfer to monomer. The compositions of the graft polymers were determined by NMR. The efficiency of the starch alkoxides in the graft polymerization was low as seen from periodic acid oxidation and from the free glucose content of the acid hydrolysate of the graft polymers. The graft polymers were soluble in water, methanol and pyridine; their melting points decreased with increasing monomer concentration and with increase in the polypropylene oxide content of the graft polymers. The rate of the disappearance of the monomer increased with increasing monomer or alkoxide concentration, and also increased with increasing the electropositivity of the alkali metal in the order K > Na > Li; only potassium alkoxide caused complete conversion of the monomer.