Synthesis of poly-(epsilon)-caprolactone grafted starch co-polymers by ring-opening polymerisation using silylated starch precursors

Poly-(epsilon)-caprolactone grafted corn starch co-polymers were synthesized using a hydrophobised silylated starch precursor. The silylation reaction was performed using hexamethyl disilazane (HMDS) as the reagent in DMSO at 70 degrees C. Silylated starch with a degree of substitution (DS) between 0.45 and 0.7 was obtained. E-Caprolactone is grafted to silylated starch by a ring-opening polymerisation catalysed by Al(OiPr)(3) in THF at 50 degrees C. The grafting efficiency varies between 28% and 58%, the remainder being homopolymers of epsilon-caprolactone. The DS of the polycaprolactone graft is between 0.21 and 0.72. The poly-(epsilon)-caprolactone side chains consist of 40-55 monomer units and is a function of the reagent intakes. Experiments with native starch under similar conditions do not result in the desired poly-(epsilon)-caprolactone grafted corn starch co-polymers and unreacted starch was recovered after work-up. Removal of the silyl groups of the poly-(epsilon)-caprolactone grafted starch co-polyrners is possible using a mild acid treatment with diluted hydrochloric acid in THF at room temperature. (c) 2009 Elsevier Ltd. All rights reserved.