Aliphatic polyester-grafted starch-like polysaccharides by ring-opening polymerization

Abstract

This paper reports on the synthesis of aliphatic polyester-grafted starch by in situ ring-opening polymerization (ROP) of ϵ-caprolactone in the presence of starch-like polysaccharides that may be granular or plasticized, or a mixture of these, wherein the in situ ROP is conducted in the bulk, i.e. in the absence of solvents. The polymerization is initiated from the starch phase with the amylose/amylopectin hydroxyl functions in the presence of a catalyst such as Sn(Oct) 2, or by adequate modification/activation of the surface hydroxyls into titanium or aluminium alkoxides, thereby promoting grafting and good interfacial adhesion between the two starch/polycaprolactone (PCL) phases. Evidence for coupling of the active initiator species onto the starch hydroxyls, aluminium alkoxides for instance, is shown by an aluminium peak in the X-ray photoelectron spectroscopy scan of a starch surface reacted with triethylaluminium. Good interfacial adhesion is confirmed by scanning electron microscopy images of surface fractures and by selective extraction experiments in toluene, which is a good solvent for solubilizing the non-grafted PCL chains.