Aliphatic polyester-based biodegradable materials:: new amphiphilic graft copolymers

Biodegradable brush-like amphiphilic. graft copolymers were synthesized by covalently grafting poly(epsilon -caprolactone) PCL sequences onto a natural and mainly linear alpha (1-6) exopolysaccharide backbone, i.e. dextran. A three-step procedure is proposed to control the synthesis which consists in the reversible protection of the hydroxyl groups of the polysaccharide backbone by silylation, followed by the ring-opening polymerization of epsilon -caprolactone initiated by the remaining free hydroxyl groups of the partially silylated dextran after adequate activation into Al alkoxide active species. The third and final step involves the deprotection of the polysaccharide hydroxyl groups under very mild conditions. The high efficiency of grafting and the control over the graft molecular weight and molecular weight distribution rely upon the well-known "living" character of the coordination-insertion mechanism of the ring-opening polymerization that is initiated by aluminum alkoxides. Poly(epsilon -caprolactone)-grafted dextran copolymers with precise composition and well controlled number and length of PCL grafts were incorporated into PCL/granular corn starch composites by melt kneading at 130 degreesC. When located at the filler/matrix interface, the copolymers proved to be very efficient compatibilizers, enhancing the interfacial adhesion, and accordingly the mechanical properties of the composite materials as evidenced by tensile testing. To ensure the migration of the amphiphilic graft copolymer at the starch/PCL interface, it is better to first precipitate it onto the filler surface or to blend it with the starch granules before melt blending with the polyester matrix. (C) 2001 Elsevier Science Ltd. All rights reserved.