Highly efficient metal-free organic catalysts to design new Environmentally-friendly starch-based blends

Abstract

A one-step process is reported to directly synthesize blends of poly(trimethylene carbonate) (PTMC) with a modified granular starch. Trimethylene Carbonate (TMC) ring-opening polymerization is performed in the presence of native starch particles in bulk conditions at 150 °C and the efficiency of metal-free organic catalysts (TBD and phosphazene superbases P1-t-Oct, P2-t-bu, and P4-t-bu) are investigated to replace the organo-metallic stannous octanoate initiator. TMC monomer is successively converted into PTMC and the robustness of organic catalysts is highlighted with significant activities at very low concentrations (<100 ppm), where stannous octanoate is inefficient. Reactivity of starch toward TMC ROP is deeply investigated by NMR techniques and a starch-graft-PTMC is indirectly evidenced. Starch substitution degree reaches 0.9% indicating that PTMC grafting only occurs at the surface of swollen granular starch. PTMC graft length from the starch surface remained low in the range 2–12 and model ROP reactions highlight the role of TMC hydrolysis on PTMC graft length. Despite low PTMC grafts, a fine dispersion of intact starch particles into the PTMC matrix is evidenced. Consequently, metal-free organic catalysts at low concentrations are promising candidates for synthesizing blends of PTMC with high loadings of surface-modified starch (32% by weight) in 2 min within a one-step process. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 493–503