Diblock and triblock copolymers catalyzed by benzo-12-crown-4 bridged N-heterocyclic carbene: synthesis, characterization and degradation behavior

The sequential ring-opening polymerizations (ROP) of epsilon-caprolactone (epsilon-CL) and L-lactide (LLA) with benzo-12-crown-4-imidazole carbene (B-12-C-4imY) as the catalyst have been performed. Using either benzyl alcohol or ethylene glycol as an initiator, the corresponding poly(epsilon-caprolactone)-poly(L-lactide) (PCL-b-PLLA) diblock or poly(L-lactide)-poly(epsilon-caprolactone)-poly(L-lactide) (PLLA-PCL-PLLA) triblock copolymers were easily prepared. The results indicated that B-12-C-4imY was quite effective for the copolymerization. The diblock copolymerization of epsilon-CL with LLA could only be achieved when epsilon-CL was first polymerized followed by LLA. Feeding the two monomers simultaneously, however, only resulted in the formation of LLA homopolymers. Thermogravimetric analysis (TGA) measurements demonstrated that block copolymers exhibited the decomposition temperature lower than the PCL homopolymer. The copolymers were characterized by H-1 NMR and C-13 NMR, FT-IR, GPC, and DSC analyses. 20x10mm(2) rectangular specimens made of the triblock copolymer were allowed to degrade in a pH=7.4 phosphate buffer at 37 degrees C. Degradation was monitored by various analytical techniques such as GPC, IR, and ESEM.