Synthesis and properties of poly(L-lactide-co-glycolide)-b-Poly(ɛ-caprolactone) multiblock copolymers formed by self-polycondensation of diblock macromonomers

Poly(L-lactide-co-glycolide)-b-poly(ɛ-caprolactone) multiblock copolymers (PLGA-PCL MBCs) were synthesized via the self-polycondensation of PLGA-PCL diblock copolymers (PLGA-PCL DBCs) in the presence of condensation agents. PLGA-PCL DBCs were synthesized via the ring-opening copolymerization of lactide and glycolide initiated by benzyl-protected PCL in the presence of tin 2-ethylhexanoate (Sn(Oct)2) or organic catalysts (N-cyclohexyl-N’-[3,5-(trifluoromethyl)phenyl]thiourea (TU) and Tris[2-(dimethylamino)ethyl]amine (Me6TREN)). The introduction of glycolide segments hampered the formation of poly(L-lactide) (PLLA) crystals in PLGA-PCL MBCs, which was confirmed by wide-angle X-ray diffraction (WAXD) measurements. Despite the loss of crystallinity, PLGA-PCL MBCs showed better tensile strength and modulus than the PLLA-PCL random copolymer. The phase-segregated PLGA domains observed by small-angle X-ray scattering (SAXS) measurements acted as hard domains improving the tensile properties. The hydrolytic degradation of PLGA-PCL MBC in phosphate-buffered saline (PBS: pH=7.4) proceeded much faster than that of PLLA-PCL MBC. Both the loss of PLLA crystallinity and the presence of glycolide–glycolide and glycolide–lactide bonds contributed to the enhanced hydrolysis behavior of PLGA-PCL MBCs. The good tensile properties and degradation behavior in PBS expand the applicability of PLGA-PCL MBCs in biomedical applications, particularly for elastic implanting materials.