Microstructure, thermal and rheological properties of poly(L-lactide-co-ε-caprolactone) tapered block copolymer for potential use in biomedical applications

Abstract

This work investigates the thermal and rheological properties of the poly(L-lactide-co-ε-caprolactone), PLC, tapered block copolymer synthesized by ring-opening polymerization (ROP) using stannous octoate (Sn[Oct]2) as an initiator. The PLC copolymer (LL: CL = 48.9:51.1 mol% from 1H-NMR) was obtained as a transparent, elastomeric material with a tapered monomer sequencing (R = 0.38 from 13C-NMR data) due to randomizing effect of transesterification. The Mn, Mw, and ĐM of the PLC copolymer from GPC are 8.04 × 104, 1.36 × 105, and 1.69 respectively. The obtained moduli of the copolymer at 100% and 300% strain are rather low at 0.91 and 1.16 MPa. The rheological properties of the PLC melt are studied in terms of steady and oscillatory shear flow. The master curves at a reference temperature of 150°C with 5% and 100% strain suggest that the copolymer melt may contain some regular microstructures, such as small crystalline domains of poly(L-lactide), which remained intact at high strain deformation. The flow curve of the PLC melt at 150°C constructed from a cross model shows a Newtonian viscosity ((Formula presented.)) of 6754 Pa-s, a consistency index (k) of 0.59, and a Power Law index of 0.35 where the onset of Power Law behavior is observed at around 10 s−1. For the fabrication of the PLC nerve tubes, the best result is observed from the extruded PLC tubes with a combination of PEG porosifying agent leaching and phase immersion precipitation at 2°C using DMF/1,4-dioxane (1:1) as a mixed solvent and ethanol/chloroform (9:1) as a non-solvent. The porous tube obtained under this condition has a pore diameter and pore depth of approximately 2.3–2.5 and 30 μm respectively.