Degradable polyurethane networks based on d,l-lactide, glycolide, ε-caprolactone, and trimethylene carbonate homopolyester and copolyester triols

Abstract

Several trifunctional, hydroxy-telechelic polyester and poly(ester-carbonate) homopolymers and copolymers were synthesized by the triol-initiated, ring-opening bulk polymerization of d,l-lactide, glycolide, ε-caprolactone, and/or trimethylene carbonate. The molar compositions of the copolymers were determined from 13C n.m.r. spectra; hydroxy equivalent weights were determined by acetylation titration, and the glass transition temperatures ( T g) and melting points were determined by differential scanning calorimetry (d.s.c.). Crosslinked polyurethane networks were prepared by reacting the hydroxy-telechelic prepolymers with tolylene diisocyanate. Network characterization included determination of sol content by solvent extraction, T g by d.s.c., tensile properties by stress-strain measurements, and degradation properties by hydrolytic degradation studies. Equilibrium swelling results indicated that the per cent weight gains correlated well with the prepolymer hydroxy equivalent weights, with the exception of the poly(glycolide- co-trimethylene carbonate) network. The poly( d,l-lactide) and poly( d,l-lactide- co-trimethylene carbonate) (PLTMC) networks had the highest tensile strengths of 49.60 and 41.27 MPa, respectively, and glass transition temperatures of 51.3 and 21.3°C, respectively. All other networks were highly flexible with tensile strengths of 12 MPa or less. Hydrolytic degradation studies were conducted by placing network samples in a solution of phosphate-buffered saline (pH = 7.4) at 37°C. Weight uptake of buffer and weight loss of the networks were monitored gravimetrically over time. Tensile properties, monitored as a function of degradation time, indicated that the poly(ε-caprolactone- co- d,l-lactide) and PLTMC networks displayed a linear loss of strength with respect to weight during the first 30 days of degradation; the other networks degraded either too slowly or too quickly to establish such a linear relationship.