HYDROLYZABLE POLY(ESTER-URETHANE) NETWORKS FROM L-LYSINE DIISOCYANATE AND D,L-LACTIDE EPSILON-CAPROLACTONE HOMOPOLYESTER AND COPOLYESTER TRIOLS

Bioabsorbable poly (ester-urethane) networks were synthesized from ethyl 2,6-diisocyanatohexanoate (L-lysine diisocyanate) (LDI) and a series of polyester triols. LDI was synthesized by refluxing L-lysine monohydrochloride with ethanol to form the ester, which was subsequently refluxed with 1,1,1,3,3,3-hexamethyldisilazane to yield a silazane-protected intermediate. This product was then phosgenated using triphosgene. Polyester triols were synthesized from D,L-lactide, epsilon-caprolactone, or comonomer mixtures thereof, using glycerol as initiator and stannous octoate as catalyst. Polyurethane networks were cured using [NCO]/[OH] = 1.05 and stannous octoate (0.05 wt %) for 24 h at room temperature and pressure and 24 h at 50-degrees-C and 0.1 mm Hg. LDI-based polyurethane networks were totally amorphous and possessed very low sol contents. Networks based on poly (D,L-lactide) triols were rigid (T(g) congruent-to 60-degrees-C) with ultimate tensile strengths of approximately 40-70 MPa, tensile moduli of approximately 1.2-2.0 GPa, and ultimate elongations of approximately 4-10%. Networks based on epsilon-caprolactone triols were low-modulus elastomers with tensile strengths and moduli of approximately 1-4 MPa and approximately 3-6 GPa, respectively, and ultimate elongations of approximately 50-300%. Networks based on copolymers displayed physical properties consistent with monomer composition and were tougher than the networks based on the homopolymers. Tensile strengths for the copolymers were approximately 3-25 MPa with ultimate elongations up to 600%. Hydrolytic degradation under simulated physiological conditions showed that D,L-lactide homopolymer networks were the most resistant to degradation, undergoing virtually no change in mass or physical properties for 60 days. epsilon-Caprolactone-based networks were resistant to degradation for 40 days, and high-lactide copolymer-based networks suffered substantial losses in physical properties after only 3 days. (C) 1994 John Wiley & Sons, Inc.