Hydrolyzable poly(ester‐urethane) networks from L‐lysine diisocyanate and D,L‐lactide/ϵ‐caprolactone homo‐ and copolyester triols

Abstract

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, ϵ‐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°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 ∽ 60°C) with ultimate tensile strengths of ∼ 40–70 MPa, tensile moduli of ∼ 1.2–2.0 GPa, and ultimate elongations of ∼ 4–10%. Networks based on ϵ‐caprolactone triols were low‐modulus elastomers with tensile strengths and moduli of ∼ 1–4 MPa and ∼ 3–6 GPa, respectively, and ultimate elongations of ∼ 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 ∼ 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. ϵ‐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. © 1994 John Wiley & Sons, Inc.