SYNOPSISBioabsorbable 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, c-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 5OoC 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 ( Tg E 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 c-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. e-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.

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A biodegradable aliphatic thermoplastic polyurethane based on L-lysine diisocyanate and 1,4-butanediol hard block segments, and 2000 g/mol poly(e-caprolactone) diol soft block segments was synthesized. The resulting polymer was a tough thermoplastic with ultimate tensile strength of 33 MPa and elongation of 1000%. The polymer displayed classic segmented thermoplastic elastomer morphology with distinct hard block and soft block phases. Thermal and dynamic mechanical analyses determined that the material has a useful service temperature range of around À40 8C to þ40 8C, making it an excellent candidate for low-temperature elastomer and film applications, and potentially as a material for use in temporary orthopedic implant devices.

The Jonscher universal power law for ac conductivity versus frequency (f = ω/2π) in the dispersion region was tested for a multiwall carbon nanotube/epoxy nanocomposite. The effect of changes in agglomerate morphology on the fitting parameters A and n in the equation σac = Aωn was investigated. Changing nanotube agglomerate morphology was tracked by optical microscopy through curing. Evolving morphology was compared alongside ac conductivity obtained via a broadband dielectric spectrometer to elucidate possible physical meaning of the universal power law in the context of this system. The −logA/n was unaffected by changes in agglomerate morphology affected during cure, yet connected with each other in their dependence on temperature. For this system, the relationship between the fitting parameters in the universal dynamic response equation remains empirical at this stage with regard to biphasic “texture” or morphology within such a network. Electrical conductivity σ versus frequency ω for a composite consisting of agglomerated multiwalled carbon nanotubes dispersed throughout a cured epoxy matrix was discovered to follow the empirical universal dynamic response equation of Jonscher. The frequency behavior of the exponent n is discussed in terms of underlying morphology throughout which charge carriers migrate. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1918–1923

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A new family of poly(ethylene glycol) (PEG) based membranes for CO2 separation was developed using thiol–ene photopolymerization. Compared to photopolymerized PEG-containing acrylate membranes, these new thiol–ene based membranes offer improved mechanical properties and processing advantages. The starting material, a combination of a trithiol cross-linker and a PEG diene, was gradually modified with a PEG dithiol while maintaining 1:1 thiol:ene stoichiometry. This approach made it possible to decrease the network cross-link density, resulting in simultaneous increases in free volume and PEG content. Materials with high concentrations of dithiol were very stretchable, with largely, up to 500%, improved elongation at break, yet they exhibited commendable CO2/N2, O2, H2, and CH4 permeability-selectivity performance. The average molecular weight of polymer chains between cross-links, M c, was determined experimentally by fitting the classic network affine model to stress–strain data obtained via tensile testing. M c was also calculated assuming an ideal, lattice-like, network structure based on monomer stoichiometry. The effect of M c on glass transition temperature and gas permeation behavior was studied. A free volume based model was employed to describe experimental gas permeability (diffusivity) trends as a function of M c.