Synthesis and characterization of second-order nonlinear optical polyurethane with high thermal stability

A second-order nonlinear optical polyurethane was formed with an X-type multi-dimensional charge-transfer (CT) chromophore (DNPIPDHPI) and 3,3^′-dimethoxy-4,4^′-diphenyl diisocyanate. Simultaneous poling and polymerization and in situ second harmonic generation (SHG) measurement technique was carried on to evaluate the thermal stability of the poling induced orientation. The SHG signal of the poled polymer film was not decay below 150 °C and remains 90% of relative d₃₃ value at 200 °C, which is better than the results reported in literature. Comparison of thermal stability indicates that the X-type chromophores possess better property in controlling the decay of the SHG activity than classic chromophores.     

Synthesis and properties of biodegradable elastomeric epoxy modified polyurethanes based on poly(ε-caprolactone) and poly(ethylene glycol)

Biodegradable polyurethane elastomers with potential for applications in medical implants with tunable degradation rate and physical properties were synthesized from reaction of epoxy terminated polyurethanes (EUP) with 1,6-hexamethylene diamine (HMDA) as curing agent. Poly(ε-caprolactone) (PCL) and poly(ethylene glycol) (PEG) as well as 1,6-hexamethylene diisocyanate (HDI) were used for preparation of isocyanate terminated polyurethanes which were subsequently blocked with glycidol to prepare EUPs. All materials were characterized by conventional methods, and their properties were studied fully. Results showed that elastomers based on PEG exhibit superior degradation rate and inferior mechanical properties in comparison to elastomers based on PCL. Optimum degradation rate and mechanical properties were obtained from elastomers made from mixture of PCL and PEG base EUPs.     

A pressure vessel for studying gas foaming of thermosetting polymers: sorption,synthesis and processing

We herein report the design of an apparatus for studying the concurrent chemo-physical processes occurring during gas foaming of thermosetting polymers. In particular, to address the recent interest in combining the gas (physical) foaming with the classical (chemical) polyurethane foaming, a novel instrumented pressure vessel was designed for investigating: i) gas sorption under high pressure on the different reactants, kept separate; ii) synthesis under high gas pressure, upon mixing and iii) foaming upon release of the pressure. The design of the new pressure vessel relies on two key features. From the processing side, we make use of a rubber impeller to keep the two reactants separate during gas sorption and to allow for an efficient mixing at the end of the sorption stage. From the analytic side, we utilized a sapphire window beneath the sample holder to use diffuse reflectance near-infrared spectroscopy to measure both the amount of sorbed gas and the reaction kinetics under gas pressure. Preliminary results are reported for the polyol-isocyanate/CO₂ system.     

Polyurethane vascular prostheses in pigs

Microporous, compliant vascular prostheses made from segmented polyurethanes of various molecular stability, have been implanted in the infrarenal aorta of young pigs. Prostheses prepared from a hydrolytically suble polyetherurethane showed a limited patency up to 1 month. Composite prostheses with the wall made from a hydrolytically stable polyurethane and the lumen side prepared from a degradable polyurethane, were patent up to one year. A degradable layer of this composite prosthesis induced the growth of a neo-artery. Prostheses prepared from a degradable polyurethane alone, were substituted within 4 months with a functional neo-artery.Presented in part at the 17th International Biomaterials Symposium, San Diego, California, April 1985.     

FTIR studies on the compatibility of hard-soft segments for polyurethane-imide copolymers with different soft segments

The polyurethane-imide (PUI) copolymers with different soft segments (polyethylene-co-propylene adipates, polyethylene glycol, or polypropylene-oxide) were studied. FTIR spectroscopy shows the different absorption bands of imide-I groups and reveals the different intermolecular interactions due to hydrogen bonding in these PUI copolymers. FTIR results suggest there is a good compatibility between hard and soft segments in either polyester-PUIs or polyether-PUIs having short soft segments. On the other hand, DSC analysis reveals that the glass transition temperature for hard segments (T_gh) of polyether-PUIs is higher than that of polyester-PUIs, and it increases with the soft segment length in PUIs consisting of the same type soft segments, which further supports the conclusions drawn from the FTIR data.     

Thermal stability of polyurethanes

Summary The combined application of thermogravimetry reactiongas chromatography and gel-permeation chromatography permits to follow the heat degradation of polyurethane polymers in inert gas, air and water-saturated environment. The examinations give information on the rate of thermal degradation, the individual volatile degradation components, the critical points of the polymer chains and on the change of their molecular-weight distribution. Gas chromatographic examinations also permit the identification of the chain-extending components of different types of polyurethanes.     

Polyurethane Ionomers,a New Class of Block Polymers

Linear polyurethanes containing ionic centers at wide intervals are heteropolymers having a pronounced segment structure, i.e. ionomers. As a result of interactions between chains (Coulomb forces and hydrogen bonds), their properties are similar to those of crosslinked elastomers. They are strongly associated both in organic and in aqueous solutions. Polyurethane ionomers in polar organic solvents spontaneously form stable aqueous dispersions on addition of water, with the ionomer as the disperse phase. The particle size can be varied between 20 nm and 1 mm.     

Depolymerization behavior of thermoplastic poly(urethane) (TPU) and its dependence on initial molecular weight

The quantitative and qualitative depolymerization behavior of thermoplastic poly(urethane) (TPU) consisting of 4,4′-methylenediphenyldiisocyanate (MDI), 1,6-hexanediol (HD) and 1-hexanol (HEX) was described using temperature-modulated differential scanning calorimetry and Fourier transform infrared (FT-IR) spectroscopy. The depolymerization behavior could be altered by lowering the starting molecular weight. This resulted not only in a higher ceiling temperature, but also in a faster decrease of the molecular weight as a function of temperature once the depolymerization has started. The increase in the ceiling temperature for low molecular weight TPUs is attributed to the lower entropy of polymerization for these compounds compared to high molecular weight TPUs.     

STRUCTURAL EVOLUTION IN BIORENEWABLE SOY BASED POLYURETHANES

Spectroscopic studies have revealed that the amount of polyureas formed and the kinetics of their formation in soy based polyurethane systems are considerably different from traditional systems employing ethylene oxide-propylene oxide (EO-PO) based polyols.The aggregation of polyureas was characterized by the hydrogen bonds formed utilizing FTIR spectroscopy.This study offered the opportunity to assign the previously undefined infrared features.The structural transformation is reflected in the segmental ...