Xuehai Yu

Synthesis and properties of polyurethane modified with aminoethylaminopropyl poly(dimethyl siloxane)

A series of polyurethanes with different siloxane contents were synthesized, which were based on 4,4′-methylene diphenyl diisocyanate (MDI), poly(tetramethylene oxide) (PTMO), aminoethylaminopropyl poly(dimethyl siloxane) (AEAPS), and butanediol (BD). The chemical compositions, structures, and bulk and surface properties were investigated using an infrared surface quantitative analysis technique (FTIR-ATR), surface contact angle, electron spectroscopy for chemical analysis (ESCA), stress–strain analysis, and dynamic mechanical thermal analysis (DMTA). It was shown that siloxane concentration on the surface region of the elastormers was higher than that in the bulk for a resulting surface enrichment of the siloxane, and the tensile properties of these elastomers were not changed significantly with the AEAPS modification.

Physical and blood contacting characteristics of propyl sulphonate grafted Biomer

Propyl sulphonate groups were grafted on to the backbone of Biomer, a polyetherurethaneurea, in an attempt to improve its blood-contacting properties. The bulk, surface and blood-contacting properties of this series of sulphonated polymers were evaluated. Differential scanning calorimetry and dynamic mechanical analysis indicated that propyl sulphonate incorporation increased the microphase separation of the polymers. The ultimate tensile strength was also increased with sulphonation at the expense of the polymers extensibility. Dynamic contact angle analysis showed that, in water, the sulphonated Biomer surfaces were more polar than the Biomer sample indicating the propyl sulphonate groups were enriched at the surface. Canine ex vivo blood-contacting results showed that the incorporation of propyl sulphonate groups dramatically reduced the number and activation of platelets adherent to the polymer surface. In addition, fibrinogen deposition increased with increasing sulphonate content, despite the low level of platelet activation.

Preparation of Highly Monodisperse Hybrid Silica Nanospheres Using a One-Step Emulsion Reaction in Aqueous Solution

Highly monodisperse hybrid spherical silica nanoparticles with diameters ranging from 30 to 200 nm were prepared by a one-step emulsion polymerization in aqueous solution. In contrast with the former method for preparing the hybrid silica materials, our method has three advantages. (1) Through this one-pot route, hybrid silica particles with organic functional groups on the surface are prepared in aqueous solution. (2) The particles are created in a size range of 30-200 nm and highly monodisperse. (3) The size of the particles can be effectively well-defined and precisely controlled depending upon the synthesis conditions such as the concentration of surfactant. Other kinds of organosilane monomers have also been tried in the same way. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS) were performed to elucidate the morphologies of the hybrid silica particles. Thermogravimetric analysis (TGA), (29)Si NMR, and (13)C NMR were used to gain information about thermal properties and detail structure. This approach may open a new broad avenue for the hybrid material in the field of photocrystal, electronic enveloping.

Blends of thermoplastic polyurethane and polyether–polyimide: preparation and properties

Abstract A series of blends of thermoplastic polyurethane(PU) and polyether–polyimide (PI) were prepared in two steps. The first step was the preparation of polyether–amic acid by the reaction of an oligmer based on polytetramethylene oxide glycol di-p-aminobenzoate (APTMO) of different molecular weight (650, 1000, and 2000) with benzenetetracarboxylic acid dianhydride (PMDA). The second step was mixing polyether–polyurethane and polyether–polyamic acid solution at room temperature in various weight ratios, and the blend films were obtained by casting and then heat imidization. Infrared spectroscopy (IR), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), small-angle X-ray scattering (SACS) and wide-angle X-ray diffraction(WAXD) were used to study this family of blends. DSC analysis of the films showed that glass transition temperature (Tg) of PU–PI 650 and PU–PI 1000 series shifted depending on the ratio of PU and PI components. The shift of Tg, along with the transparency of the films, gave the evidence that soft segments of PU and PI were miscible to some extent in the PU–PI 650 and PU–PI 1000 series. DMA results indicated that the blends exhibited a well phase-separated structure and had a broad rubbery plateau from about −30 to 200°C, which varied with the PU content. Thermal stability of PU was found to increase by the incorporation of PI. The excellent tensile properties of the blends suggested that they could be potentially used as heat resistant thermoplastic elastomers.

Development of chitosan-coated gold nanoflowers as SERS-active probes

Surface-enhanced Raman scattering (SERS) has been intensely researched for many years as a potential technique for highly sensitive detection. This work, through the reduction of HAuCl(4) with pyrrole in aqueous solutions, investigated a facile one-pot synthesis of flower-like Au nanoparticles with rough surfaces. The formation process of the Au nanoflowers (AuNFs) was carefully studied, and a spontaneous assembly mechanism was proposed based on the time-course experimental results. The key synthesis strategy was to use pyrrole as a weak particle stabilizing and reducing agent to confine crystal growth in the limited ligand protection region. The nanometer-scale surface roughness of AuNFs provided several hot spots on a single particle, which significantly increased SERS enhancement. Good biocompatible stable Raman-active probes were synthesized by coating AuNFs with chitosan. The conservation of the SERS effects in living cells suggested that the chitosan-capped AuNFs could be suitable for highly sensitive detection and have potential for targeting of tumors in vivo.

Synthesis and properties of polyurethane modified with an aminoethylaminopropyl-substituted polydimethylsiloxane. II. Waterborne polyurethanes

A series of polyurethane (PU) emulsions modified with aminosilicone were synthesized, based on 2,4-toluene diisocyanate (TDI), poly(tetramethylene oxide) (PTMO), and dimethylolpropionic acid (DMPA) as a prepolymer which was chain-extended with aminoethylaminopropyl polydimethylsiloxane (AEAPS) in an aqueous emulsion. Their chemical compositions, structures, bulk and surface properties, and emulsion morphologies were investigated using Fourier transform infrared spectrum analysis (FTIR), tensile and surface contact angle measurements, electron spectroscopy for chemical analysis (ESCA), water swellablity, an emulsion stability test, and transmission electron microscopy (TEM). It was shown that the PU emulsions were stable and the siloxane chains were enriched on the PU surface. The water resistance of the PU film increased but the bulk tensile properties of the PU film were not changed significantly with a small amount siloxane modification up to 6 wt %.

Synthesis, properties of fullerene-containing polyurethane–urea and its optical limiting absorption

Based on the typical two step polyurethane – urea synthesis, self-crosslinkable polyurethane – urea compounded of poly(tetramethylene oxide), MDI (4,4 0 -diphenylmethane diisocyanate) and extended by AEAPS (aminoethylaminopropyltrimethoxysilane) were prepared. On the other hand, a C60-amine adducts by reacting C60 with excessive APES (aminopropyltrimethoxysilane) were synthesized and introduced into the polyurethane – urea to form the homogenous and transparent C60 containing polyurethane – urea films. FT-IR, UV, Electron Spectroscopy for Chemical Analysis, Wide-angle X-ray diffractions, dynamic mechanical thermal analysis and mechanical properties of samples were recorded. The optical limiting properties were also measured. The results show that the C60 containing polyurethane – urea is a kind of homogenous material with the ranging of C60 content. The solution state before processing makes it easy to be cast as variety configurations. With the difference in C60 content in polymers, the optical limiting properties are various and the required transmittance and transmitted energy can be altered with the C60 contents in polymers. q 2003 Elsevier Science Ltd. All rights reserved.

A novel synthetic strategy to aromatic‐diisocyanate‐based waterborne polyurethanes

Based on aromatic diisocyanate [e.g., 2,4-tolylene diisocyanate (TDI)], a novel synthetic strategy to waterborne polyurethanes was introduced. Ionized polyoxyethylated amine (NPEO) played an important role in the preparation process as both a polyether soft segment and an internal emulsifier. First, a segmented surfactant prepolymer was synthesized. Second, the prepolymer was charged to a water dispersion of a hydrophobic polyol [e.g., polytetrahydrofuran (PTMO)] directly to obtain a stable emulsion. Third, a chain-extension procedure was performed directly in water with PTMO to achieve a stable aqueous polyurethane dispersion. Neither aliphatic diisocyanate nor excess isocyanate group fraction was added. An extra end-capping reaction or external emulsifier was also unnecessary. Films cast from emulsions exhibited reasonable mechanical properties.

Synthesis and properties of main‐chain liquid crystalline polyurethane elastomers with azoxybenzene

Liquid crystalline polyurethane elastomers (LCPUE) were synthesized by a two-step block copolymerization reaction. The main-chain LCPUE were based on two azoxybenzene-type mesogenic diol chain extenders (HA2 and HA6), a poly(tetramethylene oxide) (PTMO) soft segment, and different diisocyanates, including 4,4′-diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), and hexamethylene diisocyanate (HDI). The polyurethanes were characterized by FTIR, DSC, DMA, WAXD, UV, and polarized optical microscopy. Most of the polyurethane samples exhibited nematic thermotropic liquid crystal behavior and had physical properties typical of thermoplastic elastomers. The liquid crystal properties were strongly related to the interaction between the hard and soft segments of the polyurethane. As the compatibility of the soft and hard segments increased, the thermal stability of the liquid crystal phase and the transition temperatures decreased and the range of the transition became narrower.

Effects of matrix polarity and ambient aging on the morphology of sulfonated polyurethane ionomers

SummaryEthylene oxide units were incorporated into the backbone of Na+ sulfonated polyurethane ionomers in an attempt to induce aggregate dissociation at elevated, but observable, temperatures by reducing the incompatibility between ions and polymer. However, no dissociation could be observed by small-angle x-ray scattering (SAXS) before the onset of degradation, even when the polyol was pure EO. At 100°C and above, the SAXS patterns for all samples were quite similar, indicating morphological similarity. However, after annealing for several days at room temperature, two of the specimens appeared to develop a greater degree of microdomain order as evidenced by a narrowing of the main peak at q* and the development of a shoulder at 2q*x.