Polyurethane Phase Research Articles

Mechanical properties of hand‐cast and reaction injection molded polyurethane and vinyl ester resin interpenetrating polymer networks

AbstractA series of simultaneous interpenetrating polymer networks (SINs) composed of polyurethane (PU) and vinyl ester resin (VER) was prepared from different rigid phase components, where the pendent hydroxyl groups of VER were retained or capped, and through different molding processes, i.e., hand‐casting or reaction injection molding (RIM). It was recognized that the occurrence of chemical binding between PU and VER networks through the reaction of the diisocyanate and the pendent hydroxyl groups of VER played an important role in determining the mechanical properties of these SINs. The hand‐cast SINs, with VER containing pendent hydroxyl groups as the rigid phase component and with these pendent hydroxyl groups counted for the metering of diisocyanate besides that due to polyether polyol and chain extender of PU phase, behaved like the hybrid polyester matrix. For the RIM‐molded SIN samples, an obvious reinforcing effect of VER network, whose pendent hydroxyl groups were capped with acetyl groups, upon PU network was observed. These results correlated well with the knowledge of polymerization kinetics and morphology development of these PU/VER SINs.

Thermal and Rheological Characterization of Semi-II Interpenetrating Polymer Networks from Poly(methyl methacrylate) and Castor Oil-based Polyurethane

Abstract The synthesis and characterization of semi-II interpenetrating polymer networks (IPN) based on poly(methyl methacrylate) (PMMA) and on castor oil polyurethane (PU) of composition 70/30 are reported. Various degrees of crosslinking of the PU phase were obtained by varying the weight ratio of HDI/N-100 while maintaining the NCO/OH ratio fixed at 1.5. Thermal characterization was performed by thermomechanical analysis (TMA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Two distinct glass transition temperatures were observed, indicating a two-phase morphology. This was also supported by scanning electron microscopy (SEM) observations. Rheological characterization was performed using a capillary rheometer. Shear thinning flow behaviour and reprocessing were confirmed for all semi-II IPN. All the results demonstrate that a higher crosslinking level leads to better overall properties.

Characterization of Simultaneous Interpenetrating Polymer Networks from MethylMethacrylate and Castor Oil

Abstract The synthesis and characterization of simultaneous interpenetrating polymer networks (SINs) based on methyl methacrylate and castor oil are reported. A mixture of 50/50 in weight of HDI/N-100 was employed for the polymerization and crosslinking of the polyurethane phase. The SINs over the whole composition range have only one single glass transition temperature T g, as determined by TMA (thermomechanical analysis) which suggests a single phase morphology even though the linear chain blends are completely immiscible. This is also supported by scanning electron microscopy observations. The SINs exhibit a higher heat resistance than pure PMMA but lower than N-100. They also exhibit a maximum tensile strength and impact strength at a composition of PU around 30%. This synergistic effect resulted from a strong entanglement between two networks as well as chain transfer phenomenon.

Polyurethane−Polyacrylate Interpenetrating Networks. 2. Morphology Studies by Direct Nonradiative Energy Transfer Experiments

Two sequential urethane−acrylate interpenetrating network (IPN) systems were prepared in which the polyurethane (PU) phase is labeled with donor and acceptor dyes. Direct nonradiative energy transfer (DET) measurements on these systems indicate less efficient energy transfer in the IPN than in the corresponding pure PU matrix. This result is interpreted in terms of dilution of the dyes by mixing at the molecular level between the polyacrylate (PA) and PU components. Quantitative analysis of the changes in DET efficiency allows the extent of phase mixing to be calculated. The two SeqIPN's, and were labeled by incorporating phenanthrene and anthracene diols into the reaction mixture. Fluorescence decays of phenanthrene in these samples were measured by the single-photon-timing technique and analyzed in terms of both the Forster model for DET and the Perrin model for static quenching. Both analyses gave similar extents of phase mixing, and these values are in good accord with the results of electron microsco...

Interpenetrating polymer networks of poly(allyl diglycol carbonate) and polyurethane: effect of composition and crosslink density on morphology and mechanical properties

Simultaneous interpenetrating polymer networks (SINs) of poly(allyl diglycol carbonate) (ADC) and a polyurethane (PU) were synthesized. The effects of the network composition and the crosslink density of the PU phase on the morphology, mechanical properties and thermal transition behaviour of the PU/ADC SIN were studied. At 10% composition, dynamic mechanical analysis revealed complete phase miscibility. As the PU content increased, although phase separation occurred, the samples retained their optical transparency. Modulus and tensile strength decreased, whilst elongation increased, as the PU content increased. At 30% PU content, transmission electron micrograph studies revealed a co-continuous phase morphology, and the domain sizes increased as the PU crosslink density increased. Modulus, tensile strength and fracture toughness also increased with increasing crosslink density.

Thermal properties of polyamide 6/polyurethane blends

Equilibrium melting temperatures and crystallization parameters of polyamide 6/polyurethane blends were investigated. Thermal properties of the crystalline phase of blends obtained from polyamide 6 and polyurethane containing 40 wt% of hard segments, are only limited influenced by the overall blend compositon. Because from separate measurements single glass transitions for all samples were estimated, so in the investigated case the blending process may occur mainly between amorphous fraction of polyamide 6 and the polyurethane or, what is more probable, the polyurethane phase is dispersed in the continuous polyamide matrix, although some interactions exist.

Antithrombogenicity of hydrophilic polyurethane-hydrophobic polystyrene IPNs. I. Synthesis and characterization.

A series of interpenetrating polymer networks (IPNs) composed of hydrophilic polyurethane (PU) and hydrophobic polystyrene (PS) were prepared by the simultaneous polymerization method. The PU network was synthesized via the isocyanate-terminated PU prepolymer based on polyethylene glycol (PEG), a highly hydrophilic oligomer, and hexamethylene diisocyanate (HDI). The bulk and surface characteristics of these materials were analyzed by differential scanning calorimetry (DSC), tensile testing, scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared (ATR-FTIR), electron spectroscopy for chemical analysis (ESCA), and contact angle measurement. The PU/PS IPNs prepared in this study exhibited phase separated structures, which had dispersed PS domains in the continuous PU matrix, in both the bulk and surface showing two transition temperatures. The IPN containing 50 wt% of PS showed good mechanical properties. The enrichment of PU phase in the surface was revealed by SEM, ATR-FTIR, ESCA, and contact angle measurement.

Dynamic mechanical thermal analysis of polyamide 6/thermoplastic polyurethane blends

Blends obtained from polyamide 6 and polyester or polyether polyurethanes were investigated by means of DMTA. The blends were prepared by compounding in a twin-screw Brabender —Plasticorder. Changes in composition did not influence the glass temperature of the amorphous fraction of the polyamide, but also no distinct transition for separated polyurethane soft segment was visible. Therefore the blends seem to be multiphase systems, where the elastomeric polyurethane phase is dispersed in a continuous polyamide phase. From changes in the β relaxation region of the polyamide better miscibility of polyester polyurethanes comparing to polyether polyurethanes was explained by hydrogen bonding in the common amorphous phase.

Effect of polyol molecular weight on the physical properties and haemocompatibility of polyurethanes containing polyethylene oxide macroglycols

The physical properties and haemocompatibility of polyurethanes containing polyethylene oxide (PEO) of varying molecular weights but constant weight fraction of hard segment are investigated. The PEO molecular weights studied were 600, 1450 and 8000. Analysis of Polyurethane phase separation and crystallinity using dynamic-mechanical analysis and differential scanning calorimetry show that the degree of phase separation and crystallinity increase with polyol molecular weight, but level off at the highest molecular weights. The degree of water absorption increases substantially with increasing PEO molecular weight, levelling off at the highest molecular weight. Tensile data show a maximum in extensibility at a polyethylene glycol (PEG) molecular weight of 1450, while ultimate strength increases with increasing segment length. When the materials are hydrated, there is a significant drop in the modulus, ultimate stress and ultimate elongation. Dynamic contact angle measurements show that surface hydrophobicity decreases as the soft segment molecular weight increases. Using electron spectroscopy for chemical analysis (ESCA) to determine the surface composition of these polyurethanes, it was found that the hard segment content at the surface increases as the polyol block length decreases. The haemocompatibility of these polyurethanes was investigated in an ex vivo canine blood-contacting model. Only for the shortest block length studied, PEG-600, are differences in blood compatibility observed. This material was found to be the most thrombogenic. The PEG-1450 sample shows comparable blood compatibility to PEG-8000. Biomaterials (1994) 15, (9) 695–704

Dynamic mechanical and microcalorimetric studies on the phase structure in blends of two multiblock copolymers: 1. Poly(ether-ester) and poly((ether-carbonate)-urethane) blends

The physical properties and phase structure of blends of the multiblock poly(ether-ester) elastomer (PEE) and the multiblock poly((ether-carbonate)-urethane) elastomer (PUC) have been investigated using the methods of differential scanning calorimetry and dynamic mechanical analysis. The blends were prepared in the melt. The system is characterized by one glass transition temperature ( T g) for the soft phase, which points to the occurrence of partial miscibility. The blends appear to possess two hard phases, a polyester phase and a polyurethane phase, with glass transition temperatures and melting points close to the temperatures of the initial copolymers. Suggestions have been made regarding the possibility of occurrence of an intermediate phase conspicuous by extra glass transition and crystallization temperatures.

Dielectric relaxation properties in polypropylene–polyurethane composites

AbstractAC dielectric relaxation properties of polypropylene/polyurethane composites have been studied. The segmented polyurethane (PUR) component contained a poly(propylene oxide) soft segment, and a diphenyl methane diisocyanate/butanediol hard segment. The molecular weight of the soft segment, the concentration of the latter in the polyurethane phase, and the PUR content of the blends were changed systematically. It was observed that the polypropylene is phase‐separated with respect to both PUR segments and that the dielectric relaxation properties are determined largely by the PUR component. Two transitions attributable to the glass transitions of the soft and hard phases, respectively, were observed. The soft segment transition temperature decreases with increasing molecular weight of the latter. The transition temperatures are somewhat dependent on the PUR content in the blend, indicating some interaction between the phases. Model calculations show that these shifts and some intensity anomalies are not due simply to the existence of a heterogeneous structure. The ohmic interfacial relaxation process does not play an important role in the temperature and frequency range studied.

Hydrophilic/hydrophobic IPN membranes for the pervaporation of ethanol-water mixture

Pervaporation of ethanol-water mixture was examined on IPN membranes composed of hydrophilic polyurethane(PU) and hydrophobia polystyrene(PS). The IPN membranes showed preferential pervaporation of water over ethanol and revealed high permeation rate. As the content of hydrophobic PS was increased, the permeation rate decreased while the separation factor increased, indicating that the PS domains suppressed the swelling of the PU phase and reduced the plasticizing effect. The average diffusion coefficient, computed from the permeation rate and solubility, was highly dependent on the viscosity and concentration of the permeant in the membrane.

Rheological changes during the polymerization of polyurethane based interpenetrating polymer network(IPN)

AbstractExperimental results on reactions forming polyurethanes and polyurethane‐polyester Interpenetrating polymer network (IPN) are discussed with particular interest in rheological and kinetic changes before the gel point. In the IPN formation, viscosity rise is affected by the amount of styrene and polyester in the reaction system. Plots of reduced viscosity vs. conversion do not fall into a single curve. The results may be explained by the concept of having intra‐molecular reaction or ring formation. The existence of hydroxyl group at the end of polyester molecule causes the graft reaction between the polyurethane phase and the polyester phase, which may speed up the viscosity rise of the reactive system. A simple method which based on rheological measurements only is proposed. This method of plotting reduced viscosity vs. reduced reaction time provides similar results as in the plots of reduced viscosity vs. conversion.

Composites formed by interstitial polymerization of vinyl monomers in polyurethane elastomers: 6. Low angle X-ray scattering and turbidity

Low angle X-ray scattering (LAXS) from an interstitially polymerized poly(methyl methacrylate)-polyurethane system has been analysed in terms of a model due to Debye to give the mean chord intercept lengths of the disperse phase (PMMA) and matrix (PU). The model was found to fit the scattering within the experimental errors and the results are in excellent agreement with the results of electron microscopy. A theoretical expression is derived relating the turbidity with (a) the difference in refractive indices between the polyvinyl and polyurethane phases, (b) the size of the two phase domain structure, and (c) the volume fraction of the phases. The expression has been tested experimentally. The domain sizes derived from the turbidity equation agree reasonably with those observed by LAXS and electron microscopy.