Thermoelastic properties of urethane elastomers

Several polyurethanes based on poly(ethylene adipate), 4,4′-diphenylmethane diisocyanate, 1,4-butanediol, and 3,3′-dichloro-4,4′-diaminodiphenylmethane were prepared. The thermoelastic properties of these polyurethanes depend on compositional variables and are interpreted in terms of the extent and stability of microphase separation.     

Microphase separation and properties of urethane elastomers

Several polyurethanes were prepared from poly(ethylene adipate)glycol, 4,4′-diphenylmethane diisocyanate, 1,4-butanediol, or 3,3′-dichloro-4,4′-diaminodiphenylmethane. Thermomechanical curves were determined for all investigated systems, and the glass transitions found thereof formed the basis of subsequent analysis. The analysis showed that the investigated systems belonged to those polyurethanes that can undergo microphase separation. It was also shown that the separation in the diamine-extended elastomers was less sensitive to changes in chemical composition than in the diol-extended systems. The diamine-based polyurethanes were also closer to the ideal separation than the diol-extended elastomers. Examinations of elastomers of varying amount of chemical crosslinking revealed a joint action of the crosslinking and microphase separation in determining mechanical properties of the systems. Together with swelling measurements, the examinations showed that optimum mechanical properties were obtained while keeping a very careful balance between these two factors.     

Properties of urethane elastomers

Summary The dielectric relaxation processes in poly(azourethaneurea) prepared from diphenylmethane-4,4-diisocyanate (MDI) and poly(ethylene adipate) glycol were studied in the range 200–390 K using thermally stimulated depolarization currents (TSDC). The TSDC spectra obtained on original sample, annealed sample, and both annealed and stretched sample showed significant differences which were explained in terms of the supramolecular structure of polymers. It was accepted that the polymers have a multiphase supramolecular structure.     

Properties of urethane elastomers

Summary The dielectric relaxation processes in polyurethanes based on 4,4-dibenzyle diisocyanate and saturated polyester in the temperature range of 250–400°K using thermally stimulated depolarization currents method have been investigated. The structure of the relaxation thermograms, location and intensity of the constituent peaks depend both on the precipitation temperature and thermal history of the polymer. The relaxation processes have been associated with the molecular motions within domains with distinct morphological structures. The morphological structure of the samples was evidenced using electron microscopy method.     

Properties of urethane elastomers

Summary The thermally stimulated depolarization currents(TSDC) from polyurethanes based on 4,4-dibenzyle diisocyanate(DBDI) and both saturated and unsaturated polyesters were studied over the temperature range 240–410 °K. Pour relaxation peaks were observed. The structure of the TSDC thermograms, location and intensity of the constituent peaks depend both on the urethane content and thermal history of the polymerr The morphological structure of the samples was evidenced using electron microscopy method.     

Swelling properties of urethane elastomers and their bearing on microphase separation

Several polyurethanes were prepared from polyethylene adipate glycol, 4,4′-diphenylmethane diisocyanate, 1,4-butanediol, and 3,3′-dichloro-4,4′-diaminodiphenylmethane. The temperature dependence of swelling and dynamic mechanical properties were determined. Analysis of the data shows that microphase separation leaves its mark on the swelling properties and that some information on the extent and perfection of microphase separation can be obtained from swelling. The conclusions were found to be in general agreement with the modulus–temperature relationships.     

Influence of urethane group on properties of crosslinked polyurethane elastomers

Three series of weakly crosslinked polyurethanes based on a hydroxyterminated polybutadiene, hydroxyterminated butadiene–acrylonitrile copolymer, and hydroxyterminated ethylene–adipate–maleate–fumarate copolymer were prepared while varying the hard segment content between 1.72 and 2.36 mol ? NH? COO? /1000 g polymer. Information on the microphase structure and the properties of the synthesized polyurethanes was obtained by differential scanning calorimetry, wide‐angle X‐ray scattering, and mechanical studies. Up to a urethane concentration of around 2 mol ? NH? COO? /1000 g polymer, there is a mixture of hard–hard and hard–soft segments. Above this concentration a large part of the hard–soft segments passes into hard–hard crystallites, liberating the soft segments. The best mechanical properties of the studied polyurethanes were found for a urethane concentration of around 2 mol ? NH? COO? /1000 g polymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1858–1867, 2003     

New castor oil-based urethane elastomers

Urethane elastomers with a wide range of properties were prepared by reaction of toluene diisocyanate, diphenylmethane diisocyanate or an aliphatic diisocyanate with a series of castor oil derivatives. The castor derivatives included amides prepared by reaction of castor oil with mono- or dialkanolamines, amides of ricinoleic acid with long chain di- and triamines, butanediol diricinoleate and the commercial products-castor oil itself and the monoricinoleates of propylene glycol and pentaerythritol. Elastomers were also prepared from commercial polyether diols for comparison. Properties evaluated include hardness, resilience, tear strength, stress-strain properties, compression set and resistance to water and oil. Particularly high tensile and tear strengths were obtained from the amides. Softer products with good properties were obtained from propylene glycol monoricinoleate and from mixtures of the amides with castor oil or butanediol diricinoleate. Improved products were obtained by the use of diphenylmethane diisocyanate in place of toluene diisocyanate. Presented at the AOCS Meeting, Los Angeles, April 1972. ARS, USDA.     

Miscibility and physical properties of conducting poly(urea‐urethane) thermoplastic elastomers

A series of amine‐terminated polyaniline oligomer (OPA)‐based conducting poly(urea‐urethane) thermoplastic elastomers (PUUs) was synthesized by two‐stage solution polymerization and characterized by FTIR. Various percentages of OPA were introduced into PUUs as chain extenders to form hard segments of PUUs with urea‐linkages. Spectroscopic and differential scanning calorimetry, as well as dynamic mechanical analysis, were conducted to elucidate the interaction and degree of miscibility between hard and soft segments, which were related to the stress–strain properties of PUUs. The hydrogen bonding index (HBI) measured by FTIR was employed to show the degree of interchain hydrogen bonding. Copolymer films with higher OPA content exhibit higher HBI and the degree of miscibility is significantly improved. The resultant conducting copolymers have higher tensile strength, higher Young's modulus, and lower elongation at break, because of the long rigid structure of OPA and the increase in the number of hydrogen bonds among the copolymers blocks. Incorporating OPA in PUUs increases the mass of the residue at temperatures over 600°C, according to thermogravimetric analysis. The conductivity of PUUs is found to range from 0.83 S/cm for neat OPA to 6.11 × 10^?5 S/cm for PUUs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3803–3810, 2007     

The effect of annealing on the thermal properties of reaction injection molded urethane elastomers

Reaction injection molded (RIM) polyurethanes, especially reinforced RIM polyurethanes, are promising candidates to replace metal exterior body panels on automobiles. One of the most important performance properties which these RIM parts must possess is thermal dimensional stability. Thermal dimensional stability is defined as the ability of a part to withstand distortion or change in size during thermal cycles. This property is important for two reasons. First, during paint operations parts are exposed to high paint bake temperatures. Second, parts may be exposed to relatively high temperatures in use. Thermal dimensional stability is mostly controlled by formulation and post-treatment. Formulation can change the structure of the polymer leading to different thermal properties. Posttreatment such as annealing can change (a) the degree of hard segment phase order, (b) the degree of phase separation and (c) the relative continuity of the phases. Experimental evidence is given to support all these factors.     

Thermoplastic urethane elastomers IV. Effects of cycloaliphatic chain extender on dynamic mechanical properties

The dynamic mechanical properties of a series of thermoplastic urethane elastomers have been studied as a function of molecular composition and temperature. Polymers based on polycaprolactone diol, an isomeric mixture of tolylene diisocyanate and hydrogenated Bisphenol-A as the chain extender were prepared at various relative concentrations of hard and soft segments. The glass transition temperatures of these polymers progressively shifted to higher temperatures as the relative hard segment content was increased. This variation was accurately described by the Fox relationship for amorphous copolymers. These results can be interpreted in terms of the relative degree of segregation between the segment of the block copolymers.     

Thermomechanical and surface properties of novel poly(ether urethane)/polyhedral oligomeric silsesquioxane nanohybrid elastomers

A series of linear polyurethane (PU) elastomers containing various amounts (ca. 2–10 wt%) of a diol‐functionalized polyhedral oligomeric silsesquioxane (diolPOSS) were synthesized from organic solvent dispersions. Fourier transform infrared spectroscopy was used to characterize the chemical structure of the diolPOSS‐reinforced PU. Transmission electron microscopy (TEM) indicated that the diolPOSS aggregation was formed in the polymer matrix at the scale of 20–50 nm. The introduction of diolPOSS into such system led to high glass transition temperature, enhanced storage modulus, and improved stability compared with the pristine PU according to the differential scanning calorimetry, dynamic mechanical analysis, and thermal gravimetric analysis, respectively. Moreover, contact angle measurements indicated a significant enhancement in surface hydrophobicity as well as a reduction in surface free energy after introducing diolPOSS into the synthesized PU. The improvement of surface properties could be ascribed to the enrichment of the diolPOSS moiety on the surface of the hybrids. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Overall NCO/OH ratio and microphase separation in urethane elastomers

Several polyurethanes were prepared from poly(ethylene adipate) glycol, 4,4′-diphenylmethane diisocyanate (MDI), and 1,4-butanediol. The overall NCO/OH ratio was allowed to vary from 0.94 to 1.21. Thus, the obtained elastomers differed in the amount of allophanate groups and perfection of microphase separation. These effects were studied by dielectric and pulsed NMR techniques. The results show that quite subtle effects concerning molecular mobility and its restriction due to interfacial region, perfection of the separation, and inadequacy of thermomechanical measurements can be investigated in the presented way.     

Shear induced finite orientational order in urethane/urea elastomers

New experimental results on urethane/urea free standing thin films (60 μm) prepared from a polypropylene oxide isocyanate terminated triol prepolymer (PU) and polybutadiene diol (PBDO) in the amount of 60% (PU/60PBDO) by weight of polybutadiene, which exhibit periodic patterns upon the application of a mechanical field are used to critically analyse these systems. We focus in this work on the analysis of the casting conditions and on the solid film characterization before and after UV irradiation. The casting of the different solutions was observed by polarizing optical microscopy (POM) coupled to a shearing system. The stress-strain and swelling data collected for the film before UV irradiation allowed the detection of an orientational order induced by the solution casting conditions, involving shear and evaporation of the solvent, which manifests itself in the anisotropy of the stress-strain and swelling film's properties in toluene. After UV irradiation of the elastomeric film, the interlinking of PBDO chains and amines linkages enhances the orientational order enabling instabilities to appear and the mesophase to become evident in the system as shown by POM, stress-strain and small angle light scattering data. Segregated soft and hard parts of the copolymer are thought to constitute the material unit, which is anisotropically distributed. The results here presented reinforce the earlier made claim that these systems do have an anisotropic structure akin to liquid crystallinity.     

Microphase separation in urethane elastomers as seen through NMR measurements

Urethane elastomers were prepared from poly(ethylene adipate) glycol or poly(tetramethyleneoxide) glycol, 4,4′-diphenylmethane diisocyanate, 1,4-butanediol, or 3,3′-dichloro-4,4′-diaminodiphenylmethane, or ethylenediamine as chain extenders. The glass transition of the polymers was determined from thermomechanical measurements. The essential conclusions were derived from pulsed NMR investigations. These made it possible to determine the extent of microphase separation, to evaluate the contribution due to the interface between the hard and soft domains, and to show that the glass transition itself may lead to ambiguous conclusions regarding the perfection of the separation. It was also suggested that the second moment can be related to the purity of hard domains.     

Thermoplastic urethane elastomers. I. Effects of soft-segment variations

A series of thermoplastic urethane elastomers with soft segments of varying sequence length was prepared and their dynamic mechanical properties were characterized over a wide temperature range. The polymers were prepared using various molecular weight polycaprolactone diols as the soft segment and 4,4′-diphenylmethane diisocyanate and 1,4-butanediol as the hard segment. The urethane elastomer exhibited soft-segment crystallization when a polycaprolactone diol greater than 3000 M?_n was used. The glass transition temperature of these materials progressively shifted to lower temperatures as the chain length of the soft segment was increased. This dependence was interpreted in terms of a molecular weight relationship similar to that associated with amorphous homopolymers. The dynamic mechanical properties of these polyurethanes appear to be consistent with responses observed for compatible copolymers.     

Thermoplastic urethane elastomers. II. Effects of variations in hard-segment concentration

The dynamic mechanical properties of thermoplastic urethane elastomers have been charac-terized for polymers composed of varying hard-segment concentrations and for two different molecular weight polyester diols as soft segments. The urethane polymers based on an 830 M?_n polycaprolactone diol exhibited a progressive increase in glass transition temperature at increased levels of hard segments. In contrast, a similar series of polymers prepared with a 2100 M?_n polycaprolactone diol as the soft segment maintained a relatively constant glass transition temperature. These differences are attributed to the relative degree of phase separation between the constitutive blocks of the copolymer. The polymers of both series possessed two lower-temperature, secondary relaxations, which are ascribed to methylene sequence mobility within the polycaprolactone units and to possible disruption of interfacial associations between the hard- and soft-segment structures.     

Thermoplastic urethane elastomers. III. Effects of variations in isocyanate structure

The dynamic mechanical properties of thermoplastic urethane elastomers have been compared for materials based on different diisocyanate structures, either 4,4′-diphenylmethane diisocyanate (MDI) or an isomeric ratio of tolylene diisocyanate (TDI). Two comparable series of polymers were prepared with a polycaprolactone diol as the soft segment and varying concentrations of hard segments based on the respective diisocyanates and 1,4-butanediol. Over the composition range studied, the polymer glass transition temperatures increased for the TDI-based polyurethanes, but remained relatively constant for the series containing MDI. Differences in the degree of macroscopic order within the hard segments, due to variations in the symmetry of the diisocyanate structures, are suggested as an explanation of these dynamic mechanical properties.     

Thermoplastic urethane elastomers V. Compatible and incompatible blends with various polymers

Various blends over extended compositional ranges have beer, prepared for combinations of a thermoplastic urethane elastomer with polystyrene, a styrene-acrylonitrile copolymer, a polyhydroxyether (Phenoxy A), and poly(vinyl ethyl ether). The thermoplastic urethane elastomer was based on a polycaprolactone diol of approximately 2100 number average molecular weight, 4,4′-diphenylmethane diisocyanate and 1,4-butanediol at a molar ratio of 1/2/1, respectively. At ambient temperature, the tensile properties of the blends typically are intermediate between the values of the two separate components. Characterizations of the dynamic mechanical properties of the blends show the relative degree of compatibility for the thermoplastic urethane elastomer and the respective polymers. Two separate glass transitions are obtained for blends of polystyrene and the styrene-acrylonitrile copolymer with the thermoplastic urethane elastomer. This behavior demonstrates that these blend systems are incompatible. The blends of Phenoxy A and the thermoplastic urethane elastomer exhibit a single glass transition for which the temperature is dependent on the respective concentration of the components. These mixtures are considered to be compatible in nature.