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. 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 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.     

Thermoplastic elastomers via radical polymerization. I

Thermoplastic elastomers were synthesized using a method for preparation of block copolymers introduced by Tobolsky and Rembaum. A hydroxy-terminated polyester or polyether was chain extended with tolylene diisocyanate and capped with cumene hydroperoxide. The high molecular weight peroxycarbamate was used as initiator for polymerization of styrene, methyl methacrylate, or acrylonitrile monomer. Their physical properties were investigated by modulus–temperature curves. The effect of composition on modulus was also examined.     

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.     

Thermoplastic elastomers

Thermoplastic elastomers are crosslinked by secondary valence interactions. They show rubber elasticity at service temperatures but may be thermoplastically processed at elevated temperatures, i.e. they may be injection-moulded or, in special cases, spun from solution. Secondary valence interactions give rise to a continuous crosslink spectrum controlling the segment mobility in its low temperature region but controlling the crosslinking stability in its high temperature region. Crosslinking, which partly breaks down on heating the sample, is restored when the sample is cooled. Consequently, a stress crosslinking may be distinguished from strain crosslinking which is formed on cooling the deformed material, thus stabilizing the deformation. Stress and strain crosslinking systems reflecting the thermomechanical history are seen from shrinkage experiments.     

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 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.     

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.     

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.     

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.     

Thermoplastic elastomers by hydrogen bonding

Summary By reacting polybutadiene with 4-Phenyl-1, 2, 4-triazoline-3, 5-dione (PTD) urazole groups are added to the polymer. The formation of hydrogen bonds between different urazole groups is investigated by IR-spectroscopy at various temperatures. The carbonyl stretching vibrations at 1700 and 1723 cm^–1 could be attributed to hydrogen bonded and free urazole groups. With increasing temperature the fraction of bonded groups decreases. From the overall change in the absorption the ratio of the extinction coefficients of bonded and free C=O is determined. The stability of the hydrogen bonds is explained by a chelate like complex between two urazole groups.     

Thermoplastic elastomers by hydrogen bonding

Summary Poly(butadienes) were modified by an ene-reaction using 4-phenyl-1, 2,4-triazoline-3,5-dione (1) 3-nitro-4-hydroxyphenyl-1, 2,4-triazoline-3,5-dione (2) and 4-hydroxyphenyl1, 2,4-triazoline-3,5-dione (3). The resulting hydrogen bond complexes between urazole groups act as thermoreversible crosslinks and alter the melt rheological behaviour. While dimeric chelate-like complexes are formed in polymers modified with 1 or 2, a three dimensional structure of hydrogen bond complexes is formed if 3 is used as the modifying agent. The thermorheologically complex behaviour of the latter material is interpreted by structural changes in the three dimensional structure with temperature.     

Thermoplastic elastomers by sequential monomer addition

The living carbocationic polymerization (LC Pzn) of p-methylstyrene (pMeSt) was achieved by the use of the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl₄ initiating system in the presence of triethylamine (Et₃N) electron donor in CH₃Cl/nC₆H₁₄ mixed solvent at-80°C. Next, the synthesis, characterization, and some physical-mechanical characteristics of a series of poly (p-methylstyrene-b-isobutylene-b-p-methylstyrene) (PpMeSt-PIB-PpMeSt) triblocks is described. The latter synthesis involved two steps in one reactor: 1) The generation of diliving polyisobutylene dications (PIB) by the dicumyl chloride (DiCumCl)/TiCl₄ system under similar conditions followed by 2) The addition of pMeSt and growth of living PpMeSt cations. The PpMeSt-PIB-PpMeSt triblocks are soft thermoplastic elastomers (TPEs).Paper L in the series Living Carbocationic Polymerization     

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.     

Thermoplastic polyurethane elastomers from modified oleic acid

Two novel potentially biodegradable thermoplastic polyurethane elastomers with unique structure and morphology were prepared from modified oleic acid. The hardness and mechanical properties were controlled by adjusting the soft segment concentration (SSC). Epoxidized methyl oleate was converted to methyl‐9‐ or ?10‐hydroxystearate (hydroxystearate) by catalytic hydrogenation. The formed hydroxystearate was transesterified with 1,6‐hexanediol to obtain polyesterpolyol with molar mass 2500. Segmented polyurethanes with 50% and 70% SSC were prepared using the prepolymer method by reacting polyesterpolyol with diphenylmethane diisocyanate and 1,4‐butanediol as chain extender. Thermal and mechanical properties of the polymers indicated good micro‐phase separation. Both soft and hard segments displayed a certain degree of crystallization. Tensile strengths were 18 and 2.4 MPa for samples with 50% and 70% SSC, respectively. Elongations of 130% (50% SSC) and 43% (70% SSC) were somewhat lower than in comparable materials, presumably due to lower molar mass. © 2014 Society of Chemical Industry     

Thermoplastic elastomers from NBR and polyvinyl chloride

This paper will discuss recently developed technology that demonstrates the effectiveness of a thermoplastic polyvinyl chloride/nitrile rubber alloy versus commercially available thermoplastic elastomers and conventionally cured rubbers. Compounding variations, mixing and processing of thermoplastic elastomers such as low temperature properties, compression set, heat resistance, flex properties, and oil and fuel resistance will be examined. Compounding variations of the PVC/NBR allows will be explored to show how recipe changes can affect these important properties.     

Viscoelastic properties and heat generation in urethane elastomers

Static and dynamic properties were studied in a series of polyurethane elastomers as a function of selected compositional variables such as curative system, curative level, catalyst level, and curing temperature. A number of physical properties including swelling ratio, density, glass transition temperature, stress–strain behavior, and thermal conductivity were also measured on these elastomers. The selected variables affect dynamic mechanical properties as well as heat buildup. A good correlation was noted between the loss modulus and the heat generation. The loss modulus and the heat generation decrease with decreasing curative level. The elastomers cured with a mixture of triol and diamine give lower loss modulus and heat buildup than those cured with diamine alone. These responses are believed due to the increase in covalent crosslinks. The observed low heat generation of the elastomer cured with 0.2 phr azelaic acid as a catalyst level was also attributed to the high crosslink density. The curing temperature, in the range investigated, appears to have very little effect on the properties. Thus, the choice of formulation variables, especially the use of diamine–triol blends, provides an effective means of minimizing heat generation in dynamic applications of polyurethane elastomers.     

Thermoplastic elastomers from reclaimed rubber and waste plastics

Thermoplastic elastomeric compositions from reclaimed rubber and scrap plastics were prepared. The physical properties, dynamic mechanical properties, rheological behavior, and phase morphology of the blends were studied. A 50:50 rubber/plastic ratio was found to be the best for processability, ultimate elongation, and set properties. A sulfur‐accelerator system was found to be better than a peroxide system for dynamic crosslinking. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2035–2042, 2002