Partial crystalline organosilicon-based polysiloxane-polyurethane copolymers

The phase separation and morphology in poly(urethane urea)s were investigated as soft segment length and chain extender structure were varied. Increases in soft segment length led to increased phase separation that resulted in greater mobility of the soft segment. This was shown by lower soft segment glass transition temperatures in differential scanning calorimetry (DSC) as well as a shift of Emax″ and tan δmax to lower temperatures. Also the structure of the chain extender affected the degree of phase separation and mixing of the soft and the hard blocks in an interphase. Atomic force microscopy (AFM) was used to visualize the structure of the phase‐separated domains. The hard domains were in the form of spheres 5–10 nm, or long needles 5 nm thick and 50–300 nm long. As the soft segment length increased, there were more pure soft segment phase areas between the hard domains. At high hard segment content, a larger scale structure was found, consisting of both hard and soft segments.DSC thermograms of poly(urethane urea)s containing different soft segment lengths.magnified imageDSC thermograms of poly(urethane urea)s containing different soft segment lengths.

Effect of soft segment length on the thermal behaviors of fluorinated polyurethanes

Effect of intersegmental interactions on the morphology of segmented polyurethanes with mixed soft segments: A coarse-grained simulation study

The internal structure and orientation behavior of two series of spandex fibers, which were made with different spinning methods and different soft and hard segment types, were studied by FTIR (Fourier Transform Infrared Spectroscopy), polarizing light microscopy, and Instron. The orientation behavior of hard and soft segments was studied with FTIR and those of polymeric chains with polarizing miscroscopy while the fibers were being stretched by the mechanical stretcher. The orientation behavior of dry-spun fibers was observed to be very different from that of the melt-spun fibers, which may be explained in terms of the internal structural difference such as the degree of phase separation and mechanical stability of the hard domains between the two types of fibers. In general, the dry-spun fibers showed better elastic recovery property than the melt-spun fibers. Since the polymer for the dry-spun fibers was synthesized with ethylene diamine as a chain extender resulting in the urea groups in the hard segments, it forms more stable hard domain due to the high cohesion energy between the urea groups. The change of the birefringence values during the cyclic deformation was studied with the polarizing light microscopy. The birefringence behaviors of the two dry-spun fibers were similar, whereas there was a noticeable difference between the two melt-spun fibers. The difference was explained in terms of the effect of crosslinking agent in one of the melt-spun fibers, which can stabilize the hard domain structure against the external stress. Mechanical hysteresis values measured gave results consistent with those of FTIR and birefringence measurements. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1821–1832, 1997

Effect of the degree of soft and hard segment ordering on the morphology and mechanical behavior of semicrystalline segmented polyurethanes

The thermoplastic polyurethanes are linear segmented copolymers which consist of alternating soft and hard segment units. The soft segment is commonly a low molecular weight polyether or polyester whereas the hard segment generally consists of an aromatic diisocyanate condensed with a low molecular weight diol. It is now generally accepted that the properties of these materials are primarily due to the phase segregation of soft and hard segments leading to the formation of hard segment domains which are dispersed in the rubbery matrix. There are a wide variety of compositional variables which can affect the degree of phase segregation and hard segment organization and, accordingly, the sample properties. In this paper we report the results obtained on an extensive series of polyurethanes based on 2,4-toluene diisocyanate (2,4 TDI) and 2,6-toluene diisocyanate (2,6 TDI). In 2,4 TDI polymers, the asymmetric placement of the isocyanate residues with respect to the methyl group can result in some head-to-tail isomerization in the hard segment. In 2,6 TDI polymers, this problem is absent since the molecule is symmetrical. Other compositional variables examined included polyether vs. polyester soft segment, the molecular weight of the soft segment and the length of hard segment. Extensive physico-chemical techniques such as thermal analysis, wide and low angle x-ray studies and IR spectroscopic analyses have been employed to provide detailed information on the thermal transition behavior, structural organization and the properties.

The role of hard and soft segments in the thermal and mechanical properties of non-isocyanate polyurethanes produced via polycondensation reaction

Small-angle neutron scattering has been shown to be an effective technique for investigating segment conformation in two-phase multiblock copolymer systems. By choosing the appropriate isotopic compositions, either segment can be investigated, as can the whole chain. The best approach to the experiment is to use a phase-contrast matched sample, one where no interphase scattering occurs. This allows the experiments to be carried out on a single sample, simplifying the experiment, and reducing the beam time requirements. Equations (2) and (3) describe the phase-contrast matched criterion. At room temperature, the polyether soft segments in the polyurethane elastomer-and in the polyether-polyester block copolymers are somewhat extended on the average relative to the bulk oligomer conformation. In the polyether-polyester with a lower hard-segment content, the soft segments are less extended than in the higher ester content material. A distribution of conformations occurs in these materials, with a majority of the soft segments being nearly in a random-coil conformation. A substantial number of segments are fairly taut, leading to an average conformation that is somewhat extended relative to the random coil conformation. The soft-segment radius of gyration in the polyurethane material initially decreases with increasing temperature. As the temperature rises, the retractive force on the taut soft segments increases, thus facilitating the extraction of hard segments from the amorphous hard phase into the soft phase. One would expect that the degree of phase separation would decrease with increasing temperature due to such a mechanism, and in fact this is borne out by small-angle x-ray scattering studies. Above 150°C, an upturn in the soft-segment radius of gyration is observed. Koberstein et al. propose a phase mixing transition around this temperature in polyurethane systems. Such a transition implies a greater compatibility between the hard and soft segment types at elevated temperatures. Thus, a swelling of the soft segments is seen due to favorable interactions with the hard segments located in the soft phase. A schematic diagram of the polyurethane microstructure and chain conformation is presented in Figure 9. The soft-segment radius of gyration in the polyether-polyester materials decreases smoothly with increasing temperature. This is primarily due to a decrease in the number of taut tie molecules present at elevated temperatures due to the rearrangement of the hard crystalline domains. In addition, relaxation of stresses introduced by molding these samples below the hard-segment crystalline melting temperature may contribute to the decrease in the soft-segment Rg.

Chemical synthesis and physical blending methods were used to prepare thermal sensitive polyurethanes (TSPU) with single or double thermal switches. In the design of the formula, polycaprolactone diol (PCL) with a molecular weight 10,000 and 4,000 and polytetramethylene glycol (PTMG) with a molecular weight 3,000 and 2,000 were used as the soft segments. The effects of the crystallinity and compatibility of the soft segments on the phase transition temperatures of the soft segments of TSPU (defined as switch temperature, Ts) were investigated in detail. To examine the thermal sensitivity of the thermal switch, water vapor permeability (WVP) experiments were performed to investigate the mass transport as a function of temperature. Differential scanning calorimetry (DSC) indicated that all the original TSPUs had a phase separated structure that was independent of the phase transition temperature of the soft and hard segments. The Ts values are determined mostly by the melting temperatures of the soft segments. On the other hand, for their blends, the Ts values are determined by the compatibility of the soft segments and the blending weight ratio. The blends of the PCL-based TSPUs showed good compatibility and single Ts due to the similar structure of the soft segments (just a difference in molecular weight), whereas for the PCL-based and PTMG-based TSPUs (the molecular structure is very different) blends, the Ts two independent values and blending weight ratio-dependent features due to the difference in the structure of the soft segments. Water vapor permeability analysis revealed the mass transport showed switching features to thermal stimuli, i.e. when the temperature reached the Ts, the WVPs of membranes showed rapid changes. On the other hand, the sensitivity of the thermal switch characterized by WVP improvement showed a dependence on the degree of crystallinity of the soft segments, i.e. well-organized soft segment structure is beneficial for improving the thermal sensitivity. Overall, TSPU membranes with a single Ts and different thermal sensitivity can be prepared using different crystalline poly-diols as the soft segments and blending two types of TSPUs with similar soft segments in the molecule structure, whereas TSPU with a double Ts can be achieved easily by blending two types of TSPUs with different soft segments.

The phase behavior of a set of high hard block content (50% to 100% hard segment by weight) linear thermoplastic polyurethanes has been investigated mainly via differential scanning calorimetry (DSC). The soft segment was based on a polypropylene oxide polyol end-capped with ethylene oxide and the hard segment on a 4,4‘-methylene diphenyldiisocyanate (MDI) chain extended by 2-methyl-1,3-propanediol (MP-Diol). By investigating thermal behavior of the samples, it has been possible to assign the observed high-temperature endothermic transitions to the disruption of an ordered structure appearing in the hard phase under certain annealing conditions and to the microphase mixing of the soft and hard segments. These results suggest a two-step melting process: (1) melting of the ordered structure present in the hard phase; (2) microphase mixing of the soft and hard segments. Wide-angle X-ray scattering experiments gave further support to this assignment. In addition, investigation of the melt-quenched samples ha...

Despite the use of polyurethanes in a number of blood-contacting applications, little is known about the contributing effects of the various polyurethane components in thrombogenesis. In order to investigate blood-polyurethane interactions, a number of different polyurethanes were examined in an acute canine ex vivo series shunt experiment. Multiprobe surface characterization techniques, including contact angle measurements, ESCA, ATR-IR, and SEM were used to obtain surface property information on the materials studied. The polyurethanes examined included several with different soft segment types, a series of materials with different hard segment diisocyanates and chain extenders, a series consisting of the same polymer cast from different solvents, a zwitterionomer, and a hard segment analog. Two commercial urethanes were also examined, and the effect of methanol extraction on these materials was studied. The blood-contact and surface characterization results indicated that both the surface concentration and type of hard segment were of importance in determining blood response. The relative concentration of hard segment on the polymer surface was found to affect the observed blood-material interaction, although the extent of this effect was found to depend on the hard and soft segment components of the copolymer system. Both the surface properties and thrombogenicity of a particular polyurethane were changed by casting from different solvents, indicating the need to optimize and control fabrication conditions. Methanol extraction was found to improve the thromboresistance of the commercial polyurethanes.

The preparation and physical properties of a group of polyether-polyester copolymers are described. Where the polyester component has a high homopolymer melting point, the resulting copolyesters are tough, resilient, thermoprocessable elastomers. Polymer hardness and modulus characteristics may be varied from a fairly soft elastomer to an impact-resistant plastic by varying the relative amounts of polyether (soft segment) and polyester (hard segment). The general characteristics of these polymers suggest that these materials have a continuous amorphous polyether phase tied together with crystalline hard segment domains. Properties such as tear strength, flex resistance, and oil resistance may be modified by incorporating a second ester component; in these latter polymers, the crystalline phase contains one, but not both, of the hard segment ester components. Melting points of the copolymers depend upon the mole fraction of crystallizable hard segment.

Microstructure and properties of polyurethanes derived from castor oil

Functionalization of polyurethanes by incorporation of alkyne side-groups to oligodiols and subsequent thiol–yne post-modification

One of the key design components of nature is the utilization of hierarchical arrangements to fabricate materials with outstanding mechanical properties. Employing the concept of hierarchy, a new class of segmented polyurethane/ureas (PUUs) was synthesized containing either a peptidic, triblock soft segment, or an amorphous, nonpeptidic homoblock block soft segment with either an amorphous or a crystalline hard segment to investigate the effects of bioinspired, multiple levels of organization on thermal and mechanical properties. The peptidic soft segment was composed of poly(benzyl-l-glutamate)-block-poly(dimethylsiloxane)-block-poly(benzyl-l-glutamate) (PBLG-b-PDMS-b-PBLG), restricted to the β-sheet conformation by limiting the peptide segment length to <10 residues, whereas the amorphous soft segment was poly(dimethylsiloxane) (PDMS). The hard segment consisted of either 1,6-hexamethylene diisocyanate (crystalline) or isophorone diisocyanate (amorphous) and chain extended with 1,4-butanediol. Thermal and morphological characterization indicated microphase separation in these hierarchically assembled PUUs; furthermore, inclusion of the peptidic segment significantly increased the average long spacing between domains, whereas the peptide domain retained its β-sheet conformation regardless of the hard segment chemistry. Mechanical analysis revealed an enhanced dynamic modulus for the peptidic polymers over a broader temperature range as compared with the nonpeptidic PUUs as well as an over three-fold increase in tensile modulus. However, the elongation-at-break was dramatically reduced, which was attributed to a shift from a flexible, continuous domain morphology to a rigid, continuous matrix in which the peptide, in conjunction with the hard segment, acts as a stiff reinforcing element.