Polyurethanes phase separation behavior

To investigate how the high MW aromatic diol monomer affects the phase separation behavior of polyurethane elastomers. 

Lee D, Seung-Heon L, Sangcheol K, Kookheon C, Jae HP, Bae YH. Micro-phase-separation behavior of amphiphilic polyurethanes involving poly(ethylene oxide) and poly(tetramethylene oxide). J Polym Sci B 2003 41 2365-2374. 

Wilkes and Emerson (97) studied the time-dependent behavior of a polyester polyurethane (MDI-BD based 40% hard segment) which was heated to 160°C for 5 min, then rapidly quenched to room temperature. To monitor changes in phase separation, SAXS intensity values (at a fixed angle) were recorded as a function of time. Furthermore, the elastic modulus and soft-segment Tg were followed with time. The results, shown in Figure 14, reveal an approximately exponential decay toward equilibrium with a good correlation between properties (Tg and modulus) and structure (inferred by SAXS intensities). 

The compressive, ultrasonic velocity at 6 MHz at room temperature was used to study cast films of PMMA/PVAc, PMMA/PS, PVC/CR, and PS/EPDM blends [Singh and Singh, 1983 Shaw and Singh, 1987]. A linear correlation between the sound velocity and composition was observed for miscible blends, whereas immiscibility, viz. in PMMA/PS blends the dependence was irregular. The phase separation in PVC/CR was detected at w = 70 wt % of CR, as a sudden departure from the linear correlation. The ultrasonic absorption vs. composition gave even stronger evidence of immiscibility. Ultrasonics have been successfully used to study the phase behavior in polyurethanes [Volkova, 1981]. 

Microdomain size in phase-separated copolymers plays a fundamental role in determining various macroscopic physical properties in the solid state. The difference in segmental mobility between the hard and soft domains governs the physical properties of microphase-separated polyurethane elastomers [7]. In this respect, the development of structure-property relations at the molecular level which relate directly to macroscopic behavior is the focus of this sub-section. One can exploit the well-documented difference between domain mobility [7-10] and the i3C NMR chemical shift distinction between the 0 .H2 resonances in the hard and soft segments to probe the microdomain morphology of polyether-... 

The soft segment Tg is often defined as the maximum in the tan 8 versus temperature curve which determines the low temperature behavior of urethane elastomers. The resnlts obtained are summarised in Table 8.18. The Tg obtained from the tan 8 curves confirms again that a good phase separation existed with HER elastomer. As a consequence, the HER-based polyurethane has a higher flexibility at low temperature. 

S. C. Kim, D. Klempner, K. C. Frisch, H. L. Frisch, and H. Ghiradella, Polyurethane-Polystyrene Interpenetrating Polymer Networks, Polym. Eng. Sci. 15(5), 339 (1975). Polystyrene/polyurethane SINs. Phase Separation. Tg and mechanical behavior. 

The Arrhenius plot of these polyurethanes is representative of thermoplastics with phase-separated structure (Fig. 6.25).The data for the DC conductivity show a typicd VTFH-type behavior [Eq. (6.24)] (Tuncer et al. 2005), consistent with the coupling of the conductivity mechanism with cooperative segmental motions usually observed in linear polyurethanes and several other thermoplastics. The glass transition temperatures determined by DEA (Tg diei), DSC (TgDsc), and thermally stimulated current (Tg xsc) show very good agreement. In addition, the majority of published works on polymers [e.g., see... 

Heterogeneous blends (including phase separated block copolymers) showing the expected sigmoidal behavior over the entire composition range include studies on polysulfone-siloxane block copolymers [174], styrene-mefhacrylonitrile (SMAN) block copolymers [175] and polystyrene/polyurethane blends [176]. 

It has been recognized diat many of die unique properties of the polyedier or ester based polyurethanes are due to their phase-separated structure the hard segment (urethane or urea) rich domains provide the "solid attributes, while the soft segment (polyether or ester) rich domains account for die elastomeric behavior. Previous work... 

In this paper, we present results on shape memory behavior of polyurethane (PU)/clay nanocomposites. These nanocomposites were prepared via bulk polymerization method and contained exfoliated clay particles as revealed by transmission electron microscopy and wide angle X-ray diffraction method. The PU matrix contained a crystalline soft segment, which was responsible for shape fixity. The presence of clay decreased the crystallinity of soft segments and consequently shape fixity, but the magnitude of shape recovery stress increased, e.g., by 20% with only 1 wt% clay. The mechanism of reinforcement was studied by monitoring stress relaxation and phase separation. 

Thermoplastic elastomeric behavior requires that the block copolymer develop a microheterogeneous two-phase network morphology. Theory predicts that microphase separation will occur at shorter block lengths as the polarity difference between the A and B blocks increases. This prediction is borne out as the block lengths required for the polyether-polyurethane, polyester-polyurethane, and polyether-polyester multiblock copolymers to exhibit thermoplastic elastomeric behavior are considerably shorter than for the styrene-diene-styrene triblock copolymers. 

In the 1970s, several research groups came up with foam-filled columns for GC and HPLC [14-17]. These open pore polyurethane foam stationary phases, which were prepared via in situ polymerization, were shown to possess comparatively good column performance and separation efficiency. They could, however, not achieve general acceptance and broader application due to insufficient mechanical stability and strong swelling behavior. 

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