Segmented copolyurethane

Comparative studies are presented that demonstrate that homopolyurethane and segmented copolyurethane elastomers and plastics and rubber-modified polyurethane glasses with properties similar to counterparts formed from oil-... 

Both series of polyurethanes were prepared using a prepolymer technique in which reactants were mixed at 70 °C/1 hour, cast into molds at 105 °C/2 hours, and cured at 80 °C/14 hours. The BD/MDI hard segment contents ranged from 0% (transparent, colorless homopolyurethanes) to 30% w/w (opaque, white copolyurethanes). All elastomers were characterized using DSC, dynamic mechanical, and tensile stress-strain measurements. 

Figure 5. Dynamic shear modulus-temperature behavior (torsion pendulum, 1 Hz) of 50% w/w HS copolyurethanes based on diisocyanates FDI-a (F) and MDI (M). Soft segment glass transition and hard-segment melting are in the temperature regions indicated, respectively, by and Tm.

The urea segments and interfacing urethane linkage were modeled by an alternating copolyurethane-urea synthesized from methylene bis(4-phenylisocyanate),... 

The results which are portrayed in Fig. 3.17 and 3.18 show the dependence of thermomechanical properties on the sequential ordering of the block copolyurethane blocks. As seen in Fig. 3.17 in the case of PUs based on PTHF soft segments, the course of the thermal creep curves achieved on original PU as obtained after synthesis did not depend essentially on the sequential block ordering. 

Numerous polymers have been proposed as shape-memory polymers (SMPs), and many of them are based on polyurethanes. This is because of the intrinsic versatility of segmented copolyurethane systems. By suitable choice of diisocyanate and macrodiol, a wide variation in properties may be obtained, allowing the possibility of tuning the shape-memory response to suit different applications. Usually they are phase-segregated materials. For example, a dispersed rigid phase (usually based on the diisocyanate) provides physical crosslinks, while the macrodiol provides a soft amorphous phase with low glass transition that provides the trigger temperature for shape recovery [63]. 

C.P. Buckley, C. Prisacariu, A.A. Caraculacu, Constitutive response of model segmented copolyurethane elastomers (2002), pp. 96-99. Euromech Colloquium and Workshop... 

An alternate approach to increase compliance of urethane block copolymers is to vary the structure of the soft polyether block to lower the initial modulus. In our analysis of structure-property relationship of the block copolyurethanes, it would appear that a polyether segment based on a... 

The approach that was adopted [66-69] was to prepare a series of urethane-diacetylene copolymers in which polydiacetylene units are incorporated into segmented copolyurethanes. It was shown in Section 8.1.1 that large strain-induced Raman band shifts can be obtained during the deformation of polydiacetylene single crystal fibers [8-12]. In fact, it is found that the largest shift measured so far (—20cm"V% strain) is for the C=C triple bond stretching band of polydiacetylenes (Table 8.1). 

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