A technique of linear viscoelasticity measurements coupling with temperature scanning was found effective in the detection of microphase separation transition (MST) and in the determination of MST temperature. The validity and accuracy of the technique were confirmed and reinforced by atomic force microscopy and differential scanning calorimetry (DSC). The technique was applied to a study of the MST of a series of 13 polyurethane (PU) elastomers based on mixed toluene diisocyanate (TDI), 1,4 butadiol, and poly(tetramethylene oxide) (PTMO) of two different molecular weights; the MST temperatures of the PU elastomer samples were measured. Although each of the 13 polymer samples had distinct hard segment content and used PTMO of different chain lengths, or mixed PTMO, the MST temperatures of the 13 samples formed a linear master curve when the MST temperature was plotted against the fraction of hard segment. The master curve indicated that the MST temperature is independent of the length and type of PTMO. It was also found that 2,4 TDI prevailing over its isomer 2,6 TDI played a dominant role in the MST of this series of PU elastomers.
Articles you may be interested inPoly(D-lactic acid) as a rheological modifier of poly(L-lactic acid): Shear and biaxial extensional flow behavior Abstract. The transient and viscoelastic behavior of a segmented block copolymer, poly(ether-b-amide) was carefully studied. Upon a sudden shear the stress of the copolymer melt shows a fluctuation when the shear rate exceeds a critical value. The recoverable strain at the onset of the fluctuation is found approximately at a constant value of 0.6. The fluctuation is independent of materials of shearing apparatus and depends on the roughness of the shearing surfaces. Increasing the roughness of the surface suppresses the stress fluctuation. The copolymer melt also exhibit an abnormal terminal behavior in viscoelasticity. A plateau of storage modulus emerges upon a temperature raise which may relate to the domain structure change induced by the dissociation of hydrogen bonding.
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