Tf. Hsu et Yd. Lee, PROPERTIES OF THERMOPLASTIC POLYURETHANE ELASTOMERS CONTAINING LIQUID-CRYSTALLINE CHAIN EXTENDER (I) SYNTHESIS AND PROPERTIES OF HARD SEGMENTS, Polymer, 40(3), 1999, pp. 577-587
Polyurethanes prepared from 1,6-diisocyanate hexane (HDI) and 2,4-toly
lene diisocyanate (2,4-TDI) with liquid crystalline chain extender 4,4
'-bis(n-hydroxyalkyloxy)biphenyl (n-PBP, n = 2, 3, 6) were reported. C
haracterizations of monomers and polymers were performed by infrared s
pectroscopy (IR), H-1-NMR, solid-state C-13-NMR, and elemental analysi
s. The phase transition behaviors of polyurethanes were investigated b
y Global TSC, DSC, and polarized microscopy (POM). Our results showed
that monomers 4,4'-bis(n-hydroxyalkyloxy) biphenyl exhibit smectic typ
e mesophase. It was observed that the longer the spacer length of poly
urethanes, the higher the chain mobility, the larger DOD (degree of di
sorder) value and the lower the relaxation time. Also the phase transi
tion temperature of polyurethanes decreases with increasing spacer len
gth. DSC measurements and texture observations indicated that H2, H3,
H6 and T6 exist in both mesophase and crystal phase. Quantitative anal
ysis of temperature dependence hydrogen bonding revealed that hydrogen
bonded content (X-b) Of the C=O group for all samples decreased with
increasing temperature. For the H series, both X-b and Delta H decreas
e with increasing spacer length of the mesogenic diol. (C) 1998 Elsevi
er Science Ltd. All rights reserved.