SYNTHESIS AND THERMOTROPIC PROPERTIES OF POLYURETHANES PREPARED FROM 2,5-TOLYLENE DIISOCYANATE AND 2,6-BIS(OMEGA-HYDROXYALKOXY)NAPHTHALENES

A series of thermotropic polyurethanes containing no mesogenic unit we re synthesized by polyaddition of a para-type diisocyanate such as 2,5 -tolylene diisocyanate (2,5-TDI) with 2,6-bis(omega-hydroxyalkoxy)naph thalenes (BHNm: HO(CH2)mOC(10)H(6)O(CH2)(m)OH; m is the carbon number in the hydroxyalkoxy group). Intrinsic viscosities of the polymers wer e in the range of 0.27-0.48 dL g(-1). The thermal properties of these polymers were studied by differential scanning calorimetry, thermograv imetric analysis, polarizing microscopy, and X-ray diffractometry. Pol yurethane 2,5-TDI/BHNm's (m = 5, 6, 8, 11) prepared from BHNm and 2,5- TDI having methyl substituent on the phenylene unit exhibited monotrop ic liquid crystallinity. For example, polyurethane 2,5-TDI/BHN8 with [ n]=0.30 exhibited a mesophase from 139 to 111 degrees C on cooling. Ho wever, in the series of polyurethanes prepared by polycondensation of 4, 4-phenylene diisocyanate (1,4-PDI) with BHNm, no explicit mesomorph ic behavior was observed by DSC measurement and polarizing microscopic observation.