MOLECULAR ORDER AND DYNAMIC-MECHANICAL BEHAVIOR OF POLYURETHANES BASED ON LIQUID-CRYSTALLINE DIOL

Citation
M. Ilavsky et al., MOLECULAR ORDER AND DYNAMIC-MECHANICAL BEHAVIOR OF POLYURETHANES BASED ON LIQUID-CRYSTALLINE DIOL, Journal of macromolecular science. Physics, B37(5), 1998, pp. 645-666
Citations number
28
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Polymer Sciences
ISSN journal
0022-2348
Volume
B37
Issue
5
Year of publication
1998
Pages
645 - 666
Database
ISI
SICI code
0022-2348(1998)B37:5<645:MOADBO>2.0.ZU;2-P
Abstract
Synthesis of the liquid crystalline (LC) diol 6,6'-[ethylenebis(1,4-ph enylene-oxy)]-dihexanol (I) is described. The structure of polyurethan es prepared from diol I and 4,4'-methylenedi(phenyl isocyanate) (MDI), 4,4'-methylenedi(cyclohexyl isocyanate) (HMDI), or 2(4)-methyl-1,3-ph enylene diisocyanate (TDI) at 1:1 molar ratios of isocyanate and hydro xy groups is studied by dynamic mechanical spectroscopy, differential scanning calorimetry (DSC), polarizing microscopy, and x-ray scatterin g. The polymer prepared from HMDI and the diol (I/HMDI) shows, on cool ing, thermal behavior typical of amorphous polymers. A frequency-tempe rature superposition could be applied to the mechanical data, and the horizontal shift factor satisfied the Williams-Landel-Ferry (WLF) equa tion. A more-complex thermal behavior was found for I/HMDI polymer dur ing subsequent heating; above 70 degrees C, the formation of an ordere d structure takes place, and this structure melts at about 120 degrees C. Complex thermal behavior is exhibited by I/TDI polymer. On cooling its melt, the polymer forms a nematic phase at about 80 degrees C, wh ich freezes into the LC glassy state. On heating, the mesophase melts, and, subsequently, a better-ordered smectic phase is formed at 95 deg rees C, which melts at 120 degrees C. This structure buildup is accomp anied by a rapid increase in storage modulus G', and the sample shows thermorheologically complex mechanical behavior. The polymer formed fr om the diol and MDI (I/MDI) exhibits a most-complex thermal behavior. On cooling and heating, four transitions can be detected in its therma l mechanical behavior, and the structure of the polymer is strongly de pendent on its thermal history.