ISSN:
1022-1352
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Two side-chain polyurethanes, HMDI-PU (2a) and TDI-PU (2b), have been synthesized from 2,2′-iminodiethanol (“diethanolamine”) N-substituted with a nitrostilbene group on a hexamethylene spacer with, respectively, hexamethylene diisocyanate and 1-methyl-2,4-phenylene diisocyanate (“2,4-toluenediisocyanate”). 2a showed a smectic liquid-crystalline phase; 2b proved to be amorphous. The phase behavior was characterized by means of differential scanning calorimetry, polarization microscopy and wide-angle X-ray scattering. Thermally stimulated discharge current measurements (TSD) revealed at least two strong relaxation processes above the glass transition temperature Tg which are related to the dynamic glass transition involving the backbone part (α) and the mesogenic units (λ). Non-linear optical analysis of 2a showed that the Pockels coefficient r13 was low in the mesophase and high in the isotropic phase. Contrary to expectation, poling in the mesophase did not enhance the Pockels effect. The amorphous 2b gave both a high and a stable Pockels coefficient (r33 around 6.0 pm/V). The stability could be improved by ageing and prolonged poling at the ageing temperature. However, the Pockels coefficient proved to be dependent on the temperature: high above 85°C, low below 85°C (provided that the sample had been heated once before). This was attributed to an antiparallel association of the chromophores. The role of hydrogen bonds influencing poling has been assessed by temperature-dependent infrared spectroscopy.
Additional Material:
10 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1996.021971213
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