ORIENTATIONAL BEHAVIOR OF SIDE-CHAIN LIQUID-CRYSTALLINE POLYSILOXANESDEDUCED FROM MEASUREMENTS OF 2ND-HARMONIC GENERATION

Side-chain functionalized polysiloxanes were prepared via polymer-anal ogous esterification of poly[(3-chloroformylpropyl)methylsiloxane] wit h 4-(4-hydroxyphenylazo)nitrobenzene (P1), 4-[4-(omega-hydroxyalkyloxy )phenylazo]nitrobenzene (P2-P4), -(2-hydroxyethyl)-N-methyl]anilinoazo }nitrobenzene (P5), 4-(4-hydroxypiperidino)nitrobenzene (P6), or 4-[4- (2-hydroxyethyl)piperidino]nitrobenzene (P7). P1, P3, P4 and P5 exhibi t liquid crystallinity, as deduced from differential scanning calorime try, polarized microscopic observations and X-ray diffraction measurem ents. The liquid-crystalline phase of P1 and P5 is a nematic phase, an d that of P3 and P4 is a smectic one. The second harmonic generation ( SHG) measurement of a spin-coated film of P1 was carried out by the Ma ker fringe method using a Q-switched Nd:YAG laser (1064 nm). The SHG p rofile after the heat treatment of a spin-coated film suggests a perpe ndicular orientation of the mesogenic molecules to the glass substrate . The SH light intensity of a corona-poled film was 20-fold higher tha n that of a film which was only heated, though no differences were obs erved in their UV-vis absorption spectra. These findings suggest that the mesogenic-molecular dipole moments are aligned to the same directi on in the crystalline or liquid-crystalline phase by a poling treatmen t.