THERMAL DYNAMICS OF SIDE-CHAIN COPOLYMETHACRYLATES AS STUDIED BY THE DIELECTRIC-SPECTROSCOPY AND RELAXATION OF 2ND-HARMONIC GENERATION

A series of copolymethacrylates with different contents of tolane-base d mesogenic groups have been synthesized. The mesogenic group content was characterized with H-1 n.m.r. The phase behaviours were determined using a differential scanning calorimeter and optical polarizing micr oscopy. A smectic A phase was obtained when the mesogenic group conten t was increased up to 80 mol.%. Dielectric relaxation results indicate d that the amplitude of the alpha-relaxation was suppressed significan tly due to the presence of the liquid crystalline phase. The reduction of the molecular motion is beneficial to the enhancement of the tempo ral stability of the effective second-harmonic coefficient for the pol ymer with a higher mesogenic group content. Moreover, the second harmo nic coefficient is enhanced as the mesogenic group content increases. The self-alignment nature of the liquid crystal phase is favourable fo r alignment of the NLO-active mesogenic group under an applied electri c field and preserving such alignment after removal of the electric fi eld. The relationship between thermal dynamic behaviour and second-ord er nonlinear optical properties is also discussed. (C) 1998 Elsevier S cience Ltd. All rights reserved.