2ND-HARMONIC GENERATION IN POLY(ALPHA-AMINO ACID) AND POLY(ISOCYANATE) FILMS

Films of poly(gamma-benzyl-L-glutamate) (PBLG) and poly(hexylisocyanate) (PHIC) were cast from solution whilst under electric fields generated between parallel strip electrodes placed at the surface. Because of their chain rigidity and large macromolecular dipole moments, this procedure induces some parallel chain alignments in the field direction, even if the fields are low (less-than-or-equal-to 300 V mm-1). The field induces a degree of non-centrosymmetric order in the films which is retained after the field is removed. In these ordered states such films were found to have second-harmonic generating (SHG) ability under 1.06-mu-m irradiation and this ability did not age over a period of 6 months. The SHG activity varied with the angle of polarized radiation relative to the poling direction, showing a single maximum and minimum for PHIC (uniaxial symmetry) and double maxima and minima for PBLG (biaxial symmetry) over pi-radians. Optical microscopy of the PBLG films formed under electric fields showed regions of nematic as well as cholesteric order.