Physical Properties of Liquid Crystalline Solution of Once-Broken Rod Poly(γ-benzyl L-glutamate)

Abstract

ABSTRACT:Poly(γ-benzyl L-glutamate) (PBLG) whose molecule is a straight rod in shape and a large permanent dipole moment along the rod axis and once-broken (OB)-PBLG which has two anti-parallel permanent dipoles in its molecule composed of two α-helices jointed by a flexible chain of the bifunctional initiator (trimethylenediamine) in the manner of head to head, were synthesized and the behavior of concentrated solutions were investigated. The solution of OB-PBLG formed a cholesteric liquid crystal as well as that of straight (S)-PBLG. Temperature and concentration dependency of cholesteric texture for both polymers were similar, except for OB-PBLG having a lower molecular weight, M v < 5 × 10 4 . Alignment of molecules in a thin cell is different for the two polymers. As dynamics of the electro-optic response, differences for the two polymers are clearly evidently. Response time of OB-PBLG is 60 to 70 times as long as that of ordinary S-PBLG, under similar experimental conditions. KEY WORDS Once-Broken Rod / Poly(γ-benzyl L-glutamate) / Liquid Crystalline Texture / Electro-Optic Response / In-Plane Cell / Poly-γ-benzyl L-glutamate (PBLG) forms a liquid crystal (LC) in a helicogenic organic solvents above a certain concentration, C A . 1, 2 The theories 3-5 of transition between isotropic and anisotropic phases were developed based on geometry of rod like particles, that is, axial ratio of rods, and neglecting special interactions between polymer-solvent and polymer-polymer. The cholesteric liquid crystalline texture formed by PBLG 1, 2 has been shown the norm due to the optical activity of the PBLG molecule, and nematics under some particular conditions are rather exceptional. [6][7][8][9] Since PBLG molecules in helical conformation have large permanent dipole moment along the helical axis, alignment of dipoles in the cholesteric texture and properties in an electric field are very interesting. The texture and properties of the liquid crystal formed by oncebroken rods, 10-15 where two rods having a large permanent dipole respectively are connected in head to head manner with a hinge, the dipoles along a molecular axes are anti-parallel with each other, and may swing or rotate on the hinge in the dilute solution were studied. We prepared once-broken PBLG (OB-PBLG) introducing a hinge, as initiator, between two helical rods, and investigated the liquid crystalline texture and properties with reference to those of ordinary, single straight rod, PBLG (S-PBLG).To make clear the dipolar interaction between molecules in the liquid crystalline phase, solutions of OB-and S-PBLG were prepared by several helicogenic solvents having different dielectric constants and differences of the liquid crystal formation, texture and properties were investigated. EXPERIMENTALTwo PBLGs were prepared as follows. To obtain a narrow distribution of molar mass, the Ncarboxyanhydride (NCA) of γ-benzyl L-glutamate (γ-BLG-NCA) was initially polymerized in dimethylformamide (DMF) containing n-butylamine for S-PBLG and trimethylenediamine (TM...