Nonlinear Optical Polymers. 2. Novel NLO Linear Polyurethane with Dipole Moments Aligned Transverse to the Main Backbone

Abstract

This paper presents a novel class of nonlinear optical (NLO) polymer for second harmonic generation (SHG). This new class of NLO polymer consists of the linear polyurethane, T-polymer, of tolylene 2,4-diisocyanate (TDI) with 3-[(2-hydroxyethyl)amino]-5-(hydroxymethyl)-4‘-nitroazobenzene (T-AZODIOL), whose dipole moment is aligned transverse to the main chain backbone. For comparison, the linear polyurethane L-polymer, whose NLO chromophore is incorporated into the main chain, is synthesized from TDI with 4-[N-(2-hydroxyethyl)-N-methylamino]-3‘-(hydroxymethyl)azobenzene (AZODIOL). T-polymer poled at optimum conditions of a corona poling voltage 8.0 kV, a temperature of 95 °C, and a time of 60 min shows a large second-order nonlinearity of d 33 = 1.6 × 10-7 esu (67 pm/V) with good thermal stability at room temperature. The oriented NLO dipole moments for T-polymer do not show significant relaxation at ambient conditions after 60 days except for small depression a few days after poling, whereas, the SHG activity of L-polymer is largely decayed at room temperature. The better thermal stability of this new class of T-polymer is related to the smaller free volume in T-polymer.

Charge transfer interactions in polyesters with a donor‐(σ‐bridge)‐acceptor moiety in the repeating unit

“…This is suggested by the fact that DA polymers are often reasonably soluble. 28 There are indeed indications that intrachain rather than interchain effects are operative in polymers with donor-acceptor azobenzene side groups. 29 Interactions between DA moieties are predominantly electrostatic in nature.…”

Synthesis and Properties of Novel T-type Nonlinear Optical Polyurethane Containing Tricyanovinylthienyl Group with Enhanced Thermal Stability of Dipole Alignment

“…This d 33 value is somewhat lower than that of the Y-type polyurethane and other NLO polyurethanes. 19 Since the second harmonic wavelength is at 780 nm, which is not in the absorptive region of the resulting polyester, there is not resonant contribution to this d 33 value. In the isotropic model, the ratio of d 33 /d 31 is predicted to be about 3.…”

“…[17][18] Polyurethanes with a NLO chromophore, whose dipole moment is aligned transverse to the main chain backbone, show large second-order nonlinearity with good thermal stability. [19][20] Physically cross-linked systems via hydrogen bonds have the advantages such as homogenity and good processability relative to chemically cross-linked systems, which suffer from significant optical loss and poor solubility. Recently we reported novel Y-type NLO polyurethanes with enhanced thermal stability of second harmonic generation.…”

Preparation of Novel T-type Polyurethanes with High Thermal Stability of Second Harmonic Generation and Their Nonlinear Optical Properties

“…9,10 Polyurethanes with a NLO chromophore, whose dipole moment is aligned transverse to the main chain backbone, showed a large second-order nonlinearity with good thermal stability. [11][12] Recently we reported novel Y-type NLO polyurethanes with enhanced thermal stability of second harmonic generation. [13][14][15][16][17] In this work we have prepared novel T-type polyurethanes containing 2,5-dioxybenzylidenemalononitrile group as a NLO-chromophore.…”