Thermal stability of the dipole orientation in nonlinear optical guest-host, side-chain and cross-linked polymer electrets

As the thermal stability of nonlinear optical polymer electrets is essential for their application in waveguide devices, three typical polymers were studied by means of isothermal pyroelectricity measurements and thermally stimulated depolarization experiments. The fundamental difference between the three sample materials is the connection between the polymer backbone and the nonlinear optical molecules: The guest-host polymer is just doped with chromophore molecules, in the side-chain material, the chromophore is chemically linked to the main-chain, and in the cross-linked system, chromophore movement is still further restricted. The numerical evaluation reveals how the isothermal relaxation deviates from an exponential decay, and the TSD results yield the product of activation energy and stretching parameter. The behavior of guest-host and side-chain polymers can be described by a single broad relaxation process, whereas cross-linking yields a rigid dipole polymer network with a high activation temperature of the dipole orientation.