Effect of the methacrylic group on the degradation of polar achiral composites after successive poling cycles and appearance of antiferroelectric behaviour

Abstract We are studying a polar system composed of a polymer and its monomer in a 2:1 ratio. Although both components are non-chiral, their mixture shows a high spontaneous polarization due to hydrogen bond structuration. The original system shows a decrease in the spontaneous polarization through successive poling cycles. We replace the methacrylic moiety on two monomers with different aliphatic tail length (octyloxy/dodecyloxy) for a non-polymerizable isobutyric group. We study their mesomorphism as pure molecules and forming part of the composites by differential scanning calorimetry, polarizing optical microscopy and powder X-ray diffraction. We compare how the successive poling cycles affects the polar response as pyroelectric signal (γ) and loop hysteresis of these new polymer-isobutyric monomer composites vs their conventional counterpart polymer-methacrylic monomer composites. We found a decrease in the pyroelectric response with successive poling cycling in all composites. Regarding the structure of the composites obtained with the new saturated monomers, they exhibited polar behaviour. Surprisingly, for the isobutyric monomer with a dodecyloxy tail, the composite shown antiferroelectric behaviour unlike the ferroelectric methacrylic counterpart. The new phenomena must be due to steric hindrance caused by the bulky isobutyric group, forcing the monomers to lie between the sidechain of the polymer with the bulkier isobutyric group at the alkyl chain layer interface rather than near the polymeric main chain.