Synthesis and pyroelectric response of disperse red 1 functionalized silicones: cyclic monomer, homopolymer, and block copolymer derivatives

Abstract

Pyroelectric materials enable the direct conversion of thermal fluctuations into electrical energy, offering a promising approach to waste heat recovery. While pyroelectric polymers are highly valued for their scalable synthesis, mechanical flexibility, and tunable properties, the field is currently dominated by poly(vinylidene fluoride) (PVDF)-based materials, which present environmental and processing challenges. To develop fluorine-free alternatives and elucidate the influence of molecular architecture on thermal-to-electrical conversion, we synthesized a series of siloxane-based materials functionalized with Disperse Red 1 (DR1) moieties, including a cyclic siloxane monomer, a homopolysiloxane, and a block copolysiloxane. Differential scanning calorimetry confirms the semicrystalline nature of these siloxanes, with glass transitions (T_g) near room temperature and melting temperatures of about 80 °C. Notably, even unpoled samples exhibit a measurable pyroelectric response at elevated temperatures. The pyroelectric response at low temperatures is significantly enhanced by poling the crystalline domains in an electric field above the melting transitions (T_m). Among the synthesized materials, the homopolymer exhibited the highest pyroelectric response (0.66 µC m⁻² K⁻¹ at 60 °C). While this value is significantly lower than the typical values for PVDF (>20 µC m⁻² K⁻¹), it should be noted that the processing and poling steps differ substantially. Under similar conditions, the PVDF value was only twice that of the homopolymer. Even more interesting, in an unpoled sample, the homopolymer shows a response similar to that of the poled sample, while PVDF shows almost no response. The superior response for the unpoled sample is attributed to the synergistic effects of DR1 self-ordering and secondary pyroelectricity—the strain-induced changes in dipole density resulting from thermal expansion. These findings provide a framework for designing high-performance, silicone-based pyroelectric transducers through precise structural control.