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 (Tg) 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 (Tm). Among the synthesized materials, the homopolymer demonstrated the highest pyroelectric response. This superior response 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.New conceptsThis work introduces fluorine-free, polysiloxane-based materials for pyroelectricity, shifting from the conventional semi-crystalline fluoropolymer paradigm. We demonstrate that pyroelectricity can be achieved by exploiting H-aggregate formation within a highly functionalized polysiloxane matrix. This approach shifts the design focus from the forced alignment of ferroelectric crystalline domains to the architectural control of chromophore stacking, providing a fluorine-free alternative to conventional fluorinated polymers.The distinguishing feature of this study is the identification and exploitation of stable polarization in unpoled samples, which persists even at elevated temperatures. In contrast to many other materials, which undergo dipole randomisation once the matrix becomes mobile, resulting in a loss of pyroelectric response, it is demonstrated that H-aggregates persist, thereby enabling a measurable response without the necessary post-processing external high electric-field treatment. This work demonstrates that molecular architecture, rather than high voltage poling, can lead to pyroelectricity in soft matter. By showing how structural motifs (cyclic, homo-, and block-copolymers) govern aggregate stability, we provide a toolkit for designing "selfpolarised" materials that could serve as an alternative to current fluorinated polymers.