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Elastomeric Polydimethylsiloxane Endcaps to Achieve Solubility and Melt-Processability in DPP-based Polymer Semiconductors

Subject Area Polymer Materials
Solid State and Surface Chemistry, Material Synthesis
Synthesis and Properties of Functional Materials
Mechanical Properties of Metallic Materials and their Microstructural Origins
Preparatory and Physical Chemistry of Polymers
Term from 2020 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 436376809
 
Final Report Year 2024

Final Report Abstract

In the field of bioelectronics, materials need not only electronic conductivity but also mechanical flexibility to interact effectively with living organisms. Traditional inorganic components possess a significantly higher elastic modulus than biological tissue, which can incite encapsulation and inflammatory responses within a responsive living system. Novel materials must integrate electronic capabilities with a low elastic modulus, capable of enduring mechanical strains from bodily movements. While polymers exhibit promise due to their inherently low elastic modulus compared to inorganic counterparts, the elastic modulus of polymer semiconductors (PSCs) (typically 0.1 - 1 GPa) remains orders of magnitude higher than that of human skin (0.1 - 10 MPa) due to the extended conjugated system. Various approaches have been explored over time to achieve low-modulus PSCs, such as statistically incorporating non-conjugated spacers or altering the polymer's backbone regioregularity or sidechains. However, reducing modulus generally corresponds to a decrease in mobility. The DFG project explored the phase separation of block copoymers, a well known phenaomenon in polymer engineering, to approach the problem: Block copolymers consist of two polymer chains that are covalently linked at their terminal ends. The polymer chains separate on the nanoscale, resulting in two phases that retain the properties (Tg, etc) of the respective polymer. In our study, we synthesized triblock co-polymers (TBCs) by covalently endcapping the PSC poly-diketopyrrolopyrrole-thienothiophene (PDPP-TT), with two elastomeric polydimethyl-siloxanes (PDMS) chains. PDPP-TT is a state-of-the-art polymer semiconductor, while PDMS is a biocompatible elastomer. The resulting triblock co-polymers are soft and durable: the TBC with the highest PDMS content has a low modulus (5.5 MPa) in the range of mammalian skin and achieves a mobility of 0.1 cm²V⁻¹s⁻¹, in the range of the pure PDPP-TT (0.7 cm²V⁻¹s⁻¹). In a doped state, the TBC maintains electronic functionality over more than 1500 cycles at 50% strain. Also, the TBC can be shear-coated at high speeds to yield smooth films with increased thickness without degradation of the electrical performance. Using physisorption onto the active channel, OFET-based biosensors were fabricated which detect both SARS-CoV-2 antigens as well as anti-SARS-CoV-2 antibodies in less than 20 minutes. The device demonstrates a high sensitivity of about 19%/dec and limit of detection (LOD) 0.36 fg/mL for anti-SARS-Cov-2 antibodies, and at the same time, a sensitivity of 32%/dec and LOD of 76.61 pg/mL for the virus antigen detection. The project's results demonstrate that the phase separation of block copolymers enables the creation of biocompatible materials. These materials effectively integrate electronic functionality with mechanical flexibility and a low elastic modulus. Such findings have the potential to advance the development of novel material systems and wearable (bio)sensors.

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