Determining the Absolute Molecular Weights of Pi-Conjugated Polymers for Mechanically Flexible and Stretchable Electronics

Creation of next-generation soft materials for mechanically robust high-performance DoD communication and sensing optoelectronics will require diverse conjugated polymer structures, architectures, and functionalities to impart desirable processing, physical, and electronic properties, as well as to enable fabrication via high-throughput inexpensive fabrication techniques. In recently funded AFOSR project FA9550-18-1-0320 PIs Tobin Marks and Antonio Facchetti proposed multiple synthetic and processing strategies for increasing the performance and mechanical properties of organic thin-film transistors (OTFTs) and organic electrochemical transistors (OECTs), as well as their electronic circuitry. Essential to creating next-generation -conjugated polymers is accurate determination of molecular mass to understand and optimize processing and device performance, as well as batch-to-batch performance reproducibility. Quantifying the polymer number average molecular weight (Mn) and polydispersity index (Đ) is therefore of critical importance, and such parameters are typically determined using high-temperature (>100 °C) gel-permeation chromatography (HT-GPC) in conjunction with columns calibrated to polystyrene standards. Although this methodology is common in this field, it is limited due to significant structural differences between -conjugated polymer structures and polystyrene. A strategy that can provide the absolute molar mass without the need for reference standards is multi-angle light scattering (MALS) detection. Until recently, MALS detection found few applications in conjugated polymers due to inherent difficulties in accounting for light absorption and emission scattering by typical samples. Recently, MALS detection technology has advanced significantly, now allowing determination of absolute molar mass for opto-electronic polymers. Thus, incorporating MALS into a high-HT-GPC will allow unprecedented semiconducting polymer characterization, supporting precision synthesis and processing, as well as more meaningful interpretation of physical properties. This DURIP proposal seeks state-of-the-art instrumentation that will provide new capabilities and accelerate ongoing research regarding the absolute determination of Mn/Đ for semiconducting polymers used in AFOSR-funded OTFT and OECT research. The specific instrumentation requested is for a HT-GPC (either a Polymer Char GPC-IR5 or Tosoh EcoSEC HT-GPC instrument) equipped with MALS detection (Wyatt DAWN UHT). The choice of HT- GPC instrument is tied to the Budget Plan options which are explained below. The coupling of a HT-GPC with a MALS detector will enable the absolute determination of the molecular mass, pinpointing Mn and Đ effects on device performance with complete accuracy and precision. Below we show specifically how the requested instrumentation will directly benefit the PI’s AFOSR funded research program, national collaborators having AFOSR grants, as well as multiple groups at NU, providing advanced research capabilities that are currently unavailable.