Pi-Conjugated semiconducting polymers are a rapidly developing field of research, spanning a breadth of applications including organic light-emitting diodes, thin-film transistors, and solar cells. The tunability of their molecular structure allows modification of their electronic and mechanical properties. Indacenodithiophene (IDT)-based polymers are a particularly intriguing area of research; their rigid planar donor-accepting backbone promotes intrachain charge delocalization and has shown to facilitate efficient charge-carrier mobility in films despite limited long-range crystalline order.
Previous research in this lab has found promise incorporating benzothiadiazole (BT) and thienopyrroledione (TPD) via direct arylation polymerization (DArP) to create a unique terpolymer that incorporates the desired electronic qualities of BT and the tunability and material properties of TPD. However, understanding and controlling the properties of these materials requires an in-depth kinetic study to learn about the monomer reactivities, molecular weight, and polymerization mechanism. In this project, the methods used to collect this data were developed. Defining proper controls and techniques to take time points of a nonhomogeneous solution were optimized, as well as picking a suitable internal standard to use for NMR. Using 1H-NMR to integrate diagnostic monomer peaks and leveraging the sequencing resulting from DArP, the conversion of all three monomer was able to be calculated. The results showed that IDT has higher reactivity with TPD than BT and an initial inhibition period in the polymerization.
A method to quantitatively separate the monomer and polymer part of each time point was also developed and subsequent GPC analysis corroborated the conversation data. Future characterization techniques will be used to further analyze the polymers, and repeated kinetics experiments tuning different variables (e.g. monomer ratios, catalyst concentration) will continue understanding of this complex terpolymer system.