Graft Length and Density Govern Morphology and Optoelectronic Properties of Poly(caprolactone)-graft-oligo(3-hexylthiophene)s

Abstract

Compositional modifications of conducting polymer-based graft copolymers enable precise tuning of their properties, including conductivity, degradation and opto-electrochemical properties. This work investigates how the composition of poly(caprolactone)-graft-oligo(3-hexylthiophene)s, (P(CL-co-AVL)-g-O3HT), previously shown to be degradable, effects the morphological and opto-electrochemical properties of the copolymers. Effect of different grafting density and the length of the O3HT grafts on the material's properties were investigated using a range of advanced techniques, such as, spectroelectrochemistry, cyclic voltammetry, 2D-GIXRD and 4D-STEM. Short O3HT grafts (n = 15) yielded amorphous copolymers, whereas longer grafts (n = 30, 40) produced semi-crystalline material with distinct crystalline and amorphous redox signatures. High grafting density promoted formation of interconnected nanoscale O3HT crystallites. Thermal annealing (40–60 °C) or trace acetonitrile (1 vol.%) in casting solutions enhanced intrachain order and crystallization, and, in turn, enhanced optoelectronic properties of the high-density, long grafts copolymers. These findings establish structure - property relationship in conducting polymer-based graft copolymers, guiding their macromolecular design, including for transient electronics.