Influence of the dispersity and molar mass distribution of conjugated polymers on the aggregation type and subsequent chiral expression

Abstract

This study aims to determine the influence of the dispersity on the aggregation of conjugated polymers and their subsequent chiral expression. Dispersity has been thoroughly investigated for industrial polymerizations, but research on conjugated polymers is lacking. Nonetheless, knowledge thereof is crucial for controlling the aggregation type (type I versus type II) and its influence is therefore investigated. For that purpose, a series of polymers is synthesized via metered initiator addition, resulting in dispersities ranging from 1.18–1.56. The lower dispersity polymers yield type II aggregates and the resulting symmetrical electronic circular dichroism (ECD) spectra while the higher dispersity polymers are predominantly type I due to the longer chains effectively acting as a seed and therefore yield asymmetrical ECD spectra. Furthermore, a monomodal and bimodal molar mass distribution of similar dispersity are compared, demonstrating that bimodal distributions show both aggregation types and therefore more disorder, leading to a decrease in chiral expression.