Glass Transition Temperature from the Chemical Structure of Conjugated Polymers

The glass transition temperature (T_g) is a key property that dictates the applicability of conjugated polymers. The T_g demarks the transition into a brittle glassy state, making its accurate prediction for conjugated polymers crucial for the design of soft, stretchable, or flexible electronics. In this work, only one adjustable parameter is used to build a relationship between the T_g and the molecular structure of 32 semiflexible (mostly conjugated) polymers that differ drastically in aromatic backbone and alkyl side chain chemistry. An effective mobility value, m, is calculated using an assigned atomic mobility value within each repeat unit. The only adjustable parameter in the calculation of m is the ratio of mobility between conjugated and non-conjugated atoms; the value for this ratio is supported by results from molecular dynamics simulations. We show that m correlates strongly to the T_g, and that this simple method predicts the T_g with a root-mean-square error of 13 K for alkylated conjugated polymers.