Direct Measurement of Polymer-Chain-End-to-End Distances by Using RAFT Chain Transfer Agent as the FRET Acceptor

Fo''rster resonance energy transfer (FRET) is a powerful tool for measuring distances between two molecules (donor and acceptor) in close proximity (1-10 nm), which can be employed for determining polymer end-to-end distances (Ree). However, previous works for labeling FRET pairs on chain-ends often involve relatively complex steps for materials preparation, potentially limiting their broad use in synthetic polymer systems. In this work, we introduce an anthracene-functionalized chain -transfer agent for reversible addition-fragmentation chain-transfer (RAFT) polymerizations, which can directly yield polymers containing FRET donor and acceptor molecules on respective chain -ends. This approach enables the direct use of FRET for characterizing the averaged Ree of polymers. Building on this platform, we investigate the averaged Ree of polystyrene (PS) and poly(methyl methacrylate) (PMMA) in a good solvent as a function of their molecular weight. Notably, the FRET results show good agreement with simulation results obtained from all-atom molecular dynamics, confirming its measurement accuracy. Overall, this work provides a facile and broadly applicable platform to directly determine the Ree of low molecular weight polymers by using FRET-based methods.

Automated summary

In this study, a new method is developed to directly introduce FRET donor and acceptor molecules at the chain ends of polymers, enabling the measurement of the averaged end-to-end distance. The application of this method to polystyrene and poly(methyl methacrylate) confirms the agreement between FRET results and molecular dynamics simulation results.