End‐To‐End FRET Enabling Direct Measurement of Oligomer Chain Conformations and Molecular Weight in Reaction Solutions

Förster resonance energy transfer (FRET) is an established tool for measuring distances between two molecules (donor and acceptor) on the nanometer scale. In the field of polymer science, the use of FRET to measure polymer end-to-end distances (R_ee) often requires complex synthetic steps to label the chain ends with the FRET pair. This work reports an anthracene-functionalized chain-transfer agent for reversible addition-fragmentation chain-transfer (RAFT) polymerization, enabling the synthesized chains to be directly end-labeled with a donor and acceptor without the need for any post-polymerization functionalization. Noteworthily, this FRET method allows for chain conformation measurements of low molecular weight oligomers in situ, without any work-up steps. Using FRET to directly measure the average R_ee of the oligomer chains during polymerization, the chain growth of methyl methacrylate, styrene, and methyl acrylate is investigated as a function of reaction time, including determining their degree of polymerization (DP). It is found that DP results from FRET are consistent with other established measurement methods, such as nuclear magnetic resonance (NMR) spectroscopy. Altogether, this work presents a broadly applicable and straightforward method to in situ characterize R_ee of low molecular weight oligomers and their DP during reaction.