Direct Observation of Chain Lengths and Conformations inOligofluorene Distributions from Controlled Polymerization byDouble Electron−Electron Resonance

Dennis Bücker, Annika Sickinger, Julian D. Ruiz Perez, Manuel Oestringer, Stefan Mecking and Malte Drescher J. Am. Chem. Soc. DOI: 10.1021/jacs.9b11404

ABSTRACT: Synthetic polymers are mixtures of chains with different lengths, and their chain length and chain conformation are often experimentally characterized by ensemble averages. We demonstrate that double electron−electron resonance (DEER) spectroscopy can reveal the chain length distribution and the chain conformation and flexibility of the individual n-mers in oligo-(9,9-dioctylfluorene) from controlled Suzuki−Miyaura coupling polymerization. The required spin-labeled chain ends were introduced efficiently via a TEMPO-substituted initiator and chain-terminating agent, respectively, with an in situ catalyst system. Individual precise chain length oligomers as reference materials were obtained by a stepwise approach. Chain length distribution, chain conformation, and flexibility can also be accessed within poly(fluorene) nanoparticles.