Main-Chain Scission of a Charged Fifth-Generation Dendronized Polymer

During divergent synthesis of the next higher-generation dendronized polymer (DP), the fifth-generation DP, PG5, with a number-average degree of polymerization, (i.e., number of monomeric units) Pn, of ca. 500 underwent main-chain scission. This happened in the step when its peripheral Boc groups were removed by the treatment with trifluoroacetic acid (TFA), and thus a heavily charged polyelectrolyte formed as an intermediate. Atomic Force Mircoscopy (AFM) analysis of the product after drop-casting onto mica showed a large majority of short deprotected PG5 chains with Pn of ca. 40, as well as some smaller features that by MALDI-TOF mass spectrometry and 1H-NMR spectroscopy were assigned to the hypothetical monomer, deprotected MG5. This behavior is compared to a recently reported main-chain scission of a closely related PG5 which, however, resulted in significantly longer fragments. While this difference cannot yet be fully explained, questions are formulated which will guide future research.