Ion exchange enables Maldi-Tof mass spectrometry analysis for sequence-controlled polymers with positively charged backbone

Abstract

Transforming negative ions of cationic polymers with positively charged backbone into Tf2N-((SO2CF3)2N-) or FSI-((SO2F)2N-) through an ion exchange reaction makes it possible to achieve the matrix-assisted laser desorption ionization-time of flight (Maldi-Tof) mass spectrometry analysis. Series of sequence-defined polymer with positively charged backbone were synthesized via alternately processing Menshutkin reaction and Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) click reaction in this work to verify the feasibility of the method. The electron cloud density of the cation determines the pattern of fragment appearance in mass spectra. Such method is available for positively charged polymer with molecule weight up to 4000 containing 9 cations. The sequence of the cationic polymer can be elucidated through the molecular ion peak and regular fragment peaks, making it a valuable method for sequence, component and end group analysis. Such advantages make it an easy route to achieve coding-decoding process with sequence-defined cationic polymers.