Block length determination of a poly(ethylene oxide)-b-poly(p-phenylene ethynylene) diblock copolymer by means of MALDI-TOF mass spectrometry combined with fragment-ion analysis

Post-source decay (PSD) experiments using a matrix assisted laser desorptio n/ionization time-of-flight; (MALDI-TOF) mass spectrometer have been applie d to the structural determination of a poly(ethylene oxide)-b-poly(p-phenyl ene ethynylene) diblock copolymer (PEO-b-PPE). After desorption of the inta ct copolymer molecules, chains with a defined mass are selected and undergo fragmentation. By use of appropriate experimental conditions, the fragment -ion mass spectra reveal a main cleavage of the copolymer chain between the two blocks. The length of each block thus can be clearly determined. This is especially important in the case of copolymer chains with nearly the sam e nominal masses but different copolymer compositions, which can be analyze d unambiguously by their fragment ions. This investigation is the first rep orted structural determination of a diblock copolymer by means of fragmenti on analysis carried out with MALDI, and even more complicated polymer struc tures can be expected to be determined that way.