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 desorption/ionization time-of-flight; (MALDI-TOF) mass spectrometer have been applied to the structural determination of a poly(ethylene oxide)-b-poly(p-phenylene ethynylene) diblock copolymer (PEO-b-PPE). After desorption of the intact 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 same nominal masses but different copolymer compositions, which can be analyzed unambiguously by their fragment ions. This investigation is the first reported structural determination of a diblock copolymer by means of fragmention analysis carried out with MALDI, and even more complicated polymer structures can be expected to be determined that way.