An innovative approach for the chemical structural characterization of poly(styrene 4-vinylpyridine) copolymers by matrix assisted laser desorption/ionization time of flight mass spectrometry

Poly(styrene-co-4-vinylpyridine) random copolymers with different molar composition were synthesized by nitroxide-mediated controlled-radical polymerization using 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide (TIPNO) as a mediator. We record the matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) spectra under various conditions, and we find (at last) that they show mostly intact ions [using 2(-4-hydroxyphenylazo-)benzoic acid as M ALDI matrix]. Spectra are highly resolved, and thus they allow for the determination of all end-groups, even some less-abundant ones. Spectra are dominated by intact "dorman t" copolymer chains terminated with TIPNO at one end and with (4-Bromo-phenyl)ethyl group (starting fragment) at the other one. Applying the mass analysis of copolymers (MACO) statistical model to the spectra, we show that the MACO/MALDI-TOF mass spectrometry (MS) analysis can be successfully applied to copolymers having a difference between the mass of the comonomers as small as 1 g mol -1 (the styrene and 4-vinylpyridine units are 104.15 and 105.15 g/mol, respectively), which results in overlapping isotopic patterns. The results are accurate: chemical composition evaluated by means of MS agrees with that calculated by 1H-nuclear magnetic resonance, for all copolymers investigated. This analytical method allows to extract detailed information on the composition of the copolymer samples and their structure. Glass transition temperatures of copolymers were also determined by differential scanning calorimetry.