Structural characterization of a poly(methacrylic acid)/poly(methylmethacrylate) copolymer by activated electron photo-detachment dissociation

Tandem mass spectrometry of co-oligomers composed of methacrylic acid (MAA) and methyl methacrylate (MMA) units was performed after activated electron photo-detachment dissociation (activated EPD). In this technique, doubly charged MAA/MMA co-oligomers were first produced in negative mode electrospray ionization. Species produced upon electron photo-detachment (220 nm) of these doubly charged co-oligomers were observed to spontaneously eliminate a carbon dioxide molecule. The so-formed radical anions were then activated by collision. In contrast to CID of negatively charged MAA/MMA co-oligomers, which does not provide informative data with regards to the end-groups, activated EPD is shown here to promote efficient radical-induced dissociation reactions thanks to the oxidation of a carboxylate pendant group upon laser irradiation. Product ions generated after backbone bond cleavages only contained the anionic initiating group. Combining these MS/MS results with the sum of the end-group masses determined from MS data allowed the terminating group to be characterized. As compared to activated EPD data obtained for a PMAA homopolymer holding the same end-groups, an additional product ion series was generated in the case of MAA/MMA copolymers, strongly suggesting that the hydrogen bond network established between neighboring MAA monomers is disrupted when MMA units are inserted in the polymeric backbone.

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► Activated EPD of MAA/MMA oligomers was investigated.
► Radical-induced backbone cleavages allowed each end-group to be mass-characterized.
► Activated EPD is a useful alternative to CID for MAA/MMA copolymer.