Molecular level differentiation between end-capped and intramolecular azofunctional oligo(ε-caprolactone) positional isomers through liquid chromatography multistage mass spectrometry

End‐capped and intramolecular azofunctional oligocaprolactones were characterized at molecular level by liquid chromatography electrospray ionization mass spectrometry (ESI MS) and NMR spectroscopy. The Disperse Red 19 (DR19) azofunctional oligomers, DC, were synthesized by ring‐opening oligomerization of ε‐caprolactone (ε‐CL) initiated by the hydroxyl groups of DR19 azo dye. The reaction products consist of a minor fraction of end‐capped azo functional oligocaprolactone (α‐DC), that is, a single CL arm oligomer, and a major fraction of intramolecular azo functional oligocaprolactone (β‐DC), that is, a two CL arms oligomer. The chromatographic separation was used to discriminate between α‐DC and β‐DC, and the results were confirmed by MS/MS performed on an ESI ion trap instrument. The results supported by accurate mass data obtained for product ions using an ESI quadrupole time of flight instrument demonstrate the qualitative discrimination at the molecular level between intramolecular and end‐capped azofunctional oligoesters isomers through a relatively simple multistage mass spectrometry experiment. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 DR19 azofunctional oligocaprolactone were prepared through ring ring‐opening oligomerization. The obtained products were a major fraction of in‐chain functionalized oligomer and a minor fraction of end‐capped oligomers. This was evidenced by NMR, HPLC with UV‐–vis detection supported by electrospray ionization mass spectrometry ESI (MS). Moreover, liquid chromatography (LC) MS/MS analysis allowed differentiating the positional isomers at molecular level based on their unique fragmentation patterns.