Structural characterization of hyperbranched polyesteramides: MS n and the origin of species Sander Koster a , Chris G. de Koster b , Rolf A.T.M. van Benthem b , Marc C. Duursma a , Jaap J. Boon a , and Ron M.A. Heeren a,* a Unit for Macromolecular Mass Spectrometry, FOM-Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ, Amsterdam, The Netherlands b DSM Research, P.O.Box 18, 6160MD Geleen, The Netherlands Received 14 December 2000; accepted 28 January 2001 Abstract Four hyperbranched synthetic polyesteramides were synthesized by the polycondensation of the trifunctional diisopropano- lamine (D) and difunctional anhydrides (X) of succinic acid, glutaric acid, 1,2-cyclohexane dicarboxylic acid, and phthalic acid. The polymers were analyzed with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The most intense oligomer series observed was X n D n+1 containing diisopropanolamine end groups as expected from the polycondensation conditions. A series of oligomers X n D n+1 ™H 2 O is observed as well, which can have its origin in the polymerization process or alternatively could result from in-source fragmentation of X n D n+1 . Breakdown diagrams of the protonated parent ions X 3 D 4 and additional MS n (n = 1, 2, 3) measurements gave insight in the fragmentation behavior of the polymers. Three main fragmentation pathways have been observed for all polymers of which the loss of H 2 O to oxazolonium ions has the lowest onset energy followed by the rearrangement of the amide and ester bonds also leading to oxazolonium ions. The loss of a second H 2 O to allylic or morpholine end groups has highest onset energy. MS 3 experiments demonstrated that the presence of a series of oligomers X n D n+1 ™H 2 O can be attributed to the polymerization process. Most probably an allylic end group has formed from one of the alcohol end groups. The formation of allylic end groups partly terminates the polymerization reaction and results in a change of the composition of the molecular weight distribution and decrease of the number average molecular weight. (Int J Mass Spectrom 210/211 (2001) 591– 602) © 2001 Elsevier Science B.V. 1. Introduction Soft ionization techniques for synthetic polymer characterization like matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) have become widely used in mass spectrometry mainly because intact protonated or cationized molec- ular ions are generated [1– 6]. This makes a determi- nation of the monomer and end group mass by linear regression easy [7–9]. Sequence information of co- polymers can be obtained with postsource decay (PSD) and collisionally activated dissociation (CAD) studies in sector and time-of-flight instruments and ion traps like Fourier transform ion cyclotron reso- nance (FTICR) [10 –12]. Most studies concern linear polymers although some branched polymers have been successfully analysed [13–17]. An example of a * Corresponding author. E-mail: heeren@amolf.nl 1387-3806/01/$20.00 © 2001 Elsevier Science B.V. All rights reserved PII S1387-3806(01)00416-X International Journal of Mass Spectrometry 210/211 (2001) 591– 602 www.elsevier.com/locate/ijms