Structural characterization of hyperbranched polyesteramides: MSn and the origin of species

Four hyperbranched synthetic polyesteramides were synthesized by the polycondensation of the trifunctional diisopropanolamine (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_nD_n+1 containing diisopropanolamine end groups as expected from the polycondensation conditions. A series of oligomers X_nD_n+1 - H₂O is observed as well, which can have its origin in the polymerization process or alternatively could result from in-source fragmentation of X_nD_n+1. Breakdown diagrams of the protonated parent ions X₃D₄ and additional MSⁿ (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 H₂O 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 H₂O to allylic or morpholine end groups has highest onset energy. MS³ experiments demonstrated that the presence of a series of oligomers X_nD_n+1 -H₂O 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.