The CID spectra of M⁺PSn exclusively shows small M⁺-fragment ions containing each end group of the oligomer (A₁, A₁, A₁, B₁, B₁, B₁, see CID Results Section) but the theoretical results show no evidence that the M⁺ cation prefers to be near the ends of the oligomer. So, the question is how are small A₁, A₁ and B₁, B₁ fragments formed?
     The most likely answer, and one that has been published (see the references listed in the CID Results Section), is that the PS oligomer is randomly cleaved along the backbone and then rapidly depolymerizes to each end. This mechanism was also proposed for PMMA but the theoretical results for this system indicated that the M⁺ cation preferred to remain with larger fragments and so depolymerization would be an energetically uphill battle. The M⁺PMMAn structures were also determined to be U-shaped which led to another possible fragmentation mechanism. For M⁺PSn, there is no energetic preference for M⁺ to remain attached to larger fragments as seen in the calculated M⁺-PSn binding energies. This consistency in binding energy is most likely due to the fact that the metal cation only interacts with two phenyl groups and any additional styrene units has little effect on the M⁺-PSn interaction. Thus, each depolymerization step is likely to be thermoneutral and high-energy collisions with the buffer gas during the CID experiments should be more than enough to induce successive depolymerization steps.