Unraveling the architecture of plasma polymers by electrospray tandem mass spectrometry

Convenient visualization of high‐resolution tandem mass spectra of synthetic polymer ions using Kendrick mass defect analysis – the case of polysiloxanes

“…Three examples of KMD plots are proposed here as an alternative and convenient way to visualize the CID data of poly(siloxanes)a class of polymers of prime industrial importanceextensively commented on in other articles. [7] Those studies have highlighted the influence of the end-groups and charge state [8][9][10] or architecture of polysiloxanes [7,11] on their MS/MS fingerprints that are sometimes difficult to describe precisely. The chosen examples comprise the CID of a (trimethylsilyl, methyl)-ended polydimethylsiloxane ((SiC 3 H 9 , CH 3 )-PDMS) [8,10] from Polymer Standard Service (Mainz, Germany), a polycyclic (SiC 3 H 9 , CH 3 )-PDMS from a plasma polymerized hexamethyldisiloxane (PPHMDSO) [12] and an octakis(3-ammoniumpropyl) octasilsesquioxane ((nPrNH 2 )-POSS).…”

“…In spite of its simplicity and that of the associated KMD plotthis CID process has been previously presented as the archetypal MS/MS behavior of PDMS regardless of terminations and degree of polymerization. [7,8] It will thus allow a simple description of the KMD analysis. Figure 1(a) displays the ESI-MS/MS spectrum of the 24-mer adducted with one ammonium cation at m/z 1882.5.…”

“…Its fragmentation under CID produces a main b n + product ion series (according to the nomenclature proposed by Wesdemiotis et al [3] ) formed upon either the cleavage of the Si-O backbone and the release of ammonia and silanol neutral or the expulsion of ammonia and methane followed by chain depolymerization through the release of cyclic (SiOC 2 H 6 ) n neutrals. [7][8][9] The generic elemental composition of the so-formed b n + congeners (m/z 221.1, 295.1 and 369.1 in Fig. 1(a) with n = 2-4) carrying the initiating end-group is in the form of Fig.…”

“…Polysiloxane chains found in PPHMDSO have been described as polycyclic PDMS chains carrying trimethylsilyl and methyl terminations. [7,12] The ESI-MS/MS spectrum of the ammoniated 10-mer from a (SiC 3 H 9 , CH 3 )-ended polysiloxane distribution with four cyclic rings in its backbone is depicted in Fig. 2(a) with the generic structure of the precursor ion.…”

“…The polycyclic PDMS chains found in PPHMDSO could be conveniently seen as co-oligomers composed of DMS and cyclized DMS as repeating units. With no consideration of the ring size, cyclizing DMS units formally leads to the abstraction of two methyl groups and the addition of one oxygen atom to a linear SiO(CH 3 ) 2 unit, [7,12] i.e. a (hypothetical) SiO 2 repeating unit.…”