Molecular Weight Dependent Fragmentation of Selectively Deuterated Polystyrenes in ToF−SIMS

Abstract

Two series of monodisperse polystyrenes were synthesized by an anionic polymerization initiated with sec-butyllithium. The number average molecular weights of the macrochains range from 1700 to 93300. The first series consist of deuterated repeat units and hydrogenated end groups (sec-PD8S−H). The other one was fully hydrogenated except for one end group, which was selectively deuterated (sec-PS−D). The sample molecular structures are C4H9(C8D8) n H and C4H9(C8H8) n D, respectively. These polymers were then analyzed by time-of-flight secondary ion mass spectrometry (ToF−SIMS). All secondary ion intensities are corrected for the carbon and deuterium isotopic distributions. Static SIMS spectra of sec-PD8S−H show characteristic peaks with even masses (fully deuterated, i.e., C7D7 +, C6D5 + at m/z = 98, 82) and odd peaks (containing at least one hydrogen atom, i.e., C7HD6 +, C6HD4 + at m/z = 97, 81). Typically, these odd peaks show decreasing intensities as the molecular weight increases. In the sec-PS−D SIMS spectra, the characteristic peaks are similar to those observed for the usual polystyrene with a more specific peak at m/z = 92 which is related to the deuterium end group. From the molecular weight dependent intensities, it can be deduced that a hydrogen transfer occurs from the sec-butyl end group to the first repeat unit and promotes the formation of the tropylium fragment. A rearrangement ion formation mechanism is proposed. For both polymers, characteristic peaks of the end group are detected. With the intensity ratios of a main chain fragment and these end groups characteristic peaks, we are able to calibrate the number average molecular weight at the polymer surface. Moreover, it is shown that the main chain deuteration influences the end group segregation toward the surface.

Investigation of molecular weight effects of polystyrene in ToF-SIMS using C60+ and Au+ primary ion beams

“…The first series of peaks More central to this study are the trends observed in moving from low to high molecular weight polymer samples. As observed in other studies of molecular weight trends of polystyrene polymer systems, the intensity of the ions under investigation decrease with increasing molecular weight [16][17][18]. However, the degree of intensity loss over the molecular weight range is different when the systems are analyzed with the Au + or C 60 + primary ion source.…”

“…The depth profiling was performed at room temperature. [16][17][18]26,27]. The spectral data from m/z 5 to 250 shows a typical enhancement of ion intensities as a consequence of using a polyatomic source over a monoatomic source, which ranges in enhancement from 50-to 500-fold.…”

“…Polystyrene (PS) was chosen as the first in a series of polymers investigated both because of its commercial viability and the wide range of molecular weights that can be synthesized with low polydispersity. PS has been previously investigated to determine the effects of molecular weight on the SIMS data of polymers using monoatomic sources of Ar + and Ga + [16][17][18]. Polystyrene has also been investigated with polyatomic primary sources both experimentally [2,3,9,14,[19][20][21] and with molecular dynamic simulations [22,23], although molecular weight effects were not the primary investigation in those studies.…”

Study of the end‐group contribution to ToF‐SIMS and G‐SIMS spectra of poly (lactic acid) using deuterium labelling

“…18,19 In this study, PLA oligomer and polymer end-groups are deuterated according to Scheme 1, 20 and compared to non-deuterated PLA to observe the end-group contribution on the surface of the PLA. Similar studies using deuterium labelling have been reported/performed by Shard et al 20 on poly (ethylene glycol) and Vanden Eynde et al 21 on polystyrene. We also use G-SIMS to demonstrate that end-group ions result from a low energetic process (a low T p ), consistent with the requirement for only one bond to be broken to liberate an end-group fragment (main chain fragments require two or more bond scissions).…”

ToF‐SIMS for the characterization of hyperbranched aliphatic polyesters: probing their molecular weight on surfaces based on principal component analysis (PCA)

“…These methods were used to probe the molecular weight of monodispersed poly(methylmethacrylate) (PMMA) 36 and polystyrene standards. 37,38 In this frame, Vanden Eynde et al also proposed a model of the ion intensity dependencies with the M n of polystyrene polymer chains, which accounted for the influence of end-groups. An effect of the molecular weight was observed up to 130 000 Da.…”