Quantification of polystyrene blend surfaces based on end group ToF-SIMS analysis

In this work, two sets of low molecular weight polystyrene blends were studied. The first one is composed of two polystyrenes with, at one end, tertiary or secondary butyl end group (sec- and tert-) and hydrogen end group (-H) at the other end. ToF-SIMS spectra show a linear dependency with bulk concentration. Due to the slight difference of molecular structures between sec- and tert-butyl end group, no difference of surface free energy and surface state is expected. Then, the observed linear dependency implies that the matrix effect is insignificant. The second set of polymer blends are composed of polystyrenes with, at one end, tertiary or secondary butyl end group (sec- or tert-) and at the other end, hydrogen (-H) or trimethyl silyl (-Si(CH3)(3), TMS) end group, respectively. With the results from the first set of blends, we were able to quantify the sec-PS-Si concentration at the surface as compared to the bulk, using univariate and multivariate techniques. The different methods establish that all these polystyrene blends present a bulk-like surface. The principal component analysis (PCA) seems to be interesting for the study of ternary polymer blends. (C) 1999 Elsevier Science B.V. All rights reserved

Combined XPS and ToF-SIMS study of miscible polymer blend surfaces: Polystyrene/poly(2,6-dimethyl-1,4-phenyl oxide) (PS/PDMPO)

The influence of polystyrene concentration in polystyrene and poly(2,6-dimethyl-1,4-phenylene oxide) (PS/PDMPO) miscible polymer blends has been studied by the combined techniques of x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The O 1s/C 1s ratio in SPS and the peak intensities of characteristic fragments in ToF-SIMS are found to be linearly dependent on bulk concentrations. Angle-resolved x-ray photoelectron spectroscopy measurement does not show any concentration profile from the surface to the bulk. Both techniques confirm that the polymer surface concentrations are directly related to the bulk concentrations. Possible explanations for this absence of segregation are discussed. Copy-right (C) 1999 John Wiley & Sons, Ltd

Static SIMS spectra of polystyrene obtained by 'living' radical polymerization - Part II: Molecular weight quantification based on end groups

A series of low-polydispersity polystyrenes with molecular weight ranging from 2000 to 130000 synthesized by atom transfer radical polymerization were analyzed by time-of-flight secondary ion mass spectrometry. The polymer end groups obtained by this polymerization process are hydrogen at one end and bromide at the other end. The great sensitivity of these end groups towards the ion beam-induced emission yield of secondary ion fragments allows the direct quantification of the molecular weight of the polystyrene at the surface. However, before applying any quantification method, several steps have to be performed: the peak assignment of the characteristic end group fragments and the choice of the spectrum normalization method. The influence of two normalization procedures is compared for two quantification methods-the characteristic peak intensity ratios and a chemometric method (principal component analysis)-in order to achieve molecular weight determination of the polystyrene at the surface. It is shown that, depending on the normalization procedure used, very different results can be obtained for both quantification methods. The validity of the procedures is also discussed. (C) 1998 John Wiley & Sons, Ltd

"Matrix" effects in ToF-SIMS analyses of styrene-methyl methacrylate random copolymers

Surfaces of several styrene (St)-methyl methacrylate (MMA) random copolymers have been analyzed by ToF-SIMS and XPS in order to detect any possible surface segregation of one of the two components and/or any specific matrix effect in the fragmentation processes. The observed O/(O + C) dependency on styrene content observed by XPS indicates that styrene-methyl methacrylate copolymers exhibit bulklike surfaces over the entire composition range of the copolymer. The absolute intensity of characteristic peaks from styrene or methyl methacrylate units was monitored by ToF-SIMS as a function of the styrene content. In positive mode, hydrocarbon fragments such as CH3+, C2H3+, C2H5+, C5H5+, and C7H9+ at m/z = 15, 27, 29, 65, and 93, respectively, decreased with increasing styrene content, while the intensities of MMA fragments decreased. All fragments exhibited intensity lower than that expected from a simple linear combination calculated from intensities associated with the MMA. and St homopolymers. By contrast, some characteristic styrene peaks (such as C5H3+, C7H7+, C8H7+, and C8H9+ at m/z = 63, 91, 103, and 105, respectively) showed an absolute intensity higher than those observed for PSt and PMMA. In negative mode, fragments such as OH- and C2HO- at mit = 17 and 41 exhibited linear dependence with styrene content at the surface. Intensities for other MMA characteristic fragments such as C3H3O-, C4H5O2-, C8H13O2-, and C9H13O4- at mit = 55, 85, 141, and 185, respectively, strongly decreased with increasing styrene content. These experiments as well as previous work on polystyrenes show that specific interactions between adjacent species take place during secondary ion emission, especially for the C7H7+ fragment

Molecular weight effects on polystyrene fingerprint time-of-flight secondary ion mass spectroscopy (ToF-SIMS) spectra

Monodisperse polystyrenes (PS) of different molecular weights (Mn) synthesized by living anionic polymerization with three types of butyllithium initiator (linear, n; secondary, sec; and tertiary, tert) were analyzed by ToF-SIMS (time-of-flight secondary ion mass spectrometry). The influence of the molecular weight on the secondary ion intensities was studied in detail for the fingerprint part of the mass spectra (with m/z < 200). A drastic effect was observed for Mn values below 104, related to the presence of the saturated butyl end group. An extra hydrogen transfer originating from this end group during the secondary ion formation must be invoked to explain the data. Only the first neighbor monomer repeat units seem to be affected. This H exchange increases the intensity of ions containing more hydrogen or needing H transfer for their formation as the tropylium ion (C7H7+ at m/z = 91). The molecular structure of the butyl end group is found to influence greatly not only the intensity of their parent ion but also the PS characteristic ion intensities. Indeed, the tert-butyl end group is seen unable to produce the H transfer observed for the n- and sec-butyl ones. A model is proposed to take the influence of the end group on the PS SIMS fragmentation pattern into account. The parameters of this model allow the quantification of the end group interaction

Influence of tacticity on polymer surfaces studied by ToF-SIMS

Poly(methylmethacrylate) (PMMA) and polystyrene (PS) thin films of different tacticities have been analysed by time-of-flight (ToF) SIMS in order to look for a possible influence of the stereoregularity on their fingerprint spectra (mlz ≤ 200). Because, at first glance, the spectra of samples with different tacticities seemed rather similar, the intensity ratios between secondary ions from main polymer chain and those from pendant group were evaluated. By this procedure, it was found that isotactic PMMA can be clearly distinguished from syndiotactic and atactic PMMA. A lower concentration of the methyl-methacrylate pendant group was detected at the surface of the isotactic sample. In the case of PS, more phenyl groups were found to be present at the surface of isotactic PS and an empirical criterion is proposed to differentiate between atactic and isotactic PS

Molecular weight dependent fragmentation of selectively deuterated polystyrenes in ToF-SIMS

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

Static SIMS spectra of polystyrene obtained by 'living' radical polymerization - Part I: Molecular weight-dependent fragmentation

A series of low-polydispersity polystyrenes with molecular weight ranging from 2000 to 130 000 were synthesized by atom transfer radical polymerization and analyzed by time-of-flight secondary ion mass spectrometry. The end groups obtained by this polymerization process were hydrogen at one end and bromine at the other end. The molecular structure of the end groups and the molecular weight of the chains were found to influence significantly the absolute intensities of the end-group parent ions and the characteristic polystyrene fragments. For their formation, two different mechanisms have to be taken into account: direct scission and rearrangement before the emission. The absolute intensities of the end-group fragments in positive and negative modes exhibit a decrease when the molecular weight decreases. The protonated repeat unit fragments ([M + H](+) or C8H9+ at m/z = 105) and bromide ions (Br- at m/z = 79 and 81) are produced by a direct scission mechanism of the respective end groups. Meanwhile, the tropylium ion intensity (C8H9+ at m/z = 105) increases for the low-molecular-weight (M-n) samples. This ion cannot be produced by a direct scission but a reorganization process of the polymer structure is required before the fragment emission. It is shown that, in static SIMS, the sensitivity towards the end group and then towards the molecular weight is dependent on the stability, the electroaffinity and/or the ionization potential of the ions formed from the end group. (C) 1998 John Wiley & Sons, Ltd