Anal. Chem. 2006, 78, 3957
Mass Spectrometry of Synthetic Polymers Patricia M. Peacock and Charles N. McEwen*
DuPont Corporate Center for Analytical Sciences, Wilmington, Delaware 19880 Review Contents Scope Reviews MALDI Mass Spectrometry Electrospray Ionization Mass Spectrometry Secondary Ion Mass Spectrometry Pyrolysis (Py) Mass Spectrometry Other Mass Spectrometric Techniques Conclusion Literature Cited
3957 3957 3957 3960 3961 3961 3962 3963 3963
SCOPE This paper is a review of literature published on the subject of synthetic polymer analysis using mass spectrometry during the 2004-5 time frame. A wide array of papers was published during this period, illustrating the diverse applications of mass spectrometry (MS) for the analysis of synthetic polymers. MS has played an integral role in polymer characterization, polymeric surface analysis, polymer degradation studies, and understanding polymerization mechanisms. There were far too many publications to include them all; we have thus chosen those that we believe are representative of the genre. In addition to publications, numerous talks and posters on the topic of polymer mass spectrometry were presented during the time period. While these were informative for both the expert and novice alike, they are not within the scope of this review. We have categorized the publications reviewed in this article by ionization method in order to simplify perusal. There are several techniques for ionization that can be utilized for polymer analysis, and we hope to provide insight into the applicability of each. REVIEWS The previous review in this series covers the period 2002-3 and includes references to books, reviews, and publications dealing with mass spectrometry of synthetic polymers (1). Mass spectrometric methods such as matrix-assisted laser desorption/ ionization (MALDI), electrospray ionization (ESI), secondary ion mass spectrometry (SIMS), and gas-phase ionization by electron ionization or chemical ionization (CI) as applied to polymer characterization were referenced. Other reviews focusing on aspects of polymer characterization using MS have appeared during the period covered by the current review. Jagtap and Ambre published an overview of the literature regarding the application of MALDI MS to polymer characterization (2). In another review of MALDI MS as applied to polymers, Montaudo et al. discussed molar mass measurements and the study of thermal and oxidative processes using coupled size exclusion chromatography (SEC) and MALDI MS (3). In a review by 10.1021/ac0606249 CCC: $33.50 Published on Web 00/00/0000
© 2006 American Chemical Society
Barner-Kowollik et al., the utility of MALDI and ESI MS were discussed as tools for probing the mechanistic features of free radical polymerization with examples from conventional, nitroxidemediated, atom-transfer radical (ATR), reversible addition fragmentation chain transfer (RAFT), and catalytic chain-transfer (CCT) polymerizations (4). Hanton reviewed the use of MALDI and ESI MS for analyzing polymers of importance to coating applications (5). A few key areas of research in which mass spectrometry may advance the field of polymer characterization, especially as related to end groups and molecular weight distributions, were also reviewed during this period (6). The 2004 fall workshop of the American Society for Mass Spectrometry (ASMS) focused on mass spectrometry of synthetic polymers (7). Co-sponsored by the Polymers Division of the National Institute for Standards and Technology (NIST), this workshop was quite successful as it brought together leading experts in the field for tutorials and discussions. In 2005, NIST hosted the 4th annual Polymer MS workshop (8). The theme for this workshop was, “Future Directions in Soft Ionization of Polymers”. The format for this workshop was similar to those in 2002 and 2003, which was a mixture of invited talks, discussions, and problem solving. MALDI MASS SPECTROMETRY Several papers discussed sample preparation methods for MALDI-time-of-flight (TOF) MS analysis. Hanton et al. studied electrospray deposition as a means of preparing a MALDI target plate (9). This deposition was shown to be advantageous over hand spotting, because the accuracy of the molecular weight distribution (MWD) and data reproducibility were much improved. Wetzel et al. investigated the effect of electrospray voltage during deposition onto a MALDI target plate, using poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), and polystyrene (PS) (10). MWD was not affected by voltage for polystyrene; however, this was not the case for the other two analytes, because of fragmentation issues. This study also found that the choice of matrix affects fragmentation for hand-spotted samples. Woldegiorgis et al. utilized new matrixes based on oligomers of dioxin and thiophene for polymer-assisted laser desorption/ionization (PALDI) of low molecular weight PS and PEG (11). Below 1500 amu, PALDI produced higher signal-to-noise ratios than traditional MALDI matrixes. The paper recommended using mathematical modeling for comparison of MWDs of synthetic polymers when using MALDI. Blair et al. studied high-throughput MALDI-TOF MS of synthetic polymers, including combinatorial sample preparation and automated data analysis (12). Similarly, Enjalbal et al. discussed the possibility of using ESI and MALDI for highthroughput MS of PEG and other synthetic polymers (13). Analytical Chemistry, Vol. 78, No. 12, June 15, 2006 3957
Hanton and Parees simplified the solventless sample preparation method for MALDI-TOF MS analysis by introducing a vortex method for grinding the analyte, cationization reagent, and matrix (14). Instead of using a mortar and pestle or a ball mill, Hanton used two BBs in a small glass vial and a common laboratory vortex device. The results of this preparation in combination with loose powder transfer to the MALDI target were comparable to the previously published solventless preparation methods and avoided contamination and carryover of prior samples. The method requires only a small amount of sample, generally on the order of 0.5 mg of analyte and 50 mg of matrix. Taguchi et al. used solventless sample preparation to study an oligomeric hindered amine light stabilizer (HALS) in polypropylene by MALDI-TOF MS (15). The study monitored the changes in structure with UV irradiation, hoping to shed light on how these changes may ultimately effect the stability of the polypropylene. Although there were a number of papers on analysis of HALS during the time period covered here, this paper was unique because of its novel use of solventless preparation. Gies and Nonidez promoted the use of wet-grinding preparation for the analysis of Nomex and Kevlar polyaramids using MALDI-TOF MS (16). Similarly, Ellison et al. utilized the evaporative grinding method to prepare partially soluble analytes for MALDI-TOF MS (17). In this paper, the analyte was poly(p-phenyleneethynylene), which is used to disperse single-walled carbon nanotubes in polymers. Murgasova et al. proposed reacting polyimides to make them more amenable to MALDI-TOF MS analysis (18). Okuno et al. were able to quantify PPG mixtures using MALDITOF MS and desorption/ionization on silicon (DIOS) MS (19). MALDI mass spectra varied with analyte/matrix ratio, as well as the matrix and solvent used. DIOS mass spectra varied with analyte concentration and solvent. While both ionization methods produced acceptable spectra when preparations were optimized, DIOS was recommended over MALDI-TOF MS for this type of analysis. Arakawa et al. compared analysis of DIOS MS of lowmass polyesters with MALDI-TOF MS analyses (20). The MALDI matrixes chosen for the experiments were R-cyanohydroxycinnamic acid and 10,15,20-tetrakis(pentafluorophenyl)porphyrin. DIOS MS yielded better signal-to-noise ratios and no interference at low mass. Seino et al. also endorsed the use of DIOS MS (21). This paper discussed using DIOS for the determination of MWD more accurately and with less background interference than with MALDI. A number of publications furthered our fundamental understanding of the MALDI process and all that it entails. Mourey et al. studied mass discrimination effects in MALDI-TOF MS using several narrow poly(methyl methacrylate) (PMMA) standards and one broad PMMA standard (22). When compared with SEC, MALDI did not observe the dimer and trimer and discriminated against higher masses of PMMA. Polydispersity (PD) values of the two techniques did not correlate; however, standard deviation calculated from the PD and number average molecular weight agreed. Another paper discussing mass discrimination came from Mineo et al (23). This group investigated the affect of instrument parameters on molar mass distribution of polydisperse PEG and a blend of PEG/PMMA. Discrimination depended on grid voltage and delay time. Guttman et al. summarized an interlaboratory comparison of MALDI-TOF MS analyses of binary mixtures of 3958
Analytical Chemistry, Vol. 78, No. 12, June 15, 2006
PS with different end groups (24). This involved statistical analysis of mass fractions and mass moments. Data were collected from 14 laboratories, and it was found that the laboratory and type of MALDI instrument had a major influence on the data. Operator errors (e.g., poor calibration, poor optimization causing poor signal-to-noise ratios, poor baseline subtraction) also played a big role. However, choice of matrix and detector (linear vs reflectron) did not have much effect. Zhang et al. found that mass spectra changed dramatically depending on the matrix used when analyzing six different derivatives of poly(phenylenevinylene) (25). Different ion series, changes in peak intensities, or both occurred with different matrixes. Terrier et al. also found that the choice of matrix had a significant impact on the MALDI mass spectrum (26). In their study of triblock copolymers of poly(ethylene oxide) and poly(propylene oxide), the mass spectrum was also affected by the relative amount of cation used and the number of laser shots. In addition, they observed that the composition of the spot on the target plate depended on the matrix. 2,5-Dihydroxybenzoic acid and high Na+ content caused layering of the spot, while use of dithranol or low salt content did not produce layering. The above papers discussing mass discrimination and dependence of spectra on multiple factors have demonstrated significant limitations when using MALDI-TOF MS for determining quantitative information. Chen and He showed that quantitation is possible, however, when all of the components are similar in structure and they are low molecular weight, narrowly dispersed oligomers (27). Their study successfully quantified a mixture of PEGs with different end groups, using methyl-PEG as an internal standard. Other publications gave us insight into cationization in MALDI. Shimada et al. studied the cation affinity of PEG oligomers using five different cations and found that smaller oligomers prefer smaller cations (28). The study also included molecular dynamics simulations to calculate cation affinity for the different cations. Affinity was affected by degree of polymerization and type of cation. A paper from Jackson et al. also deduced that smaller cations such as sodium and lithium ionized smaller chains of poly(butyl methacrylate) (PBMA) and PMMA more efficiently, while larger cations worked better for higher mass chains (29). This study utilized data from MALDI collision-induced dissociation (CID) and ESI-MS/MS for end group identification and sequence information. Hoteling et al. investigated the solubility of matrix with analyte using high-performance liquid chromatography (HPLC) to aid in the preparation of MALDI samples (30). Matrixes that eluted at times similar to that of the polymer in HPLC produced strong signals in MALDI. In contrast, those matrixes and analytes with significantly different HPLC retention times yielded poor MALDI mass spectra. Thus, the study proposed using HPLC retention times for matrix selection for MALDI-TOF MS analysis of unknowns. The same group also examined the significance of solubility in the analysis of poly(ethylene terephthahlate) (PET) (31). Poor spectra were observed when the analyte was not completely in solution. Pure solvent and solvent blends were utilized in the study. As in the previous paper, the highest quality spectra were obtained when the matrix used had HPLC retention time similar to the analyte.
Several laboratories exploited the strength of combining separation techniques with MALDI-TOF MS for polymer chanracterization. Al-Jareh et al. analyzed a polydisperse fluorosurfactant using capillary electrophoresis/MALDI, MALDI, and ESI (32). Cheguillaume et al. utilized MALDI, ESI, liquid chromatography (LC), and LC/MS to characterize a mixture of three PEG surfactants (33). Weidner et al. identified the end groups of modified polyamide 6,6 using LC/MALDI-TOF MS (34). Liu et al. analyzed poly(dimethyl siloxane) (PDMS) with UV-curable end groups using gel permeation chromatography (GPC)/MALDITOF MS (35). Separation was needed in this case due to overwhelming fragmentation at low mass. Separation also allowed an impurity to be observed that could be identified and quantitated. Basile et al. directly connected thermal field flow fractionation to a MALDI target plate, which facilitated continuous deposition of analyte via an oscillating capillary nebulizer (36). It is also helpful to supplement MALDI-TOF MS data with that from other analytical techniques, such as nuclear magnetic resonance (NMR). There were a number of publications illustrating this advantage. Colomines et al. utilized MALDI-TOF MS in combination with NMR, SEC, and thermogravimetric analysis to study the structure of PET that had been glycosylated by oligoesters (37). MALDITOF MS, NMR and differential scanning calorimetry allowed Samperi et al. to characterize copolymers made from the reactive melt mixing of polyamides (38). MALDI-TOF MS was applied extensively for the investigation of polymerization reactions. By itself or combined with separations and other analytical methods, this technique provided valuable insights. Kona et al. studied the epoxidation of polyisoprene and polybutadiene with MALDI-TOF MS and used GPC/MALDI for higher mass samples (39). Ji et al. examined the living anionic polymerization of primary amine-terminated polymers with MALDITOF MS (40). SEC and MALDI-TOF MS provided complementary information on poly(butyl cyanoacrylate) nanoparticles in a study by Bootz et al. (41) However, the MWD as determined by MALDITOF MS was lower than by SEC, even when coupled with SEC offline. This paper also reported the influence of pH on the degree of polymerization and the uniformity of the nanoparticles. Their highest yield occurred at pH 1. Mazzaglia et al. utilized both MALDI and ESI to characterize poly(amidoamine)-platinum(II) complex reaction products (42). Jayakannan et al. employed MALDI-TOF MS to study the effect of catalyst and reaction conditions on the end group composition of regioregular poly(3octylthiophene)s (43). The MS data were complemented by NMR data, which showed it was regioregular, and SEC, which provided the degree of polymerization. Kricheldorf et al., however, only needed MALDI-TOF MS to determine reaction mechanisms and study the effect of different initiators on the polymerization of pivalolactone (44). Quirk et al. employed MALDI MS to study the polymerization of 1,3-cyclohexadiene using different initiators (45). Somogyi et al. synthesized two similar low-mass copolymers and analyzed the products using MALDI-TOF MS (46). The only difference between the two copolymerizations was that one used 3-hydroxybenzoic acid (3-HBA) and the other used 4-hydroxybenzoic acid (4-HBA). The copolymer with 3-HBA was found to be stable; however, the product with 4-HBA showed evidence of degradation by MALDI. Arnould et al. used MALDI-TOF MS to
compare the efficiency of chain end functionalization techniques in living anionic polymerizations (47). The study found that the use of functionalized initiators were not as effective as postpolymerization reactions, which provided better control of functionalization. Campbell et al. combined MALDI-TOF MS data with preparative GPC coupled with 13C NMR to determine the hightemperature polymerization mechanism for styrene synthesis (48). The study found that the dominant branching mechanism occurred with cyclization to the third or fifth carbon, followed by β-scission. MALDI-TOF MS also provided the distribution of unsaturated ends. Gies et al. found MALDI-TOF MS to be useful for monitoring the conversion of poly(amic acid) to polyimide (49). The experiment included studying the products formed at various thermal intervals, as well as mass growth and end group composition. Gas chromatography/mass spectrometry (GC/MS) was used to identify gas trapped during vapor deposition as monomer. The critical temperature of imidization was reported to be 130-160 °C. In a study by Bednarek and Kubisa, MALDI-TOF MS enabled the determination of functionality and number of bromine atoms in each molecule of a macroinitiator for atom-transfer radical polymerization, which was made from a highly branched, hydroxylated polymer (50). D’Agosto et al. polymerized a saccharidic monomer via living cationic polymerization and formed aldehyde ends (51). The ends were then functionalized and the product was characterized by MALDI-TOF MS and NMR. Mezlova et al. employed MALDI-TOF MS to characterize electropolymerization synthesis products (52), and Gies used the technique to determine the distribution of end groups and cyclic oligomers in several poly(m-phenyleneisophthalamide)s (53). MALDI-TOF MS monitored the growth of the second block of PS-block-polyisoprene, in a study by Willemse et al. (54). Discrimination due to differences in ionization efficiencies was not observed. Lee et al. reported that MALDI-TOF MS and NMR yielded insight into a novel synthesis route to star polymers (55). MALDI-TOF MS and NMR were also utilized by Ameduri et al. to characterize the synthesis of vinylidene fluoride telomers (56). The experiments furthered the understanding of the reaction mechanism and observed regioselectivity. Ray et al. employed MALDI-TOF MS and NMR to determine chain ends in the RAFT polymerization of poly(Nisopropylacrylamide)s (PNIPAMs) (57). Mechanisms of degradation and fragmentation were determined by several labortories using MALDI-TOF MS. Schulte et al. reported an observation that in mass spectra of PNIPAMs using ESI and MALDI MS, only the MALDI Fourier transform ion cyclotron resonance MS results showed chain-end degradation of nitroxide-terminated oligomers (58). A mechanism for chainend degradation was proposed. Rizzarelli et al. used MALDI-TOF/ TOF-MS/MS to acquire structural information on poly(ester amide)s and post source decay-MALDI-TOF MS to gain insight into fragmentation mechanisms (59). The experiments led to the conclusion that main cleavage occurs via β-H transfer rearrangement. Carroccio et al. published two papers using MALDI-TOF MS data to deduce photooxidation mechanisms for nylon 6,6 and poly(butylene succinate) (60, 61). Samperi et al. used MALDITOF MS to investigate the degradation of PET at high temperatures (62). MALDI-TOF MS provided evidence of cyclic oligomers and aldehyde-containing oligomers. NMR confirmed these data Analytical Chemistry, Vol. 78, No. 12, June 15, 2006
3959
and also showed evidence of acetaldehyde. From the MALDITOF MS data, it could be concluded that the addition of p-toluenesulfonic acid caused hydrolysis of PET and a higher abundance of carboxyl-terminated polyester chains. Samperi et al. used the same methodology to study thermal degradation of poly(butylene terephthalate) (PBT) as well (63). Wollyung et al. synthesized a rotaxane made up of MC-12 crown ether and an end-capped poly(tetrahydrofuran) (64). This rotaxane, analyzed using MALDI-TOF MS, showed a small amount of rotaxane and larger amounts of the individual rotaxane components. Unfortunately, GPC did not produce any information because the rotaxane and the MC-12 crown ether coeluted. Several MALDI-TOF MS and ESI-quadrupole ion trap experiments showed that the rotaxane does not fall apart in MALDI, but it does ionize less efficiently than its subunits. HPLC showed 11% rotaxane and 89% subunits, which confirmed the MALDI-TOF MS data. Jaber and Wilkins saw significant fragmentation when analyzing hydrocarbons using conventional vacuum MALDI-TOF MS (65). However, with an external MALDI ion source, FTMS experiments yielded silver cationized oligomers up to 12 000 amu with no fragmentation. ELECTROSPRAY IONIZATION MASS SPECTROMETRY MALDI is a much more utilized technique for the characterization of intact synthetic polymer than ESI primarily because of the added complexity of multiple charging in ESI and the more stringent solvent requirements of ESI. Nevertheless, ESI has some important advantages over MALDI such as more readily available instrumentation for CID MS/MS studies and the ease of interfacing to liquid separation methods. Because ESI involves a continuous flow of liquid to the ionization region, it is also well suited for kinetic studies. Di Lena et al. used ESI to measure the rate constants for active species in the polymerization of ethylene by MAO-activated metallocene catalysts quenched with carbodiimides (66). The method looks to be general for this type of ZieglerNatta polymerization. Buback et al. used ESI for polymer end group analysis to follow the polymerization of methyl acrylate initiated by the thermal decomposition of various peroxypivalates (67). These authors identified the type and concentrations of fragments that initiated the polymerization following peroxypivalate degradation. Liquid separation methods coupled to ESI were used to study polymeric systems. In an interesting experiment, Watkins et al. used ion-molecule reactions to determine the number of functional groups on polyols and polyol mixtures by ESI MS and LC/ ESI-MS (68). Ions produced by positive ion ESI were allowed to react with diethylmethoxyborane in the gas phase, resulting in the derivatization of the hydroxy groups. The mass shift allowed determination of the number of functional groups present. Martinez et al. used LC/ESI-MS to look for the nonylphenol polyethoxylates and their metabolites in water (69). Interest in this type of material in water is due to evidence suggesting they may be estrogenic. SEC/ESI-MS was employed by Felderman et al. to determine the products from free radical RAFT-mediated acrylate polymerizations (70). The information provided insight into the RAFT process in acrylate free radical polymerization. Toy et al. also used SEC coupled to ESI-MS to study the strongly rate retarded RAFT polymerization of methyl acrylate (71). Neither of the above studies identified three- or four-armed star polymers 3960
Analytical Chemistry, Vol. 78, No. 12, June 15, 2006
in these polymerizations, suggesting that irreversible crosstermination reactions are of minor importance in these systems. ESI was also employed extensively with MS/MS to investigate various polymeric systems. Zhou et al. used ESI to study the products of tetrahydrofuran polymerization initiated by phosphorus oxychloride (72). Tandem ESI-MS was used to confirm the product structures. Dolan and Wood used ESI to characterize polyaniline up to the 9-mer and identified various end groups using MS/MS (73). ESI MS/MS of PMMA and PBMA was reported by Jackson et al. (29). These authors found that, for higher MW oligomers, ionization with higher mass alkali metal cations gave superior structural information, whereas for low MW oligomers, Na+ or Li+ was the favored cation for obtaining structural information. Adamus et al. used ESI and ESI MS/MS to characterize a series of copolyesters made from the bulk reaction of butyrolactone with 6-hydroxyhexanoic acid and 2-hydroxyhexanoic acid (74). The molecular structures including the chemical composition of the end groups were determined, and the arrangement of the comonomer units along the oligopolyester chain was verified by MS/MS. Collins and Rimmer used tandem ESI-MS to study poly(vinyl acetates) with either isopropylol or (1-hydroxyethyl)-2-oxyisopropanyl end groups (75). Comparing results obtained in this study with fragmentation patterns reported by Giguere and Mayer (76), Collins and Rimmer noted a strong influence of end group structure on the progress of CID. Yaun and Zhou used ESI and MSn (n ) 2-6) to study the fragmentation mechanism of polyamides containing N-methylimidazole and N-methylpyrrole (77). Wang et al. also studied the ESI fragmentation of a series of polyamides containing N-methylpyrrole and N-methylimidazole but in the negative ion mode (78). ESI of polyesters composed of isophthalic acid and neopentyl glycol produced carboxylate anions in the negative ion mode and Na+ cationized oligomers in the positive ion mode (79). Arnould et al. found that these polyester oligomers having different end groups fragment by similar mechanisms in the positive and negative ion modes but that anion fragmentation was the method of choice for determining block length, end group structure, and copolymer sequence so long as a carboxylic acid end group is present. The negative ion ESI MS spectra of dicarboxylated poly(ethylene glycol)s were reported by Franska et al. (80) These authors found that the ratio of the [M - 2H]2-/[M - H]abundances was effected by the chain length, solvent polarity, analyte concentration, and applied cone voltage. ESI MS was used along with MALDI MS by Schulte et al. to characterize the nitroxide-mediated free radical polymerization of N-isopropylacrylamide (58). Interestingly, they discovered degradation of the nitroxide-terminated polymer during MALDI analysis but apparently not during ESI analysis. Macromonomers consisting of a butyl acrylate tail and either R-methylstyrene or benzyl methacrylate unsaturated termini synthesized by CCT polymerization were characterized using ESI MS and NMR (81). Miyauchi et al. used hydrobromic acid hydrolysis to produce degradation products of poly(oxyethylene)-grafted nylon 6 and characterized these products using ESI MS and NMR (82). Guaratini et al. showed that the formation of radical molecular cations in ESI and MALDI MS for polyenes correlated with their oxidation potential (83). Murgasova et al. used N-ethanolamine and hydrazine as selective reagents to overcome solubility issues with certain polyimides
allowing characterization by MALDI and ESI in solvents friendly to these techniques (18). Prebyl and Cook used Fourier transform to deconvolute the unresolved envelope observed in the ESI mass spectrum of strongly ionic polymers (84). These authors were able to take ESI mass spectra made uninterpretable by the combination of polymer MW, charge, and isotope distributions and using Fourier transform analysis obtain monomer mass, charge distribution, and polydispersity. SECONDARY ION MASS SPECTROMETRY SIMS continues to be used extensively for characterization of polymer surfaces and for depth profiling. The application of polyatomic primary ions in static SIMS for the characterization of polymer surface layers received considerable attention. Specifically, SF5+ has been shown to provide a substantial increase in the secondary ion signal for some polymer types at low penetration depth and high damage removal rates. This combination of attributes was shown to improve depth profiling and quantitation. Wagner and Gillen studied ion beam damage as a function of impact energy of SF5+ on PMMA and found that, after a surface transient regime, characteristic ions from PMMA remained relatively constant (85). Increased impact energy increased the sputter rate with only a minor increase in surface damage. Wagner was able to show that, for PMMA, depth profiling using SF5+ depends only on the desired sputter rate (86). This is in contrast to use of Cs+ primary ions in which the secondary ion yield for PMMA decreases rapidly even at moderate primary ion doses. Comparison of the sputter rate for PMMA with that of poly(methyl acrylate) (PMA) and poly(methacrylic acid) (PMAA) showed that the damage rate for PMA and PMAA using SF5+ was higher than with PMMA and the sputter rate was lower (87). The results were consistent with radiation damage studies of these polymers in which removal of the main chain or pendant methyl groups reduced the rate of depolymerization and increased the rate of cross-linking. In a companion study, SF5+ ion beam damage was studied for poly(n-alkyl methacrylates) to determine the effect of alkyl pendant group length (88). In this study, the sputter rate and stability of characteristic secondary ion yields decreased linearly with the alkyl pendant group length. Studies were carried out to assess the damage inflicted by SF5+ ion bombardment to thick films of poly(2-hydroxyethyl methacrylate) (PHEMA) and PHEMA derivatized with trifluoroacetic anhydride. The ion-induced damage accumulation rate and sputter rate for PHEMA was found to be similar to poly(n-alkyl methacrylate) polymers with similar pendant group length but was much higher for PHEMA derivatized with trifluoroacetic anhydride (89). Wagner also conducted a dual-beam TOF SIMS experiment using 5-keV SF5+ as the sputter ion and 10-keV Ar+ for analysis of a multilayer spin-cast film composed of PMMA, PHEMA, and PHEMA derivatized with trifluoroacetic anhydride (90). Characteristic positive and negative secondary ions were observed and showed that sputter rates and surface damage are dependent on the order of the polymers in the multilayer. Boschmans et al. characterized thin layers of polylactic acid (PLA) using Ga+, Xe+, and SF5+ primary ions (91). Relative to Ga+, Xe+ and SF5+ gave 1.5-2- and 7-12-fold increases in structural ions, respectively. In a depth profiling study of PLA/poly(ethylene
oxide-co-propylene oxide) triblock copolymer, Mahoney et al. found using static SIMS that SF5+ primary ion bombardment allowed quantitation for the first time as a function of depth for a multicomponent blend (92). Van Royen et al. compared Ga+ primary ion bombardment in static SIMS with polyatomic SF5+ bombardment of various spin coated thick film poly(-caprolactone) (PCL), poly(butylene adipate) (PBA), and poly(ethylene adipate) (PEA) polyesters (93). These authors report an increase in structurally relevant secondary ions with polyatomic versus Ga+ bombardment of 10×, 30×, and 10× for PCL, PBA, and PEA, respectively. Static and dynamic SIMS was applied to a number of polymer characterization studies using atomic primary ion beams. Oran et al. used static SIMS to study pulsed plasma-deposited styrene and ethylene films in order to obtain chemical information before and after exposure to air (94). They found that films with higher regularity had lower oxygen uptake. Static SIMS was compared with X-ray photoelectron spectroscopy as a means of characterizing PDMS-contaminated PS films (95). Ultrasonication in hexane was found to be an effective way of removing PDMS contamination. Kim et al. used a surface derivatization technique to quantify the surface density of amine groups in ethylenediamine films polymerized on glass using inductively coupled plasma (96). Surfaces derivatized with 4-nitrobenzaldehyde or pentafluorobenzaldehyde gave a linear correlation between UV-visible measurements and the results from static SIMS. Static SIMS was used by Norrman et al. to observe chemical changes on the surface of poly(ether sulfone) ultrafiltration membranes after photoirradiation (254 nm) in a nitrogen atmosphere (97). They observed that at higher irradiation doses cross-linking is dominant and at low irradiation doses chain scission dominates. Multvariate statistical analysis was used to demonstrate that 11 polymers could be identified from databases containing noncharacteristic secondary ions measured under steady-state SIMS conditions (98). Van Gennip et al. showed that all 11 polymers could be identified using principle component analysis (98). Segalman et al. used dynamic SIMS to measure the diffusion of deuterium-labeled atactic PS from the surface of a polydisperse isotactic PS (99). Dynamic SIMS was also used by Bulle-Lieuwma et al. to characterize photoactive films of poly(p-phenylenevinylene)/methanofullerene blends (100). A dynamic increase in phase segregation on a submicrometer level was observed using imaging TOF-SIMS. PYROLYSIS MASS SPECTROMETRY Thermal methods combined with mass spectrometry or with GC/MS continue to be an active method for characterization of polymers and for identification of additives and contaminants. Pyrolysis (Py) is the method most frequently employed, but lower temperature and slower heating rates are sometimes used to advantage. Thermal methods are especially important for characterizing solubility-intractable polymers and additives/pendant groups that cannot be readily dissolved, extracted, or hydrolyzed. An especially interesting example of the use of thermal methods for the analysis of additives was provided by Boutin et al. (101). These authors used temperature-programmed heating to liberate additives in polymers and metastable ion bombardment ionization MS to obtain molecular ion information with minimal fragmentation. Hsu et al. combined Curie point Py with ESI as a novel means Analytical Chemistry, Vol. 78, No. 12, June 15, 2006
3961
of observing the polar components in pyrolysates (102). By pyrolyzing polymer standards near the tip of an electrospray capillary, these authors were able to distinguish the polymers by their polar components that are ionized in the electrospray plume. Meruva et al. developed a Py-GC/MS instrument based on UV laser pyrolysis at 266 nm (103). To achieve fast analysis, a timeof-flight analyzer was employed. These authors then optimized the laser Py-GC/MS instrument using polyethylene standards (104). Pyrolysis methods are often distinguished from thermal degradation methods based on the rate at which heat is applied to the analyte. In an example of the use of thermal degradation, White employed heat in combination with MS to investigate the decomposition of novel nitroaromatic polymers (105). Jang and Wilkie used GC/MS and LC/MS to study the thermal degradation of polycarbonate under nitrogen gas (106). The primary degradation pathways involved chain scission of the isopropylidene linkage and hydrolysis/alcoholysis with rearrangement of the carbonate linkages. In companion studies, Samperi et al. used isothermal conditions between 270 and 350 °C to study the thermal degradation of PET and poly(butylene terephthalate) with product analysis by MALDI MS and NMR (62, 63). Badawy used low-temperature direct pyrolysis (D-Py) MS in combination with electron ionization to identify some commercial and synthetic polymers (107). The use of different pyrolysis temperatures combined with mass spectral subtraction routines were used to elucidate repeat unit and end group structures and examine degradation pathways, even for copolymers. D-Py of polymers was used in a number of studies as a method to rapidly obtain characteristic information. Aslan et al. used this method to investigate thermal characteristics of electrochemically polymerized polydecanedioic and poly(terephthalic acid) esters (108). They were able to ascertain that growth of the polyesters occurred through the 2 and 5 positions except when the ester linkages contained rigid groups that hindered growth through the 2 position. PMMA, poly(vinyl acetate) (PVAC) and a binary blend of PMMA and PVAC coalesced from host cyclodextrin were shown by Uyar et al. using D-Py MS to have significantly different degradation mechanisms relative to the solution blended samples (109). Oguz et al. used D-Py MS to characterize a poly(thiophene) (PTh)/poly(acrylonitrile) (PAN) sample prepared by electrochemically polymerizing thiophene on a PAN-coated anode (110). In another example of electrochemically prepared PTh, Gozet et al. demonstrated that BF4--doped polymer thermally degraded during Curie point Py-GC/MS and by D-Py MS in two steps (111). The steps involved loss of the dopant followed by degradation of the polymer backbone. Similar results were found for BF4-doped, methyl-substituted polythiophene and for PF6-doped PTh (112, 113). Athar et al. used D-Py MS to characterize p-toluenesulfonatedoped polypyrole-thiophene-capped PMMA (114, 115). The MS data indicate that degradation of the poly(methylthienyl methacrylate) polymer occurred during the electrochemical polymerization of the pyrrole. Ertas et al. used D-Py MS to characterize a homopolymer of succinic acid bis(4-pyrrol-1-ylphenyl) ester and proposed a three-step mechanism for the thermal decomposition process (116). The steps involve cleavage of the C4H4NC6H4O end groups followed by decomposition of the phenyl ester units forming polypyrrole chains having quinoid structure. The final 3962
Analytical Chemistry, Vol. 78, No. 12, June 15, 2006
step is thermal degradation of the polypyrrole chains that have aromatic structure. Pyrolysis combined with GC/MS continues to be an important tool for the characterization of polymers and polymer additives. As mentioned above, Curie point Py-GC/MS was used to study doped PTh polymers (111-113). Odermatt et al. used Py-GC/ MS to quantify paper additives from three polymeric materials: a styrene acrylate copolymerizate latex, a urea formaldehyde resin, and a poly(vinyl acetate) (117). Because of the separation achieved by GC, they were able to increase the sensitivity of the analysis by using single ion monitoring and quantify several additives in a single Py-GC/MS run. Cobalt phthalocyanine sheet polymer was characterized by Py-GC/MS at temperatures ranging from 500 to 1000 °C (118). Achar et al. characterized the likely structures of the pyrolysate and proposed tentative mechanisms for thermal degradation (118). Py-GC/MS was used by Sundarrajan et al. to characterize saturated and unsaturated polythioethers (119). They reported that the saturated polythioether produced fewer pyrolysis products than the unsaturated version, suggesting selective cleavage of the saturated polymer. Coulier et al. demonstrated that Py-GC/MS was a fast and straightforward method for identifying polymers containing polymeric hindered amine light stabilizers (120). OTHER MASS SPECTROMETRIC TECHNIQUES Here we highlight some of the unique methods used to characterize polymeric materials. An interesting application of laser-induced acoustic desorption coupled to chemical ionization mass spectrometry was used to analyze low MW polyethylene as described by Campbell et al. (121). These authors used the cyclopentadienyl cobalt radical cation to produce quasi-molecular ions (R + CpCo - 2H2) of a low MW polyethylene. Pegus et al. used laser ablation/ionization MS to depth profile PS nanoparticles (122). Measurements were made at different wavelengths. At the longest wavelength (523 nm), surface-bound material was dominant, and at the shortest wavelength (266 nm), the dominant ions were from the core of the PS nanoparticle. Ion mobility mass spectrometry was used by Anderson et al. along with modeling methods to examine the gas-phase conformations of polyhedral oligomeric silsesquioxane propyl methacrylate oligomers (123). MALDI was used to produce M + Na+ ions, and ion mobility MS was used to measure the collision cross sections of these ions in helium. Interestingly, only one confomer was observed for the sodiated 1-mer and 3-mer, but at least two conformers were observed for the 2-mer. Resano et al. combined laser ablation and inductively coupled plasma for multielement analysis of polymers (124). Accurate results for polyethylene standards were obtained from submicrogram to milligram per gram levels. Inductively coupled plasma was also employed by Sun and Ko to determine trace impurities in photoresists (125). LC/atmospheric pressure chemical ionization (APCI)-MS was used to investigate γ-irradiated PET for low molecular weight constituents by Buchalla and Begley (126). These authors found only small differences in irradiated and nonirradiated PET, primarily an increase in terephthalic acid ethyl esters. Hydrolysis products of a poly(ether ester) segmented block copolymer were characterized using both positive and negative ion LC/MS by Hayen et al. (127). These authors found degradation in both the
hard and soft segments of the PEG/PBT copolymer. Combs et al. used LC/APCI-MS and in-source CID as well as MS/MS for end group characterization of polyethoxylates (128). Low-mass oligomers (100 Da) aided end group identification. Wollyung et al. also used tandem MS to determine the connectivity of amine functional groups added to polyisobutylenes (PIB) using a facile synthesis that functionalized the PIB frame terminally and centrally (64). GC/ MS was used by Kawamoto et al. to quantify the methyl derivatives of dimethyldithiocarbamate and ethylenebisdithiocarbamate from alkali-decomposed polycarbamates (129). GC/MS was also used to determine the residual styrene monomer in PS granules (130). Several extraction methods were evaluated in developing a method for detecting the toxic monomer. Hoai et al. used GC/MS with electron and isobutane chemical ionization to determine the degradation products of nonylphenol polyethoxylates (131). CONCLUSION The wide range of applications discussed in this review demonstrates the power of mass spectrometry in the analysis of synthetic polymers. Polymerization and degradation mechanisms, identification of additives, and polymer structure characterization were some of the areas studied using various MS ionization methods. The increase in publications relating “real world” analyses illustrates the value of mass spectrometry in the polymer arena. However, the significant number of papers studying fundamental aspects tells us that we still have much to learn. Patricia A. Peacock is a Staff Technologist in the Dupont Corporate Center for Analytical Sciences in Wilmington, DE. She studied materials engineering at Virginia Polytechnic Institute and State University, and chemistry at the University of Delaware. She has 12 publications and 21 years experience in polymer characterization. Her current research interests include practical applications of mass spectrometry for the characterization of a wide variety of industrial and research polymers. Other areas of interest include structure elucidation of small organic molecules using mass spectrometry and laser light scattering analyses of macromolecules. She is Chair of the American Society for Mass Spectrometry Polymeric Materials Interest Group and the Delaware Valley Mass Spectrometry Discussion Group. Charles N. McEwen is a Research Fellow in the Dupont Corporate Center for Analytical Sciences in Wilmington, DE. A member of the American Chemical Society and the American Society for Mass Spectrometery, he is the author, coauthor, or editor of books, book chapters, and numerous scientic publications that reflect his interest in using mass spectrometry to study diverse materials. He received a B.S. degree in chemistry from the College of William and Mary, M.S. degree in chemistry from Atlanta University, and Ph.D. degree in chemistry from the University of Virginia.
LITERATURE CITED (1) Peacock, P. M.; McEwen, C. N. Anal. Chem. 2004, 76, 34173428. (2) Jagtap, R. N.; Ambre, A. H. Bull. Mater. Sci. 2005, 28, 515528. (3) Montando, G.; Carroccio, S.; Montaudo, M. S.; Puglisi, C.; Samperi, F. Macromol. Symp. 2004, 218, 101-112. (4) Barner-Kowollik, C.; Davis, T. P.; Stenzel, M. H. Polymer 2004, 45, 7791-7805. (5) Hanton, S. D. JCT Coatings Technol. 2004, 1, 62-68. (6) McEwen, C. N. Adv. Mass Spectrom. 2004, 16, 215-227. (7) Wallace, W. E. J. Am. Soc. Mass Spectrom. 2005, 16, 291-293. (8) Wallace, W. E. J. Am. Soc. Mass Spectrom. 2006, 17, 280-282. (9) Hanton, S. D.; Hyder, I. Z.; Stets, J. R.; Owens, K. G.; Blair, W. R.; Guttman, C. M.; Giuseppetti, A. A. J. Am. Soc. Mass Spectrom. 2004, 15, 168-179. (10) Wetzel, S. J.; Guttman, C. M.; Flynn, K. M. Rapid Commun. Mass Spectrom. 2004, 18, 1139-1146. (11) Woldegiorgis, A.; Loewenhielm, P.; Bjoerk, A.; Roeraade, J. Rapid Commun. Mass Spectrom. 2004, 18, 2904-2912. (12) Blair, W. R.; Wallace, W. E.; Byrd, H. C. M.; Quintavalle, J. S.; Guttman, C. M. PMSE Prepr. 2005, 93, 501-502.
(13) Enjalbal, C.; Lamaty, F.; Martinez, J.; Aubagnac, J.-L. Chem. Anal. 2004, 163, 125-135. (14) Hanton, S. D.; Parees, D. M. J. Am. Soc. Mass Spectrom. 2005, 16, 90-93. (15) Taguchi, Y.; Ishida, Y.; Ohtani, H.; Matsubara, H. Anal. Chem. 2004, 76, 697-703. (16) Gies, A. P.; Nonidez, W. K. Anal. Chem. 2004, 76, 1991-1997. (17) Ellison, S.; Gies, A.; Nonidez, W.; Xue, C.; Liu, H. Int. J. Polym. Anal. Charact. 2005, 10, 245-258. (18) Murgasova, R.; Hercules, D. M.; Edman, J. R. Macromolecules 2004, 37, 5732-5740. (19) Okuno, S.; Wada, Y.; Arakawa, R. Int. J. Mass Spectrom. 2005, 241, 43-48. (20) Arakawa, R.; Shimomae, Y.; Morikawa, H.; Ohara, K.; Okuno, S. J. Mass Spectrom. 2004, 39, 961-965. (21) Seino, T.; Sato, H.; Torimura, M.; Shimada, K.; Yamamoto, A.; Tao, H. Anal. Sci. 2005, 21, 485-490. (22) Mourey, T. H.; Hoteling, A. J.; Balke, S. T.; Owens, K. G. J. Appl. Polym. Sci. 2005, 97, 627-639. (23) Mineo, P.; Vatilini, D.; Scamporrino, E.; Bazzano, S. Rapid Commun. Mass Spectrom. 2005, 19, 2773-2779. (24) Guttman, C. M.; Wetzel, S. J.; Flynn, K. M.; Fanconi, B. M.; VanderHart, D. L.; Wallace, W. E. Anal. Chem. 2005, 77, 45394548. (25) Zhang, Z.; Deng, H.; Deng, Q.; Zhao, S. Rapid Commun. Mass Spectrom. 2004, 18, 2146-2154. (26) Terrier, P.; Buchmann, W.; Cheguillaume, G.; Desmazieres, B.; Tortajada, J. Anal. Chem. 2005, 77, 3292-3300. (27) Chen, H.; He, M. J. Am. Soc. Mass Spectrom. 2005, 16, 100106. (28) Shimada, K.; Matsuyama, S.; Saito, T.; Kinugasa, S.; Nagahata, R.; Kawabata, S.-i. Int. J. Mass Spectrom. 2005, 247, 85-92. (29) Jackson, A. T.; Slade, S. E.; Scrivens, J. H. Int. J. Mass Spectrom. 2004, 238, 265-277. (30) Hoteling, A. J.; Erb, W. J.; Tyson, R. J.; Owens, K. G. Anal. Chem. 2004, 76, 5157-5164. (31) Hoteling, A. J.; Mourey, T. H.; Owens, K. G. Anal. Chem. 2005, 77, 750-756. (32) Al-Jarah, S. Y.; Sjoedahl, J.; Woldegiorgis, A.; Emmer, A. J. Sep. Sci. 2005, 28, 239-244. (33) Cheguillaume, G.; Buchmann, W.; Desmazieres, B.; Tortajada, J. Chromatographia 2004, 60, 561-566. (34) Weidner, S. M.; Just, U.; Wittke, W.; Rittig, F.; Gruber, F.; Friedrich, J. F. Intn. J. Mass Spectrom. 2004, 238, 235-244. (35) Liu, X. M.; Maziarz, E. P.; Quinn, E.; Lai, Y.-C. Int. J. Mass Spectrom. 2004, 238, 227-233. (36) Basile, F.; Kassalainen, G. E.; Williams, S. K. R. Anal. Chem. 2005, 77, 3008-3012. (37) Colomines, G.; Robin, J.-J.; Tersac, G. Polymer 2005, 46, 32303247. (38) Samperi, F.; Montaudo, M. S.; Puglisi, C.; DiGiorgi, S.; Montando, G. Macromolecules 2004, 37, 6449-6459. (39) Kona, B.; Weidner, S. M.; Friedrich, J. F. Int. J. Polym. Anal. Charact. 2005, 10, 85-108. (40) Ji, H.; Baskaran, D.; Mays, J. W. Am. Chem. Soc. Polym. Prepr. 2005, 46, 452-453. (41) Bootz, A.; Russ, T.; Gores, F.; Karas, M.; Kreuter, J. Eur. J. Pharmacol. Biopharmacol. 2005, 60, 391-399. (42) Mazzaglia, A.; Scolaro, L. M.; Garozzo, D.; Malvagna, P.; Romeo, R. J. Organomet. Chem. 2005, 690, 1978-1985. (43) Jayakannan, M.; Lou, X.; Van Dongen, J. L. J.; Janssen, R. A. J. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 1454-1462. (44) Kricheldorf, H. R.; Garaleh, M.; Schwarz, G. J. Macromol. Sci., Pure. Appl. Chem. 2005, A42, 139-148. (45) Quirk, R. P.; You, F.; Wesdemiotis, C.; Armnould, M. A. Macromolecules 2004, 37, 1234-1242. (46) Somogyi, A.; Bojkova, N.; Padias, A. B.; Hall, H. K., Jr. Macromolecules 2005, 38, 4067-4071. (47) Arnould, M. A.; Polce, M. J.; Quirk, R. P.; Wesdemiotis, C. Int. J. Mass Spectrom. 2004, 238, 245-255. (48) Campbell, J. D.; Allaway, J. A.; Teymour, F.; Morbidelli, M. J. Appl. Polym. Sci. 2004, 94, 890-908. (49) Gies, A. P.; Nonidez, W. K.; Anthamatten, M.; Cook, R. C. Macromolecules 2004, 37, 5923-5929. (50) Bednarek, M.; Kubisa, P. J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 608-614. (51) D’Agosto, F.; Charreyre, M. T.; Pichot, C.; Dessalces, G.; Delolme, F. Rapid Commun. Mass Spectrom. 2004, 18, 664-672. (52) Mezlova, M.; Aaron, J. J.; Svoboda, J.; Adenier, A.; Maurel, F.; Chane-Ching, K. J. Electroanal. Chem. 2005, 581, 93-103. (53) Gies, A. P.; Nonidez, W. K.; Ellison, S. T. Anal. Chem. 2005, 77, 780-784. (54) Willemse, R. X. E.; Staal, B. B. P.; Donkers, E. H. D.; van Herk, A. M. Macromolecules 2004, 37, 5717-5723. (55) Lee, J. S.; Roderic, P.; Foster, M. D. Macromolecules 2004, 37, 6385-6394. (56) Ameduri, B.; Ladaviere, C.; Delolme, F.; Boutevin, B. Macromolecules 2004, 37, 7602-7609. (57) Ray, B.; Isobe, Y.; Matsumoto, K.; Habaue, S.; Okamoto, Y.; Kamigaito, M.; Sawamoto, M. Macromolecules 2004, 37, 17021710. (58) Schulte, T.; Siegenthaler, K. O.; Luftmann, H.; Letzel, M.; Studer, A. Macromolecules 2005, 38, 6833-6840.
Analytical Chemistry, Vol. 78, No. 12, June 15, 2006
3963
(59) Rizzarelli, P.; Puglisi, C.; Montando, G. Rapid Commun. Mass Spectrom. 2005, 19, 2407-2418. (60) Carrocciio, S.; Puglisi, C.; Montaudo, G. Macromolecules 2004, 37, 6037-6049. (61) Carroccio, S.; Rizzarelli, P.; Puglisi, C.; Montando, G. Macromolecules 2004, 37, 6576-6586. (62) Samperi, F.; Puglisi, C.; Alicata, R.; Montando, G. Polym. Degrad. Stab. 2004, 83, 3-10. (63) Samperi, F.; Puglisi, C.; Alicata, R.; Montando, G. Polym. Degrad. Stab. 2004, 83, 11-17. (64) Wollyung, K. M.; Wesdemiotis, C.; Nagy, A.; Kennedy, J. P. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 946-958. (65) Jaber, A. J.; Wilkins, C. L. J. Am. Soc. Mass Spectrom. 2005, 16, 2009-2016. (66) di Lena, F.; Quintanilla, E.; Chen, P. Chem. Commun. 2005, 5757-5759. (67) Buback, M.; Frauendore, H.; Vana, P. J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 4266-4275. (68) Watkins, M. A.; Winger, B. E.; Shea, R. C.; Kenttaemaa, H. I. Anal. Chem. 2005, 77, 1385-1392. (69) Martinez, E.; Gans, O.; Weber, H.; Scharf, S. Water Sci. Technol. 2004, 50, 157-163. (70) Feldermann, A.; Toy, A. A.; Davis, T. P.; Stenzel, M. H.; BarnerKowollik, C. Polymer 2005, 46, 8448-8457. (71) Toy, A. A.; Vana, P.; Davis, T. P.; Barner-Kowollik, C. Macromolecules 2004, 37, 744-751. (72) Zhou, G.-J.; Xu, P.-X.; Ye, Y.; Zhao, Y.-F. Eur. J. Mass Spectrom. 2005, 11, 319-324. (73) Dolan, A. R.; Wood, T. D. Synth. Met. 2004, 143, 243-250. (74) Adamus, G.; Montaudo, M. S.; Montaudo, G.; Kowalczuk, M. Rapid Commun. Mass Spectrom. 2004, 18, 1436-1446. (75) Collins, S.; Rimmer, S. Rapid Commun. Mass Spectrom. 2004, 18, 3075-3078. (76) Giguere, M.-S.; Mayer, P. M. Int. J. Mass Spectrom. 2004, 231, 59-63. (77) Yuan, G.; Zhou, J. Rapid Commun. Mass Spectrom. 2004, 18, 1397-1402. (78) Wang, J.; Zhou, J.; Yuan, G. J. Mass Spectrom. 2005, 40, 688689. (79) Arnould, M. A.; Vargas, R.; Buehner, R. W.; Wesdemiotis, C. Eur. J. Mass Spectrom. 2005, 11, 243-256. (80) Franska, M.; Zgola, A.; Rychlowska, J.; Szymanski, A.; Lukaszewski, Z.; Franski, R. Rapid Commun. Mass Spectrom. 2004, 18, 356-359. (81) Chiu, T. Y. J.; Heuts, J. P. A.; Davis, T. P.; Stenzel, M. H.; BarnerKowollik, C. Macromol. Chem. Phys. 2004, 205, 752-761. (82) Miyauchi, K.; Sumiyama, Y.; Jinda, K. Int. J. Polym. Anal. Charact. 2004, 9, 339-349. (83) Guaratini, T.; Vessecchi, R. L.; Lavarda, F. C.; Maia Campos, P. M. B. G.; Naal, Z.; Gates, P. J.; Lopes, N. P. Analyst 2004, 129, 1223-1226. (84) Preby, B. S.; Cook, K. D. Anal. Chem. 2004, 76, 127-136. (85) Wagner, M. S.; Gillen, G. Appl. Surf. Sci. 2004, 169-4332. (86) Wagner, M. S. Anal. Chem. 2004, 76, 1264-1272. (87) Wagner, M. S. Surf. Interface Anal. 2005, 37, 42-52. (88) Wagner, M. S. Surf. Interface Anal. 2005, 37, 53-61. (89) Wagner, M. S. Surf. Interface Anal. 2005, 37, 62-70. (90) Wagner, M. S. Anal. Chem. 2005, 77, 911-922. (91) Boschmans, B.; Van Royen, P.; Van Vaeck, L. Rapid Commun. Mass Spectrom. 2005, 19, 2517-2527. (92) Mahoney, C. M.; Yu, J.; Gardella, J. A., Jr. Anal. Chem. 2005, 77, 3570-3578. (93) Van Royen, P.; Taranu, A.; Van Vaeck, L. Rapid Commun. Mass Spectrom. 2005, 19, 552-560. (94) Oran, U.; Swaraj, S.; Friedrich, J. F.; Unger, W. E. S. Surf. Coat. Technol. 2005, 200, 463-467. (95) Oran, U.; Unveren, E.; Wirth, T.; Unger, W. E. S. Appl. Surf. Sci. 2004, 227, 318-324. (96) Kim, J.; Shon, H. K.; Jung, D.; Moon, D. W.; Han, S. Y.; Lee, T. G. Anal. Chem. 2005, 77, 4137-4141.
3964
Analytical Chemistry, Vol. 78, No. 12, June 15, 2006
(97) Norrman, K.; Kingshott, P.; Kaeselev, B.; Ghanbari-Siahkali, A. Surf. Interface Anal. 2004, 36, 1533-1541. (98) van Gennip, W. J. H.; Thune, P. C.; Dijkstra, J. B.; Niemantsverdriet, J. W. Appl. Phys. Lett. 2004, 84, 1789-1791. (99) Segalman, R. A.; Jacobson, A.; Kramer, E. J.; Lustig, S. R. Macromolecules 2004, 37, 2613-2617. (100) Bulle-Lieuwma, C. W. T.; Van Duren, J. K. J.; Yang, X.; Loos, J.; Sieval, A. B.; Hummelen, J. C.; Janssen, R. A. J. Appl. Surf. Sci. 2004, 0169-4332. (101) Boutin, M.; Lesage, J.; Ostiguy, C.; Bertrand, M. J. J. Am. Soc. Mass Spectrom. 2004, 15, 1315-1319. (102) Hsu, H.-J.; Kuo, T.-L.; Wu, S.-H.; Oung, J.-N.; Shiea, J. Anal. Chem. 2005, 77, 7744-7749. (103) Meruva, N. K.; Metz, L. A.; Goode, S. R.; Morgan, S. L. J. Anal. Appl. Pyrolysis 2004, 71, 313-325. (104) Metz, L. A.; Meruva, N. K.; Morgan, S. L.; Goode, S. R. J. Anal. Appl. Pyrolysis 2004, 71, 327-341. (105) White, D. R.; White, R. L. J. Appl. Polym. Sci. 2005, 95, 351357. (106) Jang, B. N.; Wilkie, C. A. Polym. Degrad. Stab. 2004, 86, 419430. (107) Badawy, S. M. Eur. J. Mass Spectrom. 2004, 10, 613-617. (108) Aslan, E.; Toppare, L.; Hacaloglu, J. Synth. Met. 2005, 155, 191195. (109) Uyar, T.; Aslan, E.; Tonelli, A. E.; Hacaloglu, J. Polym. Degrad. Stab. 2005, 91, 1-11. (110) Oguz, G.; Hacaloglu, J.; Onal, A. J. Macromol. Sci., Part A: Pure. Appl. Chem. 2005, A42, 1387-1397. (111) Gozet, T.; Hacaloglu, J.; Oenal, A. M. J. Macromol. Sci., Pure Appl. Chem. 2004, A41, 713-725. (112) Gozet, T.; Hacaloglu, J. Polym. Int. 2004, 53, 2162-2168. (113) Gozet, T.; Hacaloglu, J. J. Anal. Appl. Pyrolysis 2005, 73, 257262. (114) Athar, I.; Hacaloglu, J.; Toppare, L. Int. J. Polym. Mater. 2004, 53, 879-887. (115) Athar, I.; Hacaloglu, J.; Toppare, L. Polym. Int. 2004, 53, 926930. (116) Ertas, M.; Hacaloglu, J.; Toppare, L. Polym. Int. 2004, 53, 11981204. (117) Odermatt, J.; Ringena, O.; Teucke, R.; Reiter, C.; Gerst, M. Appita J. 2005, 58, 462-469. (118) Achar, B. N.; Lokesh, K. S.; Fohlen, G. M.; Mohan Kumar, T. M. React. Funct. Polym. 2005, 63, 63-69. (119) Sundarrajan, S.; Surianarayanan, M.; Srinivasan, K. S. V. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 638-649. (120) Coulier, L.; Kaal, E. R.; Tienstra, M.; Hankemeier, T. J. Chromatogr., A 2005, 1062, 227-238. (121) Campbell, J. L.; Fiddler, M. N.; Crawford, K. E.; Gqamana, P. P.; Kenttaemaa, H. I. Anal. Chem. 2005, 77, 4020-4026. (122) Pegus, A.; Kirkwood, D.; Cairns, D. B.; Armes, S. P.; Stace, A. J. Phys. Chem. Chem. Phys. 2005, 7, 2519-2525. (123) Anderson, S. E.; Baker, E. S.; Mitchell, C.; Haddad, T. S.; Bowers, M. T. Chem. Mater. 2005, 17, 2537-2545. (124) Resano, M.; Garcia-Ruiz, E.; Vanhaecke, F. Spectrochim. Acta, Part B: At. Spectrosc. 2005, 60B, 1472-1481. (125) Sun, Y.-C.; Ko, C.-J. Microchem. J. 2004, 78, 163-166. (126) Buchalla, R.; Begley, T. H. Radiat. Phys. Chem. 2006, 75, 129137. (127) Hayen, H.; Deschamps, A. A.; Grijpma, D. W.; Feijen, J.; Karst, U. J. Chromatogr., A 2004, 1029, 29-36. (128) Combs, M. T.; Johnson, D. D.; Szekely-Klepser, G. J. Surfactants Deterg. 2005, 8, 263-269. (129) Kawamoto, T.; Yano, M.; Makihata, N. J. Chromatogr., A 2005, 1074, 155-161. (130) Garrigos, M. C.; Marin, M. L.; Canto, A.; Sanchez, A. J. Chromatogr., A 2004, 1061, 211-216. (131) Hoai, P. M.; Tsunoi, S.; Ike, M.; Inui, N.; Tanaka, M.; Fujita, M. J. Chromatogr., A 2004, 1061, 115-121.
AC0606249
