William J. Simonsick

Cage-like structure formation during sol-gel polymerization of glycidyloxypropyltrimethoxysilane

Abstract The sol–gel polymerization of 3-glycidyloxypropyltrimethoxysilane (GTMS) was followed by size exclusion chromatography and 29Si NMR. Extensive non-random cyclization under formation of polyhedral cycles – cubic cages – predominates at the beginning of the reaction. Structure growth of polysilsesquioxanes proceeds by combining the incompletely condensed cage frameworks. The extent of the cage formation increases with dilution and the amount of water and depends appreciably on a catalyst. The cage fraction was isolated from a reaction mixture using preparative size exclusion chromatography and identified by 29Si NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). High content of polyhedral cages prevents gelation of the trifunctional GTMS monomer. Reaction of pendant epoxy groups is much slower; however, at a late reaction stage the epoxy hydrolysis can be significant. Under some conditions, like base catalysis, polysilsesquioxane clusters are crosslinked by intermolecular condensation of SiOH with hydrolyzed epoxy groups and the system gels. The cage with epoxide functionalities may serve as a rigid precursor of crosslinking.

Preparation and characterization of alkoxysilane functionalized isocyanurates

Alkoxysilane functionalized isocyanurates were prepared from hexamethylene diisocyanate (HDI) isocyanurate and 3-aminopropyltriethoxysilane. The reactants and functionalized isocyanurate were characterized by 1H, 13C and 29Si NMR, IR and electrospray ionization-mass spectrometry. Two-dimensional NMR was necessary to accurately assign the proton and carbon spectra for both the reactants and functionalized products. The composition of the HDI isocyanurate was a mixture of oligomers ranging from two to three HDI monomers. The functionalization reaction was performed neat, and as a function of dilution. As expected, substitution on the isocyanurate becomes more uniform with increasing solvent content.

Studies of higher temperature polymerization ofn-butyl methacrylate andn-butyl acrylate

Free-radical acrylic polymerizations of n-butyl methacrylate and n-butyl acrylate at temperatures above 120°C show significant departure from classic free-radical kinetics. An extended model of depropagation, where the equilibrium monomer concentration varies with temperature and polymer content, is postulated and shown to adequately explain the data for n-butyl methacrylate. Intramolecular chain transfer and scission is postulated to explain the apparent reduction in molecular weight and rate of polymerization seen in n-butyl acrylate polymerization, with supporting experimental evidence found via electrospray-ionization mass spectrometry.

Gel permeation chromatography coupled to fourier transform mass spectrometry for polymer characterization.

We report an on-line coupling of gel permeation chromatography (GPC) to Fourier transform mass spectrometry (FTMS) using a modified commercial electrospray ionization (ESI) interface. Selected oligomer profiles for the sodiated (1+ through 5+ charge states) oligomer ions of a narrow-molecular-weight poly(methyl methacrylate) were generated and used for obtaining a calibration curve. Using the MS-generated calibration curve and the refractive index response for quantification, an accurate molecular weight distribution was calculated and showed an excellent agreement with the value specified by the supplier. GPC/ESI/FTMS also allowed for an unequivocal end-group determination and characterization of a secondary distribution due to the formation of cyclic reaction products. We analyzed a glycidyl methacrylate/butyl methacrylate copolymer with a broad molecular weight distribution, where fractionation and high resolving power were required for adequate characterization. Molecular weight distribution data showed the advantage of coupling high-resolution MS and GPC to overcome the difficulty of analyzing polydisperse polymers with MS alone.

Synthesis of reactive diluents for cationic cycloaliphatic epoxide UV coatings

Abstract Reactive diluents for cationic cycloaliphatic epoxide UV coatings were synthesized using caprolactone polyols and tetraethyl orthosilicate (TEOS). The structures of the TEOS functionalized polyols were characterized using IR, 1 H-NMR, 29 Si-NMR, and ESI-FTMS spectroscopy. The resulting siloxane functionalized polyols were used to formulate cationic UV coatings with 3, 4-epoxycyclohexylmethyl-3, 4-epoxycyclohexane carboxylate (a cycloaliphatic diepoxide). The crosslinking reactions were monitored using IR and 29 Si-NMR spectroscopy. The cured films were evaluated in terms of tensile properties and glass transition temperature. The resultant coatings showed greater tensile modulus, lower elongation, and higher glass transition temperature. In addition, the siloxane functionalized polyols also effectively reduced the viscosity of the coatings formulations. Based on the curing behaviors and spectroscopic data, possible crosslinking reaction(s) were postulated.

Analysis of copolymers by laser desorption fourier transform mass spectrometry

A series of methylmethacylate/butylacrylate, methylmethacrylate/styrene, and poly-(ethylene glycol)/poly(propylene glycol) copolymers were analyzed by laser desorption Fourier transform mass spectrometry. Molecular weight distributions and overall copolymer compositions were determined. Typical spectra arise from a distribution of alkali metal cationized oligomer ions reflecting copolymer composition. Number- and weight-average molecular weights were calculated for each category of copolymer series as well as for overall copolymer mixtures. In addition, mass spectra were analyzed to estimate copolymer monomer contributions; these results were compared with manufacturer free mix ratios as a test of the relative accuracy of the analysis. Although a dual-cell Fourier transform mass spectrometer was used, all copolymer analyses reported were carried out as single (source) cell measurements to ensure that no mass discrimination would occur. A series of Fourier transform mass spectrometry dual-cell experiments also were performed to evaluate the effect of ion transfer time on molecular weight averages and compositions. As expected, mass discrimination occurred when short transfer times and analyzer cell detection were employed. Under these conditions, molecular weight averages varied by more than 50% from values obtained in the single-cell measurements.

The fundamentals of applying electrospray ionization mass spectrometry to low mass poly(methyl methacrylate) polymers

Electrospray ionization (ESI) is capable of ionizing many soluble polymers. The ESI spectra are complex because of overlap of the multiply charged ions of the oligomer distribution, causing current computer transform programs to fail. However, it is possible to determine the origin of the multiply charged ions, making it feasible to write a program designed to transform ESI polymer spectra. To assess the value of such a program for polymer analysis, isolated monodisperse methyl methacrylate (MMA) oligomers (25 and 50 repeat units) were used to determine molar signal response and propensity for fragmentation.The sum of the peak areas for the multiply charged MMA 50-mer was found to be only about 66% of the summed peak areas for the 25-mer for the same molar concentration. However, conversion of the multiply charged peak areas to the singly charged representations, with peak area compression taken into account, gave equal signal responses for the 25-and 50-mers. Signal response variations due to the tacticity of the MMA oligomers were not observed. Fragmentation of the MMA oligomers also was shown not to occur under normal ESI conditions. Therefore, transformation of the polymer spectra to the singly charged molecular ion distribution should allow accurate calculation of average molecular weights, polydispersity, end group mass, and repeat unit mass.

Electrospray ionization mass spectrometric and liquid chromatographic–mass spectrometric studies on the metabolism of synthetic dynorphin A peptides in brain tissue in vitro and in vivo

Metabolic stability of synthetic dynorphins [N-terminal fragments of dynorphin A (Dyn A)] were evaluated in vitro and in vivo. These peptides were applied at concentrations 100-1000 times higher than those of the endogenous dynorphins. Degradation kinetics of these peptides were studied in rat brain homogenate by using microbore gradient RP-LC assay, and limited information on their metabolism was obtained by electrospray ionization mass spectrometry (ESI-MS) of the isolated metabolites. In vivo cerebral microdialysis, in which the peptides were introduced via the probe placed in striatum region of the brain of the experimental animals, was used to circumvent contamination arising from autoproteolysis of brain during incubation of the samples in vitro. Metabolites of Dyn A (1-13) and Dyn A (1-11) were identified from electrospray ionization mass spectra of the microdialysates without chromatographic separation; the identification of peptides in the mixtures were supported by medium resolution ESI Fourier-transform ion cyclotron resonance MS. LC-MS was used to fully characterize the complex peptide mixture obtained after the striatal perfusion of Dyn A (1-12).

Identification, Composition, and Asymmetric Formation Mechanism of Glycidyl Methacrylate/Butyl Methacrylate Copolymers up to 7000 Da from Electrospray Ionization Ultrahigh-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

Glycidyl methacrylate (GMA) and butyl methacrylate (BMA) have the same nominal mass (142 Da) but differ in exact mass by 0.036 Da (CH(4) vs O). Therefore, copolymers formed from the two isobaric monomers exhibit a characteristic isobaric distribution due to different monomer compositions. Here, we show that electrospray ionization FT-ICR mass spectrometry at 9.4 T resolves the isobaric components of copolymers as large as 7000 Da with a resolving power (m/Δm(50%)) of ∼500 000 in a gel permeation chromatography fractionated polymer sample. That resolution provides for complete and unequivocal component analysis of such copolymers of the size used for high solid content automobile coatings. All five possible copolymer products predicted by the polymerization mechanism are resolved and identified in the mass spectrum. Two of those polymer series (each with saturated end group) were previously unresolved by mass spectrometry because they differ in mass from the two other unsaturated products by only 0.0089 Da. Finally, analysis of the asymmetrical isobaric distribution for the copolymer n-mers, (GMA)(m)(BMA)(n)(-)(m), 0≤ m ≤ n, in which species with adjacent values of m differ from each other in mass by 36 mDa (i.e., the mass difference, CH(4) vs O, between GMA and BMA) proves that GMA is less reactive than BMA in the polymerization process.

Recent changes in automotive paint formulation using pyrolysis-gas chromatography/mass spectrometry for identification

Abstract The analysis of paint fragments recovered during forensic investigations using Pyrolysis-GC/MS (PyGC-MS) has a long standing history. Pyrograms generated from intact fragments or separated layers are used to match paint evidence to known paint formulations in an effort to narrow the scope of the search, help identify involved vehicles, and exclude others. The peaks which appear in any pyrogram of an automotive paint may be a complex mixture of polymer pyrolysate, additives, plasticizers and other ingridients, each of which has a specific function in the performance of the paint as a product. Automotive paint formulations undergo constant evolution and revision based on the needs of the industry, including appearance, longevity, repair, and economics. Recently, environmental concerns have been added to the mix, with the mandate to reducc volatile organic emissions from paints. Newer formulations may include a higher solids load, changed polymer chemistries, water-based products and the results of other new technologies. How these formulation changes present themselves when the dried paint is examined as forensic evidence is presented, together with comparisons of older formulations.