Determination of molecular weight distributions of tert-octylphenol ethoxylate surfactant polymers by laser desorption Fourier transform ion cyclotron resonance mass spectrometry and high-performance liquid chromatography

Triton polymers are commercial surfactants whose molecular weight distributions are conventionally determined by means of high-performance liquid chromatography (HPLC). However, in the case of the important octylphenol ethoxylates [p-C8H17-C6H4-O-(CH2CH2O)n-H], HPLC cannot resolve individual oligomers of high molecular weight Triton surfactants (e.g., greater than 2000 u or so; u = unified atomic mass unit). In this paper, we show that laser desorption Fourier transform ion cyclotron resonance mass spectrometry (LD/FT/ICR/MS) provides a simple and accurate measure of such Triton surfactant molecular weight distributions up to at least 3500 u, based on a single-shot laser pulse measurement of a few seconds duration. Comparison of LD/FT/ICR/MS and HPLC molecular weight distributions of low molecular weight surfactants shows that laser desorption/ionization produces minimal fragmentation and thus offers an accurate measure of the relative abundances of the neutral oligomers, without the need for prior chromatographic separation of the components. Moreover, for all Triton polymer molecular weight distributions (700-3000 u), LD/FT/ICR/MS provides much more highly resolved profiles of oligomer relative abundances. Finally, LD/FT/ICR/MS reveals the presence of poly(ethylene oxide) side products of the polymerization process, which are not observed by HPLC with conventional ultraviolet absorption detection.     

A reactive molecular dynamics model of thermal decomposition in polymers: I. Poly(methyl methacrylate)

The theory and implementation of reactive molecular dynamics (RMD) are presented. The capabilities of RMD and its potential use as a tool for investigating the mechanisms of thermal transformations in materials are demonstrated by presenting results from simulations of the thermal degradation of poly(methyl methacrylate) (PMMA). While it is known that depolymerization must be the major decomposition channel for PMMA, there are unanswered questions about the nature of the initiation reaction and the relative reactivities of the tertiary and primary radicals formed in the degradation process. The results of our RMD simulations, performed directly in the condensed phase, are consistent with available experimental information. They also provide new insights into the mechanism of the thermally induced conversion of this polymer into its constituent monomers.     

Development and application of a new method for amplification and detection of human rhinovirus RNA

Motor nerve terminals on abdominal body-wall muscles 6A and 7A in larval flesh flies were investigated to establish their general structural features with confocal microscopy, transmission electron microscopy, and freeze-fracture procedures. As in Drosophila and other dipterans, two motor axons supply these muscles, and two morphologically different terminals were discerned with confocal microscopy: thin terminals with relatively small varicosities (Type Is), and thicker terminals with larger varicosities (Type Ib). In serial electron micrographs, Type Ib terminals were distinguished from Type Is terminals by their larger cross-sectional area, more extensive subsynaptic reticulum, more mitochondrial profiles, and more clear synaptic vesicles. Type Ib terminals possessed larger synapses and more synaptic contact area per unit terminal length. Although presynaptic dense bars of active zones were similar in mean length for the two terminal types, there were almost twice as many dense bars per synapse for Type Ib terminals. Freeze-fractures through the presynaptic membrane showed particle-free areas indicative of synapses on the P-face, within which were localized aggregations of large intramembranous particles indicative of active zones. These particles were similar in number to those found at active zones of several other arthropod neuromuscular junctions. In general, synaptic structural parameters strongly paralleled those of the anatomically homologous muscles in Drosophila melanogaster. In live preparations, simultaneous focal recording from identified varicosities and intracellular recording indicated that the two terminals produced excitatory junction potentials of similar amplitude in a physiological solution similar to that used for Drosophila.     

Mechanism of the thermal decomposition of bisphenol C polycarbonate: nature of its fire resistance

Quantum chemical methods have been used to identify reaction pathways of the thermal decomposition of bisphenol C polycarbonate, one of the most fire-resistant polymers known to the scientific community. Despite substantial interest in its unusual high-temperature behavior, the mechanism of its thermal decomposition has been unknown. On the basis of computational results, a mechanism is proposed where the main feature is a shift of Cl atom from the β-styrene position to the adjacent aromatic ring, which leads to crosslinking and cyclization of the polymer. The proposed mechanism is consistent with experimental observations of char, HCl, and CO₂ as the main pyrolysis products.     

Recent contributions of flame-sampling molecular-beam mass spectrometry to a fundamental understanding of combustion chemistry

Flame-sampling molecular-beam mass spectrometry of premixed, laminar, low-pressure flat flames has been demonstrated to be an efficient tool to study combustion chemistry. In this technique, flame gases are sampled through a small opening in a quartz probe, and after formation of a molecular beam, all flame species are separated using mass spectrometry. The present review focuses on critical aspects of the experimental approach including probe sampling effects, different ionization processes, and mass separation procedures. The capability for isomer-resolved flame species measurements, achievable by employing tunable vacuum-ultraviolet radiation for single-photon ionization, has greatly benefited flame-sampling molecular-beam mass spectrometry. This review also offers an overview of recent combustion chemistry studies of flames fueled by hydrocarbons and oxygenates. The identity of a variety of intermediates in hydrocarbon flames, including resonantly stabilized radicals and closed-shell intermediates, is described, thus establishing a more detailed understanding of the fundamentals of molecular-weight growth processes. Finally, molecular-beam mass-spectrometric studies of reaction paths in flames of alcohols, ethers, and esters, which have been performed to support the development and validation of kinetic models for bio-derived alternative fuels, are reviewed.     

Polymerization of methyl methacrylate with a thermal iniferter: Diethyl 2,3‐dicyano‐2,3‐di(p‐tolyl)succinate

A hexa‐substituted ethane type compound, diethyl‐2,3‐dicyano‐2,3‐di(p‐tolyl)succinate (DCDTS), was successfully synthesized and used for initiation of methyl methacrylate (MMA) polymerization. The reaction demonstrated the characteristics of a “living” polymerization; i.e., both the yield and the molecular weight of the resulting polymers increased linearly with increasing reaction time, the molecular‐weight distribution of PMMA obtained was ～1.60 and almost unaffected by the conversion, and the resultant polymer can be chain extended by adding fresh MMA. End group analysis of the resultant PMMA confirmed that DCDTS behaves as a thermal iniferter for MMA polymerization. A block copolymer was prepared from the resultant PMMA, which contains a hexa‐substituted C? C bond functional end group. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2566–2572, 2001     

Effect of Aqueous Processing Conditions on the Microstructure and Transformation Behavior in Al2O3─ZrO2(CeO2) Composites

Aqueous processing of Al₂O₃─ZrO₂ (123 mol% CeO₂) composites, combined with sintering conditions, was used to control the microstructure and its influence on the martensitic transformation temperature of t -ZrO₂ and the transformation-toughening contribution at room temperature. The resultant ZrO₂ grain sizes in the dense composites were related to the transformation-toughening behavior of t -ZrO₂. The data show that (1) the best processing conditions exist when the electrophoretic mobilities of the two solids are positive, adequately high to ensure colloidal stability, efficient packing,and uniform ZrO₂ distribution but differ greatly in magnitude, (2) the colloidal stability of ZrO₂ controls the overall stability and the rheological and processing behavior of this mixture, (3) the grain size distribution in dense pieces sintered for 1 h at 1500°C is comparable to the particle size distribution of the powders, (4) the martensite start temperature for the tetragonal to-monoclinic transformation in Al₂O₃ containing 20 and 40 vol% ZrO₂ increases and can approach 0°C with increasing average ZrO₂ grain size, and as a result, (5) the fracture toughness values at room temperature are raised from 4–5 MPa.m^1/2 to 9–12 MPa.m^1/2 for these two compositions.     

Ultrasonically initiated emulsion polymerization of n‐butyl acrylate

Ultrasonically initiated emulsion polymerization of n‐butyl acrylate (BA) without added initiator has been studied. The experimental results show that high conversion of BA can be reached in a short time by employing an ultrasonic irradiation technique with a high purge rate of N₂. The viscosity average molecular weight of poly(n‐butyl acrylate) (PBA) obtained reaches 5.24 × 10⁶ g mol^?1. The ultrasonically initiated emulsion polymerization is dynamic and complicated, with polymerization of monomer and degradation of polymer occurring simultaneously. An increase in ultrasound intensity leads to an increase in polymerization rate in the range of cavitation threshold and cavitation peak values. Lower monomer concentration favours enhancement of the polymerization rate. ¹H NMR, ¹³C NMR and FTIR spectroscopies reveal that there are some branches and slight crosslinking, and also carboxyl groups in PBA. Ultrasonically initiated emulsion polymerization offers a new route for the preparation of nanosized latex particles; the particle size of PBA prepared is around 50–200 nm as measured by transmission electron microscopy. © 2001 Society of Chemical Industry     

Back-scattering investigation of the low temperature stability of the aluminum-silver system

The large angle elastic scattering of 2.9 MeV ⁴He₂ has been used to investigate the Al-Ag system. This system has important optical applications and affords an opportunity to study directly chemical kinetics. Heretofore, only indirect measurements of the system have been made. The samples consisted of thick Si substrates covered by a 5000 Å thermal SiO₂ layer. Then 2000 Å Al and 3000 Å Ag films were deposited in both sequences without raising the system vacuum above 2 × 10^-5 torr. The back-scattering measurements were performed after each step of a sequence of isothermal annealing treatments at 135°C for times up to 6 h. This study shows that the Si-SiO₂-Al-Ag system is stable after such a treatment. Thus, for Al first depositions, no intermediate metal is necessary for a diffusion barrier at room temperature. Indirect evidence is presented which suggests that the acting diffusion barrier in the Al first depositions is probably the thin natural aluminum oxide layer expected to be formed for the deposition conditions used. However, the adherence of these films to one another is shown to require further characterization if hifh bonding values are required. By comparison in Ag first depositions, extensive intermixing of the Al and Ag has occurred after as little as 105 min at 135°C. The back-scattering measurement correlated with the previous reflectivity measurements suggest that the interdiffusion of Ag and Al without significant compound formation plays a significant role in at least the initial changes in the reflectivity of thin films of Ag and Al. Finally, this study shows that a 500 Å Cr deposition between the Ag and Al depositions serves as an adequate diffusion barrier after an anneal treatment of 60 min at 300°C.