Thermal degradation of vinylidene chloride/vinyl chloride copolymers in the presence of N-substituted maleimides

As a consequence of their excellent barrier properties vinyl chloride/vinylidene chloride copolymers have long been prominent in the flexible packaging market. While these polymers possess a number of superior characteristics, they tend to undergo thermally- induced degradative dehydrochlorination at process temperatures. This degradation must be controlled to permit processing of the polymers. Three series of N-substituted maleimides (N-alkyl-, N-aralkyl, and N-aryl) have been synthesized, characterized spectroscopically, and evaluated as potential stabilizers for a standard vinyl chloride/vinylidene chloride (85 mass%) copolymer. As surface blends with the polymer, these compounds are ineffective as stabilizers. However, significant stabilization may be achieved by pretreatment of the polymer with N-substituted maleimides. The most effective stabilization of the polymer is afforded by N-aralkyl- or N-arylmaleimides, most notably, N-benzylmaleimide and N-p-methoxyphenylmaleimide.     

Influence of the Lanthanide Ion and Solution Conditions on Formation of Lanthanide Wells–Dawson Polyoxotungstates

Lanthanide complexes of polyoxometalates, including the α₂-P₂W₁₇O₆₁ ¹⁰⁻ ligand, have been pioneered by Michael T. Pope, to whom this paper is dedicated. Examination of the solid-state and solution behavior of lanthanide complexes of the α₂-P₂W₁₇O₆₁ ¹⁰⁻ ligand are reported here to identify trends that will facilitate rational synthesis of hybrid organic lanthanide polyoxometalate complexes. Therefore, combining our data with that obtained by Pope and others a number of trends come into view. It is clear that there are two structural types for the 1:1 or 2:2 [Ln(H₂O)_X(α₂-P₂W₁₇O₆₁)]₂ ¹⁴⁻ species. The early lanthanides show a “cap to cap” structure that allows the Ln ion to be 9 coordinate and accommodates the longer bond lengths. The mid-late lanthanides show a “cap to belt” structure that allows the lanthanides to be 8 coordinate; this structural type is appropriate for the shorter bond lengths of the later lanthanides. The 1:1⇌1:2 equilibrium, that was observed by Pope for the Ce(III) analog is prevalent for the early- mid lanthanides. This equilibrium is slightly dependent on pH; however, cations have a major influence on this equilibrium. Larger, poorly hydrated cations appear to favor the 1:2 species for the early to mid lanthanides. Cations do not appear to influence the equilibrium for the later lanthanides; for all counterions, the 1:1 species was stable with no trace of the 1:2 species. Stability constants, K1 and K2, for the early to mid lanthanides were measured in this study by a competitive method and compared well with other published stability constant determinations. We suggest that the stability constants are not only dependent on the strength of interaction of the Ln with the α₂-P₂W₁₇O₆₁ ¹⁰⁻ ligand, but are also significantly influenced by the medium. The medium may bias the equilibria of the early-mid lanthanides and later lanthanides. The log K₁/log K₂ ratios are very close, suggesting that it is difficult to separate the 1:1 and 1:2 Ln: α₂-P₂W₁₇O₆₁ ¹⁰⁻ species.Electronic Supplementary Material Supplementary material for this article is available at and is accessible for authorized users.This paper is dedicated to Professor Michael T. Pope in honor of his substantial and sustained contributions to polyoxometalate chemistry and his inspiration to scientists working in the field.     

Design and evaluation of a Dean vortex-based micromixer

A mixer, based on the Dean vortex, is fabricated and tested in an on-chip format. When fluid is directed around a curve under pressure driven flow, the high velocity streams in the center of the channel experience a greater centripetal force and so are deflected outward. This creates a pair of counter-rotating vortices moving fluid toward the inner wall at the top and bottom of the channel and toward the outer wall in the center. For the geometries studied, the vortices were first seen at Reynolds numbers between 1 and 10 and became stronger as the flow velocity is increased. Vortex formation was monitored in channels with depth/width ratios of 0.5, 1.0, and 2.0. The lowest aspect ratio strongly suppressed vortex formation. Increasing the aspect ratio above 1 appeared to provide improved mixing. This design has the advantages of easy fabrication and low surface area.     

High-resolution NMR spectroscopy of membrane proteins in aligned bicelles

High-resolution solid-state NMR spectra can be obtained from uniformly (15)N-labeled membrane proteins in magnetically aligned bicelles. Fast uniaxial diffusion about the axis of the bilayer normal results in single-line spectra that contain the orientational information necessary for protein structure determination.     

Determination of residual levels of unsaturation in partially hydrogenated poly(2,3-diphenyl-1,3-butadiene) using TG

The thermal degradation characteristics of head-to-head poly(styrene) [HHPS] should provide insight with respect to the impact of head-to-head placement on the thermal stability of traditional atactic head-to-tail polymer [HTPS]. The synthesis of head-to-head poly(styrene) must be accomplished indirectly. The head-to-head polymer is most satisfactorily obtained by dissolving metal reduction of poly(2,3-diphenyl-1,3-butadiene) [PDBD] generated by radical polymerization of the corresponding diene monomer. Full saturation of the polymer mainchain requires several iterations of the reduction procedure. Since the decomposition of poly(2,3-diphenyl-1,3-butadiene) is prominent at 374°C and that for head-to-head poly(styrene) is similarly facile at 406°C, it seemed feasible that TG of partially hydrogenated PDBD might be utilized as a convenient means of monitoring the extent of hydrogenation. This has been demonstrated for various levels of unsaturation remaining - from approximately 90 to less than 10%. Within this range the peak areas from the DTG plots of the partially hydrogenated polymer provide a good reflection of the ratio of unsaturated to saturated units in the polymer. Even low levels of unsaturation in the polymer may be detected by the asymmetry of the decomposition peak for the polymer. This revised version was published online in August 2006 with corrections to the Cover Date.     

Vibrational dynamics of hydrogen‐bonded HCN complexes with OH and NH acids: Computational DFT systematic study

Vibrational properties (band position, infrared [IR], and Raman intensities) of C?N stretching mode were studied in 65 gas phase hydrogen‐bonded 1:1 complexes of HCN with OH acids and NH acids using density functional theory (DFT) calculations at the B3LYP‐6‐311++G(d,p) level. Furthermore, general characteristics of the hydrogen bonds and vibrational changes in acids OH/NH stretching bands were also considered. Experimentally observed blue shift of the C?N stretching band promoted by hydrogen bonding, which shortens the triple bond length, is very well reproduced and quantitatively depends on the hydrogen bond length. Both IR and Raman ν(C?N) band intensities are enhanced, also in good agreement with the experimental results. IR intensity increase is a direct function of the hydrogen bond energy. However, the predicted Raman intensity raise is a more complex function, depending simultaneously on characteristics of both the hydrogen bond (C?N bond length) and the H‐donating acid (polarizability). With these two parameters, ν (C?N) Raman intensities of the complexes are explained with a mean error of ±2.4%. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007