Improvement of the physical properties of poly(methyl methacrylate) by copolymerization with N-pentafluorophenyl maleimide; zero-orientational and photoelastic birefringence polymers with high glass transition temperatures

Copolymers of N-pentafluorophenyl maleimide (PFPMI) with methyl methacrylate (MMA) were synthesized by a free radical initiator, such as AIBN. The refractive indexes of the copolymers remained nearly constant (1.4970 at 532 nm) regardless of the polymer composition. These copolymers also showed high thermal stability. The orientational and photoelastic birefringence of the copolymers obtained were measured. Since both of the orientational and photoelastic birefringences of PMMA are negative whereas poly(PFPMI) exhibits positive, thus we have obtained nearly zero orientational and photoelastic birefringence polymers when the ratios of MMA/PFPMI were 91.8/8.2 and 97.0/3.0 mol%, respectively. Based on the experimental data, the ratios of MMA/PFPMI for zero birefringence were determined to be 88.9/11.1 and 93.8/6.2 mol% for orientational and photoelastic birefringence, respectively. The Tgs of corresponding copolymers were estimated to be 128 and 122 ℃.     

Hydrogen embrittlement in a magnesium grain boundary: a first-principles study

First-principles fully relaxed tensile and shear test simulations were performed on Σ10(1124)/[1100] tilt Mg grain boundary (GB) models, with and without H segregation, to investigate mechanisms of H embrittlement of Mg. Strengthening as a result of covalent-like characteristics of Mg-H bonds prevailed over weakening of Mg-Mg bonds resulting from charge transfer; as a result, an H atom strengthened the GB. In addition, because the strong Mg-H bonds suppressed macroscopic GB fracture, elongation to failure was not reduced by H segregation. However, the resistance to GB shearing was increased by H segregation. It is therefore suggested that H segregation enhances crack growth at the GB, because dislocation emission from the crack tip is suppressed, resulting in H embrittlement of Mg.     

Measurement of a pauli and orbital paramagnetic state in bulk gold using x-ray magnetic circular dichroism spectroscopy

We show that bulk gold (Au) exhibits temperature-independent paramagnetism in an external magnetic field by x-ray magnetic circular dichroism spectroscopy at the Au L(2) and L(3) edges. Using the sum-rule analysis, we obtained a magnetic moment of 1.3 × 10(-4) μB/atom in an external magnetic field of 10 T and a paramagnetic susceptibility of 8.9 × 10(-6) for the 5d orbit. The induced paramagnetism in bulk Au is characterized by a large (≈ 30%) orbital contribution. This orbital component was retained even when Au atoms formed nanoparticles, playing an important role in stabilizing the spontaneous spin polarization in the Au nanoparticles.     

Local structure around phosphorus and silicon in the CaO–SiO2–PO2.5 system

The local structure of phosphorus and silicon in the molten CaO–SiO₂–PO_2.5 slag system was investigated by magic angle spinning nuclear magnetic resonance (MAS-NMR). The ³¹P MAS-NMR spectra revealed that phosphorus was present primarily as the monophosphate complex ion PO₄^3?, with a small amount of diphosphate ion also present. Their relative ratio to total phosphorus was independent of the phosphate concentration of the sample. In the case of the ²⁹Si MAS-NMR, the mean number of the non-bridging oxygen atoms associated with tetrahedrally coordinated silicon decreased as the phosphate concentration increased at a fixed CaO/SiO₂ ratio. This indicates that the nonbridging oxygen atoms around the silicon were replaced by bridging oxygen atoms around the phosphorus as the phosphate concentration in the samples increased.To elucidate the basicity dependence of the structure of slag, the relationship between the structure and optical basicity was also investigated. The relative ratio of Qⁿ (Qⁿ means the silicon atoms tetrahedrally bonded with “n” number of bridging oxygen atoms) strongly depends on the optical basicity. These optical basicity dependencies of the structures of phosphorus and silicon can be explained clearly by the basicity equalization concept (Duffy and Ingram, 1976) [12].     

Mixed-Valent Trinuclear CoIII-CoII-CoIII Complex with 1,3-Bis(5-chlorosalicylideneamino)-2-propanol

A mixed-valent trinuclear complex with 1,3-bis(5-chlorosalicylideneamino)-2-propanol (H₃clsalpr) was synthesized, and the crystal structure was determined by the single-crystal X-ray diffraction method at 90 K. The molecule is a trinuclear Co^III-Co^II-Co^III complex with octahedral geometries, having a tetradentate chelate of the Schiff-base ligand, bridging acetate, monodentate acetate coordination to each terminal Co³⁺ ion and four bridging phenoxido-oxygen of two Schiff-base ligands, and two bridging acetate-oxygen atoms for the central Co²⁺ ion. The electronic spectral feature is consistent with the mixed valent Co^III-Co^II-Co^III. Variable-temperature magnetic susceptibility data could be analyzed by consideration of the axial distortion of the central Co²⁺ ion with the parameters Δ = –254 cm⁻¹, λ = –58 cm⁻¹, κ = 0.93, tip = 0.00436 cm³ mol⁻¹, θ = –0.469 K, g_z = 6.90, and g_x = 2.64, in accordance with a large anisotropy. The cyclic voltammogram showed an irreversible reduction wave at approximately −1.2 V·vs. Fc/Fc⁺, assignable to the reduction of the terminal Co³⁺ ions.     

Spontaneous proton-transfer copolymerization of 2-methyl-2-oxazoline with itaconic acid

Copolymerization of two monomers, 2-methyl-2-oxazoline (1) and itaconic acid (2) was carried out. The copolymerization proceeded spontaneously in 1:1 monomer feed ratio to give 2:1 copolymer 3. The mechanism for the production of such a 2:1 copolymer was explained by the in situ formation of monomer 5 from 1 and 2. Then, the propagation proceeded between 5 and 1 via zwitterionic intermediates. When the ratio of 1 in the feed was higher, the homopropagation of 1 took place.     

Development of miniaturized sample preparation with fibrous extraction media

Introducing fine polymeric filaments as the extraction medium, a miniaturized sample preparation technique for micro-column liquid chromatography (micro-LC) has been developed along with the investigation of a reproducible preparation scheme of the extraction capillary. The polymeric filaments were packed longitudinally into either a fused-silica capillary or a polyether ether ketone (PEEK) capillary of appropriate dimensions, and the extraction capillary was installed to the injection valve in micro-LC system. The number of packed filaments should be precisely counted before the packing process to make sure the reproducible preparation of the extraction capillary. With conventional stationary phase materials for open-tubular gas chromatography, polymeric coating to the surface of the filaments was also studied in order to further enhance the extraction performance and selectivity. Coated with the polymeric material suitable for the extraction of particular analyte, a dramatic improvement on the extraction power was obtained. The results suggest that the future possibility of novel tailored fibrous extraction medium with an appropriate coating on it, especially for the analysis of complex sample matrices.     

A single-chain magnet formed by a twisted arrangement of ions with easy-plane magnetic anisotropy

A unique "single-chain quantum magnet" was formed by an alternating arrangement of high-spin FeII/low-spin FeIII ions. Although the predominant spin-carrier components (high-spin FeII) possess easy-plane magnetic anisotropy (D > 0), twisted arrangement of easy-planes along the chain axis defines a novel class of one-dimensional Ising system.     

Photocrosslinking of polymers bearing epoxy or epithio groups by quinones in the solid state

Photocrosslinking of poly(glycidyl methacrylate) (PGMA) and a copolymer of 2,3-epithiopropyl methacrylate and methyl methacrylate [P(ETMA-co-MMA)] was studied in the solid state in the presence of various quinones. The efficiency of photocrosslinking was strongly dependent upon the structures of quinones and the kinds of polymers. For example, the alkyl-substituted quinones such as 2-ethyl-p-benzoquinone (EQ), 2-tert-butyl-p-benzoquinone (tBQ) and 2,5-di-tert-butyl-p-benzoquinone (2,5-dtBQ) did not induce photocrosslinking of poly(methyl methacrylate) (PMMA), whereas they acted as efficient photocrosslinking agents in PGMA and P(ETMA-co-MMA). The formation of charge transfer complexes did not play a principal role in this effective photocrosslinking, because the order of the photocrosslinking efficiency [EQ > tBQ > 2,5-dtBQ > p-benzoquinone (Q)] was not in agreement with that of the magnitude of the electron affinities of quinones, i.e., Q > EQ > tBQ > 2,5-dtBQ. Photopolymerization of propylene sulfide (PS) in the presence of tBQ or Q was also investigated. The presence of tBQ induced polymerization of PS upon UV irradiation. From these results, it was deduced that the photocrosslinking of P(ETMA-co-MMA) film containing tBQ proceeds via a cationic polymerization of epithio groups. A similar mechanism should be applicable to the photocrosslinking of PGMA film containing tBQ.     

Short metal capillary columns packed with polymer-coated fibrous materials in high-temperature gas chromatography

The high-temperature gas chromatographic (GC) separation of several semivolatile compounds is studied with a short metal capillary column packed with fibrous material, having a polydimethylsiloxane coating thereon. Taking advantage of the excellent heat-resistance of the fiber and also the combination of the surface-deactivated metal capillary, a temperature-programmed separation up to 450 degrees C is successfully demonstrated for the separation of polymer standard samples. The average molecular weight of the commercially-available polymer standard samples for size exclusion chromatography (SEC) is estimated by high-temperature GC analysis and compared with the nominal value determined by a conventional SEC method. Although a slight deviation for the number-average molecular weight is observed between the GC and SEC analysis, the data for the weight-average molecular weight shows a good agreement in these methods. The results also suggest the future possibility of the fiber-packed metal capillary as a miniaturized GC column with an increased sample loading capacity.