Demonstration of isospecific free radical polymerization of acrylate controlled by conformation and chirality of monomer

Radical polymerization of lactic acid‐based chiral and achiral methylene dioxolanones, a model for conformationally s‐cis locked acrylate, was carried out with AIBN to demonstrate an isospecific free radical polymerization controlled by chirality and conformation of monomer. Polymerization of the dioxolanones proceeded smoothly without ring opening to give a polymer with moderate molecular weight and 100% of maximum isotacticity. ESR spectrum indicated a twisted conformation of the growing poly(methylene dioxolanone) radical in contrast to an acyclic analogous radical, suggesting a restriction of the free rotation around main chain C_α? C_β bond of the growing radical center. Chirality as well as the polarity and bulkiness of monomer affected the polymer tacticity, and chiral alkyl substituent would afford a high isotactic polymer, in which higher the enantiomeric excess of the monomer was, higher the isotacticity of the polymer was. While, achiral or polar substituents including dibenzyl and trichloromethyl groups would afford an atactic polymer. In addition, glass transition temperature (T_g) of the resulting polymers was significantly high, ranging from 172.2 to 229.8 °C, and even for an isotactic polymer T_g was as high as 206.8 °C. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2007–2016     

Synthesis of hyperbranched polyacetals via an + b2‐type polyaddition (n = 3, 8, 18, and 21): Candidate resists for extreme ultraviolet lithography

Polyaddition (A_n + B₂) reactions of 1,1,1‐tris(4‐hydoxyphenyl) ethane (THPE; A₃‐type monomer), calix[4]resorcinarene (CRA[4]; A₈‐type monomer), α‐cyclodextrin (α‐CD; A₁₈‐type monomer), and β‐cyclodextrin (β‐CD; A₂₁‐type monomer) with 1,4‐bis(4‐vinyloxy)cyclohexane (BVOC; B₂‐type monomer) afforded corresponding soluble hyperbranched polyacetals. The physical properties, including solubility, thermal stability, and film‐forming ability, the ultraviolet‐induced degradation reactivity, and the solubility‐switch in an extreme ultraviolet (EUV) exposure tool indicated that poly(THPE‐co‐BVOC) and poly(CRA[4]‐co‐BVOC) are candidate next‐generation photo‐resists. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2343–2350     

Analyzing the Case for Bifunctional Catalysis

Bifunctional coupling of two different catalytic site types has often been invoked to explain experimentally observed enhanced catalytic activities. We scrutinize such claims with generic scaling‐relation‐based microkinetic models that allow exploration of the theoretical limits for such a bifunctional gain for several model reactions. For sites at transition‐metal surfaces, the universality of the scaling relations between adsorption energies largely prevents any improvements through bifunctionality. Only the consideration of systems that involve the combination of different materials, such as metal particles on oxide supports, offers hope for significant bifunctional gains.     

Analysis of magnetic and structural phase transition behaviors of La1−xSrxCrO3 for preparation of phase diagram

The phase transition behavior of perovskite-type compounds, La_1−xSr_xCrO₃, was investigated by differential scanning calorimetry (DSC), dilatometry, dc magnetic susceptibility measurement and X-ray diffraction analysis. Both second-order magnetic phase transition from antiferromagnetic to paramagnetic and first-order structural phase transition from orthorhombic to rhombohedral were observed in the DSC or dilatometric curve of every specimen. The temperatures of both these magnetic and structural phase transitions decreased linearly with an increase in Sr content. The structural phase transition temperature of La_1−xSr_xCrO₃ with x less than 0.11 is higher than the magnetic phase transition temperature; however, a larger decrease in structural phase transition temperature than in magnetic phase transition temperature was observed with an increase in Sr content, resulting in a structural phase transition temperature lower than the magnetic phase transition temperature for La_1−xSr_xCrO₃ with x of more than 0.12. It was also observed that the heat of absorption of the structural phase transition decreased with an increase in x. In the dependence of dc magnetic susceptibility on temperature, variations by not only magnetic but also structural phase transitions were observed. It was also revealed that thermal expansion coefficient is affected not only by structural phase transition but also magnetic phase transition. Magnetic and structural phase diagram of La_1−xSr_xCrO₃, suggesting the existence of two Sr contents and temperatures at which triple phases coexist, was proposed.     

Simultaneous determination of testosterone and androstadienone (sex attractant) in human plasma by gas chromatography-mass spectrometry with high-resolution selected-ion monitoring

Androsta-4,16-dien-3-one (androstadienone) and androst-4-en-3-one-17 beta-ol (testosterone) in healthy human plasma were simultaneously determined under several experimental conditions by gas chromatography-mass spectrometry with high-resolution selected-ion monitoring. Internal standards were [2,2,4,6,6-2H5]androstadienone and [2,2,4,6,6-2H5]testosterone. Samples were extracted with an Extrelut column, purified using Lipidex 5000 and converted into hydroxime-trimethylsilyl derivatives for determination. Physiological concentrations of androstadienone and testosterone found in eleven healthy men were 2.05 +/- 0.74 and 18.6 +/- 4.9 pmol/ml in plasma (mean +/- S.D.), respectively. No correlation was observed between these steroid concentrations.     

Polymer design for thermally stable polyimides with low dielectric constant

We successfully prepared a series of thermally stable polyimides (PIs) with low dielectric constant (k) by introducing bulky diphenyl fluorenylidene moieties in backbone. The lowest k was found to be 2.77 among non-fluorinated PIs and 2.35 among fluorinated ones. In order to prove the lowest limit of k in PIs, we prepared soluble and thermally stable polyarylenes (PArs) without polar imide linkage with the same aromatic moieties by coupling polymerization. The lowest k was 2.7 without fluorine (F) and 2.2 with F atom, which showed also promising for low k materials. From these results, PIs we prepared were estimated to the lowest k values among PIs. On the basis of statistics on these results, we could express contour lines of k as a function of imide concentration and F content with high correlation factor (r= 0.96) in PIs and PArs.