Glass transition temperature of polyurethane foams derived from lignin by controlled reaction rate

Sodium ligninosulfonate (LS)-based polyurethane (PU) foams were prepared using three kinds of ethylene glycols, diethylene glycol, triethylene glycol or polyethylene glycol. Two kinds of industrial NaLS, acid-based and alkaline-based NaLS, were mixed with various ratios, and foaming reactions were controlled. Mixing, cream, and rise time were used as an index of foaming reaction. Mixing time was defined as the time interval from adding isocyanate to detection of evolved heat under stirring, cream time as the time interval from termination of stirring to starting of foaming, and rise time as the time interval from starting to completion of foaming. The above reaction time increased with increasing amount of acid base NaLS content in polyols. Apparent density, compression strength and compression modulus of PU foams linearly increased with reaction time. Thermal decomposition temperature was measured by thermogravimetry and glass transition temperature by differential scanning calorimetry. Glass transition temperature can be controlled in a temperature range from 310 to 390 K by changing the mixing rate of two kinds of LS and molecular mass of ethylene glycols. It was found that mechanical and thermal properties of PU foams are controllable through the foaming reaction rate using two kinds of industrial lignin.     

Theoretical analysis of correlation between ionization threshold fluence in IR‐MALDI and IR absorption spectrum of matrix molecules

To investigate the correlation between the wavelength dependence of ionization threshold fluence of target molecule in matrix‐assisted laser desorption/ionization by infrared (IR) laser and the IR absorption spectrum of matrix molecule, we have analyzed the IR absorption spectra of four matrix molecules using density functional theory and correlated ab initio molecular orbital method. The calculated IR absorption spectra of the isolated molecules showed more qualitative correlation with the wavelength dependence of ionization threshold fluence than those of the solid state structures. We can consider that a portion of matrix molecules lost the ordered crystal structure and that the transition to the diluted or isolated state occurred at the early process of IR laser irradiation. © 2012 Wiley Periodicals, Inc.     

Thermotropic liquid crystal behaviour of gemini imidazolium-based ionic amphiphiles

Thermotropic ionic liquid crystals (LCs) are useful for a number of applications such as anisotropic ion transport and as organised reaction media/solvents because of their ordered fluid properties and intrinsic charge units. A large number of different ionic LC architectures are known, but only a handful of examples of gemini (i.e. paired or dimeric) ionic LCs have been prepared and studied. In this work, a series of 20 new symmetric, imidazolium-based, gemini cationic LCs containing two bridged imidazolium cations and two pendant alkyl chains was synthesised, and the thermotropic LC behaviours were characterised. The imidazolium unit provides a highly tunable and modular platform for the design and synthesis of gemini cationic LCs which offers excellent structure control. As expected, the thermotropic LC properties of these new amphilphilic, gemini ionic LCs were found to be strongly influenced by the length of the spacer between the imidazolium units, the length of the pendant alkyl tails, and the nature of the anion. Smectic A (SmA) thermotropic LC phases were observed in more than half of the gemini imidazolium LC systems studied.     

Solvent-Vapor-Induced Reversible Single-Crystal-to-Single-Crystal Transformation of a Triphosphaazatriangulene-Based Metal–Organic Framework

A triphosphaazatriangulene (H₃L) was synthesized through an intramolecular triple phospha-Friedel–Crafts reaction. The H₃L triangulene contains three phosphinate groups and an extended π-conjugated framework, which enables the stimuli-responsive reversible transformation of [Cu(HL)(DMSO)⋅(MeOH)]_n, a 3D-MOF that exhibits reversible sorption characteristics, into (H₃L⋅0.5 [Cu₂(OH)₄⋅6 H₂O] ⋅4 H₂O), a 1D-columnar assembled proton-conducting material. The hydrophilic nature of the latter resulted in a proton conductivity of 5.5×10⁻³ S cm⁻¹ at 95 % relative humidity and 60 °C.     

A concise route to (+)-lactacystin

A facile chromatography-free route to Kang's intermediate for the synthesis of (+)-lactacystin, a potent proteasome inhibitor, has been developed starting with Brown's asymmetric crotylation of tert-butyl 5-formyl-2,2-dimethyl-1,3-dioxan-5-ylcarbamate, easily available from 2-amino-2-(hydroxymethyl)propane-1,3-diol (Tris).     

Thermomechanical Analysis of Polysaccharide Hydrogels in Water

Application of thermomechanometry to the measurement of hydrogels containing a large amount of water was carried out by static and dynamic methods. A thermomechanical analyzer (TMA) equipped with a quartz compression probe immersed in water was used. Polysaccharide hydrogels containing ca 98% water were measured. Creep of hydrogels in water was analyzed in a stress range from 1.04⋅10³ to 5.2⋅10³ Pa and loading rate from 0.3⋅10³ to 3.0⋅10³ Pa min⁻¹.Stress relaxation was measured in compressed ratio range from 0.02 to 0.45 m m⁻¹ and in compressing rate was 0.09 to 0.15 m m⁻¹ min⁻¹. Dynamic viscoelasticity was measured by TMA when dynamic Young’s modulus which was larger than 1⋅10⁴ Pa in frequencies ranging from 0.02~0.2 Hz. This revised version was published online in July 2006 with corrections to the Cover Date.     

Slow spin relaxation of Rb atoms confined in glass cells filled with dense 4He gas at 1.85 K

At temperatures below 2.1 K, long-lived gaseous Rb atoms in glass cells have been generated with a simple method: irradiating the cells, containing 4He gas and Rb metal, with a cw laser. The obtained atomic Rb density ( approximately 10(8) cm(-3)) decreases with a 1/e time constant of about 10 s at 1.85 K. We have performed optical pumping of the Rb atoms and measured the longitudinal electronic spin relaxation time at 1.85 K as well. For processes (such as Rb-He collisions) which do not remove the atomic Rb from the vapor, this relaxation time is found to be about 60+/-15 s.