Thermosensitive poly(methyl methacrylate) emulsion prepared in the presence of poly(vinyl alcohol) with a cloud point as a protective colloid

An emulsion of poly(methyl methacrylate) (PMMA) was prepared using poly(vinyl alcohol) (PVA) of low degree of hydrolysis with a cloud point as a protective colloid. The behaviour of an aqueous solution of PVA with 80% degree of hydrolysis was first investigated in terms of the Huggins constant in viscometry. MMA was polymerized using the PVA at 20 °C, where no abnormality in the aqueous PVA was observed. The change in transmittance of the emulsion observed with a UV–vis photometer revealed that in the case of UV light of wavelength 370 nm, the transmittance decreased markedly at around 30 °C with an increase in temperature, and then increased with a decrease in temperature. The thermosensitive property resulted from PVA with a low degree of hydrolysis with a cloud point, at a higher temperature of which the PVA loses solubility in water owing to weakening of the hydrogen bond between PVA molecules and water.     

Electrochemical characterization of cationic surfactants’ adsorption on a disturbed n-alkanethiolate self-assembled monolayer-modified polycrystalline gold electrode

The adsorption of cetyltrimethylammonium bromide (CTAB) on disturbed n-alkanethiolate self-assembled monolayers (SAMs) was investigated by electrochemical methods with potassium ferricyanide [K₃Fe(CN)₆] as a probe. Compared with the completely restrained signal at ordinary compact n-alkanethiolate SAMs, the electrochemical response of K₃Fe(CN)₆ at the disturbed n-alkanethiolate SAMs was partly restored and became progressively reversible in the presence of increasing concentrations of CTAB, which was employed to characterize the adsorption of cationic surfactants on hydrophobic SAMs. The effect of CTAB concentration on electrochemical impedance spectroscopy (EIS) plots indicated that CTAB experienced two different types of adsorptive behavior at the disturbed n-alkanethiolate SAMs: monomer adsorption at low concentrations below 1×10^–6 M and monolayer adsorption at CTAB concentrations above 1×10^–5 M. The adsorption of a series of cationic surfactants with similar structures to CTAB on disturbed n-alkanethiolate SAMs was also explored. These surfactants had similar adsorptive behavior and showed nearly linear adsorption characteristics with the length of their hydrophobic tails.     

Synthesis and Characterization of a Novel Calix[4]arene‐Based Periodic Mesoporous Organosilica

Summary: A new calix[4]arene‐based periodic mesoporous organosilica has been synthesized using tetraethoxysilane (TEOS) and a calix[4]arene‐based silane monomer as the precursors and cetyltrimethylammonium bromide (CTAB) surfactant as the structure‐directing template, and is shown to be capable of visual detection and entrapment of NO₂.

Synthesis of the novel mesoporous organosilica material containing covalently bound tetra‐O‐alkylated calix[4]arene hosts.     

Analysis of particle formation under monomer-starved conditions in emulsion polymerization reactors

An important characteristic of monomer-starved nucleation in semibatch reactors is that the rate of growth of particles is controlled by the rate of monomer addition. The reduced rate of growth of particles prolongs the nucleation interval by slowing down the rate of emulsifier micelle depletion and forms a larger number of particles (N_p). Model calculations show how N_p varies with the formulation parameters as the monomer-flooded nucleation shifts into monomer-starved one. Particle formation in the intermediate conversion of interval III of the styrene batch emulsion polymerization also showed an enhancement because of a low rate of growth of newly formed particles. However, at a higher conversion, the rate of particle formation decreased significantly. Modeling results show that the reduction in the rate of particle formation at high conversions could not be simply explained by existing theories which rely on the decrease in monomer concentration in the aqueous phase as a means to explain the decrease in the rate of radical capture.     

Octadecyltrimethylammonium surfactant-immobilized cation exchange membranes for solid-phase extraction of phenolic compounds

In this study, octadecyltrimethylammonium surfactant was immobilized onto a cation exchange membrane for the application in solid-phase extraction of phenolic compounds. The results indicate that an HCl prewashing step and the use of hydroxide (or methoxide) counter ion could greatly improve the immobilized surfactant capacity. Through elemental and thermogravimetric analyses, the resulted immobilization percentage on the membrane (compared to membrane ion exchange capacity) was about 50, 100, and 150%, respectively, for the feed surfactant amount of 150, 2000, and 5000 μmol (volume = 20 mL). Phenol, 4-nitrophenol, 2,4-dimethylphenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, and bisphenol A were the tested compounds in a breakthrough volume experiment. The order of the obtained breakthrough volume values is similar to that of K_ow values of the phenolic compounds. In the solid-phase extraction process from a feed mixture of 0.1 ppm for 4-nitrophenol, 2,4-dichlorophenol, and 4-chloro-3-methylphenol, high concentration factors and almost complete recoveries were achieved. Moreover, by increasing the membrane volume, a larger sample volume could be processed without any deterioration in performance.     

Catalyst electronic polarizability and enantiomeric excess in asymmetric hydrogenation

In the classical rhodium-diphosphine complexes-catalyzed asymmetric hydrogenation of enamide substrates, examination on the role of catalyst electronic polarizability in the origin of enantioselectivity reveals its linear free energy relationship with the product enantiomeric ratio that is much more pronounced than analogous correlation with steric effect in the same systems. From a conceptually novel scenario, this work suggests that the often-overlooked chiral catalyst local polarizability property may function as a controlling force in enantioselection thus has important implication in rational catalyst design.     

Transition‐Metal‐Free Formal Sonogashira Coupling and α‐Carbonyl Arylation Reactions

Transition‐metal‐free formal Sonogashira coupling and α‐carbonyl arylation reactions have been developed. These transformations are based on the nucleophilic aromatic substitution (S_NAr) of β‐carbonyl sulfones to electron‐deficient aryl fluorides, producing a key intermediate that, depending on the reaction conditions, gives the aromatic alkynes or α‐aryl carbonyl compounds. The development of these reactions is presented and, based on investigations under basic and acidic conditions, mechanisms have been proposed. To develop the formal Sonogashira coupling further, a milder, two‐step protocol is also disclosed that expands the reaction concept. The scope of these reactions is demonstrated for the synthesis of Sonogashira and α‐carbonyl arylated products from a range of electron‐deficient aryl fluorides with a variety of functional groups and aryl‐, heteroaryl‐, alkyl‐, and alkoxy‐substituted sulfone nucleophiles. These transition‐metal‐free reactions complement the metal‐catalyzed versions in terms of substitution patterns, simplicity, and reaction conditions.