Enhancing the fraction of grafted polystyrene on silica hybrid nanoparticles

Polymer-grafted inorganic nanoparticles are being developed for a diverse array of applications, ranging from drug delivery to multifunctional composites. In many instances, performance of these core-shell hybrids is limited by relatively broad distributions of size and composition, as well as the presence of impurities, such as unattached polymer chains. Herein, further synthetic improvements, and associated characterization techniques, to enhance the fraction of the grafted polystyrene shell on silica hybrid nanoparticles are discussed. We found that during surface-initiated atom transfer radical polymerization (SI-ATRP) from the silica nanoparticles, thermal self-initiation of styrene produces unattached polymer chains. Size exclusion chromatography afforded a facile approach to quantify the mass of the unattached polymer, and provide a substantial refinement to estimates of chain graft density beyond traditionally-used approaches, such as thermogravimetry. This fraction of unattached polymer is still present even after post-polymerization work-up via precipitation and re-dissolution. Removal necessitates additional procedures, such as high speed centrifugation. Selection of a lower polymerization temperature, in concert with a more reactive Cu complex, significantly reduces the amount of unattached polystyrene impurity. The improved polymerization conditions and post-polymerization purification provide more refined polystyrene-grafted silica nanoparticles to clarify structure-property relationships of these core-shell hybrids.     

Hydrogenation of nitriles with iridium-triphenylphosphine complexes

Reactions of cationic iridium(I)-COD (COD = 1,5-cyclooctadiene) complexes, [Ir(COD)(PhCN)(PPh₃)]ClO₄ (1), [Ir(COD)(PPh₃)₂]ClO₄ (2) and [Ir(COD)(PhCN)₂]ClO₄ (3) with nitriles under H₂ catalytically produce primary, secondary and tertiary amines. Hydrogenation of nitriles (RCN) gives HCl salts of amines (RCH₂NH₂HCl, (RCH₂)₂NH HCl) in CH₂Cl₂. Secondary and tertiary amines seem to be produced by the reactions of RCN with primary and secondary amines, respectively under H₂ in the presence of catalysts. The hydrogenation in the presence of1 and2 is homogeneously catalyzed by soluble iridium-PPh₃ complexes formed in the reactions of1 and2 with H₂ and RCN whereas the hydrogenation in the presence of3 is heterogeneous by metallic iridium powders produced in the reduction of3 by H₂.     

The synthesis and characterization of novel 2-nitrobenzyl sulfonate photo-generators of acid

Methodology was developed for the synthesis of novel 2-substituted o-nitrobenzyl chromophores, which were derivatized as the tosylate esters. The thermal stabilities of these new tosylates fell within the range predicted from an empirical model. Lithographic sensitivities of deep UV resists made from these new esters and poly(4-(tert-butoxycarbonyloxy)styrene-sulfone) ranged from 45 to 90 mJ/cm².     

Electrorheological responses of particulate suspensions and emulsions in a small-strain dynamic shear flow: Viscoelasticity and yielding phenomena

The dynamic rheological behavior of multiphase electrorheological (ER) fluids was considered, as continuation of a previous paper [Chin and Park, 2000]. Oil-in-oil emulsions, which differ in electrical conductivity and dielectric constant, were employed for an ER-active emulsion and also for a multiphase ER fluid with enhanced performance. The polyaniline particle suspension in an electric field showed viscoelastic behavior within a very limited range of strain amplitude, indicating the transition from viscoelasticity to viscoplasticity. Within the region of visco-elasticity, the linear region was restricted below the amplitude of 0.1%, whereas the ER-active emulsions showed a rather wide linear regime. Frequency dependence of the storage shear modulus in the linear viscoelastic region revealed the typical features of an elastic solid. When the fraction of emulsion drops (Ф) in multiphase ER fluids increased, the limiting strain for viscoelasticity showed a higher value.     

Factors Impacting the Formation of 3-MCPD Esters and Glycidyl Esters During Deep Fat Frying of Chicken Breast Meat

The effect of the frying temperature, frying duration and the addition of NaCl on the formation of 3‐monochloropropane‐1,2‐diol (3‐MCPD) esters and glycidyl esters (GE) in palm olein after deep frying was examined in this study. The eight frying systems were deep‐fat frying (at 160 and 180 °C) of chicken breast meat (CBM) (with 0, 1, 3 and 5% sodium chloride, NaCl) for 100 min/day for five consecutive days. All oil samples collected after each day were analyzed for 3‐MCPD ester, GE, and free fatty acid (FFA) contents, specific extinctions at 232 and 268 nm (K₂₃₂ and K₂₆₈), p‐anisidine value (pA), and fatty acid composition. There was a significant (p < 0.05) decrease in the 3‐MCPD esters and a significant (p < 0.05) decrease in the GE with the increasing of the frying duration. There were significant (p < 0.05) increases in the 3‐MCPD esters formed when the concentration of NaCl increased from 0 to 5%. The addition of NaCl to the CBM during deep frying had no significant effect on the GE generation. The FFA contents, K₂₃₂ and K₂₆₈ and pA showed that all the frying oils were within the safety limit.     

Development of a Coconut- and Palm-Based Fat Blend for a Cookie Filler

Thirteen fat blends intended for cookie filler (CF) production that consist of 20–70 % palm mid-fraction (PMF), 20–70 % virgin coconut oil (VCO), and 0–10 % palm stearin (POs) were developed based on the solid fat contents (SFC) of the fat portions extracted from five commercial CF samples: A, B, C, D, and E. A mixture design was applied for fat blend optimization, and the combination that best approached the target SFC values was composed of 70 % PMF, 20 % VCO, and 10 % POs. The optimized coconut- and palm-based fat blend (O-CP) exhibited a steeper SFC profile, with 8.2 % (±0.2) SFC at 25 °C (room temperature) and 0.2 % (±0.2) SFC at 37 °C (body temperature); lower slip melting point of 34.0 °C (±0.0); and a lower iodine value (IV) of 40.25 g/100 g (±1.04). In addition, O-CP contained higher proportions of medium-chain fatty acids (MCFA) and lauric acid (C12:0) of 3.2 % (±0.18) and 9.7 % (±0.43), respectively. In terms of its thermal profile, O-CP showed no significant difference in terms of its crystallization range, 49.7 °C (±2.66) with the exception of sample C, but it exhibited a smaller melting range, 65.8 °C (±1.47), compared to the fat portions of the commercial samples. The ranges represented the span between the onset and offset temperatures of both crystallization and melting profiles as determined by differential scanning calorimetry.     

Production of Furfural from Lignocellulosic Biomass Using Beta Zeolite and Biomass-Derived Solvent

The production of furfural from the C₅ monosaccharides xylose, arabinose and ribose, as well as from real biomass (corn fiber), was studied using H-Beta zeolite as catalyst in a monophasic system with the biomass-derived solvent, gamma-valerolactone. Due to the combination of Brønsted and Lewis acid sites on this catalyst (Brønsted:Lewis ratio = 1.66), H-Beta acts as a bifunctional catalyst, being able to isomerize (Lewis acid) and dehydrate (Brønsted acid) monosaccharides. The combination of Lewis and Brønsted acid functionality of H-Beta was shown to be effective for the isomerization of xylose and arabinose, followed by dehydration. While no advantages were found in the conversion of xylose, higher furfural yields were achieved from arabinose, using H-Beta, 73 %, compared to sulfuric acid (44 %) and Mordenite (49 %). The furfural yields from corn fiber for H-Beta, H-Mordenite and sulfuric acid were 62, 44, and 55 %, respectively, showing that H-Beta is particularly effective for conversion of this biomass feedstock composed of 45 wt% hemicellulose, of which 66 % is xylose and 33 % arabinose.     

Regeneration of PAC saturated by bisphenol A in PAC/TiO2 combined photocatalysis system

This study investigated a dual function system combining powdered activated carbon (PAC) and TiO₂ for the removal of trace organics together with the in-situ regeneration of PAC. The combined system with PAC adsorption and TiO₂ photo-oxidation for in-situ regeneration of the PAC was studied as a batch process. Bisphenol A (BPA), an endocrine disrupting compound present at low concentration levels, was used as a model compound. When UV light and 0.5 l min^− 1 of oxygen were introduced to the PAC/TiO₂ batch system, the removal of BPA was 2.3 to 3.1 times faster than that of neat TiO₂ oxidation in the pH range of 4 to 10. However, mass transfer of the adsorbed BPA by diffusion from the PAC to oxidation sites on the surface of the TiO₂ was found to be limited because PAC has a strong affinity to adsorb BPA. During in-situ regeneration of PAC by TiO₂ photo-oxidation at pH 7 for 6 h, the removal of BPA from the PAC which was fully saturated with BPA was about 50%. The regeneration of the PAC was improved by increasing the UV-irradiation time (4 h to 12 h) and the light intensity (0.13 mW cm^− 2 to 0.425 mW cm^− 2), but it was not enhanced by increasing temperature, operating at basic conditions, or adding H₂O₂. The results suggest that a process with in-situ regeneration of PAC by TiO₂ oxidation may be feasible.