Structural symmetry breaking of silicon‐containing poly(amide‐imide) oligomers and its relation to electrical conductivity and Raman‐active vibrations

Optically active poly(amide‐imide) oligomers were synthesized by direct polycondensation between an aromatic diamine and a dicarboxylic acid both containing a diphenylsilylene unit. The reaction was carried out using triphenyl phosphite/pyridine in the presence of CaCl₂ and N‐methyl‐2‐pyrrolidone as solvent. Oligomers were obtained in good yields and showed high solubility in common aprotic polar solvents. The precursors, monomers and poly(amide‐imide) oligomers were characterized using elemental analysis and Fourier transform infrared and NMR (¹H, ¹³C, ²⁹Si) spectroscopy. Additionally, the main vibrations of the functional groups (C?O, C?C or N? H) in the oligomers with respect to temperature were characterized using Raman spectroscopy. The glass transition temperature was determined by studying the Raman spectra and corroborated using differential scanning calorimetry. The thermal stability was studied using thermogravimetric analysis. The molecular mass of the compounds was obtained from matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry and their optical properties were analyzed using UV‐visible diode array spectrophotometry. The electronic properties of the oligomers as well as the delocalization of charge carriers within their structures were analyzed using conductance‐voltage curves, which showed that these materials are excellent candidates for integrated optoelectronic applications. Copyright © 2011 Society of Chemical Industry     

Thiophene‐ and silarylene‐containing polyesters. Resonance effect on conductivity after polarization in an external electric field

Polyesters were synthesized by direct polycondensation of thiophene‐2,5‐dicarboxylic acid and five different silarylene‐containing diphenols using a tosyl chloride/pyridine/N,N‐dimethylformamide system as a condensing agent. Polymers were obtained in good yields and were characterized using Fourier transform infrared and NMR (¹H, ¹³C, 135‐DEPT and ²⁹Si) spectroscopy and elemental analysis. All polymers were completely soluble in aprotic organic polar solvents such as dimethylformamide, dimethylsulfoxide and N‐methyl‐2‐pyrrolidone. The range of effective mass of the polymers (m/z) was 1 × 10⁵–2 × 10⁵, determined using electrospray ionization mass spectrometry. Asymmetry and steric hindrance prevented dense packing of the polymeric chains, showing glass transition temperatures between ? 78 and ? 51 °C and loss of thermal stability at 177–199 °C (10% weight loss). Additionally, the melting points of the polyesters were found to be in the range 62–67 °C. Because of this, the samples were semi‐solid at room temperature. The optical band gaps of the polymers were observed between 4.54 and 4.48 eV, corresponding in all cases to insulator behavior. The molecular structure of the samples was studied using X‐ray diffraction, showing a degree of order that was associated with two monoclinic lattices. Additionally, the conductivity was studied using a two‐point method with contacts on top of polymer films. Prior to the electrical measurement, the samples were polarized in an external electric field of 0.8 to 6.4 V cm^?1, and the alignment of the dipoles increased the electrical conductivity. Copyright © 2012 Society of Chemical Industry     

Copolymerization of styrene by diphenylzinc-additive systems. Part II: Copolymerization of styrene/1-alkene by Ph2Zn-metallocene-MAO systems

Summary The copolymerization of styrene with 1-alkene (1-hexene, 1-decene and 1-hexadecene) has been tested using combined diphenylzinc-additive initiator systems, including diphenylzinc (Ph₂Zn), a metallocene and methylaluminoxane (MAO). The metallocene were biscyclopentadienyltitanium dichloride, bis(n-butylcyclopentadienyl)titanium dichloride, cyclopentadienyltitanium trichloride and bisindenylzirconium dichloride. For Ph₂Zn-metallocene-MAO systems, titanocenes gave mainly syndiotactic homo polystyrene irrespective of the styrene/1-alkene proportion in the initial feed. Systems including Ind₂ZrCl₂ were able to copolymerize styrene 1-alkene with the copolymers incorporating alkene in a lower proportion than the present in the initial feed. Keywords: Styrene copolymerization; diphenylzinc; metallocene catalysts; tacticity. Received: 17 November 2000/Revised version: 9 May 2001/Accepted: 10 May 2001     

Tert-butyl acetate: Non-HAP solvent for high-solids epoxy formulations

Xylene is the traditional diluent solvent for formulating epoxy/amine paints used in protective coatings and linings. Currently, it is under regulatory pressure because it is on the hazardous air pollutant (HAP) list and it is also a volatile organic compound (VOC). Ketones and acetate esters are powerful solvents, but their use is limited by their reaction with the amine curatives before paint application. Tert-butyl acetate (t-BAc) proposed as a VOC-exempt solvent, is a nonreactive, non-HAP solvent suitable for both the epoxy resin and amine curative sides of a two-component epoxy system. Molecular modeling predicts very low reactivity of the t-BAc ester functionality with amine nucleophiles as a result of steric hindrance. Long-term aging studies with amine curatives in t-BAc solutions confirm these theoretical results. Kinetics of the reaction of amines with t-BAc and its n-butyl acetate isomer support the view that steric hindrance plays a major role in amine solution stability. Presented at the International Waterborne, High-Solids, and Powder Coatings Symposium, February 21–23, 2001, New Orleans, LA. 3801 West Chester Pike, Newtown Square, PA 19073.     

Experimental analyses of the poly(vinyl chloride) foams' mechanical anisotropic behavior

Assessing a full set of mechanical properties is a rather complicate task in the case of foams, especially if material models must be calibrated with these results. Many issues, for example anisotropy and heterogeneity, influence the mechanical behavior. This article shows through experimental analyses how the microstructure affects different experimental setups and it also quantifies the degree of anisotropy of a poly(vinyl chloride) foam. Monotonic and cyclic experimental tests were carried out using standard compression specimens and non‐standard tensile specimens. Results are complemented and compared with the aid of a digital image correlation technique and scanning electron microscopy analyses. Mechanical properties (e.g., elastic and plastic Poisson's ratios) are evaluated for compression and tensile tests, for two different material directions (normal and in‐plane). The material is found to be transversely isotropic. Differences in the results of the mechanical properties can be as high as 100%, or even more depending on the technique used and the loading direction. Also, the experimental analyses show how the material's microstructure behavior, like the evolution of the herein identified “yield fronts” and a “spring back” phenomenon, can influence the phenomenological response and the failure mechanisms as well as the hardening curves. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Distributed Control Strategy with Smith's Predictor in a Pilot-Scale Diabatic Distillation Unit

Intrinsic characteristics of distillation such as dead time and high nonlinearities do not allow the complete elimination of transient times when any external disturbance or set-point change occurs. Thus, aiming at the use of easy-tuning systems, a distributed-action control in trays of a diabatic distillation unit with Smith's predictor was implemented in the Simulink environment to further reduce transient times and out-of-specification product. The distributed-action strategy with Smith's predictor led to a reduction of 33.3 min (33 %) in the transient time of the top temperature control loop and 66 % in out-of-specification product, when compared with the conventional strategy, and thus is shown to be an efficient approach to increasing the productivity of distillation plants.     

Coenzyme Q10: Novel Formulations and Medical Trends

The aim of this review is to shed light over the most recent advances in Coenzyme Q₁₀ (CoQ₁₀) applications as well as to provide detailed information about the functions of this versatile molecule, which have proven to be of great interest in the medical field. Traditionally, CoQ₁₀ clinical use was based on its antioxidant properties; however, a wide range of highly interesting alternative functions have recently been discovered. In this line, CoQ₁₀ has shown pain-alleviating properties in fibromyalgia patients, a membrane-stabilizing function, immune system enhancing ability, or a fundamental role for insulin sensitivity, apart from potentially beneficial properties for familial hypercholesterolemia patients. In brief, it shows a remarkable amount of functions in addition to those yet to be discovered. Despite its multiple therapeutic applications, CoQ₁₀ is not commonly prescribed as a drug because of its low oral bioavailability, which compromises its efficacy. Hence, several formulations have been developed to face such inconvenience. These were initially designed as lipid nanoparticles for CoQ₁₀ encapsulation and distribution through biological membranes and eventually evolved towards chemical modifications of the molecule to decrease its hydrophobicity. Some of the most promising formulations will also be discussed in this review.     

New Formulation of a Methylseleno-Aspirin Analog with Anticancer Activity Towards Colon Cancer

Aspirin (ASA) has attracted wide interest of numerous scientists worldwide thanks to its chemopreventive and chemotherapeutic effects, particularly in colorectal cancer (CRC). Incorporation of selenium (Se) atom into ASA has greatly increased their anti-tumoral efficacy in CRC compared with the organic counterparts without the Se functionality, such as the promising antitumoral methylseleno-ASA analog (1a). Nevertheless, the efficacy of compound 1a in cancer cells is compromised due to its poor solubility and volatile nature. Thus, 1a has been formulated with native α-, β- and γ-cyclodextrin (CD), a modified β-CD (hydroxypropyl β-CD, HP-β-CD) and Pluronic F127, all of them non-toxic, biodegradable and FDA approved. Water solubility of 1a is enhanced with β- and HP- β-CDs and Pluronic F127. Compound 1a forms inclusion complexes with the CDs and was incorporated in the hydrophobic core of the F127 micelles. Herein, we evaluated the cytotoxic potential of 1a, alone or formulated with β- and HP- β-CDs or Pluronic F127, against CRC cells. Remarkably, 1a formulations demonstrated more sustained antitumoral activity toward CRC cells. Hence, β-CD, HP-β-CD and Pluronic F127 might be excellent vehicles to improve pharmacological properties of organoselenium compounds with solubility issues and volatile nature.