Versatility of a succinimidyl‐ester functional alkoxyamine for controlling acrylonitrile copolymerizations

Styrene/acrylonitrile (S/AN) and tert‐butyl methacrylate/acrylonitrile (tBMA/AN) copolymers were synthesized in a controlled manner (low polydispersity $ {{\overline M _w } / {\overline M _n }} $ with linear growth of number average molecular weight $ \overline M _n $ vs. conversion X) by nitroxide mediated polymerization (NMP) with a succinimidyl ester (NHS) terminated form of BlocBuilder unimolecular initiator (NHS‐BlocBuilder) in dioxane solution. No additional free nitroxide (SG1) was required to control the tBMA‐rich copolymerizations with NHS‐BlocBuilder, a feature previously required for methacrylate polymerizations with BlocBuilder initiators. Copolymers from S/AN mixtures (AN molar initial fractions f_AN,0 = 0.13–0.86, T = 115°C) had $ {{\overline M _w } / {\overline M _n }} $ = 1.14–1.26 and linear $ \overline M _n $ versus conversion X up to X ≈ 0.6. tBMA/AN copolymers (f_AN,0 = 0.10–0.81, T = 90°C) possessed slightly broader molecular weight distributions ( $ {{\overline M _w } / {\overline M _n }} $ = 1.23–1.50), particularly as the initial composition became richer in tBMA, but still exhibited linear plots of $ \overline M _n $ versus conversion X up to X ≈ 0.6. A S/AN/tBMA terpolymerization (f_AN,0 = 0.50, f_S,0 = 0.40) was also conducted at 90°C and revealed excellent control with $ \overline M _n $ = 13.6 kg/mol, $ {{\overline M _w } / {\overline M _n }} $ = 1.19, and linear $ \overline M _n $ versus conversion X up to X = 0.54. Incorporation of AN and tBMA in the final copolymer (molar composition F_AN = 0.47, F_tBMA = 0.11) was similar to the initial composition and represents initial designs to make tailored, acid functional AN copolymers by NMP for barrier materials. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Lewis acid–base properties of cellulose acetate phthalate‐polycaprolactonediol blend by inverse gas chromatography

The net retention volumes, V_N, of n‐alkanes and five polar probes are determined on cellulose acetate phthalate–polycaprolactonediol blend column by inverse gas chromatography in the temperature range 323.15–363.15 K. The dispersive surface energy, $\gamma _{\bf S}^{\bf d}$ , of the blend has been calculated using the V_N values of n‐alkanes and the $\gamma _{\bf S}^{\bf d}$ at 333.15 K is 12.6 mJ/m². The $\gamma _{\bf S}^{\bf d}$ values are decreasing linearly with increase of temperature. The V_N values of the five polar solutes are used to calculate the specific component of the enthalpy of adsorption, ${\Delta }{H}_{\bf a}^{\bf S}$ . The Lewis acid–base parameters, K_a and K_b, are derived using ${\bf \Delta }{H}_{\bf a}^{\bf S}$ values and are found to be 0.019 and 0.403, respectively. The K_a and K_b values indicate that the blend surface contain more basic sites and interact strongly with the acidic probes. The acid–base parameters have been used to analyze the preferential interaction of the solid surface with acidic and basic probes. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

Tailoring the Degree of Polymerization of Low Molecular Weight Cellulose

The degradation of cellulose to lmw samples with $\overline {DP} _{{\rm w}} $ varying from 15 to 130 is investigated. Cellulose samples prepared from the hydrolysis of regenerated cellulose fibers in dilute HCl possess $\overline {DP} _{{\rm w}} $ = 50. Applying homogenous degradation of microcrystalline cellulose in H₃PO₄ at RT for 3 weeks, samples with $\overline {DP} _{{\rm w}} $ = 35 and a PDI of 1.58 are obtained. Decreasing the hydrolysis temperature to 8 °C results in lmw cellulose with $\overline {DP} _{{\rm w}} $ > 70. Fractionation in DMA/LiCl provides samples with $\overline {DP} _{{\rm w}} $ = 12 to 130, together with a narrow molecular weight distribution. Detailed structural analysis by 2D NMR spectroscopy reveals that the prepared lmw celluloses are suitable as mimics for cellulose.

     

Adsorptive removal of nitrate and phosphate anions from aqueous solutions using functionalised SBA‐15: Effects of the organic functional group

Adsorption of nitrate and monovalent phosphate anions from aqueous solutions on mono, di‐ and tri‐ammonium‐functionalised mesoporous SBA‐15 silica was investigated. The adsorbents were prepared via a post‐synthesis grafting method, using either 3‐aminopropyltrimethoxysilane (N‐silane) or [1‐(2‐aminoethyl)‐3‐aminopropyl]trimethoxysilane (NN‐silane) or 1‐[3‐(trimethoxysilyl)‐propyl]‐diethylenetriamine (NNN‐silane), followed by acidification in HCl solution to convert the attached surface amino groups to positively charged ammonium moieties. The nominal loading of amino moieties on the SBA‐15 surface was varied from 5% to 20% as organoalkoxysilane/silica molar ratio. The adsorption experiments were conducted batchwise at room temperature. Results showed that adsorption capacity increased with increasing the concentration of monoammonium groups on the SBA‐15 adsorbent. Nitrate adsorption capacity increased from 0.34 to 0.66 mmol ${\rm NO}_{3}^{{-} } /{\rm g}$ adsorbent while phosphate adsorption capacity increased from 0.34 to 0.63 mmol ${\rm H}_{2} {\rm PO}_{4}^{{-} } /{\rm g}$ adsorbent when the molar ratio organoalkoxysilane/silica was varied from 5% to 20%, respectively. Also, for the same organoalkoxysilane/silica molar ratio of 10%, the adsorption capacity increased with the increase of the number of protonated amines in the functional groups. Therefore, maximum adsorption capacities of 0.80, 1.16 and 1.38 mmol ${\rm NO}_{3}^{{-} } /{\rm g}$ adsorbent and 0.72, 0.82 and 1.17 mmol ${\rm H}_{2} {\rm PO}_{4}^{{-} } /{\rm g}$ adsorbent were obtained using mono‐, di‐ and triammonium functionalised SBA‐15 adsorbents, respectively. © 2011 Canadian Society for Chemical Engineering     

Dielectric properties of high coercivity barium ferrite–natural rubber composites

The effect of frequency, temperature, and BaFe₁₂O₁₉ (BF) content on the dielectric constant $ \acute\varepsilon $ , dielectric loss ε″, and tan δ were studied for barium ferrite—natural rubber composites (RFC). The dielectric constant for barium ferrite was related to the preparation method, meanwhile the dielectric constant of natural rubber (NR) is relatively large compared to the theoretical value. The results showed that $ \acute\varepsilon $ , ε″, and tan δ for RFC decrease as the frequency increases, however, at higher frequencies, the effect significantly weakens. At low ferrite loading, the dielectric properties are strongly influenced by BF content. Strong correlation between magnetic initial permeability and dielectric constant for hard magnetic material polymer composites was also observed. Increasing the content of barium ferrite in NR matrix enhances both ε″ and tan δ. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

MHD flow and heat transfer over stretching/shrinking sheets with external magnetic field,viscous dissipation and Joule effects

The present article considers the steady magnetohydrodynamic (MHD) laminar boundary layer flow of a viscous and incompressible electrically conducting fluid near the stagnation point on a horizontal stretching or shrinking surface, with variable surface temperature and a constant magnetic field applied normal to the surface of the sheet. The governing system of partial differential equations is first transformed into a system of ordinary differential equations by introducing an appropriate similarity transformation, which is then solved numerically using a finite‐difference scheme known as the Keller‐box method. The effects of the governing parameters on the skin friction coefficient, the local Nusselt number as well as the velocity and temperature profiles are determined and discussed. Results indicate that for the stretching sheet, solution exists and is unique for all values of the stretching/shrinking parameter $\lambda $ , while for the shrinking sheet, solutions only exist up to some critical values $\lambda = \lambda _{{\rm c}} $ , and these solutions may be unique, dual and sometimes triple. © 2011 Canadian Society for Chemical Engineering     

Solvent effects in the hydrodechlorination of 2,4‐dichlorophenol over Pd/Al2O3

Solvent effects in the liquid phase (0.1 MPa; 303 K) hydrodechlorination (HDC) of 2,4‐dichlorophenol have been established over Pd/Al₂O₃. In the absence of secondary reactions, catalyst deactivation, and transport limitations, a stepwise HDC yields 2‐chlorophenol and phenol, where product selectivity was insensitive to the nature of the solvent. In contrast, the initial HDC rates exhibited a marked dependence on the reaction medium and increased in the order: benzene < THF < n‐hexane < cyclohexane < alcohols < water. Higher rates result from the concomitant effect of an increase in the dielectric constant (ε) and a decrease in the molar volume ( $\overline {\nu}$ ) of the solvent, where the major (ca. 80%) contribution is due to ε. We attribute this response to the increased solvent capacity to stabilize the arenium intermediate at higher/lower ε/$\overline {\nu}$ , an effect that extends to reaction in water + organic combinations. We provide, for the first time, a reliable quantification of solvent effects that can be potentially applied to other catalytic hydrogenolysis systems. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Natural polyphenols as chain‐breaking antioxidants during methyl linoleate peroxidation

A technique based on monitoring oxygen consumption was applied to study 11 natural and model polyphenols (PP, QH₂) as well as four typical monophenolics as a chain‐breaking antioxidant during the controlled chain oxidation of methyl linoleate (ML) in bulk at 37°C. The antioxidant activities of QH₂ were characterized by two parameters: the rate constant k₁ for reaction of QH₂ with the peroxy radical ${\rm LO}_{2}^{{\bf .}} $ : (i) QH₂ + ${\rm LO}_{2}^{{\bf .}} $ → ${\rm QH}^{{\bf .}} $ + LOOH and the stoichiometric factor of inhibition, f, which shows how many kinetic chains may be terminated by one molecule of QH₂. The rate constant k₁ were reduced significantly by factor of 4 –28 as compared to these determined during the oxidation of styrene in bulk; the effect was typically more pronounced for catechol derivatives than for pyrogallol derivatives. At the same time, f for QH₂ was found to be close to two independent of the number of active OH groups, similar to that determined earlier during the inhibited oxidation of styrene. The formation of H bond between OH group of QH₂ and carboxyl group of ML is suggested as a reason for reducing effect of ML on k₁. Practical applications : This work reports rate constants for the reaction of lipid peroxyl radical with phenolics and stoichiometric coefficient of inhibition, which characterize the antioxidant activity (AOA) of 15 natural and model PP, QH₂ during the controlled peroxidation of ML. The reactivity of PP, QH₂ during the oxidation of ML is routinely lower than the reactivity during the oxidation of non‐polar model hydrocarbons. This information may be useful to estimate the AOA of natural PP, QH₂ in real systems of practical significance including plant oils, fats, food‐stuffs, biological objects, and similar.     

CLA TAG rich in cis‐9,trans‐11‐CLA is stable beyond 2 years of proper storage

We analyzed a triacylgylcerol esterified CLA preparation characteristically rich in c9,t11‐CLA and free of t10,c12‐CLA three times within a period of 2${1 \over 2}$ years by GC and silver ion‐HPLC. For the first time, we present data on the long‐term stability of this preparation with regard to the fatty acid profile and the isomeric composition of CLA under certain storage conditions, providing useful information for the planning of long‐term trials.     

Ring‐opening metathesis polymerization of bicyclo[2.2.1]hepta‐2,5‐diene (norbornadiene) initiated by new ruthenium(II) complex

The polymerization of norbornadiene (NBD) initiated by a novel ruthenium (Ru)(II) complex ( 3 ) containing 1,1′‐pyridine‐2,6‐diylbis[3‐(dimethylamino)prop‐2‐en‐1‐one] ( 1 ) as ligand has been investigated. Ru complexes exhibit more catalytic activity in the ring‐opening metathesis polymerization (ROMP) of NBD when activated with trimethylsilyldiazomethane (TMSD). The influence of the various experimental parameters such as reaction time and temperature, nature of the solvent and catalyst, ratio of the NBD/Ru, and TMSD addition has been investigated. The polymers have been obtained in high yields with a relatively low polydispersity index for ROMP and a high $ \bar M_n $ and $ \bar M_w $ values in a monomodal distribution. Their structures have been determined by means of FTIR and ¹H‐NMR spectroscopy. Thermal properties have been determined via thermogravimetric analysis and DTG methods. The NBD polymerization results that initiated by Ru‐based catalyst coordinated to amine ligand have been compared to initiated by [RuCl₂(p‐cymene)]₂. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Transfer RNA Misidentification Scrambles Sense Codon Recoding

Sense codon recoding is the basis for genetic code expansion with more than two different noncanonical amino acids. It requires an unused (or rarely used) codon, and an orthogonal tRNA synthetase:tRNA pair with the complementary anticodon. The Mycoplasma capricolum genome contains just six CGG arginine codons, without a dedicated tRNA^Arg. We wanted to reassign this codon to pyrrolysine by providing M. capricolum with pyrrolysyl‐tRNA synthetase, a synthetic tRNA with a CCG anticodon (${{\rm tRNA}{{{\rm Pyl}\hfill \atop {\rm CCG}\hfill}}}$ ), and the genes for pyrrolysine biosynthesis. Here we show that ${{\rm tRNA}{{{\rm Pyl}\hfill \atop {\rm CCG}\hfill}}}$ is efficiently recognized by the endogenous arginyl‐tRNA synthetase, presumably at the anticodon. Mass spectrometry revealed that in the presence of ${{\rm tRNA}{{{\rm Pyl}\hfill \atop {\rm CCG}\hfill}}}$ , CGG codons are translated as arginine. This result is not unexpected as most tRNA synthetases use the anticodon as a recognition element. The data suggest that tRNA misidentification by endogenous aminoacyl‐tRNA synthetases needs to be overcome for sense codon recoding.     

Diffusion of semi‐flexible polyelectrolyte through nanochannels

The diffusion of sodium polystyrene sulfonate through polycarbonate nanochanels was studied in salt‐free dilute aqueous solution. A stronger molecular weight dependence of diffusion was observed compared to free diffusion in dilute solution. Scaling exponentials relating polymer size to diffusivity were between Flory's theory (D_eff ∝ N^?0.6) and Rouse's model (D_eff ∝ N^?1), revealing a crossover regime from 3‐D diffusion to 1‐D diffusion. Diffusion was less hindered for the polyelectrolyte (D_eff/D₀), than for a rigid sphere, when the polymer/channel size ratio exceeded 0.2. This is attributed to elongated chains with reduced frictional hindrance. Simulation of the confined diffusion based on an elongated cigar model gave D ∝ N^?1 ${R_{\rm t}^{2/3}}$ while the experimental results agree with D ∝ N^?0.94${R_{\rm t}^{ 2/3}}$ . For charged polyelectrolytes, the transition to 1‐D diffusion therefore begins before the polymer radius of gyration exceeds the channel size contrary to model assumptions. We attribute this to the charged nature of the polyelectrolytes causing extended chain conformations. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Elongational flow studies of hinged rodlike molecules

Poly(amino acid) in an intermediate state of its helix-coil transition is known to be in a hinged rodlike conformation. In this work, the responses of poly(amino acids) in the hinged rodlike conformation against an elongational flow field were investigated by monitoring their flow-induced birefringence. Poly(L-glutamic acids) (PGA) and poly(γ-benzyl-L-glutamate) (PBLG) were examined as polyelectrolyte and noncharged poly(amino acids), respectively, and the results were compared. In the plots of flow-induced birefringence, Δn, against strain rate, $ {\dot \varepsilon } $, for hinged rodlike PBLG, there was a critical strain rate, $ \dot \varepsilon_0 $, below which Δn was not observed. Over $ \dot \varepsilon_0 $, the birefringence pattern observed was identical with that of rodlike molecules. The Δn vs. $ {\dot \varepsilon } $ plot for hinged rodlike PGA had characteristics of a rigid rod at any strain rate and there was no $ \dot \varepsilon_0$ observed. The rotational diffusion coefficient, D_r, of PBLG in the hinged rodlike conformation was larger than that for its helical conformation, while D_r, for the hinged-rodlike PGA was smaller than that for its helical conformation. It is concluded that the hinged-rodlike PGA molecule is in an extended form and that the hinged-rodlike PBLG is hydrodynamically more compact and rigid than that in its quiescent state. It is deduced that at $\dot \varepsilon_0$ hinged rodlike PBLG molecules collapse to a conformation optically anisotropic and mechanically rigid. © 1996 John Wiley & Sons, Inc.     

Water‐soluble/dispersible carbazole‐containing random and block copolymers by nitroxide‐mediated radical polymerisation

A series of carbazole‐containing water‐dispersible poly(acrylic acid)‐b‐(9‐(4‐vinylbenzyl)‐9H‐carbazole) block copolymers (poly(AA)‐b‐poly(VBK)) and water‐soluble poly(methacrylic acid‐ran‐(9‐(4‐vinylbenzyl)‐9H‐carbazole)) (poly(MAA‐ran‐VBK)) random copolymers were synthesised in a controlled manner (i.e. low polydispersities $(\overline {M_{{\rm w}} } /\overline {M_{n} } < 1.3)$ by nitroxide‐mediated polymerisation (NMP) using an SG1‐based alkoxyamine initiator, BlocBuilder. Poly(AA)‐b‐poly(VBK) block copolymers were most easily accessed by using poly(AA) in its protected form as the macroinitiator for the 9‐(4‐vinylbenzyl)‐9H‐carbazole (VBK) block. Controlled polymerisation of MAA was accomplished using an excess of 10 mol.% SG1 relative to BlocBuilder with VBK as controlling co‐monomer (initial molar feed content f_VBK,0 = 0.03–0.20) in dimethylformamide at 80°C. Poly(MAA‐ran‐VBK) copolymers with a final VBK molar composition of F_VBK < 0.30 resulted in water‐soluble copolymers. In addition, as macroinitiators, poly(MAA‐ran‐VBK)s were sufficiently pseudo‐living to reinitiate a second batch of monomer (90 mol.% methyl methacrylate with styrene) in organic solvent and by ab initio, surfactant‐free emulsion polymerisation. In both cases, low polydispersity, amphiphilic block copolymers resulted $(\overline {M_{{\rm w}} } /\overline {M_{{\rm n}} } < 1.3)$ . © 2012 Canadian Society for Chemical Engineering     

Polymer melt elongation—methods,results, and recent developments

For film blowing of polyethylene it has been shown previously that melt elongation is very powerful for polymer characterization. With two types of rheometers, simple (also called “uniaxial”) elongational tests as well as creep tests can be performed homogeneously. In simple elongation, the melts of branched polyethylene show a remarkable strain hardening. With respect to their advantages and disadvantages, these rheometers complement each other. For multiaxial elongations the various modes of deformation can be performed by means of the rotary clamp technique. With the strain rate components ordered such that \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₁₁ ? \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₂₂ ≥ \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₃₃, the ratio m = \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₂₂/\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₁₁ characterizes the test mode. The Stephenson definition of the elongational viscosities makes use of the linear viscoelastic material equation and proves to be very efficient because the linear shear viscosity (t) (“stressing” viscosity) can act as the reference for the nonlinear behavior in elongation. Results are given for polyisobutylene measured not only in simple, equibiaxial, and planar elongations, but also in new test modes with a change of m during the deformation. This allows one to investigate the consequences of a deformation-induced anisotropy of the rheological behavior.     

Correlations between the Shape of Viscosity Functions and the Molecular Structure of Long‐Chain Branched Polyethylenes

The viscosity functions of long‐chain branched metallocene‐catalyzed ethene homopolymers and copolymers (LCB‐mPE) were described by an extended Carreau‐Yasuda model. The two characteristic relaxation times, λ₁ and λ₂, and the slope of the viscosity function between these two characteristic relaxation times can be correlated to the zero shear‐rate viscosity, η₀, and the molar mass . The characteristic relaxation times, λ₁ and λ₂ (describing the main curvatures of the viscosity function) exhibit a power law dependency on the molar mass, . The parameterization of the viscosity function can be used for a molecular characterization and flow simulations of various kinds.

     

Stability of hydrolase enzymes in ionic liquids

In this work we attempted to evaluate the stability of penicillin G acylase (PGA) from Escherichia coli in their native form and free Candida antarctica lipase B (CaLB) in ionic liquids (ILs) at low water content. The hydrolysis of penicillin G to 6‐aminopenicillanic acid (6‐APA), and phenyl acetic acid (PAA) catalysed by PGA and the synthesis of butyl butyrate from vinyl butyrate and 1‐butanol catalysed by CaLB were chosen as activity tests. The influence of these new solvents on enzyme stability was studied by incubating the enzyme (PGA or CaLB) in ILs based on dialkylimidazolium cations associated with perfluorinated and dicyanamide anions at a given temperature. Stability studies indicate that CaLB and PGA exhibited greater stability in water‐immiscible ILs than in water‐miscible ILs. Specifically, native PGA shows greater stability in IL media than in organic solvents. For example, a half‐life time of 23 h was obtained in 1‐ethyl‐3‐methylimidazolium bis{(trifluoromethyl)sulfonyl}imide, , which was about 2000‐fold higher than that in 2‐propanol. The higher half‐life time of CaLB was observed in (t_1/2 = 84 h).     

Pilot‐scale anaerobic/anoxic/oxic/oxic biofilm process treating coking wastewater

BACKGROUND: Biological treatment efficiency of coking wastewater is rather poor, especially for chemical oxygen demand (COD) and ammonia‐nitrogen (NH$_{4}^{+}$ ‐N) removal due to its complex composition and high toxicity. RESULTS: A pilot‐scale anaerobic/anoxic/oxic/oxic (A²/O²) biofilm system has been developed to treat coking wastewater, focusing attention on the COD and NH$_{4}^{+}$ ‐N removal efficiencies. Operational results over 239 days showed that hydraulic retention time (HRT) of the system had a great impact on simultaneous removals of COD and NH$_{4}^{+}$ ‐N. At HRT of 116 h, total removal efficiencies of COD and NH$_{4}^{+}$ ‐N were 92.3% and 97.8%, respectively, reaching the First Grade discharge standard for coking wastewater in China. Adequate HRT, anoxic removal of refractory organics and two‐step aerobic bioreactors were considered to be effective measures to obtain satisfactory coking effluent quality using the A²/O² biofilm system. The correlation between removal characteristics of pollutants and spatial distributions of biomass along the height of upflow bioreactors was also revealed. CONCLUSION: The study suggests that it is feasible to apply the A²/O² biofilm process for coking wastewater treatment, achieving desirable effluent quality and steady process performance. © 2012 Society of Chemical Industry