Efficient water‐soluble drag reducing star polymers with improved mechanical stability

We describe here the first example of the synthesis of 4‐arm star poly(acrylic acid) for use as a water‐soluble drag reducing agent, by applying Cu(0)‐mediated polymerization technique. High molecular weight 4‐arm star poly(tert‐butyl acrylate) (M_n = 3.0–9.0 × 10⁵ g mol^?1) was first synthesized using 4,4′‐oxybis(3,3‐bis(2‐bromopropionate)butane as an initiator and a simple Cu(0)/TREN catalyst system. Then, 4‐arm star poly(tert‐butyl acrylate) were subjected to hydrolysis using trifluoroacetic acid resulting in water‐soluble 4‐arm star poly(acrylic acid). Drag reduction test rig analysis showed 4‐arm star poly(acrylic acid) to be effective as a drag reducing agent with drag reduction of 24.3%. Moreover, 4‐arm star poly(acrylic acid) exhibited superior mechanical stability when compared with a linear poly(acrylic acid) and commercially available drag reducing polymers; Praestol and poly(ethylene oxide). The linear poly(acrylic acid), Praestol, and poly(ethylene oxide) all showed a large decrease in drag reduction of 8–12% when cycled 30 times through the drag reduction test rig while, in contrast, 4‐arm star poly(acrylic acid) demonstrated much higher mechanical stability. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 335–344     

On the diophantine equation x 2 + 2 a · 3 b · 11 c = y n

In this note, we find all the solutions of the Diophantine equation x ² + 2 ^a · 3 ^b · 11 ^c = y ⁿ , in nonnegative integers a, b, c, x, y, n ≥ 3 with x and y coprime.     

Microwave‐Assisted Synthesis of Novel 2,4‐Dihydro‐5‐[4‐(trifluoromethyl)phenyl]‐3H‐1,2,4‐triazol‐3‐ones and Potentiometric Determination of Their pKa in Nonaqueous Solvents

The novel 4‐amino‐ or 4‐aryl‐substituted 2,4‐dihydro‐5‐[(4‐trifluoromethyl)phenyl]‐3H‐1,2,4‐triazol‐3‐ones 3a – 3g were synthesized by reaction of N‐(ethoxycarbonyl)‐4‐(trifluoromethyl)benzenehydrazonic acid ethyl ester ( 2 ) and primary amines or hydrazine by microwave irradiation. Compounds 3a – 3g were potentiometrically titrated with tetrabutylammonium hydroxide (Bu₄NOH) in four nonaqueous solvents, i.e., ⁱPrOH, ^tBuOH, MeCN, and N,N‐dimethylformamide (DMF). Also half‐neutralization potential values and the corresponding pK_a values were determined in all cases.     

Effect of micron and nano-grade titanium dioxides on the efficiency of hindered piperidine stabilizers in a model oxidative reaction

Polymer additives often show many side reactions during the ageing of polymers which change the useful life-time of the materials. In this regard nano-grade titanium dioxide additives with high surface areas and nano-particle sizes appeared in recent years to be used in polymers where the side reactions have been found to markedly influence mechanisms of ageing. The interaction between titanium dioxide pigments and stabilizers therefore is proposed as a field of great importance.In this paper the influence of nano and micron particle grade anatase and rutile titanium dioxide pigments on the efficiency of a hindered amine stabilizer, Chimassorb 119FL and Chimassorb 119 has been investigated in the system comprising the model radical reaction of cumene initiated (2,2′-azobisisobutyronitrile, AIBN) oxidation. This model reaction was designed to simulate the thermo-oxidative processes in polymers.Kinetic measurements of oxidation rates in the absence of the pigments showed strong retarding activity of the stabilizers under conditions of the model experiments. The rates depend linearly on the reciprocal square root of the concentration of the stabilizers over a sufficiently wide range thereby fitting the mechanism of addition of cumylalkyl R radicals to the Chimassorb molecules. The rate constants for the addition of cumyl R radicals to Chimassorb 119FL and Chimassorb 119 were determined to be k_(333 K) = (1.4 ± 0.2) × 10⁸ and (1.2 ± 0.2) × 10⁸ M⁻¹ s⁻¹, respectively. Hence the Chimassorb 119 family is relatively powerful retarders of thermal oxidation.Further measurements of oxidation rates in the presence of titanium dioxide particles showed that there is a significant reduction in the retarding action of the stabilizers in the presence of titanium dioxides. It occurs as a result of the initiating action of titanium additives producing an additional concentration of free radicals and inducing an additional oxidation rate which may weaken the initial inhibiting efficiency of the added hindered piperidine stabilizers. The titanium nano-samples added at a 1-wt.% into the oxidized condensed system are able to completely decrease the initial inhibiting efficiency of the stabilizers. In terms of the degree of the sensitising action the titanium dioxides can be ordered as: nano-rutile > nano-anatase treated hydroxyapatite > nano-anatase untreated > micro-anatase > micro-rutile.The behaviour of titanium dioxide particles incorporated with hindered piperidine HAS stabilizers in condensed systems may thus be used for the assessment of their performance during the thermo-oxidative degradation of polymers.     

Modelling light stabilizers as thermal antioxidants

Light stabilizers often display some degree of antioxidant activity against thermal degradation of polymers both in the solid state and the melt. Although this capacity to date has been documented in some instances such features have not been kinetically modelled for many light stabilizers. An understanding of the mechanisms of this activity is crucial in polymer materials due to the close link between prior thermal behaviour and post stabilisation.This paper considers the potential antioxidant activity of three representative UV stabilizers using a model system initiated (2,2′-azo-bisisobutyronitrile, AIBN) cumene oxidation. Kinetic measurements of oxidation rates in the presence of the stabilizers showed that the antioxidant activity as well as the mechanism and mode of inhibition was different for each of the stabilizers. Thus, whilst a triazine UV absorber (Cyasorb UV 1164) did not display any antioxidant activity, a hindered phenol (Cyasorb UV 2908) operated as a peroxy radical acceptor, and a hindered amine (Cyasorb 3529) retarded the model reaction without an induction period like many HAS stabilizers.The Cyasorb 2908 revealed weak antioxidant activity with a rate constant for the addition of cumylperoxy RO₂ radicals to the functional group of the stabilizer k₇ = 10^6.2±0.1 e^{−(3900±600)/RT}, however, the inhibition index f (80 °C) is significantly higher than that of the commercial phenolic antioxidant Irganox 1076. Oxidation rate profiles in the presence of Cyasorb 3529 displayed a strong retarding activity by the stabilizer under conditions of the model experiments. The rates were found to depend linearly on the reciprocal square root of the concentration of the stabilizer over a sufficiently wide range thereby fitting the mechanism for the addition of cumylalkyl R radicals to the Cyasorb molecules. The rate constants for the addition of cumyl R radicals to the Cyasorb were determined to be k_(333-353 K) = (2.0 ± 0.8) × 10⁸ M⁻¹ s⁻¹. This value surpasses even the rate constants for other related HAS Chimassorb [Zeynalov EB, Allen NS. Effect of micron and nano-grade titanium dioxides on the efficiency of hindered piperidine stabilizers in a model oxidative reaction. Polym Degrad Stab 2006;91(4):931-9.] stabilizers and it follows that Cyasorb 3529 is a powerful retarder of thermal oxidation.     

Chitosan-based tyrosinase optical phenol biosensor employing hybrid nafion/sol-gel silicate for MBTH immobilization

The development of an optical biosensor based on immobilization of 3-methyl-2-benzothiazolinone hydrazone (MBTH) in hybrid nafion/sol-gel silicate film and tyrosinase in chitosan film for the detection of phenolic compounds has been described. Tyrosinase was immobilized in chitosan film deposited on the hybrid nafion/sol-gel silicate film containing MBTH. The enzymatic oxidation product of phenolic compounds were stabilized through formation of adduct with MBTH to produce a maroon color adduct. The color intensity of adduct was found to increase proportionally with the increase of the substrate concentrations after 5 min exposure. The linearity of the biosensor towards phenol, catechol and m-cresol were in the respective concentration range of 0.5-7.0, 0.5-10.0 and 1.0-13.0 mg/L with detection limit of 0.18, 0.23 and 0.43 mg/L, respectively. The biosensor shows a good stability for at least 3 months.     

Synthesis characterization and biological study of diorganotin(IV) complexes of monomethyl phthalate

The synthesis and characterization of new coordination compounds of some organotin(IV) chlorides with monomethyl phthalate is reported; the ligand molecules appear to be bound to the tin atom through carbonyl oxygen atoms. Their structures have been characterized by elemental analyses, molar conductance, and bonding in these complexes is discussed in terms of their IR, (1)H, (13)C, (119)Sn NMR and (119 m)Sn M?ssbauer spectral studies. The spectroscopic results obtained are in full agreement with the proposed 2:1 stoichiometry. The complexes soluble in DMSO have been screened against a wide spectrum of bacteria and the results obtained are quite promising. The LD(50) values have also been determined in the albino rats. Some of the complexes also exhibit high anti-inflammatory activity.     

Derivatization of 2-chlorophenol with 4-amino-anti-pyrine: a novel method for improving the selectivity of molecularly imprinted solid phase extraction of 2-chlorophenol from water

Molecularly imprinted polymer (MIP) may not selectively recognize small template of limited number of functional groups, such as 2-chlorophenol (2-CP). In this work, a novel method was proposed to improve the recognition ability of the molecularly imprinted solid phase extraction (MISPE) of 2-CP from environmental waters. This was achieved by derivatization of 2-CP with 4-amino-anti-pyrine (4-AAP) to enlarge its molecular size and add more binding sites. For that purpose, two MISPE methods of 2-CP were developed. In method 1, a polymer imprinted with 2-CP was used as the extracting sorbent but it suffered from low selectivity and high detection limit of 2-CP (7.10 ng L⁻¹). In method 2, a polymer imprinted with 4-AAP derivatized 2-CP (2-CP-4-AAP) was used as the extracting sorbent. Prior to loading the water sample it was subjected to a simple derivatization procedure with 4-AAP. Method 2 showed high recognition ability/selectivity towards 2-CP-4-AAP with lower detection limit of 0.05 ng L⁻¹ for 2-CP-4-AAP. Method 2 was able to detect the presence of 2-CP-4-AAP in unspiked real water samples and almost full spike recovery was achieved.