Using controlled radical polymerization to confirm the lower critical solution temperature of an N‐(alkoxyalkyl) acrylamide polymer in aqueous solution

N‐(3‐Methoxypropyl) acrylamide (MPAM) was polymerized by controlled radical polymerization (CRP) methods such as nitroxide‐mediated polymerization (NMP) and reversible addition–fragmentation chain‐transfer polymerization (RAFT). CRP was expected to yield well‐defined polymers with sharp lower critical solution temperature (LCST) transitions. NMP with the BlocBuilder (2‐([tert‐butyl[1‐(diethoxyphosphoryl)‐2,2‐dimethylpropyl]amino]oxy)‐2‐methylpropanoic acid) and SG1 ([tert‐butyl[1‐(diethoxyphosphoryl)‐2,2‐dimethylpropyl]amino] oxidanyl) initiating system revealed low yields and lack of control (high dispersity, ? ～ 1.5–1.6, and inhibition of chain growth). However, RAFT was far more effective, with linear number average molecular weight, , versus conversion, X, plots, low ? ～ 1.2–1.4 and the ability to form block copolymers using N,N‐diethylacrylamide (DEAAM) as the second monomer. Poly(MPAM) (with = 13.7–25.3 kg mol^?1) thermoresponsive behavior in aqueous media revealed cloud point temperatures (CPT)s between 73 and 92 °C depending on solution concentration (ranging from 1 to 3 wt %). The and the molecular weight distribution were the key factors determining the CPT and the sharpness of the response, respectively. Poly(MPAM)‐b‐poly(DEAAM) block copolymer ( = 22.3 kg mol^?1, ? = 1.41, molar composition F_DEAAM = 0.38) revealed dual LCSTs with both segments revealing distinctive CPTs (at 75 and 37 °C for poly(MPAM) and poly(DEAAM) blocks, respectively) by both UV–Vis and dynamic light scattering. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 59–67     

Gelation in dilute aqueous L-cysteine-AgNO<Subscript>3</Subscript> solutions

Gelation in dilute aqueous L-cysteine solutions containing various electrolytes is studied by rotational viscometry in different dynamic regimes. It is revealed that gels are formed at rather low concentrations of cysteine of no higher than 0.1 vol %. In the linear range of mechanical actions, gels of all examined compositions behave as elastic solid-like media; their elastic moduli, which lie in a range of 10–100 Pa, are independent of frequency and their mechanical losses are low. However, these gels exhibit dualistic properties and can flow at low shear stresses with a Newtonian viscosity on the order of 10³–10⁵ Pa s. On reaching a critical stress (yield point), gels are destroyed, their viscosity decreases by six to seven decimal orders of magnitude, and they are transformed into low-viscosity liquids. At rest, the initial structure and properties are recovered. Mechanisms of percolation network formation are proposed.     

Maximal subclasses of local fitting classes

A Fitting class $ \mathfrak{F} A Fitting class is said to be π-maximal if is an inclusion maximal subclass of the Fitting class of all finite soluble π-groups. We prove that is a π-maximal Fitting class exactly when there is a prime p ∊ π such that the index of the -radical in G is equal to 1 or p for every π-subgroup of G. Hence, there exist maximal subclasses in a local Fitting class. This gives a negative answer to Skiba’s conjecture that there are no maximal Fitting subclasses in a local Fitting class (see [1, Question 13.50]). Original Russian Text Copyright ? 2008 Savelyeva N. V. and Vorob’ev N. T. __________ Vitebsk. Translated from Sibirskiĭ Matematicheskiĭ Zhurnal, Vol. 49, No. 6, pp. 1411–1419, November–December, 2008.     

Synthesis of triazole-linked pseudo-oligosialic acid derivatives

Russian Chemical Bulletin - Using the CuI-catalyzed 1,3-dipolar cycloaddition of terminal alkynes to azides, neuraminic acid di-, tri-, and tetrapseudosaccharides were synthesized, in which...     

Aminoguanidinium cations and the square-bipyramidal hexachlorocuprate(II) anion in the (CH8N4)2[CuCl6] crystal structure

Synthesis and structure of a novel thermochromic complex (CH₈N₄)₂[CuCl₆] are reported. X-ray analysis of the compound was carried out for a single crystal 0.4×0.2×0.05 mm in size (a bright-yellow plate). The monoclinic unit cell parameters are a=7.167(1), b=15.561(3), c=7.328(1) Å, β=118.73(3)°, V=716.7(2) ų, space group P2₁, Z=2 (CH₈N₄)₂[CuCl₆] d_calc=1.99 g/cm³, μ(MoK_α)=2.65 mm^?1, R=0.0264, and R_w=0.0290 for 1411 I_hkl>2σ_I.     

Maximal fitting subclasses of the class of all finite π-groups

Call a Fitting class $\mathfrak{F}$ π-maximal if $\mathfrak{F}$ is (inclusion-)maximal in the class $\mathfrak{C}_\pi$ of all finite π-groups, where π stands for a nonempty set of primes. We establish a π-maximality criterion for a Fitting class $\mathfrak{F}$ of finite π-groups: we prove that a nontrivial Fitting class $\mathfrak{F}$ is π-maximal if and only if there is a prime p ∈ π such that, for every π-group G, the index of the $\mathfrak{F}$ -radical $G_\mathfrak{F}$ in G is equal to 1 or p. This implies Laue’s familiar result on a necessary and sufficient condition of the maximality of an arbitrary Fitting class of finite groups in the class $\mathfrak{C}$ of all finite groups. The π-maximality criterion obtained also gives a confirmation of the negative solution of Skiba’s Problem asking whether a local Fitting class has no inclusion-maximal Fitting subclasses (see Problem 13.50, The Kourovka Notebook: Unsolved Problems in Group Theory, 14th ed., Sobolev Institute of Mathematics, Novosibirsk, 1999).     

Experimental nonlinear interference comb spectroscopy

A means of nonlinear interferential comb spectroscopy with increased sensitivity is propsed. Radiation from the comb-generator of a femtosecond laser is focused at the center of a cell with vapors of rubidium atoms, mounted in an arm of a Michelson interferometer. This technique is an improvement of Rozhdestvenski hooks method, with digital registration by the detectors on a CCD array being substituted for the photographic registration of interferograms, resulting in increased interferometric sensitivity (holographic interferometry). A primary spectrogram is processed in digital form on a dual-beam interferometer equipped with a phase modulator to improve sensitivity with the possibility of an a posteriori increase in interferometric sensitivity. Dispersive signals appear in the interferogram spectrogram on two-photon absorption lines when the pumping radiation is focused at the center of a cell with Rb vapors. Nonlinear processes of coherent radiation due to nonlinear interference effects are studied. Numerical simulations are performed that confirm the proposed theoretical model.     

Molecular recognition of organic guest vapor by solid adamantylcalix[4]arene

A series of inclusion compounds prepared by saturation of the solid adamantyl[4]calixarene (host 1) with vaporous organic guests at 298 K was studied by thermal gravimetry and static headspace GC analyses. The sorption isotherms of guests by host 1, the stoichiometry of the guest—host inclusion compounds, and the Gibbs energies of their formation were determined. The data obtained give evidence of the molecular recognition of the guest shape by host 1. Hence, compound 1 can be used in sensors for recognizing volatile organic compounds with no strong hydrogen or donor-acceptor bonds involved.     

Amphiphilic Poly(4‐acryloylmorpholine)/Poly[2‐(N‐carbazolyl)ethyl acrylate] Random and Block Copolymers Synthesized by NMP

A series of random copolymers and block copolymers containing water‐soluble 4AM and fluorescent VAK are synthesized by NMP. The homopolymerizations of 4AM and VAK and 4AM/VAK random copolymerization are performed in 50 wt% DMF using 10 mol% SG1, resulting in a linear increase in versus conversion, and final polymers with narrow molecular weight distributions ( < 1.4). Reactivity ratios r_VAK = 0.64 ± 0.52 and r_4AM = 0.86 ± 0.66 are obtained for the 4AM/VAK random copolymerization. In addition, a poly(4AM) macroinitiator is used to initiate a surfactant‐free suspension polymerization of VAK. After 2.5 h, the resulting amphiphilic block copolymer has = 12.6 kg · mol^?1, = 1.48, molar composition F_VAK = 0.38 with latex particle sizes between 270 and 475 nm.