Facile synthesis of graft copolymers containing rigid poly(dialkyl fumarate) branches by macromonomer method

Graft copolymers show microphase separated structure as seen in block copolymers and have lower intrinsic viscosity than block copolymers because of a branching structure. Therefore, considering molding processability, especially for polymers containing rigid segments, graft copolymers are useful architectures. In this work, graft copolymers containing rigid poly(diisopropyl fumarate) (PDiPF) branches were synthesized by full free‐radical polymerization process. First, synthesis of PDiPF macromonomers by addition‐fragmentation chain transfer (AFCT) was investigated. 2,2‐Dimethyl‐4‐methylene‐pentanedioic acid dimethyl ester was found to be an efficient AFCT agent for diisopropyl fumarate (DiPF) polymerization because of the suppression of undesired primary radical termination, which significantly took place when common AFCT agent, methyl 2‐(bromomethyl)acrylate, was used. Copolymerization of PDiPF macromonomer with ethyl acrylate accomplished the generation of the graft copolymer having flexible poly(ethyl acrylate) backbone and rigid PDiPF branches. The graft copolymer showed a microphase separated structure, high transparency, and characteristic thermal properties to PDiPF and poly(ethyl acrylate). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2474–2480     

Synthetic studies toward swinhoeisterol A,a novel steroid with an unusual carbon skeleton

Swinhoeisterol A is a novel steroid with unusual 6/6/5/7 tetracyclic skeleton. The model compound with BCD rings is constructed by Friedel–Crafts acylation and an oxidative dearomatization as key steps.     

Structural-Deformation-Energy-Modulation Strategy in a Soft Porous Coordination Polymer with an Interpenetrated Framework

To achieve unique molecular-recognition patterns, a rational control of the flexibility of porous coordination polymers (PCPs) is highly sought, but it remains elusive. From a thermodynamic perspective, the competitive relationship between the structural deformation energy (E_def) of soft PCPs and the guest interaction is key for selective a guest-triggered structural-transformation behavior. Therefore, it is vital to investigate and control E_def to regulate this competition for flexibility control. Driven by these theoretical insights, we demonstrate an E_def-modulation strategy via encoding inter-framework hydrogen bonds into a soft PCP with an interpenetrated structure. As a proof of this concept, the enhanced E_def of PCP enables a selective gate-opening behavior toward CHCl₃ over CH₂Cl₂ by changing the adsorption-energy landscape of the compounds. This study provides a new direction for the design of functional soft porous materials.     

An Anti CuO2‐type Metal Hydride Square Net Structure in Ln2M2As2Hx (Ln=La or Sm,M=Ti,V, Cr,or Mn)

Using a high pressure technique and the strong donating nature of H⁻, a new series of tetragonal La₂Fe₂Se₂O₃‐type layered mixed‐anion arsenides, Ln₂M₂As₂H_x, was synthesized (Ln=La or Sm, M=Ti, V, Cr, or Mn; x≈3). In these compounds, an unusual M₂H square net, which has anti CuO₂ square net structures accompanying two As³⁻ ions, is sandwiched by (LaH)₂ fluorite layers. Notably, strong metal–metal bonding with a distance of 2.80 Å was confirmed in La₂Ti₂As₂H_2.3, which has metallic properties. In fact, these compounds are situated near the boundary between salt‐like ionic hydrides and transition‐metal hydrides with metallic characters.     

Two dimensional inorganic electride-promoted electron transfer efficiency in transfer hydrogenation of alkynes and alkenes

A simple and highly efficient transfer hydrogenation of alkynes and alkenes by using a two-dimensional electride, dicalcium nitride ([Ca₂N]⁺·e^–), as an electron transfer agent is disclosed. Excellent yields in the transformation are attributed to the remarkable electron transfer efficiency in the electride-mediated reactions. It is clarified that an effective discharge of electrons from the [Ca₂N]⁺·e^– electride in alcoholic solvents is achieved by the decomposition of the electride via alcoholysis and the generation of ammonia and Ca(OⁱPr)₂. We found that the choice of solvent was crucial for enhancing the electron transfer efficiency, and a maximum efficiency of 80% was achieved by using a DMF mixed isopropanol co-solvent system. This is the highest value reported to date among single electron transfer agents in the reduction of C–C multiple bonds. The observed reactivity and efficiency establish that electrides with a high density of anionic electrons can readily participate in the reduction of organic functional groups.     

Shape and structure recovery of an LCP droplet under a large step strain: observation and stress calculation

Shape recovery of a droplet of liquid crystalline polymer (LCP) hydroxypropylcellulose in a matrix of poly(dimethyl siloxane) subjected to a step shear strain has been studied via optical microscopy. Just after application of a large strain, the LCP droplet shape is flat ellipsoid, and then the droplet takes cylindrical shape and band texture perpendicular to the flow direction appears. The band texture fades away before emergence of poly-domain structure. In the final process with the shape of spheroid, poly-domain structure recovers very slowly. Except for the final process, the shape change is identical with that of isotropic droplet at strains smaller than 3, when the LCP viscosity in Region II is taken as an equivalent viscosity for normalization. For a 20:80 blend, the excess relaxation modulus is calculated based on the Doi-Ohta theory, taking account of the distribution of droplet size and compared with experimental modulus data.     

Excess enthalpies of binary mixtures of butylamines + propanols at 298.15 K

The molar excess enthalpies of eight systems of butylamines + propanols were determined at 298.15 K using a twin-microcalorimeter. All excess enthalpies were exothermic and large. An equilibrium constant K ₁ expressed in terms of mole fractions and standard thermodynamic properties of formation (Δ_f H, Δ_f G, Δ_f S) of 1:1 complex were evaluated by ideal mixtures of monomeric molecules and their associated complexes. Concentration dependence of the FT-Raman spectrum showed systematic changes of bands. Spectroscopic considerations based on this and ab initio calculations on molecules were performed at the Mp2/6-311G(d,p) level of theory. Interaction energies between butylamine and propanol were calculated by the supermolecular and NBO methods. The results were discussed with previous results to clarify the steric and positional effect of the amino and hydroxyl group.     

Synthesis of Telechelic Polystyrene by Radical Polymerization Using 1,4-Bis(p-tert-Butylphenylseleno-Methyl)benzene as a Photoiniferter

Abstract

1,4-Bis(p-tert-butylphenylselenomethyl) benzene was synthesized, and used as a bifunctional photoiniferter for the polymerization of styrene. Both the polymer yields and the number average of molecular weights (_n) of polymers increased with the polymerization. The polymerization of styrene by this iniferter permitted telechelic polystyrene containing arylseleno groups at both chain ends, and the degree of functionality was 1.9. The seleno groups of both chain ends of polystyrene were reduced quantitatively by tri-n-butyltin hydride. These seleno groups in polystyrene were also eliminated by treatment with hydrogen peroxide to give telechelic polystyrene with carbon-carbon double bond at both chain ends. Further, polystyrene with double bonds was converted to telechelic polystyrene carrying terminal functional groups as epoxy, hydroxy, and iodide group, respectively.

     

Hemin-adsorbed carbon felt for sensitive and rapid flow-amperometric detection of dissolved oxygen

Hemin was physically adsorbed onto porous carbon felt (CF), a microelectrode ensemble of micro-carbon fiber (ca. 7 μm in diameter) and possessing a three-dimensional random structure. The hemin-CF exhibited a well-defined redox wave that is due to Fe(III)/Fe(II) redox process in hemin, with a formal potential of ?0.32 V (vs. Ag/AgCl) in deoxygenated buffer solution of pH 7.0. The surface coverage of the electroactive hemin molecules on the surface of the CF was calculated to be 5.0?×?10^?11 mol cm^?2, and the apparent heterogeneous electron transfer rate constant is 3.35 s^?1. The hemin-CF electrode displays excellent electrocatalytic activity for the reduction of dissolved oxygen (DO), and the magnitude of the cathodic current increases with increasing concentrations of DO in the sample solution. The electrode was used as a flow-through detector for sensitive and rapid consecutive determination of DO. Deoxygenated pH 7.0 solutions were analyzed at a flow rate of 8.0 mL min^?1 at an applied potential of ?0.2 V, and highly reproducible cathodic peak current responses to DO were observed in the 0.72 to 13.3 mg L^?1 concentration range. The maximum throughput is 170 samples h^?1. The hemin-CF-based amperometric flow-sensor was applied to determine the concentration of DO in environmental water samples.