A novel fully end-capped hyperbranched polysiloxane (Am-HPSi) with large branching degree and amine-groups was successfully synthesized by a controlled hydrolysis of phenyltrimethoxysilane and gaminopropyl triethoxysilane, and its structure was characterized by nuclear magnetic resonance ( 1 H-NMR and 29 Si-NMR) and Fourier transform infrared (FTIR) spectra as well as gel permeation chromatography (GPC). In addition, Am-HPSi was used to develop a new modified bismaleimide resin with simultaneously improved flame retardancy and other typical properties. The incorporation of AmHPSi to 4,4 0 -bismaleimidodiphenyl methane/2,2 0 -diallyl bisphenol A (BDM/DBA) resin not only obviously increases the thermal resistance, moisture resistance, impact strength, and dielectric properties, but also remarkably improves the flame retardancy. Specifically, the average heat release rate and total heat release of modified BDM/DBA resin with 10 wt% Am-HPSi are only 37 % and 23 % of that of neat BDM/DBA resin, respectively. A synergistic flame retarding mechanism is believed to be attributed to these results, which includes improving thermal stability, producing non-combustible gas, acting in the condensed phase, and providing a barrier for heat and mass transfer owing to the introduction of Am-HPSi to BDM/DBA resin. These attractive features of Am-HPSi/BDM/DBA resins suggest that the method proposed herein is a new approach to develop high performance resins for cutting-edge industries.
An ultrahigh molecular weight polyethylene
(UHMWPE) fibrous adsorbent
with amidoxime (AO) groups, denoted as AO-UHMWPE, was prepared by
preirradiation-induced graft copolymerization of acrylonitrile (AN)
and acrylic acid (AA) on UHMWPE fibers, followed by amidoximation.
The chemical structure, thermal stability, and mechanical strength
were evaluated by means of Fourier transform infrared spectrometry,
thermogravimetric analysis, and tensile tests, respectively. The adsorption
behaviors of the AO-UHMWPE fiber were studied by batch adsorption
in 331 ppb uranium solution, and flow-though adsorption experiments
in simulated and natural seawater. It was found that the adsorption
conditions (i.e., contact time and manner, temperature, and uranyl
ion initial concentration) significantly influence the amount of uranyl
ions binding to the AO-UHMWPE fibers. The adsorption of uranium in
the batch adsorption experiment was 4.54 g-U/kg-ad in the presence
of massive amounts of interference ions.
Crystalline porous
materials such as covalent organic frameworks
(COFs) are advanced materials to tackle challenges of catalysis and
separation in industrial processes. Their synthetic routes often require
elevated temperatures, closed systems with high pressure, and long
reaction times, hampering their industrial applications. Here we use
a traditionally unperceived strategy to assemble highly crystalline
COFs by electron beam irradiation with controlled received dosage,
contrasting sharply with the previous observation that radiation damages
the crystallinity of solids. Such synthesis by electron beam irradiation
can be achieved under ambient conditions within minutes, and the process
is amendable for large-scale production. The intense and targeted
energy input to the reactants leads to new reaction pathways that
favor COF formation in nearly quantitative yield. This strategy is
applicable not only to known COFs but also to new series of flexible
COFs that are difficult to obtain using traditional methods.
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