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Polymerization of Vinyl Acetate Initiated by Hydrosilane in the Presence of Platinum Complex
Ming Yuan,Wenxian Zhu,Jiaxing Lv,Panpan Zhang,Huadong Tang 한국고분자학회 2021 폴리머 Vol.45 No.3
In this work, a series of hydrosilanes including phenylsilane, diphenylsilane, triethylsilane (TES), and tris(trimethylsilyl)silane combined with catalytical amount of platinum complex such as dichloro(1,5-cyclooctadiene) platinum (COD) and dichloro(dicyclopentadienyl)platinum have been used to initiate the polymerization of vinyl acetate (VAc) at 70-95 ℃. An ultrahigh molecular weight PVAc with number-average molecular weight (Mn) up to 1.17×10<SUP>6</SUP> Da and polydispersity index (PDI) of 2.59 has been synthesized using TES as an initiator in the presence of 9.7 ppm of COD. A kinetic study indicates that the polymerization at VAc/TES/COD molar ratio = 3.0×10<SUP>5</SUP> : 60 : 1 smoothly reached 81.0% conversion in 28.0 h at 85 ℃, producing PVAc with Mn increasing linearly from 1.41×105 to 6.01×10<SUP>5</SUP> Da with the increase of monomer conversion. A mechanistic investigation revealed that COD was firstly reduced by reductive TES, producing Pt nanoparticles and corresponding silane radicals to initiate the polymerization of VAc.
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Yuze Xue,Mingwei Zhang,Le Xin,Luchao Ren,Panpan Lv,Hang Zhan,Jing He,Jiwei Zhai 한양대학교 청정에너지연구소 2023 Journal of Ceramic Processing Research Vol.24 No.2
0.2ZnAl2O4/0.8Ba0.5Sr0.5TiO3 ceramics with good dielectric temperature stability were synthesized by controlling sinteringbehavior. The relationship between sintering conditions, microstructure, and dielectric properties of ceramics was studied. Cubic structures were confirmed in all ceramics. Double sintering (DS) behavior can effectively improve the density, and thegrain size has no obvious change compared with non-repeated sintering. The maximum dielectric permittivity (220 at 10 kHz)and minimum leakage current (3.98×10-6 A/cm2 at 0.25 kV/cm) are obtained in the DS ceramics, which is superior to thoseof the single sintering ceramics. This can be ascribed to the higher relative density of the DS ceramics in contrast to the singlesintering ceramics. More importantly, the temperature stability of the DS sample in all samples is optimal due to the highsurface energy at grain boundaries and improved density. This work demonstrates a route to produce ceramics with weaktemperature sensitivity for microwave applications.
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