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Enhanced αγ′ Transition of Poly(vinylidene fluoride) by Step Crystallization and Subsequent Annealing

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Chinese Journal of Polymer Science 2018年第5期36卷 598-603页

作者： Yi-Ran Zheng Jie Zhang Xiao-Li Sun Hui-Hui Li Zhong-Jie Ren Shou-Ke Yan State Key laboratory of chemical Resource Engineering Beijing University of Chemical Technology

Poly（vinylidene fluoride）（PVDF） exhibits pronounced polymorphs. Its γ phase is attractive due to the electroactive properties. The γ-PVDF is however difficult to obtain under normal crystallization condition. In a previous work, we reported a simple melt-recrystallization approach for producing γ-phase rich PVDF thin films through selective melting and subsequent recrystallization. We reported here another approach for promoting the αγ′ phase transition to prepare γ-phase rich PVDF thin films. To this end, a stepwise crystallization and subsequent annealing process was used. The idea is based on a quick generation of a large amount of α-PVDF crystals with some of their γ-PVDF counterparts at suitable crystallization temperature and then annealing at a temperature above the crystallization temperature for enhancing the molecular chain mobility to overcome the energy barrier of phase transition. It was found that crystallizing the PVDF melt first at 152 °C for 4 h, then quenching to room temperature and finally annealing the sample at 160 °C for 100 h was the most efficient to produce γ-PVDF rich films. This is related to the melting and recrystallization of the α-PVDF crystals produced during quenching in the annealing process at 160 °C, which favors the formation of γ-PVDF crystals for triggering the αγ′ phase transition.

关键词： Poly(vinylidene fluoride) Step crystallization Annealing Phase transition

Synthesis of mesoporous γ-AlOOH@Fe_3O_4 magnetic nanomicrospheres

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Particuology 2012年第6期10卷 751-758页

作者： Yuanyuan Zheng Shengfu Ji Hongfei Liu Ming Li Hao Yang State Key laboratory of chemical Resource Engineering Beijing University of Chemical Technology

Mesoporous γ-AIOOH@Fe3O4 magnetic nanomicrospheres were synthesized using superparamagnetic Fe304 nanoparticles as the core and aluminum isopropoxide （ALP） as the aluminum source. The obtained magnetic nanomicrospheres were characterized by X-ray powder diffraction （XRD）, transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, N2 adsorption-desorption and vibrating sample magnetometry （VSM）. The effects of preparation parameters such as hydrolysis time of AIP, concentration of AlP and coating layer number on microspheres were investigated. The results indicated that the mesoporous γ-AIOOH@Fe3O4 magnetic nanomicrospheres consisted of a mesoporous γ-AIOOH shell and a Fe3O4 magnetic core. The diameter of γ-AIOOH@Fe3O4 nanomicrospheres was about 200 nm, the thickness of mesoporous γ-AIOOH shell was about 5 nm and the average pore size was 3.8 nm. The thickness of the mesoporous γ-AIOOH shell could be controlled via layer-by-layer coating times. The formation mechanism of the mesoporous γ-AIOOH shell involved a ＂chemisorption-hydrolysis＂ process.

关键词： Magnetic nanomicrospheres Fe3O4 γ-AIOOH shellMesoporousHydrolysis

Highly efficient extraction of lithium from salt lake brine by LiAl-layered double hydroxides as lithium-ion-selective capturing material

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Journal of Energy Chemistry 2019年第7期28卷 80-87页

作者： Ying Sun Xiaoyu Guo Shaofang Hu Xu Xiang State Key laboratory of chemical Resource Engineering Beijing University of Chemical Technology

The extraction of lithium from salt lake brine in the Chinese Qaidam Basin is challenging due to its high Mg/Li and Na/Li ratios. Herein, we utilized a reaction-coupled separation technology to separate sodium and lithium ions from a high Na/Li ratio brine(Na/Li = 48.7, w/w) and extracted lithium with Li Al-layered double hydroxides(Li Al-LDHs). The Li Al-LDHs act as lithium-ion-selective capturing materials from multication brines. That is, the lithium ions selectively enter the solid phase to form Li Al-LDHs, and the sodium ions are still retained in the liquid phase. This is because the lithium ions can be incorporated into the structural vacancies of LiAl-LDHs, whereas the sodium ions cannot. The effects of reaction conditions on lithium loss and separation efficiency were investigated at both the nucleation and the crystallization stage, e.g., the nucleation rotating speed, the Li/Al molar ratio, the crystallization temperature and time, and co-existing cations. The lithium loss is as low as 3.93% under optimal separation *** sodium ions remained in the solution. Consequently, an excellent Na/Li separation efficiency was achieved by this reaction-coupled separation technology. These findings confirm that LiAl-LDHs play a critical function in selectively capturing lithium ions from brines with a high Na/Li ratio, which is useful for the extraction of lithium ions from the abundant salt lake brine resources in China.

关键词： LiAl-LDHs Lithium extraction Energy metal Salt lake brine Reaction-coupled separation technology

Synthesis of rare earth metal-organic frameworks(Ln-MOFs) and their properties of adsorption desulfurization

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Journal of Rare Earths 2014年第2期32卷 189-194页

作者：刘想王景艳李庆远蒋赛张天浩季生福 State Key laboratory of chemical Resource Engineering Beijing University of Chemical Technology

The rare earth metal-organic frameworks （Ln-MOFs） materials, Ln（BTC）（H2O）-（DMF）, were synthesized using the rare earth metal （Ln=Sm, Eu, Tb, Y） and 1,3,5-trirnesic acid （BTC） as a metal ion center and ligand, respectively. X-ray diffraction （XRD） and infrared spectroscopy （FT-IR） were employed to characterize the Ln-MOFs structural features. The property of adsorption desul- furization of Ln-MOFs materials was evaluated with thiophene/n-octane as model oil. The results showed that Ln-MOFs with rare earth metals Sm, Eu, Tb and Y had perfect crystalline and good adsorption desulfurization ability. Y（BTC）（H2O）-（DMF） material had a comparatively better activity for the adsorption desulfurization with desulfurization rate up to 80.7% and the sulfur adsorption ca- pacity was found 30.7 mgS/g（Y-MOFs）. The Ln-MOFs materials had excellent reusability.

关键词： rare earth metals metal-organic frameworks adsorption desulfurization thiophene

SYNTHESIS AND CHARACTERIZATION OF AMINO FUNCTIONALIZED LADDER-LIKE POLYSILSESQUIOXANES AND THEIR HYBRID FILMS WITH POLYIMIDE

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Chinese Journal of Polymer Science 2013年第3期31卷 427-433页

作者： Qiu-shuang Gao Guo-feng Tian Sheng-li Qi Zhan-peng Wu 武德珍 State Key laboratory of chemical Resource Engineering Beijing University of Chemical Technology

Ladder-like polysilsesquioxanes （LPSQs） with different amino contents have been synthesized by controlling of the dosage of Pd/C catalyst. The concentration and activity of amino groups were investigated by Fourier transform infrared spectroscopy. Polyimide （PI）/LPSQ hybrid films have been prepared by incorporating of the obtained LPSQs with different amino contents into PI matrix, respectively. The interfacial interactions between PI matrix and LPSQ were studied with scanning electron microscopy and X-ray photoelectron spectroscopy, meanwhile the thermal and mechanical properties of the hybrid films were studied using dynamic mechanical analysis and tensile tests. The results indicate that the functionality of LPSQ has great effects on the interfacial interactions and the properties of hybrid films. With the increase of amino content, both the interracial interactions and the cross-linking density of hybrids enhanced, which results in the decline of surface silicon concentration, increase of Young＇s modulus and drop of elongation at break. Excessive amino content makes the hybrid films brittle and leads to incomplete imidization.

关键词： Organic-inorganic Hybrid Amino functionalized ladder-like polysilsesquioxane Polyimide.

Structure and Properties of β-Polypropylene Reinforced by Polypropylene Fiber and Polyamide Fiber

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Chinese Journal of Polymer Science 2014年第4期32卷 509-518页

作者： Qi Liu Hui-hui Li 闫寿科 State Key laboratory of chemical Resource Engineering Beijing University of Chemical Technology

Matrix/fiber composites of,β-form isotactic polypropylene （iPP） matrix and α-iPP or PA6 fibers were prepared by laminating technique under different preparation temperatures. The mechanical properties and interracial morphologies of these composites were studied by tensile test, optical microscopy and scanning electron microscopy, respectively. The experimental results show that the tensile yield load and tensile modulus of β-iPP/PA6 matrix/fiber systems increased significantly at the expense of elongation at break. These mechanical properties show essentially no dependence on the sample preparation temperature. On the other hand, the mechanical properties of iPP matrix/fiber single polymer composites depend strongly on the sample preparation temperature. At low sample preparation temperature, e.g., 172 ℃, the solid cr-iPP fiber induces tr-iPP crystallization, leading to the formation of a-iPP transcrystalline layer around the fiber. This results in a remarkable increment of the tensile yield load and tensile modulus. The elongation at break is also much better than that of the iPP/PA6 matrix/fiber system. It reflects a better interracial adhesion of the single polymer composite compared with the iPP/PA6 composite. At higher sample preparation temperature, e.g., 174 ℃ or 176 ℃, the partial surface melting of the oriented fiber allows interdiffusion of iPP molecular chains in the molten fiber and matrix melt. The penetration of matrix chains into the molten iPP fiber results in some iPP molecular chains being included partially in the recrystallized fiber and the induced β-transcrystalline layers. This kind of configuration leads to an improvement of interfacial adhesion between the fiber and matrix, which causes a simultaneous increase of the tensile yield load, tensile modulus and elongation at break of β-iPP.

关键词： Polypropylene Composite Mechanical property Interfacial morphology.

Polymer nanoparticles with dendrimer-Ag shell and its application in catalysis

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Particuology 2013年第3期11卷 346-352页

作者： Gaofei Dang Yan Shi Zhifeng Fu Wantai Yang State Key laboratory of chemical Resource Engineering Beijing University of Chemical Technology

Polymer nanoparticles with dendrimer-Ag shell were prepared and their application in catalytic reduction of 4-nitrophenol （4-NP） was investigated. Cross-linked polystyrene （PS） microspheres were prepared through dispersion copolymerization of styrene, acrylic acid and crosslinking monomer 1, 2- divinylbenzene. PS microspheres with average size of 450 nm and narrow size distribution were used as support for the immobilization of dendrimer-Ag shell, The polyamidoamine （PAMAM） dendrimer shell was successively grafted onto the surface ofPS microspheres through repetitive Michael addition reaction of methyl acrylate （MA） and amidation of the obtained esters with large excess of ethylenediamine （EDA）. Silver nanoparticles were formed directly inside the PAMAM shell through reduction with NaBH4. The resulting PS@PAMAM-Ag nanopartides were packed in a stainless steel column and used successfully for catalytic reduction of 4-NP. This technique for packing catalytic polymer particles in a column could imnrove the efficiency of using the metal catalyst and the tedious seuaration in catalytic reaction.

关键词： Polymer nanoparticles Polyamidoamine dendrimer Dendrimer-metal Catalytic column Silver nanocatalyst

Crystallizability of Poly(ε-caprolactone) Blends with Poly(vinylphenol) under Different Conditions

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Chinese Journal of Polymer Science 2014年第9期32卷 1119-1127页

作者： Tian-bo Yang Xiao-li Sun Zhong-jie Ren 李慧慧 Shou-ke Yan State Key laboratory of chemical Resource Engineering Beijing University of Chemical Technology

The intermolecular interaction between poly（vinylphenol）（PVPh） and polycaprolactone （PCL） and the crystallization behavior of PCL in PCL/PVPh blends with different compositions and under different conditions were investigated by Fourier transform infrared spectra （FTIR） and differential scanning calorimetry （DSC）. It has been shown that the PCL in the blends with different blend ratios all exists in crystalline state after solution casting, even though the crystallinity decreases with increasing PVPh content. For the melt crystallized samples, PCL in its 80/20 PCL/PVPh sample can still crystallize. The crystallinity is, however, lower than that of the solution cast sample. For blends containing 50% or 20% PCL, the as-cast samples are semicrystalline and can change to compatible amorphous state after heat treatment process. FTIR analysis shows the existence of hydrogen bonding between PCL and PVPh and the fraction of hydrogen bonds increases remarkably after heat treatment process.

关键词： Poly(vinylphenol) Polycaprolactone Polymer blends Crystallinity Hydrogen bonding.

SYNTHESIS OF HIGH MOLECULAR WEIGHT POLYISOBUTYLENE VIA CATIONIC POLYMERIZATION AT ELEVATED TEMPERATURES

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Chinese Journal of Polymer Science 2013年第8期31卷 1139-1147页

作者： Qiang Huang Ping He Jue Wang 吴一弦 State Key laboratory of chemical Resource Engineering Beijing University of Chemical Technology

A novel simple but effective initiating system of H2O/AlCl3/veratrole （VE） has been developed to synthesize high molecular weight polyisobutylene （PIB） at elevated temperatures via cationic polymerization of isobutylene （IB） in solvent mixture of hexane/methylene dichloride （n-Hex/CH2Cl2 = 2/1, V/V）. VE played very important roles in decreasing cationicity of the growing chain ends, suppressing side reactions of chain transfer and termination during polymerization, leading to production of high molecular weight PIBs. PIBs with high yields, having very high weight-average molecular weight （Mw） of 1117000 and 370000 g/tool could be synthesized with H2O/AICl3/VE initiating system at VE concentration of 5.4 mmol/L at -80 and -60 ℃ respectively. Molecular weight of PIB increased remarkably with increasing VE concentration. The reaction order with respect to VE concentration was determined to be -3.52 via FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance （ATR） immersion probe. The negative reaction order of VE was consistent with its retarding effect on IB polymerization by interacting with the propagating species. Molecular weight of PIB decreased with increasing polymerization temperature. The activation energy for polymerization degree （Eop） could be determined to be around -23 kJ/mol when VE concentration was 5.4 mmol/L or 6.4 mmol/L.

关键词： Isobutylene Molecular weight Cationic polymerization Polyisobutylene Kinetics.