Co-reporter:Bing Xue, Lei Hui, Huaqin Yang, Yulai Zhao, Linxi Hou, and Wei Li
Industrial & Engineering Chemistry Research 2017 Volume 56(Issue 1) pp:
Publication Date(Web):December 20, 2016
DOI:10.1021/acs.iecr.6b03993
A macroporous SiO2 (Macro-SiO2), which has uniformed macropores, an open-framework structure, and thin walls, was synthesized to support Ziegler–Natta catalysts. The immobilization behaviors of the Ziegler–Natta catalysts inside the Macro-SiO2 were investigated. Notable agglomerations of δ-MgCl2/titanium complex were observed because of the unconstrained environment of the Macro-SiO2. A highly superficial Ti content and a heterogeneously chemical structure of Ti active sites were thus achieved inside the Macro-SiO2. The ethylene polymerization results revealed that the Macro-SiO2/MgCl2/TiCl4 exhibited much higher catalytic activity (i.e., 12.1 × 106 g PE·(mol Ti·h)−1 or 17.8 × kg PE·(g cat·h)−1) than that of the traditional 955-SiO2 supported catalyst (i.e., 2.0 × 106 g PE·(mol Ti·h)−1 or 2.7 × kg PE·(g cat·h)−1). Finally, the fragmentation behavior of Macro-SiO2/MgCl2/TiCl4 was investigated during the polymerization. This unconstrained environment of Macro-SiO2 afforded fewer resistances to the diffusion of reactants and also the polymer growth.
Co-reporter:Wei Li, Huaqin Yang, Mengying Shang, Tao Chen, and Wenqin Wang
Industrial & Engineering Chemistry Research 2016 Volume 55(Issue 32) pp:8719
Publication Date(Web):July 26, 2016
DOI:10.1021/acs.iecr.6b01312
Fe3O4@SiO2 with 3D core–shell nanoparticles were used to immobilize Fe(acac)3/2,6-bis(1-(2-isopropylanilinoethyl)) in order to polymerize ethylene in a confined geometry. Structural and morphological evolution of nascent polyethylene is particularly studied. The dependence of molecular weight, molecular weight distribution, condensed structure, and dispersion of nanoparticles on the polymerization time are investigated quantitatively. Both the molecular weight and the molecular weight distribution of synthesized polymers gradually increase as the polymerization proceeds. It is found that the nascent polymer contains a monoclinic phase and a weakly entangled state due to the confined polymerization environment and the low temperature of polymerization. This is the first time that the monoclinic phase is observed in the nascent polyethylene with Mw less than 1 × 105 g/mol. Magnetic property of the polyethylene is presented, as is expected. Finally, fragmentation of Fe3O4@SiO2 nanoparticles during the polymerization is discussed.
Co-reporter:Wei Li, Tao Chen, Chao Guan, Dirong Gong, Jingshan Mu, Zhong-ren Chen, and Qi Zhou
Industrial & Engineering Chemistry Research 2015 Volume 54(Issue 5) pp:1478
Publication Date(Web):January 21, 2015
DOI:10.1021/ie504273r
Three kinds of polyhedral oligomeric silsesquioxane (methyl-POSS, cyclohexyl-POSS, and phenyl-POSS) were chosen to adsorb [3-tert-Bu-2-O-C6H3CH═N(C6F5)]2TiCl2 catalyst (FI catalyst) in order to synthesize ultrahigh molecular weight polyethylene (UHMWPE)/POSS nanocomposites according ethylene in situ polymerization. It was shown that the characteristic of “living’’ polymerization of the FI catalyst would be maintained when alkyl-POSS was incorporated. However, the presence of alkyl-POSS could decay the catalyst activity. The incorporation of alkyl-POSS led to an increase of the crystallinity and the lamellar thickness of nascent UHMWPE, as observed by differential scanning calorimetry. This indicated that the alkyl-POSS would be used as a nucleating agent during the chain growth procedure. Interestingly, all the nanocomposites exhibited low starting storage modulus values which was a reflection of disentangled structure in the nascent UHMWPE nanocomposites. However, polymer chains were prior to entanglement with the incorporation of alkyl-POSS. Rheology and crystallization studies were used to discuss the formation mechanism of entangled structure in the synthesized UHMWPE/POSS nanocomposites.
Co-reporter:Peng Chen, Huaqin Yang, Tao Chen, and Wei Li
Industrial & Engineering Chemistry Research 2015 Volume 54(Issue 44) pp:11024-11032
Publication Date(Web):October 26, 2015
DOI:10.1021/acs.iecr.5b03059
Fe(acac)3/2,6-bis[1-(2-isopropylanilinoethyl)] pyridine catalyst was immobilized on MCM-41 zeolite to synthesize ultrahigh molecular weight polyethylene (UHMWPE) with a weakly entangled state. Microstructure, morphology, crystallization, and rheological properties of the nascent polyethylene were investigated by gel permeation chromatography, scanning electron microscope, differential scanning calorimetry, and rheometer, respectively. The polymer showed broad molecular weight distribution. We found that the synthesized UHMWPE had a weakly entangled state. The evolution of the weakly entangled state of the polymer was studied; however, it was found that the polymer synthesized in the initial stage of polymerization could be more entangled. Thus, poly[styrene-co-(acrylic acid)] (PSA) was coated on the surface of Cat-Fe/M to control the diffusion rate of ethylene, especially during the initial stage of polymerization. The decay rate of catalyst activity was decreased. The polymer synthesized at this stage then became more weakly entangled. The mechanism for achieving the weakly entangled state during polymerization was further discussed.
Co-reporter:Tao Chen;Huaqin Yang
Journal of Polymer Research 2015 Volume 22( Issue 11) pp:
Publication Date(Web):2015 November
DOI:10.1007/s10965-015-0867-3
Ultra-high molecular weight polyethylene (UHMWPE)/disilanolisobutyl polyhedral oligomeric silsesquioxane (POSS) nanocomposites in a disentangled state were synthesized by in situ ethylene polymerization. This is the first report of a detailed study on the phase structure and mechanical properties of disentangled UHMWPE/ POSS nanocomposites in a solid state. The phase structure and chain dynamics of UHMWPE nanocomposites were characterized using wide-line proton NMR and 13C cross-polarization/magic-angle spinning (CP/MAS) solid-state nuclear magnetic resonance (NMR). The results showed that a strong interaction between the POSS and nascent UHMWPE matrix occurred in a solid state, especially in the intermediate and monoclinic crystalline phases. This strong interaction between POSS particles and UHMWPE chains may result in improved melt recovery properties. Mechanical testing indicated that the lowest friction coefficients and highest breaking strength were achieved when 1 wt% loading of POSS was incorporated. The influence of the microstructure on lubrication and mechanical properties was also studied.
Co-reporter:Wei Li, Chao Guan, Jie Xu, Zhong-ren Chen, Binbo Jiang, Jingdai Wang, and Yongrong Yang
Industrial & Engineering Chemistry Research 2014 Volume 53(Issue 3) pp:1088-1096
Publication Date(Web):December 27, 2013
DOI:10.1021/ie403315v
Disentangled broad/bimodal polyethylene with an inverted distribution of short chain branches (SCBs) was synthesized with a supported hybrid catalyst. Poly[styrene-co-(acrylic acid)]- (PSA-) coated SiO2 particles were used to support the hybrid catalysts. The PSA was coated on SiO2-supported VCl3 catalyst. Then, Fe(acac)3/2,6-bis[1-(2-isopropylanilinoethyl)]pyridine was immobilized onto the PSA layer. It was demonstrated that the Fe(acac)3/2,6-bis[1-(2-isopropylanilinoethyl)]pyridine catalyst prepared linear polyethylene with a low molecular weight (MW) and C4–C22 α-olefin. Meanwhile, this α-olefin could be used as the comonomer for VCl3 to prepare high-MW polyethylene with SCBs. Hence, broad-MW-distribution polyethylene (MWD = 120) with an inverted distribution of SCBs was obtained from only one monomer (ethylene). Interestingly, this is the first time that the synthesized polyethylene was reported to exhibit a disentangled state. The isothermal kinetics of crystallization based on the Avrami and Tobin methods was studied to obtain details about the evolution of the disentangled state during the polymerization process.
Co-reporter:Chao Guan;Huaqin Yang;Danying Zhou;Jie Xu;Zhong-Ren Chen
Journal of Applied Polymer Science 2014 Volume 131( Issue 19) pp:
Publication Date(Web):
DOI:10.1002/app.40847
ABSTRACT
A [3-t-Bu-2-OC6H3CHN(C6F5)]2TiCl2 catalyst (bis(phenoxyimine)titanium dichloride complex – FI catalyst) was immobilized on disilanolisobutyl polyhedral oligomeric silsesquioxane (OH-POSS) to prepare ultrahigh molecular-weight polyethylene (UHMWPE)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites during ethylene in situ polymerization. The dispersion state of POSS in the UHMWPE matrix was characterized by X-ray diffraction measurements and transmission electron microscopy. It was shown that the OH-POSS achieved uniformed dispersion in the UHMWPE matrix, although its polarity was unmatched. The isothermal and nonisothermal crystallization behavior of the nanocomposites was investigated by means of differential scanning calorimetry. The crystallization rate of the nanocomposites was enhanced because of the incorporation of POSS during the isothermal crystallization. POSS acted as a nucleus for the initial nucleation and the subsequent growth of the crystallites. For nonisothermal studies, POSS showed an increase in the crystallinity. The crystallization rate of the nanocomposites decreased because the presence of POSS hindered the crystal growth. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40847.
Co-reporter:Wei Li, Chao Guan, Jie Xu, Jingshan Mu, Dirong Gong, Zhong-ren Chen, Qi Zhou
Polymer 2014 Volume 55(Issue 7) pp:1792-1798
Publication Date(Web):1 April 2014
DOI:10.1016/j.polymer.2014.02.023
[3-t-Bu-2-O-C6H3CHN(C6F5)]2TiCl2 catalyst (FI catalyst) was immobilized on disilanolisobutyl POSS to synthesize disentangled ultra-high molecular weight polyethylene (UHMWPE)/POSS nanocomposites during ethylene in situ polymerization. The presence of POSS significantly influenced the polymerization properties of the FI catalyst active centers. It was shown that the characteristic of “living” polymerization of the FI catalyst was retarded. Furthermore, disilanolisobutyl POSS is dispersed uniformly in the UHMWPE matrix with particles size of only several tens nanometers. Interestingly, the incorporation of the POSS into nascent UHMWPE matrix led to a strong interaction between the POSS particles and the UHMWPE chains, resulting in an increased density of entangled chains, as reflected by rheological test. Moreover, the crystallinity and the lamellae thickness of nascent UHMWPE increased upon increasing POSS loading, as observed by differential scanning calorimetry. It suggested that the POSS particles would be presented as a nucleating agent. Finally, the thermal stability and the hydrophilic property of the nanocomposites were improved due to the incorporation of POSS particles.
Co-reporter:Qi Zhou, Zhiqiang Wang, Yuli Shi, Jianghua Fang, Haoqi Gao, Leslie S. Loo
Applied Surface Science 2013 Volume 284() pp:118-125
Publication Date(Web):1 November 2013
DOI:10.1016/j.apsusc.2013.07.044
Highlights
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The migration of POSS molecular in PA6 matrix during phase inversion process was firstly studied.
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Different measurements were used to characterize the interaction between POSS and PA6 chains.
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The proposed migration mechanism was discussed.
Co-reporter:Wei Li;Linxi Hou;Qi Zhou;Liu Yan;Leslie S. Loo
Polymer Engineering & Science 2013 Volume 53( Issue 11) pp:2470-2477
Publication Date(Web):
DOI:10.1002/pen.23500
A novel organic rectorite (OREC) was prepared by treating the natural sodium rectorite (Na-REC) with ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br). The curing behaviors of nanocomposites were quantitatively studied according to the differential scanning calorimetry (DSC) and rheology methods. It was shown by DSC that the activation energies of epoxy system decreased when OREC with reactive imidazole groups were incorporated. The viscosity and viscous flow activation energy were obtained by rheology during the curing reaction. The curing kinetics of the nanocomposites was also deduced from dynamic viscosity analysis and isotherm viscosity analysis. Better dispersion states of the filler can decrease the curing reaction activation energy. The best processing conditions of the nanocomposites were found. POLYM. ENG. SCI., 53:2470–2477, 2013. © 2013 Society of Plastics Engineers
Co-reporter:Wei Li, Huaqin Yang, Jingjing Zhang, Jingshan Mu, Dirong Gong and Xiaodong Wang
Chemical Communications 2016 - vol. 52(Issue 74) pp:NaN11095-11095
Publication Date(Web):2016/08/17
DOI:10.1039/C6CC04814E
Polyhedral oligomeric silsesquioxanes (POSSs) were adsorbed on methylaluminoxane-activated silica for the immobilization of fluorinated bis(phenoxyimine)Ti complexes (FI catalyst). These POSSs have been characterized as horizontal spacers isolating the active sites and hindering the chain overlap in polymerization. The heterogeneous catalyst exhibits considerable activity in the synthesis of weakly entangled polyethylene.
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