Olefin polymerization and copolymerization
Fengtao Li; Jing Wang; Xuelian He
Abstract
In this study, a titanium-based constrained geometry catalyst, [t-BuNSiMe2(Me4Cp)]TiMe2, was synthesized and activated with methylaluminoxane for ethylene-propylene random and block copolymerization. The catalyst exhibited optimal activity at 70°C, yielding random copolymer chains with trace amounts ...
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In this study, a titanium-based constrained geometry catalyst, [t-BuNSiMe2(Me4Cp)]TiMe2, was synthesized and activated with methylaluminoxane for ethylene-propylene random and block copolymerization. The catalyst exhibited optimal activity at 70°C, yielding random copolymer chains with trace amounts of long polyethylene crystalline segments. When the ethylene content fell below 35%, random copolymers failed to crystallize. The block copolymerization system achieved maximum catalytic activity at a reaction temperature of 50°C and an ethylene block duration of 10 minutes. Shorter ethylene block durations correlated inversely with enhanced catalytic activity, increased molecular weight (peaking at 2.88 × 105 g/mol), and a narrower molecular weight distribution. The predominant component comprised extended PPP segments, constituting over 50% of the total copolymer composition. Within the polymer chains, propylene monomers were primarily incorporated as PPP and PPE structural motifs. Moreover, a progressive decrease in [PPP] content was observed with increasing ethylene block duration, whereas [PPE] content exhibited the opposite trend. This inverse relationship suggested that PPP segments gradually transform into PPE configurations via ethylene monomer insertion. These findings demonstrated that product structure and properties can be effectively tuned by adjusting initial monomer feed ratios or the timing of monomer block introduction.
Computational chemistry & molecular modeling
Fan Zhang; Jieqi Wang; Yangyang Zhao; Xuelian He
Abstract
The effect of long chain content (XL ) on the static crystallization and tensile deformation mechanisms of bimodal HDPE/UHMWPE was investigated by molecular dynamics simulations. The crystallization of HDPE/ UHMWPE undergoes three stages: nucleation, rapid growth of lamellar crystals, and stabilization. ...
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The effect of long chain content (XL ) on the static crystallization and tensile deformation mechanisms of bimodal HDPE/UHMWPE was investigated by molecular dynamics simulations. The crystallization of HDPE/ UHMWPE undergoes three stages: nucleation, rapid growth of lamellar crystals, and stabilization. The increase of XL leads to the formation of more nucleation sites, which promotes nucleation, but at the same time leads to an increase of entanglement sites, which is not conducive to the movement of the long chains to the growth front to fold and form lamellar crystals. Tensile deformation is performed on the crystallized models and the systems exhibit three stages: elastic deformation, plastic deformation and stress hardening. During deformation, the increase of XL improves the orientation nucleation and crystallinity (Xc), but when XL exceeds 4 wt.%, the entanglement effect becomes more pronounced, leading to a decrease in Xc. The effect of temperature is also taken into account: at low temperatures, a suitable range (2-4 wt.%) exists to optimize the mechanical properties of the material. At high temperatures, there is almost no stress-hardening phenomenon, but the addition of long chains has an impeding effect on the melting of the lamellar crystals, and when XL is greater than 8 wt.%, stress-induced melting is more likely to occur, accelerating the melting of the crystals.
Olefin polymerization and copolymerization
Yingying Mi; Zaixing Yang; Fei Zhou; Xuelian He
Abstract
A copolymerization reaction was carried out by adding different contents of 5-ethylidene-2-norbomene or cyclopentene to dicyclopentadiene (DCPD) using an optimized polymerization process. The effects of different amounts of the comonomers on the conversion, mechanical properties and thermal stability ...
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A copolymerization reaction was carried out by adding different contents of 5-ethylidene-2-norbomene or cyclopentene to dicyclopentadiene (DCPD) using an optimized polymerization process. The effects of different amounts of the comonomers on the conversion, mechanical properties and thermal stability of the polymer products were investigated and compared. The results showed that the addition of 5-ethylidene-2-norbomene accelerated the reaction rate and had little effect on the overall conversion rate of the reaction, while the addition of cyclopentene decreased the reaction rate and conversion rate. The tensile modulus, tensile strength, flexural modulus and flexural strength of the copolymer showed a trend of increasing and then decreasing with the increase of the comonomers content, reaching a peak at 5wt% of 5-ethylidene-2-norbomene or 3wt% of cyclopentene. At this peak condition, its impact strength could be improved by 50% compared to DCPD homopolymer. Below this peak condition, the Tg and thermal stability of the copolymer did not change significantly.
Zehan Zhang; Zaixing Yang; Fei Zhou; Xuelian He
Abstract
In this paper, the polymerization process of polydicyclopentadiene (PDCPD) obtained by using dicyclopentadiene (DCPD) and the 2nd generation Grubbs’ catalyst is optimized. The curing reaction kinetics was studied by differential scanning calorimetry (DSC), and the solidification reaction process ...
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In this paper, the polymerization process of polydicyclopentadiene (PDCPD) obtained by using dicyclopentadiene (DCPD) and the 2nd generation Grubbs’ catalyst is optimized. The curing reaction kinetics was studied by differential scanning calorimetry (DSC), and the solidification reaction process was obtained. The effects of different ratios of monomer to catalyst on the product performance were investigated. In addition, the current common modification methods of PDCPD have been summarized and improved. The results showed that with the increase of the ratio of monomer to the catalyst, the tensile strength, tensile modulus, bending strength and bending modulus of PDCPD all showed a downward trend, and the impact strength showed an upward trend. When nDCPD: nCat =10000:1, the comprehensive mechanical properties of PDCPD reached the best. The bending modulus, tensile strength and impact strength of PDCPD achieved 2100 MPa, 52.4 MPa and 30 kJ/m2, respectively. The glass transition temperature (Tg) of PDCPD also showed a decreasing trend with the increase of the ratio of monomer to the catalyst, at this ratio, the Tg of the polymer reached 147.6°C. The catalyst concentration had a large effect on the product performance.
Simulation & Modeling
Jieqi Wang; Li Zhao; Minju Song; Fenge Hu; Xuelian He
Abstract
The influence of long branches on crystallization behavior has been studied by means of molecular dynamics simulations. Using two systems: polyethylene (PE) with long branches (LCB-PE) and PE without long branches (linear-PE) with the same molecular weight, we have examined the crystallization behavior ...
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The influence of long branches on crystallization behavior has been studied by means of molecular dynamics simulations. Using two systems: polyethylene (PE) with long branches (LCB-PE) and PE without long branches (linear-PE) with the same molecular weight, we have examined the crystallization behavior of the two systems by molecular dynamics simulation. This paper explains the influence of long branches on the isothermal crystallization process and the non-isothermal crystallization process with similar initial interchain contact fraction (ICF) in terms of final ICF, crystal regions, crystallinity, concentration of tie chains and energy. It is found that the crystallization process is classified as two stages: the nucleation stage and the crystal growth stage. The existence of long branches is favorable for the first stage while unfavorable for the second stage. Knots that act as crystalline defects are excluded from the lamella, resulting in decreasing in regularity and crystallinity of molecular chains. From the perspective of potential energy and non-bond energy, LCB-PE has lower energy than linear-PE in the nucleation stage while the energy of linear-PE is lower than that of LCB-PE in the second stage. In short, the long branched chains inhibit the crystallization process.
Catalysis
Liang Zhu; Xuelian He; Ruihua Cheng; Zhen Liu; Ning Zhao; Boping Liu
Abstract
SiO2/MgCl2 (ethoxide type)/TiCl4 Ziegler-Natta catalysts for use in ethylene polymerization and ethylene/1-hexene copolymerization have been prepared using silica with a supported layer of magnesium ethoxide (Mg(OEt)2) as a catalyst precursor, followed by treating with TiCl4 at different Ti/Mg ...
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SiO2/MgCl2 (ethoxide type)/TiCl4 Ziegler-Natta catalysts for use in ethylene polymerization and ethylene/1-hexene copolymerization have been prepared using silica with a supported layer of magnesium ethoxide (Mg(OEt)2) as a catalyst precursor, followed by treating with TiCl4 at different Ti/Mg molar ratios, which showed significant effects on the active centers and pore structures of the catalysts. The formation amount of β-MgCl2 carrier increased to a maximum with increasing the Ti/Mg molar ratio from 1.50 to 2.25, and then decreased with the further increasing of Ti/Mg molar to 2.50. When the Ti/Mg molar ratio reached 2.25, the catalyst showed the best performance of polymerization, which could be attributed to the most active centers, high surface area and loose surface structure, mainly owing to the high conversion of Mg(OEt)2 to β-MgCl2. The polymers obtained showed medium and high molecular weight (Mw) with medium molecular weight distribution (MWD). In contrast to the conventional Mg(OEt)2-based ZN catalysts, the sphericity of particles was easy to control in this bi-supported catalyst. Furthermore, the prepared catalysts exhibited rather high activity, good copolymerization ability and hydrogen response.
Catalysis
Ting Fu; Ruihua Cheng; Xuelian He; Zhen Liu; Zhou Tian; Boping Liu
Abstract
Vanadium-modified (SiO2/MgO/MgCl2)•TiClx Ziegler-Natta catalysts were prepared through co-impregnation of water-soluble magnesium and vanadium salts under different pH values. Several key factors such as pH value of co-impregnation solution during catalyst preparation, catalyst performances including ...
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Vanadium-modified (SiO2/MgO/MgCl2)•TiClx Ziegler-Natta catalysts were prepared through co-impregnation of water-soluble magnesium and vanadium salts under different pH values. Several key factors such as pH value of co-impregnation solution during catalyst preparation, catalyst performances including catalytic activity, ethylene/1-hexene copolymerization and hydrogen response were investigated. It is found that the components, structures and performance of the catalysts are obviously affected by changing the pH value (pH=5, 7 and 9) of co-impregnation solution. An appropriate pH value (pH=7) can maximize catalytic activity and hydrogen response, while lower pH value (pH=5) is beneficial to the 1-hexene incorporation. The GPC results show that the polymers obtained have high average molecular weight.
Catalysis
Qiaoqiao Sun; Ruihua Cheng; Zhen Liu; Xuelian He; Ning Zhao; Boping Liu
Abstract
Chromium-vanadium (Cr-V) bimetallic catalysts are prepared by the introduction of vanadium into the Phillips catalyst which is one of the most significant industrial ethylene polymerization catalysts for tuning the Phillips catalyst performances and improving polyethylene properties. In the present work, ...
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Chromium-vanadium (Cr-V) bimetallic catalysts are prepared by the introduction of vanadium into the Phillips catalyst which is one of the most significant industrial ethylene polymerization catalysts for tuning the Phillips catalyst performances and improving polyethylene properties. In the present work, titanium species were introduced into the fluorine-modified chromium-vanadium bimetallic catalysts (Cr-V-F) and the prepared catalysts were systematically explored. The element content results of multi-component catalysts showed that a competitive inhibition interaction existed between chromium and vanadium, whereas chromium was more preferable to attach to the Ti-SiO2 than vanadium. In addition, ethylene homopolymerization and ethylene/1-hexene copolymerization were carried out and examined with different catalysts. The introduction of titanium into fluorine-modified bimetallic catalysts enhanced the molecular weight (MW) and broadened the molecular weight distribution (MWD) of polyethylene. The MW of the titanium- and fluorine-modified bimetallic catalysts (Cr-V-F/Ti) firstly rose up and then dropped down with the increasing of the Al/Cr molar ratio. The Cr-V-F/Ti catalysts showed slightly depressed hydrogen response and incorporation of 1-hexene. The short-chain branch distribution (SCBD) results, which were characterized by TREF/SSA, showed that the introduction of the titanium species increased the SCB content in low MW fractions and decreased the SCB content in the high Mw fractions of ethylene/1-hexene copolymers obtained from (Cr-V-F/3Ti)600 in contrast to that from (Cr-V-F)600.
Catalysis
Ting Fu; Ruihua Cheng; Xuelian He; Zhen Liu; Zhou Tian; Boping Liu
Abstract
A novel imido-modified SiO2-supported Ti/Mg Ziegler-Natta catalyst for ethylene and ethylene/1-hexene polymerization is investigated. The catalyst is prepared by modification of (SiO2/MgO/MgCl2)TiClx Ziegler-Natta catalysts via supporting vanadium species followed by reaction with p-tolyl isocyanate ...
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A novel imido-modified SiO2-supported Ti/Mg Ziegler-Natta catalyst for ethylene and ethylene/1-hexene polymerization is investigated. The catalyst is prepared by modification of (SiO2/MgO/MgCl2)TiClx Ziegler-Natta catalysts via supporting vanadium species followed by reaction with p-tolyl isocyanate as imido agents, to get the merits from both the SiO2-supported imido vanadium catalyst and the (SiO2/MgO/MgCl2)TiClx Ziegler-Natta catalyst. The effects of cocatalyst amount, hydrogen and dosage of 1-hexene on polymerization behavior and the microstructures of their polymers are systematically investigated. Compared with (SiO2/MgO/MgCl2)TiClx Ziegler-Natta catalysts and vanadium-modified (SiO2/MgO/MgCl2)TiClx Ziegler-Natta catalysts, the imido-modified SiO2-supported Ti/Mg catalysts show lower but more stable activity including homopolymerization, polymerization with hydrogen and copolymerization owing to imido ligands, indicating that p-Tolyl isocyanate was unfavorable to improving catalytic activity but benefited the stability, and the products of all catalysts show lower 1-hexene incorporation but much higher molecular weight (MW) with medium molecular weight distribution (MWD). The most unique feature of the novel catalysts is the excellent hydrogen response without lowering the polymerization activity, showing great potential for industrial application.
Characterization
Ning Zhao; Ruihua Cheng; Qi Dong; Xuelian He; Zhen Liu; Shiliang Zhang; Minoru Terano; Boping Liu
Abstract
SiO2-supported silyl chromate catalyst is an important industrial catalyst for production of high grade HDPE pipe materials. The control of the short chain branch (SCB) distribution using this catalyst system is still a great challenge. In this work, ethylene and 1-hexene copolymers were synthesized ...
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SiO2-supported silyl chromate catalyst is an important industrial catalyst for production of high grade HDPE pipe materials. The control of the short chain branch (SCB) distribution using this catalyst system is still a great challenge. In this work, ethylene and 1-hexene copolymers were synthesized using SiO2-supported silyl chromate catalyst combined with triisobutylaluminium (TIBA), triethylaluminium (TEA) and mixed TIBA/TEA at molar ratio 1:1 (TIBA/TEA/1:1) as three different Al-alkyl co-catalysts.The temperature rising elution fractionation (TREF) and successive self-nucleation and annealing (SSA, by DSC) methods were combined to analyze the short chain branch distribution (SCBD) of these ethylene/1-hexene copolymers. The results showed that different types of co-catalyst had a great influence on SCBD of ethylene/1-hexene copolymers. The copolymer produced with TIBA showed better SCBD than the copolymer produced with TEA, and the copolymer produced with TIBA/ TEA/1:1 showed a SCBD in between those with TIBA and TEA.
