Zhi-qiang Fan

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Name: 范志强

Organization: Zhejiang University , China

Department: Department of Polymer Science and Engineering

Title: Professor(PhD)

TOPICS

Polymer

Stimuli Responsive Polymers Polyesters Stimuli Responsive Polymers Polymer Microspheres Photo Responsive Polymers

Inorganic Chemistry

Mesoporous Material

Chemicals
References

Synthesis of Polypropylene/Poly(ethylene-co-propylene) In-Reactor Alloys by Periodic Switching Polymerization Process—Effects of Gas Phase Polymerization Time on Polymer Properties

Co-reporter:Reza Mehtarani;Lian-Fang Feng;Songtao Tu;Zhisheng Fu;Zhiqiang Fan

Industrial & Engineering Chemistry Research September 25, 2013 Volume 52(Issue 38) pp:13556-13563

Publication Date(Web):Publication Date (Web): August 29, 2013

DOI:10.1021/ie400378j

A series of polypropylene/poly(ethylene-co-propylene) in-reactor alloys was prepared by a periodic switching polymerization process (PSPP) in which the monomer feed was periodically switched between pure propylene and an ethylene/propylene mixture using a commercial TiCl4/MgCl2/phthalate–Al(C2H5)3/DCPDMS Ziegler–Natta catalyst. In this work, the influence of the total time of gas phase PSPP (tgas) on the composition, morphology, and properties of the alloys were investigated. The rate of copolymer production was almost constant in the gas phase PSPP reaction for as long as 2 h, implying that the diffusion barrier does not significantly increase with tgas in the gas phase PSPP. By fractionating the PP/EPR alloys to three fractions, random ethylene/propylene copolymer (EPR), segmented ethylene/propylene copolymer (EPS), and isotactic polypropylene (iPP), it was found that the EPR and EPS content of the alloys increased with increasing tgas. The chain structure of the fractions also changed with an increase in tgas. An increase in tgas led to a decrease in the content of [PPP] and [EEE] triads in EPS fraction, but the influence of tgas on the sequence distributions of EPR fractions can be ignored. The average size of the dispersed phase domains or EPR domains increased first and then leveled off with increase in tgas. The number of EPR domains increased with an increase in tgas. Toughness of the alloy was improved by prolonging PSPP. The impact strength at low temperature (−20 °C) was more sensitive to the EPR content than that at room temperature. The flexural modulus was sensitive to the EPS content. The toughness–stiffness balance of the alloy is significantly influenced by both tgas and the switching frequency of PSPP.

Synthesis of functional polyolefins via ring-opening metathesis polymerization of ester-functionalized cyclopentene and its copolymerization with cyclic comonomers

Co-reporter:Shaofei Song;Zhisheng Fu;Junting Xu;Zhiqiang Fan

Polymer Chemistry (2010-Present) 2017 vol. 8(Issue 38) pp:5924-5933

Publication Date(Web):2017/10/03

DOI:10.1039/C7PY01330B

In this work, a series of ester-functionalized polyolefins were synthesized via ring-opening metathesis polymerization (ROMP) of alkoxycarbonyl cyclopentene (alkyl = methyl, iso-propyl and tert-butyl) or its ROMP copolymerization with other cyclic olefins (cyclopentene, norbornene, cyclohexene and cyclooctadiene) using a ruthenium-based catalyst, and the produced polymers were characterized by 1H and 13C NMR, GPC and DSC. Under conventional polymerization conditions, a high monomer conversion of around 80% was obtained. The polymers showed a high molecular weight and relatively narrow molecular weight distribution. These ROMP polymers showed different thermal behaviors due to their chain structure variations. The incorporation ratio of methoxycarbonyl cyclopentene (CPM) into the copolymers can be well controlled by changing the comonomer feed ratio. CPM units were randomly incorporated into the copolymer chains. In addition, the pendent tert-butoxycarbonyl groups in the tert-butoxycarbonyl cyclopentene ROMP polymer were transformed into carboxyl groups via hydrolysis, providing polyolefins with regularly distributed carboxyl pendants. The new functional cyclic monomers synthesized in this work can be applied as the sources of functional moieties to prepare novel functional polyolefin materials via metathesis polymerization under mild conditions.

Kinetics and mechanism of metallocene-catalyzed olefin polymerization: Comparison of ethylene, propylene homopolymerizations, and their copolymerization

Co-reporter:Yintian Guo;Zhen Zhang;Wenqi Guo;Akbar Khan;Zhisheng Fu;Junting Xu;Zhiqiang Fan

Journal of Polymer Science Part A: Polymer Chemistry 2017 Volume 55(Issue 5) pp:867-875

Publication Date(Web):2017/03/01

DOI:10.1002/pola.28439

ABSTRACTA series of ethylene, propylene homopolymerizations, and ethylene/propylene copolymerization catalyzed with rac-Et(Ind)2ZrCl2/modified methylaluminoxane (MMAO) were conducted under the same conditions for different duration ranging from 2.5 to 30 min, and quenched with 2-thiophenecarbonyl chloride to label a 2-thiophenecarbonyl on each propagation chain end. The change of active center ratio ([C*]/[Zr]) with polymerization time in each polymerization system was determined. Changes of polymerization rate, molecular weight, isotacticity (for propylene homopolymerization) and copolymer composition with time were also studied. [C*]/[Zr] strongly depended on type of monomer, with the propylene homopolymerization system presented much lower [C*]/[Zr] (ca. 25%) than the ethylene homopolymerization and ethylene–propylene copolymerization systems. In the copolymerization system, [C*]/[Zr] increased continuously in the reaction process until a maximum value of 98.7% was reached, which was much higher than the maximum [C*]/[Zr] of ethylene homopolymerization (ca. 70%). The chain propagation rate constant (kp) of propylene polymerization is very close to that of ethylene polymerization, but the propylene insertion rate constant is much smaller than the ethylene insertion rate constant in the copolymerization system, meaning that the active centers in the homopolymerization system are different from those in the copolymerization system. Ethylene insertion rate constant in the copolymerization system was much higher than that in the ethylene homopolymerization in the first 10 min of reaction. A mechanistic model was proposed to explain the observed activation of ethylene polymerization by propylene addition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 867–875

Structure and properties of ethylene/propylene copolymers synthesized with bis(2,4,7-trimethylindenyl)zirconium dichloride activated by methyl aluminoxanes containing different amount of trimethylaluminum

Co-reporter:Yintian Guo, Zhisheng Fu, Junting Xu, Zhiqiang Fan

Polymer 2017 Volume 122(Volume 122) pp:

Publication Date(Web):28 July 2017

DOI:10.1016/j.polymer.2017.06.042

•Ethylene-propylene copolymerization was catalyzed with unbridged metallocene.•MAO type cocatalysts with different TMA content were compared.•The copolymer chain structure was markedly influenced by the cocatalyst.•Copolymer produced with TMA-depleted cocatalyst has the lowest crystallinity.Ethylene/propylene copolymerization was catalyzed under the same conditions with unbridged metallocene bis(2,4,7-trimethylindenyl)zirconium dichloride (Cat.1) activated by aluminoxane type cocatalysts having different content of trimethylaluminum (TMA). Chain structure of the copolymers was characterized by 13C NMR and thermal analysis on copolymer fractions separated based on crystallinity. Changing the cocatalyst from commercial methylaluminoxane (MAO, containing both free TMA and bond TMA) to dried MAO (dMAO, containing only bond TMA) and BHT-treated MAO (BMAO, containing almost no TMA) caused only slight differences in polymerization activity and moderate increase in copolymer molecular weight, but marked differences in copolymer chain structure. The copolymers produced using MAO (sample 1) and dMAO (sample 2) as cocatalysts contain high amount of fractions with very low propylene content and almost isolated propylene units. The copolymer produced using BMAO as cocatalyst (sample 3) has very broad composition distribution, but its fraction with the highest crystallinity has much higher content of PP dyads than the crystalline fractions of the other two samples. This sample has the lowest crystallinity among the three samples. Phase morphology and tensile properties of the copolymer changed markedly when different cocatalyst was used. Tensile properties of sample 1 and 2 were similar to mixtures of elastomer and crystalline plastic materials, but tensile properties of sample 3 were more or less like a thermoplastic elastomer. Influences of TMA on the micro scale environment of active centers were considered the main reason for the effects of cocatalyst on copolymer structure and properties.Download high-res image (209KB)Download full-size image

Functional polyethylene with regularly distributed ester pendants via ring-opening metathesis polymerization of ester functionalized cyclopentene: Synthesis and characterization

Co-reporter:Shaofei Song, Zhenyan Xing, Zhenmei Cheng, Zhisheng Fu, Junting Xu, Zhiqiang Fan

Polymer 2017 Volume 129(Volume 129) pp:

Publication Date(Web):27 October 2017

DOI:10.1016/j.polymer.2017.09.057

•Functionalized cyclopentenes carrying −COOR (R = C1−C16 alkyl) were synthesized.•ROMP of the cyclopentene monomers with ruthenium-based HG-II catalyst were conducted.•Hydrogenation of the ROMP polymer gave PE with −COOR on every five main chain carbons.•The polymers have higher side chain Xc than polyacrylates with the same side alkyl.•The PEs present crystal lamella thickness close to length of the extended side groups.A new series of functional polyethylene (PE) with ester pendant (−COOR, R = methyl, ethyl, n-propyl, n-butyl, n-octyl, n-dodecyl, n-tetradecyl and n-hexadecyl) on every five main chain carbons were prepared via ring-opening metathesis polymerization (ROMP) of COOR functionalized cyclopentene catalyzed by a ruthenium-based catalyst and subsequent hydrogenation of the ROMP products. High monomer conversions (70–80%) were achieved in all the ROMP reactions. Chain structure, molecular weight and molecular weight distribution (MWD) of the ROMP products and hydrogenated polymers were characterized by 1H, 13C NMR and GPC, which showed regular distribution of the COOR pendants along the main chain, moderate molecular weight and narrow MWD. Thermal properties and side chain crystallization behaviors of the functional PEs were investigated by differential scanning calorimetry (DSC). Glass transition temperature (Tg) of the polymer decreased for nearly 30 °C when R of the pendant COOR was enlarged from methyl to n-octyl, and the new polymers showed lower melting temperature (Tm), higher side chain crystallinity (Xc) and more precise side chain lamellar crystal thickness (lc) as compared with corresponding polyacrylates carrying the same side alkyl. The new polymers exhibited moderate thermal stability.Download high-res image (162KB)Download full-size image

Influence of trimethylaluminum on kinetics of rac-Et(Ind)2ZrCl2/aluminoxane catalyzed ethylene polymerization

Co-reporter:Yintian Guo, Feng He, Zhen Zhang, Akbar Khan, Zhisheng Fu, Junting Xu, Zhiqiang Fan

Journal of Organometallic Chemistry 2016 Volume 808() pp:109-116

Publication Date(Web):15 April 2016

DOI:10.1016/j.jorganchem.2016.02.024

•Ethylene was polymerized by rac-Et(Ind)2ZrCl2/aluminoxane (MAO, dMAO or MMAO).•Concentration of active centers and its changes with time were determined.•Three kinds of active centers were differentiated by MWD deconvolution.•Free TMA was found to take part in the formation of contact ion pairs.Ethylene polymerization with rac-Et(Ind)2ZrCl2/aluminoxane catalysts were conducted under different conditions, including varied reaction time, cocatalyst and cocatalyst concentration. Methylaluminoxane (MAO), dried MAO (dMAO) and modified MAO (MMAO) were used as cocatalyst, respectively. Changes of polymerization rate, number of active centers ([C∗]/[Zr]) and polymer molecular weight distribution (MWD) with time were traced. A method of counting active centers using 2-thiophenecarbonyl chloride as quenching agent was applied to measure [C∗]. MWD curves of polymer were deconvoluted into three Flory components, which were assigned to polymer formed by loosely associated ion pairs, contact ion pairs and ion pairs with medium cation-anion distance. The loosely associated ion pairs produce polymer of low molecular weight, and the contact ion pairs produce high molecular weight polymer. Free trimethylaluminum (TMA) in the system was found to be an important component for the formation of contact ion pairs. In ethylene polymerization activated by different cocatalysts, gradual increase of [C∗]/[Zr] with time until 30 min was observed, meaning that complete activation of all the metallocene molecules takes rather long time. Comparisons of [C∗]/[Zr] ratios at 30 min in systems activated by different cocatalysts lead to the conclusion that TMA takes part in formation of dormant active centers. The role of TMA as an efficient chain transfer agent has also been proved.

Millimeter-size polyethylene hollow spheres synthesized with MgCl2-supported Ziegler-Natta catalyst

Co-reporter:Meizhou Qi;Biao Zhang;Zhisheng Fu;Junting Xu ;Zhiqiang Fan

Journal of Applied Polymer Science 2016 Volume 133( Issue 12) pp:

Publication Date(Web):

DOI:10.1002/app.43207

ABSTRACT

Polyethylene hollow spheres with diameters of 0.4–2 mm were synthesized by a two-step slurry polymerization in a single reactor with a spherical MgCl₂-supported Ziegler-Natta catalyst activated by triethylaluminum, in which the first step was prepolymerization with 0.1 MPa propylene and the second step was ethylene polymerization under 0.6 MPa. The prepolymerization step was found necessary for the formation of hollow spherical particles with regular shape (perfectly spherical shape). The effects of adding small amount of propylene (propylene/ethylene < 0.1 mol/mol) in the reactor after the prepolymerization step were investigated. Average size of the polymer particles was increased, and the polymerization rate was markedly enhanced by the added propylene. Development of the particle morphology with polymerization time was also studied. The polymer particles formed by less than 20 min of ethylene polymerization showed hollow spherical morphology with thin shell layer. Most of the particles had ratio of shell thickness/particle radius smaller than 0.5. By prolonging the ethylene polymerization, the shell thickness/particle radius ratio gradually approached 1, and the central void tended to disappear. Central void in polymer particles formed from smaller catalyst particles disappeared after shorter time of polymerization than those formed from bigger catalyst particles. The shell layer of the hollow particles contained large number of macro-, meso- and micro-pores. The mesopore size distributions of four typical samples were analyzed by nitrogen adsorption–desorption experiments. A simplified multigrain model was proposed to explain the morphogenesis of the hollow spherical particles. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43207.

Precision ADMET polyolefins containing dithiane: Synthesis, thermal properties, and macromolecular transformation

Co-reporter:Shaofei Song;Feng He;Zhisheng Fu;Junting Xu ;Zhiqiang Fan

Journal of Polymer Science Part A: Polymer Chemistry 2016 Volume 54( Issue 16) pp:2468-2475

Publication Date(Web):

DOI:10.1002/pola.28123

ABSTRACT

1,3-Dithiane and its derivatives are widely used as powerful acyl anion equivalent to a range of useful transformations that are needed in the synthesis of natural products. In this work, a series of polyolefins containing pendant dithiane groups have been designed and synthesized via acyclic diene metathesis polymerization (ADMET) polymerization and subsequent hydrogenation. The structures of these polymers were characterized by ¹H NMR, ¹³C NMR, and FT-IR, and successful incorporation of the dithiane groups was proved. With different contents of the dithiane moieties, these ADMET polymers exhibited distinct thermal properties different from each other as evidenced by differential scanning calorimetry and thermal gravimetric analysis. The dithiane units in the ADMET polymer with 20 methylene carbons between the adjacent dithiane groups were transformed into thiol groups via reaction with Bu₃SnH. This work provided a convenient route to synthesize polyethylene with pendant thiol groups that are evenly distributed in the chain. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2468–2475

Polyethylene containing aliphatic ring and aromatic ring defects in the main chain: Synthesis via ADMET and comparisons of thermal properties and crystalline structure

Co-reporter:Shaofei Song, Wenqi Guo, Shufen Zou, Zhisheng Fu, Junting Xu, Zhiqiang Fan

Polymer 2016 Volume 107() pp:113-121

Publication Date(Web):19 December 2016

DOI:10.1016/j.polymer.2016.11.017

•Three polyethylene containing non-planar aliphatic defects were synthesized.•PE with non-planar aliphatic ether ring units showed decreased thermal stability.•The non-planar defects perturbed the crystal structure and occupy larger space.•These PE have smaller lc and lower crystallinity than their aromatic counterparts.Three polyethylene containing different non-planar aliphatic ring ether units (1,4-cyclohexylenedioxy, 4,4′-bicyclohexylenedioxy and 4,4′-isopropylidenedicyclohexylenedioxy) were synthesized via acyclic diene metathesis polymerization (ADMET) and subsequent hydrogenation. They were compared with their counterpart polymers containing aromatic ring defects in aspects of chain structural, thermal properties and crystalline structure by investigations with 1H NMR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS). Regardless of the trans/cis isomers of cyclohexane moieties in these polymers, the results demonstrated that polyethylene containing non-planar aliphatic ring units showed decreased thermal stability as compared with the corresponding PE containing aromatic ring defects. Moreover, study on crystallization behaviors indicated that in contrast to their aromatic counterparts, introduction of the non-planar aliphatic defects perturbed the corresponding crystal structure more intensively, and larger space is needed to include these defects in the solid phase. As a result, their WAXD reflections shifted to lower scattering angles that correspond to increased d-spacing, and the polymers exhibited lower melting points. SAXS results proved that non-planar aliphatic ring defects result in increased dimension of amorphous region. Calculated by melting points and enthalpy, these polymers had smaller crystalline lamella thickness and lower crystallinity than their aromatic counterparts.

Synthesis and Crystallization Behavior of Equisequential ADMET Polyethylene Containing Arylene Ether Defects: Remarkable Effects of Substitution Position and Arylene Size

Co-reporter:Shao-Fei Song, Yin-Tian Guo, Rui-Yang Wang, Zhi-Sheng Fu, Jun-Ting Xu, and Zhi-Qiang Fan

Macromolecules 2016 Volume 49(Issue 16) pp:6001-6011

Publication Date(Web):August 5, 2016

DOI:10.1021/acs.macromol.6b01324

A new series of polyethylene (PE) containing arylene ether units as defects in the main chain, which were precisely separated by 20 CH2 units, were synthesized via acyclic diene metathesis (ADMET) polymerization. The thermal stability, crystallization, and melting behaviors, crystal structure, and chain stacking were investigated with TGA, DSC, WAXD, and SAXS. It is found that the substitution position in the arylene units has a remarkable influence on the chain stacking and their location in the solid phase. The ortho-substituted phenylene units are excluded from the crystal phase, leading to a low melting temperature (Tm). In contrast, the para-substituted phenylene units can be included into the crystal, leading to a high Tm. The meta-substituted phenylene units can be partially included into the crystal, resulting in mixed crystal structures and an intermediate Tm. Such an effect of substitution position in precision PEs is different from that in poly(ethylene oxide) reported in the literature, which can be ascribed to the matchable configuration of the defects in the main chain with the conformation of PE in the crystals. When the defects become naphthylene ether units, the crystallization and melting behaviors of the polymers are similar to or different from those of the precision PEs with phenylene ether defects, depending on the substitution position. This shows that both the substitution position in the arylene ether defects and the defect size exert effects on crystallization, melting behaviors, and chain stacking of precision PEs.

Ethylene/1-hexene copolymerization with supported ZieglerNatta catalysts prepared by immobilizing TiCl3(OAr) onto MgCl2

Co-reporter:Hongrui Yang;Biao Huang;Zhisheng Fu ;Zhiqiang Fan

Journal of Applied Polymer Science 2015 Volume 132( Issue 4) pp:

Publication Date(Web):

DOI:10.1002/app.41329

ABSTRACT

Five titanium complexes TiCl₃(OAr) (Ar = C₆H₅, 2,6-Me₂C₆H₃, 2,6-i-Pr₂C₆H₃, 2,6-t-Bu₂C₆H₃, 4-Me-2,6-t-Bu₂C₆H₃) were immobilized, respectively, on MgCl₂ in semibatch reaction to form supported catalysts for olefin polymerization. Comparing with the catalysts prepared by immobilizing TiCl₃(OAr) onto MgCl₂ in batch reaction, the catalysts prepared by semibatch reaction have lower titanium content and higher ArO/Ti ratio. The aryloxy-containing catalysts studied in this work showed higher ethylene/1-hexene copolymerization activity and higher 1-hexene incorporation rate than the blank catalyst when activated by triisobutylaluminum. Similar effects of the aryloxy ligand were observed when the copolymerization is conducted in the presence of hydrogen. Introducing aryloxy ligand in the catalysts either by semibatch or batch reaction caused similar effects of enhancing copolymerization activity and α-olefin incorporation rate. Mechanism of the effects of aryloxy ligand has been discussed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41329.

Synthesis of hyperbranched polymers by free radical addition-coupling polymerization with A3/B2 and A2A/B2 approaches

Co-reporter:Yaobin Liu ;Zhiqiang Fan

Journal of Applied Polymer Science 2015 Volume 132( Issue 20) pp:

Publication Date(Web):

DOI:10.1002/app.41972

ABSTRACT

Two tribromide compounds, 1,3-(propanoic acid, 2-bromo-)-2-(2-bromo-1-oxopropylamino)propyl ester (A1) and trimethylolpropane tris(2-bromopropionate) (A2), were synthesized. By Cu/N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA)-mediated radical addition-coupling polymerization (RACP) of 2-methyl-2-nitrosopropane (MNP) with the tribromide compounds, two types of hyperbranched polymers were synthesized under mild conditions, respectively. Polymerization degrees of the polymers increased with time gradually, which is in line with a step-growth polymerization mechanism. By tracing the polymerization process by gel permeation chromatography and NMR analysis, proper reaction conditions to get hyperbranched polymers was obtained. Based on the results of NMR analysis on the polymer chain structure, mechanism of forming hyperbranched polymer has been proposed, which includes formation of carbon radicals from the tribromo monomer through single electron transfer, their reaction with MNP to form nitroxide radicals, and cross-coupling reaction of the nitroxide radicals with other carbon radicals. The gelation point of the A2-MNP system is larger than that of the A1-MNP system, indicating that probability of intramolecular cyclization in A2-MNP RACP system is higher than the A1-MNP system. The reactivity of —NHCOCH(CH₃)Br group of A1 is lower than its two —OCOCH(CH₃)Br groups, and this resulted in longer distance between two adjacent branch points in the hyperbranched polymer of A1-MNP than the A2-MNP system. It is possible to adjust the chain structure of RACP-based hyperbranched polymer by changing the reactivity of the functional groups in A₃ monomer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41972.

Improving microisotacticity of Ziegler–Natta catalyzed polypropylene by using triethylaluminum/triisobutylaluminum mixtures as cocatalyst

Co-reporter:Biao Zhang, Qi Dong, Zhisheng Fu, Zhiqiang Fan

Polymer 2014 Volume 55(Issue 19) pp:4865-4872

Publication Date(Web):15 September 2014

DOI:10.1016/j.polymer.2014.08.019

•Propylene was polymerized with supported Z–N catalyst activated by alkylaluminums.•Using TEA/TiBA mixture as cocatalyst improved the microisotacticity of PP.•Alkylation power of TEA/TiBA mixture decrease with increasing TiBA content.•Lower Lewis acidity of TEA/TiBA than TEA intensifies the role of external donor.Propylene was polymerized with TiCl4/Di/MgCl2 catalyst and cocatalysts containing triethylaluminum (TEA) and triisobutylaluminum (TiBA) in the presence of Ph2Si(OMe)2 (external donor) and hydrogen. Chain structure of the formed polypropylene (PP) was characterized by temperature-rise elution fractionation (TREF) combined with DSC and 13C NMR analysis of the main fractions. Increasing the amount of TiBA in cocatalyst leads to decrease of isotactic index of PP, meanwhile the microisotacticity of the main TREF fractions of PP was enhanced. PP produced with the catalyst activated by a 50/50 TEA/TiBA mixture has the same content of highly isotactic chains as PP produced with the TEA activated catalyst, but main TREF fractions of the former has higher microisotacticity than the later. Fast alkyl exchanges in TEA/TiBA mixtures are found by 1H NMR analysis of the mixtures. By analyzing alkanes released from hydrolyzed catalysts that have been treated with the cocatalyst, alkylation power of TEA/TiBA mixture was found to decrease with increasing its TiBA content. The effects of TEA/TiBA mixture in propylene polymerization is explained by the weaker alkylation power and lower Lewis acidity of the mixed alkylaluminums than pure TEA. Decrease in the alkylation power leads to reduction of active centers with the highest stereospecificity, meanwhile decrease in Lewis acidity intensified the role of De in enhancing stereospecificity of different active centers. When the amount of TiBA in TEA/TiBA mixture falls in a suitable range, the later effect becomes dominant, and evident improvement in microisotacticity of PP can be achieved.

Effect of the Combined External Electron Donors on the Structure and Properties of Polypropylene/Poly(ethylene-co-propylene) In-Reactor Alloys Prepared by High-Efficiency Industrial Ziegler–Natta Catalyst

Co-reporter:Zhisheng Fu, Songtao Tu, and Zhiqiang Fan

Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 17) pp:5887-5894

Publication Date(Web):March 29, 2013

DOI:10.1021/ie303216c

In this work, a series of isotactic polypropylene/ethylene–propylene rubber (iPP/EPR) in-reactor alloys were prepared by high-efficiency industrial Ziegler–Natta catalyst with diphenyldimethoxysilane/dicyclopentyldimethoxysilane (DDS/D-donor) mixtures as external electron donors. The effects of the external electron donor on the structure and mechanical properties of the iPP/EPR in-reactor alloys were studied. According to the characterization results, the iPP/EPR in-reactor alloys were mainly composed of random poly(ethylene-co-propylene), multiblock poly(ethylene-co-propylene), and highly isotactic PP. For DDS/D-donor mixtures as external electron donors and triethylaluminum (TEA) as the cocatalyst, as the amount of D-donor in DDS/D-donor mixtures increased, the molecular weight of polypropylene homopolymer and the structural uniformity of multiblock poly(ethylene-co-propylene) increased, whereas when D-donor alone was used as the external electron donor, they decreased. However, the isotacticity of polypropylene homopolymer increased as the amount of D-donor in the DDS/D-donor mixtures increased. Therefore, as the amount of D-donor in the DDS/D-donor mixtures increased, the impact strength of the iPP/EPR in-reactor alloy increased, but when D-donor alone was used as the external electron donor, the impact strength of the alloy decreased. An optimum feed ratio between DDS and D-donor was found, namely, DDS/D-donor = 1:3 (Si/Ti = 5). The iPP/EPR in-reactor alloy prepared under these conditions was the toughest. The influence of the external electron donor on the flexural modulus and flexural strength could be ignored.

Synthesis of Polypropylene/poly(ethylene-co-propylene) In-Reactor Alloys by Periodic Switching Polymerization Process: Dynamic Change of Gas-Phase Monomer Composition and Its Influences on Polymer Structure and Properties

Co-reporter:Reza Mehtarani, Zhi-Sheng Fu, Song-Tao Tu, Zhi-Qiang Fan, Zhou Tian, and Lian-Fang Feng

Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 29) pp:9775-9782

Publication Date(Web):June 24, 2013

DOI:10.1021/ie3032179

Using a MgCl2-supported Ziegler–Natta catalyst, a series of polypropylene/poly(ethylene-co-propylene) (PP/EPR) in-reactor alloys with high EPR content (>20 wt %) were prepared by a periodic switching polymerization process (PSPP) in which the monomer feed was periodically switched between pure propylene and an ethylene/propylene mixture. The change of gas-phase monomer composition with time in the PSPP process was investigated. Transition periods were identified when switching the monomer feed from propylene to ethylene/propylene mixture (or vice versa). Because the gas-phase ethylene content in the transition periods was lower than that of the monomer mixture feed, copolymer formed in these periods has lower ethylene content than those formed in the steady periods of the copolymerization stage. As a result, the transition periods led to formation of more segmented ethylene/propylene copolymer (EPS) and decreased its ethylene content. When the switching frequency was altered in an adequate range, the content of EPS in the alloy was increased by increasing the switching frequency, and dispersion of the copolymer phase in the PP matrix became more uniform. The toughness–stiffness balance of PP/EPR alloy synthesized by PSPP process with adequate switching frequency was better than the alloy synthesized by a conventional sequential polymerization process with only one copolymerization stage. When the switching frequency exceeded a certain limit, the alloy’s EPS content was decreased and its toughness–stiffness balance tended to be worse.

Mechanism of Propylene Polymerization with MgCl2-Supported Ziegler–Natta Catalysts Based on Counting of Active Centers: The Role of External Electron Donor

Co-reporter:Xian-rong Shen, Zhi-sheng Fu, Jie Hu, Qi Wang, and Zhi-qiang Fan

The Journal of Physical Chemistry C 2013 Volume 117(Issue 29) pp:15174-15182

Publication Date(Web):July 1, 2013

DOI:10.1021/jp404416n

Four R1R2Si(OMe)2 type compounds were added as an external electron donor (De) in propylene polymerization with TiCl4/Di/MgCl2 type supported Ziegler–Natta catalysts (Di = internal donor). Each polypropylene (PP) sample was fractionated into three parts (atactic, medium-isotactic and isotactic PP), and the number of active centers ([C*]/[Ti]) in each PP fraction was counted using 2-thiophenecarbonyl chloride as the quenching and tagging agent. The gradual decrease of [C*]/[Ti] with De/Ti ratio is ascribed to competitive and reversible coordination of De on either central Ti of the active center or Mg adjacent to the central Ti. The former coordination leads to deactivation of C*, and the latter one leads to still living C*. The chain propagation rate constant (kp) of the active centers producing atactic, medium-isotactic and isotactic PP change with De/Ti in different ways. Only the kp of active centers producing isotactic PP was evidently increased by De. Enhancement in isotacticity of PP product is found to be a combined result of both deactivation of active centers by De and selective activation of the active centers that produce isotactic PP. Changing the alkyl groups of R1R2Si(OMe)2 leads to an altered balance between the deactivation and activation effects of De.

Copolymerization of ethylene and 1-hexene with TiCl4/MgCl2 catalysts modified by 2,6-diisopropylphenol

Co-reporter:Sheng-jie Xia;Zhi-sheng Fu;Xiao-yan Liu

Chinese Journal of Polymer Science 2013 Volume 31( Issue 1) pp:110-121

Publication Date(Web):2013 January

DOI:10.1007/s10118-013-1201-3

A supported TiCl4/MgCl2 catalyst without internal electron donor (O-cat) was prepared firstly. Then it was modified by 2,6-diisopropylphenol to make a novel modified catalyst (M-cat). These two catalysts were used to catalyze ethylene/1-hexene copolymerization and 1-hexene homopolymerization. The influence of cocatalyst and hydrogen on the catalytic behavior of these two catalysts was investigated. In ethylene/1-hexene copolymerization, the introduction of 2,6-iPr2C6H3O- groups did not deactivate the supported TiCl4/MgCl2 catalyst. Although the 1-hexene incorporation in ethylene/1-hexene copolymer prepared by M-cat was lower than that prepared by O-cat, the composition distribution of the former was narrower than that of the latter. Methylaluminoxane (MAO) was a more effective activator for M-cat than triisobutylaluminium (TIBA). MAO led to higher yield and more uniform chain structure. In 1-hexene homopolymerization, the presence of 2,6-iPr2C6H3O- groups lowered the propagation rate constants. Two types of active centers with a chemically bonded 2,6-iPr2C6H3O- group were proposed to explain the observed phenomena in M-cat.

Probing the roles of diethylaluminum chloride in propylene polymerization with MgCl2-supported ziegler-natta catalysts

Co-reporter:Jie Hu;Bin Han;Xian-rong Shen;Zhi-sheng Fu

Chinese Journal of Polymer Science 2013 Volume 31( Issue 4) pp:583-590

Publication Date(Web):2013 April

DOI:10.1007/s10118-013-1260-5

In this article, the effect of diethylaluminum chloride (DEAC) in propylene polymerization with MgCl2-supported Ziegler-Natta catalyst was studied. Addition of DEAC in the catalyst system caused evident change in catalytic activity and polymer chain structure. The activity decrease in raising DEAC/Ti molar ratio from 0 to 2 is a result of depressed production of isotactic polypropylene chains. The number of active centers in fractions of each polymer sample was determined by quenching the polymerization with 2-thiophenecarbonyl chloride and fractionating the polymer into isotactic, mediumisotactic and atactic fractions. The number of active centers in isotactic fraction ([Ci*]/[Ti]) was lowered by increasing DEAC/Ti molar ratio to 2, but further increasing the DEAC/Ti molar ratio to 20 caused marked increase of [Ci*]/[Ti]. The number of active centers that produce atactic and medium-isotactic PP chains was less influenced by DEAC in the range of DEAC/Ti = 0–10, but increased when the DEAC/Ti molar ratio was further raised to 20. The propagation rate constant of Ci* (kpi) was evidently increased when DEAC/Ti molar ratio was raised from 0 to 5, but further increase in DEAC/Ti ratio caused gradual decrease in kpi. The complicated effect of DEAC on the polymerization kinetics, catalysis behaviors and polymer structure can be reasonably explained by adsorption of DEAC on the central metal of the active centers or on Mg atoms adjacent to the central metal.

Solid-state graft polymerization of styrene in spherical polypropylene particles in the presence of montmorillonite

Co-reporter:Zhisheng Fu;Fangli Sun;Zhiqiang Fan

Journal of Applied Polymer Science 2012 Volume 126( Issue 5) pp:1497-1504

Publication Date(Web):

DOI:10.1002/app.36651

Abstract

In this work, cetyltrimethyl ammonium bromide and methacryloyloxyethyhrimethyl ammonium chloride were used to prepare organophilic montmorillonite (O-MMT). Then, polypropylene (PP)–clay nanocomposites were prepared by the in situ grafting polymerization of styrene (St)-containing O-MMT onto PP with tert-butyl perbenzoate as an initiator in the solid state. Fourier transform infrared spectroscopy, gel permeation chromatography, transmission electron microscopy, and X-ray diffraction were applied to study the structure of the layered silicate and modified PP. The surfaces of the composites and, thus, the distribution of the clay in the PP matrix were characterized by scanning electron microscopy. The rheology and mechanical properties were studied and are discussed. According to the characterization results, OMMT and St were already grafted onto the PP main chain. Also, the intercalated structure of montmorillonite could be stabilized, and a stable exfoliated structure could be attained. Namely, intercalated PP/OMMT nanocomposites were obtained. The rheological results clearly show that these PP/OMMT nanocomposites had long-chain-branched structures. The peroxide modification of PP had minor effects on the tensile and bending strengths of the modified PP; however, this modification resulted in a significant reduction in the impact strength. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Chain transfer reactions of propylene polymerization catalyzed by AlEt3 activated TiCl4/MgCl2 catalyst under very low monomer addition rate

Co-reporter:Yue Yu, Zhisheng Fu, Zhiqiang Fan

Journal of Molecular Catalysis A: Chemical 2012 Volumes 363–364() pp:134-139

Publication Date(Web):November 2012

DOI:10.1016/j.molcata.2012.05.027

Chain transfer reactions of TiCl4/MgCl2–AlEt3 catalyzed propylene polymerization were investigated under conditions of severely starved monomer supply and suppressed chain transfer to cocatalyst. Slurry polymerization was conducted by injecting gaseous monomer at very low rate to the reactor containing preactivated catalyst. The preactivated solid catalyst has been washed by solvent to remove AlEt3 in the liquid phase, and chain transfer to AlEt3 was nearly completely suppressed. Besides 1-propen-2-yl (vinylidene) end group formed by β-H transfer after primary (1,2-)insertion, 1-propen-3-yl (allyl) end group formed by β-Me transfer after 1,2-insertion and 2-buten-4-yl formed by β-H transfer after secondary (2,1-)insertion were also detected in the polymer by 1H NMR analysis. The monomer dependences of the chain transfer reactions were studied. Because of the unimolecular nature of β-H transfer after a secondary insertion, the content of 2-buten-4-yl end group, which is too low to be detected in PP polymerized under conventional conditions, was markedly increased in the product of monomer-starved polymerization.Graphical abstractHighlights► Propylene was polymerized by TiCl4/MgCl2–AlEt3 at extremely low monomer pressure. ► Chain transfer to AlEt3 was suppressed by removing AlEt3 in the liquid phase. ► 2-Buten-4-yl end group formed by β-H transfer after 2,1-insertion was detected. ► Allyl end group formed by β-Me transfer also increased with decreasing [Pr].

Ethylene/1-hexene copolymerization with MgCl2-supported Ziegler–Natta catalysts containing aryloxy ligands. Part I: Catalysts prepared by immobilizing TiCl3(OAr) onto MgCl2 in batch reaction

Co-reporter:Shengjie Xia, Zhisheng Fu, Biao Huang, Junting Xu, Zhiqiang Fan

Journal of Molecular Catalysis A: Chemical 2012 Volume 355() pp:161-167

Publication Date(Web):March 2012

DOI:10.1016/j.molcata.2011.12.010

Novel aryloxy-containing MgCl2-supported Ziegler–Natta catalysts were prepared by treating TiCl3(OAr) (Ar = C6H5-, 2,6-Me2C6H3-, 2,6-i-Pr2C6H3-, 2,6-t-Bu2C6H3-) with MgCl2 in batch reaction. The influences of aryloxy group on the titanium content and aryloxy/Ti molar ratio in the catalysts was investigated. Because of ligand exchanges between the immobilized titanium species and TiCl3(OAr) in the solution, the aryloxy/Ti molar ratio in these catalysts were less than 1. Using triethylaluminum (TEA) or triisobutylaluminum (TIBA) as cocatalyst, these catalysts showed different catalytic behaviors in ethylene-1-hexene copolymerization. Using TIBA as cocatalyst, the aryloxy-containing catalysts showed higher activity than a TiCl4/MgCl2 blank catalyst. Although the total 1-hexene incorporation of the copolymers prepared by the novel catalysts were lower than that of the blank system, the difference in 1-hexene content between the boiling n-heptane soluble part and the insoluble part was markedly lower, and the blockiness of comonomer sequence distribution was evidently higher. The TIBA activated aryloxy-containing catalysts were found to produce poly(ethylene-co-1-hexene) with more uniform chemical composition distribution.Graphical abstractHighlights► Aryloxy-containing MgCl2-supported Ziegler–Natta catalysts were prepared. ► The aryloxy/Ti molar ratio in these catalysts were less than 1. ► Different cocatalyst brought about different catalytic behaviors. ► Activated by TIBA, these catalysts produced copolymer with more uniform CCD.

Effects of Doping LiCl into MgCl2-Supported Ziegler−Natta Catalyst on the Molecular Weight Distribution and Isotacticity of Polypropylene

Co-reporter:Xue Jiang, Hang Wang, Xiuzhi Tian, Yiqi Yang, and Zhiqiang Fan

Industrial & Engineering Chemistry Research 2011 Volume 50(Issue 1) pp:259-266

Publication Date(Web):November 30, 2010

DOI:10.1021/ie100755j

A series of MgCl2-supported Ziegler−Natta catalysts was prepared by supporting TiCl4 on LiCl-doped MgCl2, and these catalysts were used to polymerize propylene, using triethylaluminum as a co-catalyst. LiCl and MgCl2 were coprecipitated from ethanol to prepare LiCl-doped MgCl2·nEtOH adducts. The LiCl-doped catalysts were prepared by dipping the adducts into a TiCl4 solution. The crystalline and morphological structures of the adducts and catalysts were characterized by wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Two types of mixed crystals—Li2MgCl4 and LiMgCl3—were found in the catalyst that contained 18 mol % LiCl (LMSC18). The molecular weight distribution (MWD) and isotacticity of polypropylene (PP) varied with the dosage of LiCl in the catalyst. PP with a broader MWD was synthesized using LiCl-doped catalysts that contained 11−18 mol % LiCl. Deconvolution of the MWD profiles with multiple Flory “most-probable” functions were applied to analyze the distribution of active centers. There were six types of active centers in LMSC18: A, B, B′, C, D, and E. The combined productivity of (E + D)-type active centers in catalyst LMSC18 was much larger than that of the other catalysts. All the results showed that the properties and distribution of active centers of the catalysts supported on LiCl-doped MgCl2 were markedly changed at a certain range of LiCl dosage.

Effects of ethylene as comonomer on the active center distribution of 1-hexene polymerization with MgCl2-supported Ziegler–Natta catalysts

Co-reporter:Zhiqiang Fan, Letian Zhang, Shengjie Xia, Zhisheng Fu

Journal of Molecular Catalysis A: Chemical 2011 Volume 351() pp:93-99

Publication Date(Web):December 2011

DOI:10.1016/j.molcata.2011.09.021

1-Hexene homopolymerization and 1-hexene–ethylene copolymerization with TiCl4/MgCl2–Al(C2H5)3 catalyst were compared to investigate the effect of ethylene on the distribution of active centers. The polymerizations were quenched with cinnamoyl chloride, and the number of active centers ([C*]/[Ti]) was determined by measuring the cinnamoyl group labeled on the propagation chains. Both polymer samples were fractionated into 9–10 fractions according to molecular weight, and [C*]/[Ti] in each fraction was also determined. Adding small amount of ethylene in 1-hexene polymerization markedly increased the number of active centers that produce low molecular weight polymer. This phenomenon agrees with the mechanism suggesting the presence of Ti−CH(CH3)(CH2)3CH3 type dormant sites and their activation by ethylene. The kp value of the newly emerging active centers in the copolymerization system is much lower than that of the homopolymerization system. In the copolymerization system, the active centers producing polymer chains of the second highest molecular weight and isotacticity show the highest kp value, while those producing polymer of the highest molecular weight and isotacticity show only the second highest kp. On the other hand, the active centers producing polymer with lower–middle chain length show the lowest ethylene incorporation rate. These results disclose differences of catalytic properties between the multiple active center types and correlations between their different kinetic parameters, which may lead to new understanding of the active centers and polymerization mechanism.Graphical abstractThe effects of ethylene on the active center distribution of 1-hexene polymerization with TiCl4/MgCl2−Al(C2H5)3 catalyst were studied by counting the number of active centers in polymer fractions of different molecular weight. The results disclose differences of catalytic properties between the multiple active centers and correlations between their kinetic parameters.Highlights► 1-Hexene is polymerized with TiCl4/MgCl2–Al(C2H5)3 catalyst. ► Active center distribution is studied by counting active centers in polymer fractions. ► Effects of adding ethylene on the active center distribution are studied. ► Ethylene increases active centers in the low molecular weight fractions. ► Ethylene increases kp value of the medium–high molecular weight fractions.

A new method of active center determination for olefin polymerization with supported Ziegler-Natta catalysts

Co-reporter:Letian Zhang;Zhisheng Fu;Zhiqiang Fan

Macromolecular Research 2010 Volume 18( Issue 7) pp:695-700

Publication Date(Web):2010 July

DOI:10.1007/s13233-010-0709-4

Study of amphiphilic poly(1-dodecene-co-para-methylstyrene)-graft-poly(ethylene glycol). Part II: Preparation and micellization behavior of the amphiphilic copolymers

Co-reporter:Min Liu, Zhisheng Fu, Qi Wang, Junting Xu, Zhiqiang Fan

European Polymer Journal 2008 Volume 44(Issue 12) pp:4122-4128

Publication Date(Web):December 2008

DOI:10.1016/j.eurpolymj.2008.09.006

Poly(1-dodecene-co-pMS) copolymers were brominated by HBr/H2O2 system with high selectivity at the methyl groups of pMS units. It was found that longer reaction time, higher pMS content, and lower molecular weight of the copolymers were helpful for higher degree of bromination. Through a modified Williamson ether synthesis, poly(ethylene glycol) monomethyl ethers (PEG) were grafted onto the brominated copolymers, and the amphiphilic poly(1-dodecene-co-pMS)-graft-PEG copolymers which can be readily dissolved in n-octane were successfully synthesized. Due to their amphiphilic characteristics, they can self-assemble spontaneously into reverse micelles in n-octane. Their micellization behaviors were investigated by fluorescence probe technique, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The critical micelle concentrations of the three copolymers in n-octane were determined at about 1.26 × 10−4, 1.58 × 10−4, and 1.95 × 10−4 g ml−1 by fluorescence measurements. The morphologies of micelles were preliminarily explored by TEM and were found to be spheres.

Study of amphiphilic poly(1-dodecene-co-para-methylstyrene)-graft-poly (ethylene glycol): Part I. Preparation of poly(1-dodecene-co-para-methylstyrene) copolymer and its molecular weight regulation

Co-reporter:Min Liu, Zhisheng Fu, Qi Wang, Junting Xu, Zhiqiang Fan

European Polymer Journal 2008 Volume 44(Issue 10) pp:3239-3245

Publication Date(Web):October 2008

DOI:10.1016/j.eurpolymj.2008.07.030

Poly(1-dodecene-co-para-methylstyrene) copolymers with a broad composition range were prepared by an MgCl2 supported TiCl4 catalyst. The effects of temperature and hydrogen on catalyst activity were investigated. It was found that catalyst activity reached a maximum at around 60 °C, and then decreased with the rising temperature. Hydrogen showed an activation effect on the Ziegler–Natta catalyst. 1H NMR and 13C NMR spectra showed that para-methylstyrene (pMS) could be effectively and randomly incorporated into the copolymer chains. The single glass transition indicated there was no block sequence in the copolymer. The copolymerization reaction was examined by the reactivity ratios of comonomers and the relatively low reactivity ratios of 1-dodecene and pMS indicated that both of them had little tendency of consecutive insertion and should be homogeneously distributed in the copolymer chains. Furthermore, the molecular weights of copolymers were regulated by chain transfer agents (diethyl zinc and hydrogen) and temperature. The molecular weights reduced greatly with the addition of diethyl zinc and hydrogen and with the increasing temperature.

Fractionation and characterization of an ethylenepropylene copolymer produced with a MgCl2/SiO2/TiCl4/diester-type zieglernatta catalyst

Co-reporter:Qi Dong;Zhi-Sheng Fu;Jun-Ting Xu

Journal of Applied Polymer Science 2008 Volume 107( Issue 2) pp:1301-1309

Publication Date(Web):

DOI:10.1002/app.26552

Abstract

An ethylene–propylene copolymer synthesized with a Ziegler–Natta catalyst was fractionated by a combination of dissolution/precipitation and temperature-gradient extraction fractionation. The fractions were characterized with ¹³C-NMR, differential scanning calorimetry, and wide-angle X-ray diffraction. The fractionation was carried out mainly with respect to the content of ethylene, but the crystallizable propylene sequences could also exert an influence on the fractionation. The copolymer contained a series of components with wide variations in the compositions. With an increase in the ethylene content, the structure of the fractions became blockier and blockier, and the fraction extracted at 111°C had the blockiest structure. A further increase in the ethylene content led to a decrease in the length and number of the propylene sequences. Differential scanning calorimetry results showed that the composition distribution in single fractions was not homogeneous, and multiple melting peaks were observed. Wide-angle X-ray diffraction results revealed both polyethylene and polypropylene crystals in most of the fractions. Short propylene sequences could be included in the polyethylene crystals, and short ethylene sequences could also be incorporated into the polypropylene crystals. The incorporation of propylene sequences into polyethylene crystals strongly depended on the sequence distribution and crystallization conditions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Structure and morphology of polyethylene/polypropylene in-reactor alloys synthesized by spherical high-yield Ziegler–Natta catalyst

Co-reporter:Zhisheng Fu;Yanzhong Zhang;Zhiqiang Fan;Junting Xu

Journal of Applied Polymer Science 2007 Volume 103(Issue 4) pp:2075-2085

Publication Date(Web):22 NOV 2006

DOI:10.1002/app.23265

A series of spherical polyethylene/polypropylene (PE/PP) in-reactor alloys were synthesized with spherical high-yield Ziegler–Natta catalyst by sequential multistage polymerization in slurry. The morphology of PE/PP alloy granule was evaluated by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results show PE/PP in-reactor alloy with excellent morphology, high porosity, and narrow distribution of the particle size. The PE/PP in-reactor alloys show excellent mechanical properties with good balance between toughness and rigidity. It was fractionated into five fractions by temperature-gradient extraction fractionation, and every fractionation was analyzed by FTIR, ¹³C-NMR, DSC, and WAXD. The PE/PP in-reactor alloy was found to contain mainly five portions: PP, PE, segmented copolymer with PP and PE segment of different length, ethylene-b-propylene copolymer, and an ethylene–propylene random copolymer. The characteristic chain structure leads to good compatibility between the fractions of the alloy that shows a multiphase structure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2075–2085, 2007

Improvement of Structure and Properties of Polypropylene/Poly(ethylene-co-propylene) In-reactor Alloy by Modifying the Cocatalyst

Co-reporter:Zhiqiang Fan;Junting Xu;Zhisheng Fu;Qi Dong

Macromolecular Symposia 2007 Volume 260(Issue 1) pp:127-132

Publication Date(Web):7 JAN 2008

DOI:10.1002/masy.200751418

Summary: A series of polypropylene/poly(ethylene-co-propylene) in-reactor alloy were synthesized by a TiCl₄/MgCl₂/SiO₂/diester type Ziegler-Natta catalyst, using triethylaluminium (TEA), triisobutylaluminium (TIBA) or TEA/TIBA mixtures of different molar ratio as cocatalyst. Mechanical properties of the alloy are strongly influenced by the cocatalyst. Toughness-stiffness balance of the alloy synthesized using a 50/50 TEA/TIBA mixture as cocatalyst is much better than that of the alloy based on pure TEA cocatalyst. Changes in copolymer chain structure and composition distribution are thought to be the main reason for this improvement of properties.

Microstructure of Ethylene/Propylene Random Copolymers Prepared by a Fluorinated Bis(phenoxy-imine)Ti Catalyst

Co-reporter:Zixiu Du;Junting Xu;Xin Wang;Zhiqiang Fan

Polymer Bulletin 2007 Volume 58( Issue 5-6) pp:903-911

Publication Date(Web):2007 May

DOI:10.1007/s00289-006-0716-y

Living copolymerization of ethylene and propylene was catalyzed by a fluorine-containing bis(phenoxy-imine) titanium catalyst. A series of ethylene-propylene copolymers with different propylene contents were prepared and the copolymers were characterized by 13C-NMR, GPC and DSC. The copolymers were found to have the following characteristics: (1) Molecular weight distribution of the copolymer is rather narrow; (2) There exist only isolated propylene units distributed along the polymer chains even at propylene content as high as 14.9 mol%; (3) The distribution of ethylene sequence are not homogeneous. Insertion of propylene changes from 2,1-insertion in homopolymerization into 1,2-insertion when the preceding unit is ethylene.

Ethylene/1-hexene copolymerization with TiCl4/MgCl2/AlCl3 catalyst in the presence of hydrogen

Co-reporter:Yong-ping Chen, Zhi-qiang Fan

European Polymer Journal 2006 Volume 42(Issue 10) pp:2441-2449

Publication Date(Web):October 2006

DOI:10.1016/j.eurpolymj.2006.05.015

A TiCl4/AlCl3/MgCl2 (Cat-B) catalyst containing 5.2 wt.% Al was prepared by the reaction of TiCl4 with ethanol adduct of AlCl3/MgCl2 mixture. A TiCl4/MgCl2 catalyst (Cat-A) without doped AlCl3 was also prepared by the same method. Ethylene-1-hexene copolymerization catalyzed by Cat-B in the presence of hydrogen showed slightly higher efficiency and higher 1-hexene incorporation than Cat-A. Comonomer incorporation was markedly increased when the cocatalyst AlEt3 was replaced by Al(i-Bu)3. Adding Ph2Si(OMe)2 as external donor in the catalyst system caused decrease in polymerization activity and 1-hexene incorporation. Each copolymer sample was fractionated into three fractions: n-heptane insoluble fraction (fraction A), n-heptane soluble and n-hexane insoluble fraction (fraction B) and n-hexane soluble fraction (fraction C). In most cases the amount of intermediate fraction (fraction B) was smaller than the other fractions and did not increase as the total 1-hexene content increase, indicating the presence of two classes of copolymer fractions with greatly different comonomer content and clear bimodality of the copolymer composition distribution. Doping AlCl3 in the catalyst, changing cocatalyst and adding external donor mainly changed the weight ratio of fraction A to fraction C, but exerted little influences on their composition. According to the sequence distribution data of the fractions, doping AlCl3 in the catalyst resulted in slight decrease of product of reactivity ratios (r1r2) in both fraction A and fraction C.

Influence of polymerization conditions on the structure and properties of polyethylene/polypropylene in-reactor alloy synthesized in the gas phase with a spherical Ziegler–Natta catalyst

Co-reporter:Zhisheng Fu;Qi Dong;Na Li;Zhiqiang Fan;Junting Xu

Journal of Applied Polymer Science 2006 Volume 101(Issue 4) pp:2136-2143

Publication Date(Web):11 MAY 2006

DOI:10.1002/app.22429

A spherical TiCl₄/MgCl₂-based catalyst was used in the synthesis of in-reactor polyethylene/polypropylene alloys by polyethylene homopolymerization and subsequent homopolymerization of propylene in the gas phase. Different conditions in the ethylene homopolymerization stage, such as monomer pressure and polymerization temperature, were investigated, and their influences on the structure and properties of in-reactor alloys were studied. Raising the polymerization temperature is the most effective way of speeding up polymerization and regulating the ethylene content of polyethylene (PE)/polypropylene (PP) alloys, but it will cause a greater increase in the PE-b-PP block copolymer fraction (named fraction D) than in the fraction of PP-block-PE in which the PP segments have low or medium isotacticity (named fraction A). Although changing ethylene monomer pressure could influence the ethylene content of PE/PP alloys slightly, it is an effective way of regulating the structural distribution. Reducing the monomer pressure will evidently increase fractions A and D. The mechanical properties of the alloys, including impact strength and flexural modulus, can be regulated in a broad range with changes in polymerization conditions. These properties are highly dependent on the amount, distribution, and chain structure of fractions A and D. The impact strength is affected by both fraction A and fraction D in a complicated way, whereas the flexural modulus is mainly determined by the amount of fraction A. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2136–2143, 2006

Molecular weight distribution of polyethylene catalyzed by Ziegler–Natta catalyst supported on MgCl2 doped with AlCl3

Co-reporter:Yong-Ping Chen;Jian-He Liao;Shuang-Quan Liao

Journal of Applied Polymer Science 2006 Volume 102(Issue 2) pp:1768-1772

Publication Date(Web):28 JUL 2006

DOI:10.1002/app.24443

Ti-based Ziegler–Natta catalysts supported on MgCl₂ doped with AlCl₃ were prepared by the reaction of MgCl₂/AlCl₃–ethanol adduct with TiCl₄. No AlCl₃ crystallites were found in the AlCl₃-doped catalysts by WAXD analysis, suggesting that AlCl₃/MgCl₂ solid solution was formed. The effect of doping on the catalyst performance in ethylene polymerization was investigated. The results showed that the catalysts based on AlCl₃-doped MgCl₂ support exhibited a slightly higher activity than did the MgCl₂-supported catalyst and the molecular weight distribution (MWD) of polyethylene (PE) markedly increased (from 10.8 to 47.9) with the increase of AlCl₃ content in catalysts. The changes in catalyst's active center distribution were studied based on nonlinear fitting of the polymer GPC curves by multiple Flory functions. It was found that increase of types of active centers by introducing AlCl₃ into the support should be responsible for the broadening of MWD of PE. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1768–1772, 2006

Chain structure and mechanical properties of polyethylene/polypropylene/poly(ethylene-co-propylene)in-reactor alloys synthesized with a spherical Ziegler–Natta catalyst by gas-phase polymerization

Co-reporter:Zhisheng Fu;Junting Xu;Yanzhong Zhang;Zhiqiang Fan

Journal of Applied Polymer Science 2005 Volume 97(Issue 2) pp:640-647

Publication Date(Web):27 APR 2005

DOI:10.1002/app.21805

Two polyethylene/polypropylene/poly(ethylene-co-propylene) in-reactor alloy samples with a good polymer particle morphology were synthesized by sequential multistage gas-phase polymerization with a spherical Ziegler–Natta catalyst. The alloys showed excellent mechanical properties, including both toughness and stiffness. With temperature-gradient extraction fractionation, both alloys were fractionated into five fractions. The chain structures of the fractions were studied with Fourier transform infrared, ¹³C-NMR, and thermal analysis. The alloys were mainly composed of polyethylene, polyethylene-b-polypropylene block copolymer, and polypropylene. There also were minor amounts of an ethylene–propylene segmented copolymer with very low crystallinity and an ethylene–propylene random copolymer. The block copolymer fraction accounted for more than 44 wt % of the alloys. The coexistence of these components with different structures was apparently the key factor resulting in the excellent toughness–stiffness balance of the materials. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 640–647, 2005

Influence of the reaction conditions on the solid-state graft copolymerization of methyl methacrylate and polyethylene/polypropylene in situ alloys

Co-reporter:Zhi-Sheng Fu;Jun-Ting Xu;Guo-Xin Jiang;Yan-Zhong Zhang

Journal of Applied Polymer Science 2005 Volume 98(Issue 1) pp:195-202

Publication Date(Web):12 JUL 2005

DOI:10.1002/app.22050

Graft copolymers of poly(methyl methacrylate) (PMMA) with spherical, high-porosity polyethylene (PE)/polypropylene (PP) in situ alloys were synthesized by a solid-state reaction. The effects of the amount of the free-radical initiator, the feed ratio of the methyl methacrylate (MMA) monomer, the reaction temperature, and the composition of the alloys on the grafting degree of PMMA were studied. A greater amount of the initiator and a higher reaction temperature led to a higher grafting degree. The grafting degree first increased with the feed ratio of MMA but leveled off at a higher feed ratio. The obtained graft copolymer was fractionated by temperature gradient extraction fractionation into six fractions, and each fraction was characterized by Fourier transform infrared and differential scanning calorimetry. The structures of these fractions were ungrafted ethylene–propylene random copolymers and ethylene–propylene segmented copolymers, ethylene–propylene block copolymers having PE and PP segments of different lengths and grafted by PMMA, PP grafted by PMMA, and nearly pure PP. Most PMMA was grafted on propylene segments, and thus the grafting degree decreased as the content of ethylene units in the alloys increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 195–202, 2005

Propylene polymerization catalyzed by novel supported titanium catalysts MgCl2/NaCl/DNBP/TiCl4 with different NaCl content

Co-reporter:Xue Jiang, Yong-ping Chen, Zhi-qiang Fan, Qi Wang, Zhi-sheng Fu, Jun-ting Xu

Journal of Molecular Catalysis A: Chemical 2005 Volume 235(1–2) pp:209-219

Publication Date(Web):1 July 2005

DOI:10.1016/j.molcata.2005.03.045

A series of MgCl2/NaCl/ID/TiCl4 type supported catalysts were prepared by comilling NaCl with MgCl2·nEtOH adduct and reacting the mixture with TiCl4 and internal electron donor (ID = di-n-butyl phthalate). Crystallites of NaCl were found in the doped catalysts as revealed by WAXD analysis. The NaCl doped catalysts showed lower catalytic activity and higher isospecificity in catalyzing propylene polymerization. There was a marked change of the molecular weight distribution (MWD) of polymer with NaCl content. Catalyst containing 16 mol% NaCl produced PP with much broadened MWD (PDI = 13) than the undoped catalyst when TEA was used as the activator, while the TIBA activated catalyst produced PP with much narrower MWD. The changes in catalyst's active center distribution were studied based on non-linear fitting of the polymer MWD curve by multiple Flory functions. Stereochemical structure of the polymer was studied by thermal analysis. Selective and reversible deactivation of active centers by Cl− from NaCl is proposed to be the main reason for the observed changes in polymerization behaviors and polymer structure caused by doping NaCl in the catalyst.A series of MgCl2/NaCl/ID/TiCl4 type supported catalysts were prepared by comilling NaCl with MgCl2·nEtOH adduct and reacting the mixture with TiCl4 and internal electron donor (ID = di-n-butyl phthalate). The NaCl doped catalysts showed lower catalytic activity and higher isospecificity in catalyzing propylene polymerization. There was a marked change of the molecular weight distribution (MWD) of polymer with NaCl content. Catalyst containing 16 mol% NaCl produced PP with much broadened MWD (PDI = 13) than the undoped catalyst when TEA was used as the activator, while the TIBA activated catalyst produced PP with much narrower MWD.

Isothermal crystallization of metallocene-based polypropylenes with different isotacticity and regioregularity

Co-reporter:Jun-Ting Xu;Fang-Xiao Guan;Tariq Yasin

Journal of Applied Polymer Science 2003 Volume 90(Issue 12) pp:3215-3221

Publication Date(Web):13 OCT 2003

DOI:10.1002/app.12998

Three polypropylenes with various isotacticities and regioregularities were prepared with metallocene catalysts at different polymerization temperatures. WAXD results showed that the relative content of γ crystals in polypropylenes increased as isotacticity decreased. It was found that the γ crystal overcame the α crystal and became predominant in polypropylene of low isotacticity and high regioerrors. More γ crystals were also formed at higher crystallization temperatures. The isothermal crystallization kinetics of α and γ crystals were compared and the metastability of these two crystal phases was interpreted in terms of the crystallization kinetics. It was observed that the α crystal has a faster crystallization rate than that of the γ crystal and, thus, higher stability at low temperature. By contrast, the γ crystal tends to have a faster crystallization rate and becomes more stable at high temperature. The metallocene-based polypropylenes with different isotacticities have similar Avrami exponents. As the content of the γ crystal increases, double melting peaks become more evident. Equilibrium melting temperatures were derived from Hoffman–Weeks analysis and very close equilibrium melting temperatures were obtained, 185.5 and 184.0°C, for two metallocene-based polypropylenes containing major α crystals and one of 182.5°C for the polypropylene with predominant γ crystals. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3215–3221, 2003