Wen-Jun Wang - Academia.edu (original) (raw)

Papers by Wen-Jun Wang

Research paper thumbnail of Kinetics and Modeling of Semi-Batch RAFT Copolymerization with Hyperbranching

Research paper thumbnail of Kinetics of Long Chain Branching in Continuous Solution Polymerization of Ethylene Using Constrained Geometry Metallocene

Macromolecules, 1998

Our high-temperature and high-pressure continuous stirred-tank reactor (CSTR) has been used for t... more Our high-temperature and high-pressure continuous stirred-tank reactor (CSTR) has been used for the polymerization of ethylene with the constrained geometry metallocene system, [C 5 Me 4 (SiMe 2 N t Bu)]TiMe 2 (CGC−Ti)/ tris(pentafluorophenyl)boron (TPFPB)/ modified ...

Research paper thumbnail of Long chain branching in ethylene polymerization using constrained geometry metallocene catalyst

Macromolecular Chemistry and Physics, 1998

ABSTRACT

Research paper thumbnail of Morphological and mechanical properties of nascent polyethylene fibers produced via ethylene extrusion polymerization with a metallocene catalyst supported on MCM-41 particles

Journal of Polymer Science Part B: Polymer Physics, 2003

ABSTRACT Polyethylene (PE) fibers were prepared by ethylene extrusion polymerization with an MCM-... more ABSTRACT Polyethylene (PE) fibers were prepared by ethylene extrusion polymerization with an MCM-41-supported titanocene catalyst. The morphological and mechanical properties of these nascent PE fibers were investigated. Three levels of fibrous morphologies were identified in the fiber samples through an extensive scanning electron microscopy study. Extended-chain PE nanofibrils with diameters of about 60 nm were the major morphological units present in the fiber structure. The nanofibrils were parallel-packed into individual microfibers with diameters of about 1–30 μm. The microfibers were further aggregated irregularly into fiber aggregates and bundles. In comparison with commercial PE fibers and data reported in the literature, the individual microfibers produced in situ via ethylene extrusion polymerization without posttreatment exhibited a high tensile strength (0.3–1.0 GPa), a low tensile modulus (3.0–7.0 GPa), and a high elongation at break (8.5–20%) at 35 °C. The defects in the alignment of the nanofibrils were believed to be the major reason for the low modulus values. It was also found that a slight tensile drawing could increase the microfiber strength and modulus. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2433–2443, 2003

Research paper thumbnail of Living copolymerization of ethylene/1-octene with fluorinated FI-Ti catalyst

Journal of Polymer Science Part A: Polymer Chemistry, 2012

ABSTRACT Living copolymerization of ethylene and 1-octene was carried out at room temperature usi... more ABSTRACT Living copolymerization of ethylene and 1-octene was carried out at room temperature using the fluorinated FI-Ti catalyst system, bis[N-(3-methylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] TiCl2/dried methylaluminoxane, with various 1-octene concentrations. The comonomer incorporation up to 32.7 mol % was achieved at the 1-octene feeding ratio of 0.953. The living feature still retained at such a high comonomer level. The copolymer composition drifting was minor in this living copolymerization system despite of a batch process. It was found that the polymerization heterogeneity had a severe effect on the copolymerization kinetics, with the apparent reactivity ratios in slurry significantly different from those in solution. The reactivity ratios were nearly independent of polymerization temperature in the range of 0–35 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Research paper thumbnail of Rheological and thermomechanical properties of long-chain-branched polyethylene prepared by slurry polymerization with metallocene catalysts

Journal of Applied Polymer Science, 2004

A series of polyethylene (PE) samples were prepared in a slurry polymerization with bis(cyclopent... more A series of polyethylene (PE) samples were prepared in a slurry polymerization with bis(cyclopentadienyl) zirconium dichloride (Cp 2 ZrCl 2)/modified methylaluminoxane (MMAO) using a semibatch reactor. The samples had long-chain branch densities (LCBDs) of a 0.03-1.0 branch per 10,000 carbons and long-chain branch frequencies (LCBFs) up to a 0.22 branch per polymer molecule. The rheological and dynamic mechanical behaviors of these long-chain branched PE samples were evaluated. Increasing the LCBF significantly increased the 0 's and enhanced shear thinning. Long-chain branching (LCB) also influenced the loss modulus and storage modulus. Increasing the LCBF led to enhanced GЈ and GЉ values at low shear rates and broader relaxation spectrums. The samples exhibited thermorheologically complex behavior. LCB also played a significant role in the dynamic mechanical behavior. Increasing the LCBF increased the stiffness of the polymer and enhanced the damping or energy dissipation. However, LCB had little influence on the crystalline structure of the PE. The ␣and ␥-relaxations showed little dependence on the LCBF.

Research paper thumbnail of EGFR activation confers protections against UV-induced apoptosis in cultured mouse skin dendritic cells

Cellular Signalling, 2008

Ultraviolet radiation (UV) induces apoptosis and functional maturation in skin dendritic cells (D... more Ultraviolet radiation (UV) induces apoptosis and functional maturation in skin dendritic cells (DCs). However, the molecular mechanisms through which UV activates DCs have not been thoroughly investigated. In this study, we examined the mechanisms of activation and apoptosis of DC after UV irradiation by focusing on epidermal growth factor receptor (EGFR). Our previous studies have demonstrated that in addition to cognate ligands, EGFR is also activated by UVB irradiation in cultured human skin keratinocytes in vitro and in human skin in vivo. We found for the first time in this study that UV also induces EGFR activation in cultured mouse skin DCs (XS 106 cell line) as well as mouse monocyte-derived dendritic cells (MoDCs). Pharmacological inhibition of EGFR tyrosine kinase significantly inhibits UV-induced ERK, p38, and JNK MAP kinases, and their effectors, transcription factors c-Fos and c-Jun. Inhibition of EGFR also suppresses UV-induced activation of PI3K/AKT/mTOR/S6K and NF-κB signal transduction pathways. Our data demonstrated that UV induces LKB1/AMPK pathway, also dependent on EGFR trans-activation. We further observed that MAPK, LKB1/AMPK, PI3K/AKT/mTOR/S6K as well as NF-κB activation are impaired in EGFR−/− cells compared to wide type MEF cells after UV radiation. Taken together, we conclude that UV induces multiple signaling pathways mediated by EGFR trans-activation leading to possible maturation, apoptosis and survival, and EGFR activation protects against UVinduced apoptosis in cultured mouse dendritic cells.

Research paper thumbnail of Kinetics and Modeling of Semi-Batch RAFT Copolymerization with Hyperbranching

Research paper thumbnail of Kinetics of Long Chain Branching in Continuous Solution Polymerization of Ethylene Using Constrained Geometry Metallocene

Macromolecules, 1998

Our high-temperature and high-pressure continuous stirred-tank reactor (CSTR) has been used for t... more Our high-temperature and high-pressure continuous stirred-tank reactor (CSTR) has been used for the polymerization of ethylene with the constrained geometry metallocene system, [C 5 Me 4 (SiMe 2 N t Bu)]TiMe 2 (CGC−Ti)/ tris(pentafluorophenyl)boron (TPFPB)/ modified ...

Research paper thumbnail of Long chain branching in ethylene polymerization using constrained geometry metallocene catalyst

Macromolecular Chemistry and Physics, 1998

ABSTRACT

Research paper thumbnail of Morphological and mechanical properties of nascent polyethylene fibers produced via ethylene extrusion polymerization with a metallocene catalyst supported on MCM-41 particles

Journal of Polymer Science Part B: Polymer Physics, 2003

ABSTRACT Polyethylene (PE) fibers were prepared by ethylene extrusion polymerization with an MCM-... more ABSTRACT Polyethylene (PE) fibers were prepared by ethylene extrusion polymerization with an MCM-41-supported titanocene catalyst. The morphological and mechanical properties of these nascent PE fibers were investigated. Three levels of fibrous morphologies were identified in the fiber samples through an extensive scanning electron microscopy study. Extended-chain PE nanofibrils with diameters of about 60 nm were the major morphological units present in the fiber structure. The nanofibrils were parallel-packed into individual microfibers with diameters of about 1–30 μm. The microfibers were further aggregated irregularly into fiber aggregates and bundles. In comparison with commercial PE fibers and data reported in the literature, the individual microfibers produced in situ via ethylene extrusion polymerization without posttreatment exhibited a high tensile strength (0.3–1.0 GPa), a low tensile modulus (3.0–7.0 GPa), and a high elongation at break (8.5–20%) at 35 °C. The defects in the alignment of the nanofibrils were believed to be the major reason for the low modulus values. It was also found that a slight tensile drawing could increase the microfiber strength and modulus. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2433–2443, 2003

Research paper thumbnail of Living copolymerization of ethylene/1-octene with fluorinated FI-Ti catalyst

Journal of Polymer Science Part A: Polymer Chemistry, 2012

ABSTRACT Living copolymerization of ethylene and 1-octene was carried out at room temperature usi... more ABSTRACT Living copolymerization of ethylene and 1-octene was carried out at room temperature using the fluorinated FI-Ti catalyst system, bis[N-(3-methylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] TiCl2/dried methylaluminoxane, with various 1-octene concentrations. The comonomer incorporation up to 32.7 mol % was achieved at the 1-octene feeding ratio of 0.953. The living feature still retained at such a high comonomer level. The copolymer composition drifting was minor in this living copolymerization system despite of a batch process. It was found that the polymerization heterogeneity had a severe effect on the copolymerization kinetics, with the apparent reactivity ratios in slurry significantly different from those in solution. The reactivity ratios were nearly independent of polymerization temperature in the range of 0–35 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Research paper thumbnail of Rheological and thermomechanical properties of long-chain-branched polyethylene prepared by slurry polymerization with metallocene catalysts

Journal of Applied Polymer Science, 2004

A series of polyethylene (PE) samples were prepared in a slurry polymerization with bis(cyclopent... more A series of polyethylene (PE) samples were prepared in a slurry polymerization with bis(cyclopentadienyl) zirconium dichloride (Cp 2 ZrCl 2)/modified methylaluminoxane (MMAO) using a semibatch reactor. The samples had long-chain branch densities (LCBDs) of a 0.03-1.0 branch per 10,000 carbons and long-chain branch frequencies (LCBFs) up to a 0.22 branch per polymer molecule. The rheological and dynamic mechanical behaviors of these long-chain branched PE samples were evaluated. Increasing the LCBF significantly increased the 0 's and enhanced shear thinning. Long-chain branching (LCB) also influenced the loss modulus and storage modulus. Increasing the LCBF led to enhanced GЈ and GЉ values at low shear rates and broader relaxation spectrums. The samples exhibited thermorheologically complex behavior. LCB also played a significant role in the dynamic mechanical behavior. Increasing the LCBF increased the stiffness of the polymer and enhanced the damping or energy dissipation. However, LCB had little influence on the crystalline structure of the PE. The ␣and ␥-relaxations showed little dependence on the LCBF.

Research paper thumbnail of EGFR activation confers protections against UV-induced apoptosis in cultured mouse skin dendritic cells

Cellular Signalling, 2008

Ultraviolet radiation (UV) induces apoptosis and functional maturation in skin dendritic cells (D... more Ultraviolet radiation (UV) induces apoptosis and functional maturation in skin dendritic cells (DCs). However, the molecular mechanisms through which UV activates DCs have not been thoroughly investigated. In this study, we examined the mechanisms of activation and apoptosis of DC after UV irradiation by focusing on epidermal growth factor receptor (EGFR). Our previous studies have demonstrated that in addition to cognate ligands, EGFR is also activated by UVB irradiation in cultured human skin keratinocytes in vitro and in human skin in vivo. We found for the first time in this study that UV also induces EGFR activation in cultured mouse skin DCs (XS 106 cell line) as well as mouse monocyte-derived dendritic cells (MoDCs). Pharmacological inhibition of EGFR tyrosine kinase significantly inhibits UV-induced ERK, p38, and JNK MAP kinases, and their effectors, transcription factors c-Fos and c-Jun. Inhibition of EGFR also suppresses UV-induced activation of PI3K/AKT/mTOR/S6K and NF-κB signal transduction pathways. Our data demonstrated that UV induces LKB1/AMPK pathway, also dependent on EGFR trans-activation. We further observed that MAPK, LKB1/AMPK, PI3K/AKT/mTOR/S6K as well as NF-κB activation are impaired in EGFR−/− cells compared to wide type MEF cells after UV radiation. Taken together, we conclude that UV induces multiple signaling pathways mediated by EGFR trans-activation leading to possible maturation, apoptosis and survival, and EGFR activation protects against UVinduced apoptosis in cultured mouse dendritic cells.