Zhi-Feng Fu

Electrospinning nanotechnology has recently attracted lots of attention in different kinds of applications. Poly(butylene terephthalate) random-segment copolymers, named poly[(butylene terephthalate)-co-(1,4-cyclohexanedimethanol terephthalate)]-b-poly(tetramethylene glycol) (P(BT-co-CT)-b-PTMG), were synthesized in this study. On the basis of the new thermoplastic polyester elastomers (TPEEs), the fiber membranes were subsequently electrospun. With the aid of a cosolvent of trifluoroacetic acid and dichloromethane, the resulting solutions with a concentration between 24 and 32% w/v were electrospun into fibers without beads. The results also show a good spinnability for the copolymer solution in a range of voltages from 16 to 24 kV. When the molar ratio of 1,4-cyclohexanedimethanol to 1,4-butanediol was 10 : 90, the electrospun membrane prepared by the corresponding copolymers had a higher elastic modulus than the commercial TPEE (Hytrel 4056, 4.51 ± 0.35 MPa). Differential scanning calorimetry and X-ray diffraction showed that a crystalline phase existed in the electrospun poly[(butylene terephthalate)-co-(1,4-cyclohexanedimethanol terephthalate)]-b-poly(tetramethylene glycol) (P(BT-co-CT)-b-PTMG) copolymer fiber membranes. The melting point of the electrospun fibers was approximately less than that of the corresponding copolymers © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Nonisothermal crystallization behavior of biodegradable poly(butylene terephthalate-co-butylene adipate-co-ethylene terephthalate-co-ethylene adipate) copolyester

Co-reporter:Xiaohui Wang;Jun Shi;Ying Chen;Yan Shi;Zhifeng Fu

Polymer Engineering & Science 2011 Volume 51( Issue 12) pp:2535-2541

Publication Date(Web):

DOI:10.1002/pen.22019

Abstract

A series of biodegradable aliphatic-aromatic copolyester, poly(butylene terephthalate-co-butylene adipate-co-ethylene terephthalate-co-ethylene adipate) (PBATE), were synthesized from terephthalic acid (PTA), adipic acid (AA), 1,4-butanediol (BG) and ethylene glycol (EG) by direct esterification and polycondensation. The nonisothermal crystallization behavior of PBATE copolyesters was studied by the means of differential scanning calorimeter, and the nonisothermal crystallization kinetics were analyzed via the Avrami equation modified by Jeziorny, Ozawa analysis and Z.S. Mo method, respectively. The results show that the crystallization peak temperature of PBATE copolyesters shifted to lower temperature at higher cooling rate. The modified Avrami equation could describe the primary stage of nonisothermal crystallization of PBATE copolyesters. The value of the crystallization half-time (t_1/2) and the crystallization parameter (Z_c) indicates that the crystallization rate of PBATE copolyesters with more PTA content was higher than that with less PTA at a given cooling rate. Ozawa analysis was not suitable to study the nonisothermal crystallization process of PBATE copolyesters, but Z.S. Mo method was successful in treatingthis process. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Cell adhesive and growth behavior on electrospun nanofibrous scaffolds by designed multifunctional composites

Co-reporter:Ding Cao, Yi-Pan Wu, Zhi-Feng Fu, Yuan Tian, Cong-Ju Li, Chun-Ying Gao, Zhong-Liang Chen, Xi-Zeng Feng

Colloids and Surfaces B: Biointerfaces 2011 Volume 84(Issue 1) pp:26-34

Publication Date(Web):1 May 2011

DOI:10.1016/j.colsurfb.2010.12.005

Nanostructured biocomposite scaffolds of poly(l-lactide) (PLLA) blended with collagen (coll) or hydroxyapatite (HA), or both for tissue engineering application, were fabricated by electrospinning. The electrospun scaffolds were characterized for the morphology, chemical and tensile properties by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA), Fourier transform infrared (FTIR) measurement, and tensile testing. Electrospun biocomposite scaffolds of PLLA and collagen or (and) HA in the diameter range of 200–700 nm mimic the nanoscale structure of the extracellular matrix (ECM) with a well-interconnection pore network structure. The presence of collagen in the scaffolds increased their hydrophility, and enhanced cell attachment and proliferation, while HA improved the tensile properties of the scaffolds. The biocompatibility of the electrospun scaffolds and the viability of contacting cells were evaluated by 4′,6-diamidino-2-phenylindole dihydrochloride (DAPI) nuclear staining and by fluorescein diacetate (FDA) and propidium iodide (PI) double staining methods. The results support the conclusion that 293T cells grew well on composite scaffolds. Compared with pure PLLA scaffolds a greater density of viable cells was seen on the composites, especially the PLLA/HA/collagen scaffolds.Graphical abstractResearch highlights▶ Biocomposite scaffolds of PLLA were successfully prepared by electrospinning. ▶ Collagen improved the hydrophlility of the scaffolds, while HA decrease it. ▶ HA enhanced the mechanical properties of the scaffolds effectively. ▶ Biocomposite scaffolds of PLLA were beneficial for cell growth, esp. PLLA/HA/coll.

Heat and compression molded electrospun poly(l-lactide) membranes: Preparation and characterization

Co-reporter:Ding Cao, Zhifeng Fu, Congju Li

Materials Science and Engineering: B 2011 Volume 176(Issue 12) pp:900-905

Publication Date(Web):25 July 2011

DOI:10.1016/j.mseb.2011.05.015

The fibrous membranes prepared by electrospinning have great advantages, such as high porosity and high specific surface area. However, low mechanical strength of electrospun membranes has been one of the most difficult technical problems to overcome, resulting in negative impact on the application. In this paper, the heat-assisted compression approach was employed to improve the mechanical performances of electrospun poly(l-lactide)(PLLA) membranes, especially in tensile strength. It is found that the electrospun PLLA membranes crystallize in α form and strong fiber-to-fiber linkages occurred with the aid of heat and compression. The tensile properties including tensile strength and modulus of membranes treated with a press at 6 MPa and a temperature at 60 °C (80 °C and 100 °C) increased by more than 100% compared with those of the as-electrospun membranes.Highlights► PLLA electrospun membranes were treated by the heat-assisted compression method. ► Strong fiber-to-fiber linkages occurred after post-treatment. ► The tensile properties of the treated membranes enhanced.

Polymerization of 1-octene and determination of markhouwink constants of poly(1-octene)

Co-reporter:Xin-hua Yan;Yan Shi;Lin Wang 付志峰

Chinese Journal of Polymer Science 2011 Volume 29( Issue 5) pp:

Publication Date(Web):2011 September

DOI:10.1007/s10118-011-1069-z

The polymerization of 1-octene initiated by methylalumoxane (MAO)-activated Ni(II)-based-α-diimine complexes [(2,6-i-Pr)2C6H3-DAB(An)]NiBr2 was investigated. Using this catalyst, poly(1-octene)s with molecular weight between 100 × 103 and 400 × 103 and polydispersity (Mw/Mn) between 1.3 and 1.5 were synthesized successfully by varying reaction time at room temperature. The poly(1-octene)s were amorphous polymers and could be well soluble in tetrahydrofuran (THF). After fractional precipitation, poly(1-octene)s with narrow molecular weight distributions (Mw/Mn ≤ 1.12) were obtained. Their weight-average molecular weights were measured by gel permeation chromatography (GPC) in conjunction with online model BI-MwA multiangle laser light scattering (MALLS), and their intrinsic viscosities were measured by Maron’s single-point method. The k and α values in Mark-Houwink equation [η] = KMα in THF at 40°C were 0.089 mL/g and 0.61 respectively.

Controlled synthesis of branched polystyrene via free radical polymerization of novel chain transfer monomer

Co-reporter:Cui-Ping Li;Jia-Qiang Wang;Jun Lin;Yan Shi

Macromolecular Research 2011 Volume 19( Issue 8) pp:770-777

Publication Date(Web):2011 August

DOI:10.1007/s13233-011-0809-9

The free radical polymerization of styrene was carried out in the presence of a new found chain transfer monomer, p-vinyl benzene sulfonyl chloride (VBSC), which possesses both a chain transfer group and a polymerizable double bond. Branched polystyrene was formed during the polymerization, as indicated by multi-peaks gel permeation chromatography (GPC) curves of the products, the increase in the number-average molecular weight and molecular weight distribution along with monomer conversions. The structure of the obtained polystyrene was analyzed by 1H nuclear magnetic resonance (NMR) spectroscopy. The results showed that with increasing VBSC in the feed, the degree of branching and VBSC unit in the copolymer increased and a shortest polystyrene arm arose from the highest VBSC content in the feed, suggesting that the composition and structure of the branched polystyrenes could be tuned by the amount of VBSC in the feed. By tracing the structure change in the copolymer at various stages of polymerization, the main polymerization process can be regarded as the copolymerization of VBSC with styrene first and then chain transfer to polymeric radical to form branched polystyrene. This strategy is facile and less expensive than the other method.

Synthesis of AB2 miktoarm star-shaped copolymers by combining stable free radical polymerization and atom transfer radical polymerization

Co-reporter:Yan Shi, Zhifeng Fu, Bingyi Li, Liqun Zhang, Xiaoping Cai, Desheng Zhang

European Polymer Journal 2007 Volume 43(Issue 6) pp:2612-2619

Publication Date(Web):June 2007

DOI:10.1016/j.eurpolymj.2007.02.041

A stable nitroxyl radical functionalized with two initiating groups for atom transfer radical polymerization (ATRP), 4-(2,2-bis-(methyl 2-bromo isobutyrate)-propionyloxy)-2,2,6,6-tetramethyl-1-piperidinyloxy (Br2-TEMPO), was synthesized by reacting 4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy with 2,2-bis-(methyl 2-bromo isobutyrate) propanoic acid. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br2-TEMPO. The obtained polystyrene had two active bromine atoms for ATRP at the ω-end of the chain and was further used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare AB2-type miktoarm star-shaped copolymers. The molecular weights of the resulting miktoarm star-shaped copolymers at different monomer conversions shifted to higher molecular weights without any trace of the macroinitiator, and increased with monomer conversion.

Synthesis of EPR-g-styrene by anionic coupling technique

Co-reporter:Xiang Li Xi, Zi Qiang Zhao, Qian Zhang, Yan Shi, Xiao Ping Cai, Zhi Feng Fu

Chinese Chemical Letters 2007 Volume 18(Issue 8) pp:963-965

Publication Date(Web):August 2007

DOI:10.1016/j.cclet.2007.05.046

Ethylene–propylene rubber (EPR) graft copolymers were prepared successfully by anionic coupling technique between chlorinated EPR (Cl-EPR) and living anionic polystyrene chain. The EPR-g-styrene was characterized by hydrogen nuclear magnetic resonance (1H NMR) and gel penetration chromatogram (GPC).

Synthesis of Amphiphilic Polystyrene-b-Poly(acrylic acid) Diblock Copolymers by Iodide-Mediated Radical Polymerization

Co-reporter:Bingyi Li, Yan Shi, Wanchao Zhu, Zhifeng Fu and Wantai Yang

Polymer Journal 2006 38(4) pp:387-394

Publication Date(Web):

DOI:10.1295/polymj.38.387

Amphiphilic polystyrene-b-poly(acrylic acid) (PS-b-PAA) diblock copolymers were prepared by iodide-mediated radical polymerization. Firstly, free radical polymerization of styrene was carried out with AIBN as initiater and iodoform as chain-transfer agent, giving iodine atom-ended polystyrene with controlled molecular weights. Secondly, tert-butyl acrylate (tBA) was polymerization using above obtained polystyrenes as macro-chain-transfer agents and PS-b-PtBA diblock copolymers with controlled molecular weights were obtained. Finally, amphiphilic PS-b-PAA diblock copolymers were prepared by hydrolysis of PS-b-PtBA under the acid condition. The formation of PS-b-PtBA and PS-b-PAA diblock copolymers was confirmed by the use of gel permeation chromatography and 1H NMR spectroscopy.

Synthesis of well-defined polystyrene-graft-poly(methyl methacrylate)

Co-reporter:Cuiping Li;Yan Shi;Zhifeng Fu

Polymer International 2006 Volume 55(Issue 1) pp:

Publication Date(Web):12 DEC 2005

DOI:10.1002/pi.1956

A well-defined graft copolymer, polystyrene-graft-poly(methyl methacrylate), was synthesized in two steps. In the first step, styrene and p-vinyl benzene sulfonyl chloride were copolymerized via reversible addition–fragmentation chain transfer polymerization (RAFT) in benzene at 60 °C with 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate as a chain transfer agent and 2,2′-azobis(isobutyronitrile) as an initiator. In the second step, poly[styrene-co-p-(vinyl benzene sulfonyl chloride)] was used as a macroinitiator for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in toluene at 80 °C with CuCl as a catalyst and 2,2′-bipyridine as a ligand. With sulfonyl chloride groups as the initiating sites for the ATRP of MMA, high initiation efficiencies were obtained. Copyright © 2006 Society of Chemical Industry

Synthesis of comb-like polystyrene with poly(N-phenyl maleimide-alt-p-chloromethyl styrene) as macroinitiator

Co-reporter:Yan Shi;Zhifeng Fu;Wantai Yang

Journal of Polymer Science Part A: Polymer Chemistry 2006 Volume 44(Issue 6) pp:

Publication Date(Web):6 FEB 2006

DOI:10.1002/pola.21311

The copolymerization of N-phenyl maleimide and p-chloromethyl styrene via reversible addition–fragmentation chain transfer (RAFT) process with AIBN as initiator and 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate as RAFT agent produced copolymers with alternating structure, controlled molecular weights, and narrow molecular weight distributions. Using poly(N-phenyl maleimide-alt-p-chloromethyl styrene) as the macroinitiator for atom transfer radical polymerization of styrene in the presence of CuCl/2,2′-bipyridine, well-defined comb-like polymers with one graft chain for every two monomer units of backbone polymer were obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2069–2075, 2006

Synthesis of diblock copolymers by combining stable free radical polymerization and atom transfer radical polymerization

Co-reporter:Zhifeng Fu;Yan Shi;Bingyi Li;Wantai Yang

Journal of Polymer Science Part A: Polymer Chemistry 2006 Volume 44(Issue 8) pp:2468-2475

Publication Date(Web):1 MAR 2006

DOI:10.1002/pola.21321

A stable nitroxyl radical functionalized with an initiating group for atom transfer radical polymerization (ATRP), 4-(2-bromo-2-methylpropionyloxy)-2,2,6,6-tetramethyl-1-piperidinyloxy (Br-TEMPO), was synthesized by the reaction of 4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy with 2-bromo-2-methylpropionyl bromide. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br-TEMPO. The obtained polystyrene had an active bromine atom for ATRP at the ω-end of the chain and was used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare block copolymers. The molecular weights of the resulting block copolymers at different monomer conversions shifted to higher molecular weights and increased with monomer conversion. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2468–2475, 2006