Co-reporter:Huarong Nie, Dandan Liu, Chenguang Liu, Xiaojian Wang, Aihua He
Polymer 2017 Volume 117(Volume 117) pp:
Publication Date(Web):19 May 2017
DOI:10.1016/j.polymer.2017.04.005
•Wide polydispersity of TPI and viscosity between TPI and SSBR resulted in a complicated domain coarsening.•Secondary phase separation was observed and caused the trapping of SSBR drops in TPI-rich domains.•Domain interface assisted TPI crystallization by as the substrate for static heterogeneous nucleation.•Phase separation enabled the predominant formation of a-TPI.In this work, the combined effects of polydispersity and viscosity on microstructure that evolves with domain coarsening and crystallization are investigated in the blends of amorphous solution polymerized styrene-butadiene rubber (SSBR) and crystalline trans-1,4-polyisoprene (TPI). We find that the bicontinuous patterns in SSBR/TPI undergo a complicated coarsening process and evolve to microstructures where high density SSBR drops are trapped in TPI-rich domains after the secondary phase separation, which is the result of the hydrodynamic difference between TPI components with different molecular weights and the viscosity difference between SSBR and TPI. Domain interface assists crystallization by acting as the substrate for the static heterogeneous nucleation. Although TPI spherulites preferentially grow in TPI-rich domains with SSBR drops in-situ included in crystals, they still could cross over SSBR-rich phases. Owing to the polydispersity of TPI, phase separation driving low-molecular-weight TPI assembling in TPI-rich domains enables the predominant formation of polymorphic α-TPI by lowering the crystallization energy barrier.Download high-res image (476KB)Download full-size image
Co-reporter:Qingtao Niu, Chen Zou, Xiangyu Liu, Riguo Wang, Aihua He
Polymer 2017 Volume 109() pp:197-204
Publication Date(Web):27 January 2017
DOI:10.1016/j.polymer.2016.12.028
•An isothermal crystallization fractionation method is reported for trans-1,4-poly(isoprene-co-butadiene) copolymers (TBIR).•TBIR-15 and TBIR-20 are multi-block copolymers, while TBIR-40 is random copolymer.Polymer chain structural factors, like chain microstructure, comonomer content in copolymer, dyad sequence distribution, molecular weight (MW) and molecular weight distribution (MWD), etc. have a great influence on the properties and applications of polymer materials. In this paper, chain structural factors and thermal behaviors of novel trans-1,4-poly (isoprene-co-butadiene) copolymers (TBIR-15, TBIR-20, TBIR-40) with various comonomer contents synthesized by TiCl4/MgCl2-Al (i-Bu)3 catalyst system were studied by 13C-NMR, GPC, DSC and WAXD. Eight fractions for each TBIR sample were obtained through isothermal crystallization fractionation of TBIR in dilute solution. It is proved that all fractions in the TBIR samples were high trans-1,4-configuration copolymers (>89 mol%). The TBIR copolymers were mainly composed by G fractions (44∼76 wt%), which cannot be crystallized from the dilute solutions at −20 °C. The G fractions of the TBIR-15 and TBIR-20 were multi-block copolymers composed by short trans-1,4-polyisoprene (TPI) blocks with the number-average sequence length of isoprene units (nIp)∼6. The G fraction of TBIR-40 was random copolymer with the melting temperature (Tm) as low as −3.4 °C and the crystallinity (Xc) as low as 4.4%. Fractions D and E in TBIR-15 and TBIR-20 were multi-block copolymers with long TPI blocks (nIp = 6∼24) and the above two fractions show decreased Tm (29∼38 °C) from imperfect TPI crystals. A special fraction A in TBIR-40 was random copolymer containing a few TPI and trans-1,4-polybutadiene (TPB) blocks, and both TPI and TPB blocks had the ability to crystallize. The Mw for each fraction was in the range of 2–6 × 105 and Mw/Mn was in the range of 2–6. Based on the analysis, the possible chain sequence distribution model for each fraction was proposed. It was expected that this research would provide a further understanding about the TBIR copolymer chain structures and inspire the copolymer synthesis with ideal structure and composition as high performance rubber material.Based on the different crystallizability of polymer chain with different chain structures, poly (isoprene-co-butadiene) (TBIR) copolymers were fractionated into eight fractions by isothermal crystallization fractionation. The TBIR-15 is mainly composed by various multi-block copolymers with different length TPI blocks (nIp = 6∼24). The TBIR-40 is mainly composed by random copolymers, among which 69.7 wt% are elastomers, 17.1 wt% consist a few TPI and TPB blocks that both showing weak crystalline behavior.
Co-reporter:Hua-rong Nie;Chao Wang;Ai-hua He 贺爱华
Chinese Journal of Polymer Science 2016 Volume 34( Issue 6) pp:697-708
Publication Date(Web):2016 June
DOI:10.1007/s10118-016-1796-2
In this work, the optimal electrospinning conditions of trans-polyisoprene (TPI) solutions were evaluated nevertheless its lower glass transition temperature than the room temperature. Subsequently, chemical crosslinking of TPI nonwovens was firstly investigated by vulcanizing at high temperatures in the case of the persistence of nanofiber structure. For this purpose, curing agents of TPI were embedded in TPI nanofibers by co-electrospinning, and then a protect layer was coated on TPI nanofibers by filtering gelatin solution going through TPI nonwoven before the vulcanization at 140−160 °C. The results showed that the vulcanization of TPI fibrous nonwoven at high temperatures did not destroy the fiber morphology. Interestingly, TPI fibrous nonwovens after vulcanization showed excellent mechanical properties (~17 MPa of tensile strength) that could be comparable to or even higher than that of some bulk rubber materials.
Co-reporter:Huarong Nie, Cao Zhang, Yuewen Liu, and Aihua He
Macromolecules 2016 Volume 49(Issue 6) pp:2238-2244
Publication Date(Web):March 10, 2016
DOI:10.1021/acs.macromol.6b00159
In this paper, Janus hybrid particles with rubber brushes have been first fabricated by successively grafting polybutadiene chains onto polydivinylbenzene (PDVB) side and polyisoprene chains onto SiO2 side in the case of SiO2@PDVB Janus particles as the template. The weight grafting ratios (Gr) of polybutadiene (PBd) and polyisoprene (PI) brushes were determined as 19.4 and 24.8 wt %, respectively. Such Janus hybrid particles contribute to not only the retardation of phase separation but also the kinetically trapped bicontinuous phase morphology in rubber blends. The interface jamming of these Janus particles supports their promising applications as compatibilizers in polymer blends.
Co-reporter:Hua-feng Shao;Zhi-lu Li;Ai-hua He 贺爱华
Chinese Journal of Polymer Science 2016 Volume 34( Issue 7) pp:797-804
Publication Date(Web):2016 July
DOI:10.1007/s10118-016-1797-1
Trans-1,4-polyisoprene (TPI) nanofibers have been fabricated successfully through electrospinning technology. Through the control of electrospinning parameters, highly crystallized TPI fresh fibers composed mainly by β phase were produced. Morphology and diameter of TPI nanofibers can be controlled by adjusting the electrospinning conditions. The in situ observations of FTIR spectra revealed that the crystallinity of the TPI fibers decreased with aging. While for TPI nanofibers aging at 45 °C for 24 h, a decrease in crystallinity as well as β to α transformation was observed with aging and these changings happened in the first 50 h during aging. The mechanism for β-TPI formation during electrospinning process and the reduced crystallinity with aging were proposed.
Co-reporter:Hua-feng Shao;Ya-ping Ma;Hua-rong Nie 聂华荣
Chinese Journal of Polymer Science 2016 Volume 34( Issue 9) pp:1141-1149
Publication Date(Web):2016 September
DOI:10.1007/s10118-016-1823-3
Solvent annealing is a facile method for changing the aggregated microstructure and physical properties of polymer materials. In this paper, we addressed the effects of solvent vapor annealing, including chloroform and water vapor, on the polymorphic transformation in both hot-pressed film and electrospun nonwoven of isotactic polybutene-1 (PB-1) by means of in situ Fourier transform infrared spectroscopy (FTIR). The pretty rapid transition rate caused by the increased motion of molecular chains under chloroform vapor is associated with a lowest crystallinity. Also, a decreased crystallinity with the crystal transition occurred in electrospun nonwovens resulting from the relaxation of the stretched molecular chains into amorphous state rather than realignment into crystal form I predominating the crystal transition process.
Co-reporter:Hua-feng Shao;Shu-lei Wang;Xia Dong;Ai-hua He 贺爱华
Chinese Journal of Polymer Science 2016 Volume 34( Issue 2) pp:174-184
Publication Date(Web):2016 February
DOI:10.1007/s10118-016-1736-1
The effects of weight-average molecular (Mw), molecular weight distribution (MWD), and isotacticity on the linear viscoelastic behavior of polybutene-1 melts are studied. It is observed that the linear viscoelastic region becomes slightly narrower with increasing frequency. In frequency sweeps, the transition of the polymer melts flow from Newtonian flow to power-law flow can be observed. The melts with higher Mw and/or broader MWD, as well as higher isotacticity exhibit higher complex viscosity, zero shear viscosity, viscoelasticity moduli, relaxation modulus, broader transition zone, while lower critical shear rate, non-Newtonian index, and the frequency at which elasticity begins to play an important role. The relationship of zero shear viscosity on Mw has been established, which agrees with the classical power law. Furthermore, it is found that the cross-over frequency decreases with increasing Mw and the cross-over modulus increases with narrowing MWD.
Co-reporter:Baiyu Jiang, Huafeng Shao, Huarong Nie and Aihua He
Polymer Chemistry 2015 vol. 6(Issue 17) pp:3315-3323
Publication Date(Web):06 Mar 2015
DOI:10.1039/C5PY00205B
In this paper, a crystalline/crystalline polyolefin alloy – isotactic polypropylene/ isotactic polybutene-1 (iPP/iPB) in-reactor alloy with spherical particle morphology – were synthesized by sequential two-stage polymerization using a spherical MgCl2-supported Ziegler–Natta catalyst. The iPP/iPB alloys obtained were mainly composed of isotactic polybutene-1, isotactic polypropylene and polypropylene-block-poly(butene-1) block copolymers, which occupied more than 95 wt% of the total alloy. A possible polymerization mechanism was proposed to explain the block copolymer formation. The morphologies of original alloy particles and n-heptane-extracted alloy particles were characterized by SEM and a particle growth model of iPP/iPB alloy was proposed to illustrate the sequential two-stage polymerization mechanism and active-species distribution during this process.
Co-reporter:Xiu-bo Jiang;Qing-fei Zhang;Ai-hua He 贺爱华
Chinese Journal of Polymer Science 2015 Volume 33( Issue 6) pp:815-822
Publication Date(Web):2015 June
DOI:10.1007/s10118-015-1626-y
Two series of trans-1,4-poly(butadiene-co-isoprene) copolymers (TBIR) were prepared using the catalyst system TiCl4/MgCl2-Al(i-Bu)3 at different reaction temperatures. All dyad and triads sequence distributions, the number-average sequence length and the sequence concentration of the copolymers were calculated according to 13C-NMR spectra. The influences of temperature and initial molar ratio of butadiene to isoprene (Bd to Ip) on the distribution of the chain segments in the TBIR copolymers were discussed. The correlation of copolymer compositions and thermal properties were also evaluated, which facilitated the understanding of controlling the degree of crystallinity and the transition temperature by changing Bd content and temperature.
Co-reporter:Xiubo Jiang
Polymer International 2014 Volume 63( Issue 2) pp:179-183
Publication Date(Web):
DOI:10.1002/pi.4633
The discovery of Ziegler − Natta catalysts has been one of the greatest developments in technology for the synthesis of stereoregular polymers in both academy and industry since the 1950s. In particular, the development of the fourth generation Ziegler − Natta catalyst with MgCl2 as support brings a revolutionary improvement to the properties of manufactured polyolefins and stimulates people to explore the stereospecific polymerization of α-olefin and diene monomers, which supplies the power to synthesize a new type of polyolefin materials. Although research on single-site catalysts has attracted a lot of attention in recent years, the ‘old’ and conventional Ziegler − Natta catalysts are still being developed vigorously due to their unique industrial advantages such as low cost, high catalytic efficiency and high stereospecificity. In this mini-review, we mainly summarize the development of the conventional supported Ziegler − Natta catalyst system and the stereoregular polyolefins synthesized with supported Ziegler − Natta catalysts. © 2013 Society of Chemical Industry
Co-reporter:Xiubo Jiang;Xinglong Wen;Wen-Hua Sun
Journal of Polymer Science Part A: Polymer Chemistry 2014 Volume 52( Issue 17) pp:2395-2398
Publication Date(Web):
DOI:10.1002/pola.27267
Co-reporter:Qing-fei Zhang;Xiu-bo Jiang;Ai-hua He 贺爱华
Chinese Journal of Polymer Science 2014 Volume 32( Issue 8) pp:1068-1076
Publication Date(Web):2014 August
DOI:10.1007/s10118-014-1467-0
A series of trans-1,4-butadiene/isoprene copolymers were prepared using the catalyst system TiCl4/MgCl2-Al(i-Bu)3 with bulk precipitation technology at different temperatures. Monomers reactivity ratios were calculated based on the Kelen-Tüdös (K-T) method and the Mao-Huglin (M-H) method. The influence of temperature on copolymer composition and polymerization rate was discussed in detail. The increase of reaction temperature brought the decrease of butadiene reactivity ratio rBd and supplied an effective adjustment on copolymers’ composition distribution.
Co-reporter:Bao-yu Sun;Lei Cui;Xiu-bo Jiang;Bai-yu Jiang
Chinese Journal of Polymer Science 2014 Volume 32( Issue 5) pp:633-639
Publication Date(Web):2014 May
DOI:10.1007/s10118-014-1433-x
Isotactic poly(butene-1) (iPB) with spherical morphology was synthesized successfully with bulk precipitation polymerization without post-treatment of the products. The bulk precipitation polymerization process made it possible for iPB to be used as general plastic due to the acceptable decreased cost compared with the solution polymerization process. The influence of catalyst residues on the aging and thermal stability of iPB synthesized by bulk precipitation polymerization method was investigated by gel permeation chromatography, mechanical performance testing, thermogravimetric analysis and infrared spectroscopic analysis. Commercial iPB and the lab-made iPB with varied catalyst residue contents were studied. The results demonstrated that the catalyst residues played an important role in the aging process of the iPB. A possible mechanism of aging promotion by catalyst residues was proposed.
Co-reporter:Qingtao Niu, Xiubo Jiang, Aihua He
Polymer 2014 Volume 55(Issue 9) pp:2146-2152
Publication Date(Web):25 April 2014
DOI:10.1016/j.polymer.2014.03.013
Trans-polydiene rubber family as high-performance tire stock possessed excellent dynamic properties, including excellent anti fatigue, low rolling resistance, low heat buildup, good green strength, and low abrasion loss. Here, Reactor Granule Technology (RGT) was introduced into the field of synthetic rubber for the first time to produce trans-1.4-polyisoprene/trans-1,4-poly(butadiene-co-isoprene) rubber alloy, which showed significant improvement in rubber synthetic technologies and great development in abundance of trans-rubber family. A series of trans-polyisoprene alloys with excellent spherical morphology were successfully synthesized by using sequential multistage polymerization. The alloy was fractionated into four fractions by temperature-gradient fractionation, and the fractionation was analyzed by 1H NMR, 13C NMR, DSC and WAXD.
Co-reporter:Aihua He;Geng Wang;Weizhen Zhao;Xiubo Jiang;Wei Yao;Wen-Hua Sun
Polymer International 2013 Volume 62( Issue 12) pp:1758-1766
Publication Date(Web):
DOI:10.1002/pi.4490
Abstract
Polyisoprene (PI) with a high content of cis-1,4 (up to 95%) or cis-1,4/3,4 binary structures was synthesized using a cobalt system in toluene. The cobalt system, which exhibited high activities (up to 3.50 × 106 g PI (mol Co)−1 h−1), contained a series of 2-(benzimidazolyl)-6-(1-(arylimino)ethyl)pyridine cobalt(II) dichlorides activated with ethylaluminium sesquichloride. The nature of the ligands and the reaction conditions significantly affected both the catalytic performance of the cobalt complexes as well as the structures of the resultant PI. The stereospecific polymerization of isoprene could be tuned via changing either the co-catalyst or solvent: for example, increased content of 3,4 PI (up to 36.6%) was achievable in heptane in the presence of diethylaluminium chloride. Sequence distribution analysis by 13C NMR spectroscopy indicated that most 3,4 units occurred randomly in the PI chains. © 2013 Society of Chemical Industry
Co-reporter:Aihua He;Weiping Zheng;Yangwei Shi;Guoqing Liu;Wei Yao ;Baochen Huang
Polymer International 2012 Volume 61( Issue 10) pp:1575-1581
Publication Date(Web):
DOI:10.1002/pi.4250
Abstract
A series of isotactic polybutene-1/polypropylene (PB/PP) alloys with spherical morphology were prepared by MgCl2-supported Ziegler-Natta catalyst with sequential two-stage polymerization technology. The first formed PP particles were used as micro-reactors to initiate the bulk precipitation polymerization of butene-1 further. The porous PP particles as a hard framework may prevent the adhesion of PB particles during the bulk precipitation polymerization process. At the same time, the bulk precipitation polymerization process allows for maximization of the butene-1 polymerization rate and simplifies the butene-1 polymerization process considerably. Finally, spherical PB alloys with a super-high molecular weight PB component and adjustable PP component were synthesized in situ within the reactor. The structures and properties of the PB/PP alloys were characterized by gel permeation chromatography, 13C nuclear magnetic resonance, Fourier transform IR, scanning electron microscopy, differential scanning calorimetry and X-ray diffraction. The results showed that the MgCl2-supported Ziegler-Natta catalyst showed relatively high stereospecificity and efficiency for both propylene and butene-1 polymerization. The incorporation of propylene on the PB matrix affects the properties of the final products markedly. The PB/PP alloys are expected to have a broader range of applications as a new family of high performance materials. Copyright © 2012 Society of Chemical Industry
Co-reporter:Ai-hua He 贺爱华;Yang-wei Shi;Guo-qing Liu;Wei Yao
Chinese Journal of Polymer Science 2012 Volume 30( Issue 5) pp:632-641
Publication Date(Web):2012 September
DOI:10.1007/s10118-012-1149-8
Polypropylene (PP)/polybutene-1 (PB) alloys within reactor were prepared by MgCl2-supported Ziegler-Natta catalyst with sequential two-stage polymerization technology. First, propylene homo-polymerizations were carried out to form isotactic polypropylene (iPP) particles containing active catalyst. Then, butene-1 was subsequently polymerized to form polybutene-1 phase inside the iPP particles. Finally, iPP/PB alloys with spherical shape and adjustable PB content were synthesized. The catalytic activity and catalytic stereospecificity of the Z-N catalyst in the two-stage polymerization process are discussed. The composition and physical properties of the PP alloys were characterized by FT-IR, 13C-NMR, SEM, DSC and XRD. It was found that the in-reactor PP alloys are mainly composed of PP and PB with a little amount of poly(buteneco-propylene) random copolymers and poly(butene-block-propylene) block copolymers. SEM measurements verified that the PB phases with size in the range of 300–400 nm dispersed in the PP matrix uniformly. The incorporation of PB upon the PP matrix affects the properties of final products greatly.
Co-reporter:Xin Liu;Kai Du;Charles C. Han
Journal of Applied Polymer Science 2011 Volume 119( Issue 1) pp:162-172
Publication Date(Web):
DOI:10.1002/app.32335
Abstract
Polypropylene/clay nanocomposites (PPCNs) were prepared via an in situ polymerization method with a Ziegler–Natta/clay compound catalyst in which the MgCl2/TiCl4 catalyst was embedded in the clay galleries. The wide-angle X-ray diffraction and transmission electron microscopy results showed that the clay particles were highly exfoliated in the polypropylene (PP) matrix. The nonisothermal crystallization kinetics of these PPCNs were investigated by differential scanning calorimetry at various cooling rates. The nucleation activity were calculated by Dobreva's method to demonstrate that the highly dispersed silicate layers acted as effective nucleating agents. The Avrami, Jeziorny, Ozawa, and Mo methods were used to describe the nonisothermal crystallization behavior of the PP and PPCNs. Various parameters of nonisothermal crystallization, such as the crystallization half-time, crystallization rate constant, and the kinetic parameter F(t), reflected that the highly exfoliated silicate layers significantly accelerated the crystallization process because of its outstanding nucleation effect. The activation energy values of the PP and PPCNs determined by the Kissinger method increased with the addition of the nanosilicate layers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Li-mei Wang;Ai-hua He 贺爱华
Chinese Journal of Polymer Science 2011 Volume 29( Issue 5) pp:
Publication Date(Web):2011/09/01
DOI:10.1007/s10118-011-1070-6
TiCl4/MgCl2/clay compound catalyst was prepared by chemical reaction. Exfoliated polypropylene (PP)/clay nanocomposites were synthesized by in situ polymerization with this compound catalyst. Effects of polymerization temperature, polymerization time, propylene pressure, solvent consumption and pre-treat time of catalyst on catalyst activity and catalytic stereospecificity were studied. Under optimal conditions, activity of the nano-compound catalyst is about 88.3 kg/(mol Ti·h). Isotacticity of PP obtained in the nanocomposites is in the range of 89%–99%, and its melting temperature is about 159°C. The weight-average molecular weight of PP can reach 6.7 × 105 − 7.8 × 105, and the molecular weight distribution is between 7.7 and 7.9.
Co-reporter:Aihua He, Limei Wang, Wei Yao, Baochen Huang, Dujin Wang, Charles C. Han
Polymer Degradation and Stability 2010 Volume 95(Issue 4) pp:651-655
Publication Date(Web):April 2010
DOI:10.1016/j.polymdegradstab.2009.12.003
Four kinds of imidazolium surfactants with high thermal stability were designed and synthesized accordingly. The structures of these surfactants were characterized by 1H NMR spectra. The TGA results indicated that the thermal stabilities of these surfactants with saturated alkyl groups were relatively high and the initial decomposition temperatures at 5% weight loss (T0.05) were higher than 250 °C. Imidazolium(O) modified montmorillonite (MMT) was prepared by cation exchange. TGA results showed that the OMMT showed obviously higher thermal stability than the surfactants themselves and the T0.05 values of OMMT were higher than 330 °C. The dihexadecane imidazolium (DHI) with two long tails has the ability to enlarge the interlayer spacing to a bigger degree compared with other imidazolium surfactants with only one long tail. Polypropylene(PP)/OMMT nanocomposites were prepared by solution blending and the effects of these surfactants with different structures on the silicate layer dispersion in PP matrix were measured.
Co-reporter:Huarong Nie, Junxing Li, Aihua He, Shanshan Xu, Qingsong Jiang and Charles C. Han
Biomacromolecules 2010 Volume 11(Issue 8) pp:
Publication Date(Web):July 23, 2010
DOI:10.1021/bm100505j
Co-reporter:Shanshan Xu, Junxing Li, Aihua He, Wenwen Liu, Xingyu Jiang, Jianfen Zheng, Charles C. Han, Benjamin S. Hsiao, Benjamin Chu, Dufei Fang
Polymer 2009 50(15) pp: 3762-3769
Publication Date(Web):
DOI:10.1016/j.polymer.2009.06.009
Co-reporter:Xin Liu;Kai Du;Charles C. Han
Journal of Polymer Science Part B: Polymer Physics 2009 Volume 47( Issue 22) pp:2215-2225
Publication Date(Web):
DOI:10.1002/polb.21819
Abstract
Highly exfoliated isotactic-polypropylene/alkyl-imidazolium modified montmorillonite (PP/IMMT) nanocomposites have been prepared via in situ intercalative polymerization. TEM and XRD results indicated that the obtained composites were highly exfoliated PP/IMMT nanocomposites and the average thickness of IMMT in PP matrix was less than 10 nm, and the distance between adjacent IMMT particles was in the range of 20–200 nm. The isothermal crystallization kinetics of highly exfoliated PP/IMMT nanocomposites were investigated by using differential scanning calorimeter(DSC) and polarized optical microscope (POM). The crystallization half-time t1/2, crystallization peak time tmax, and the Avrami crystallization rate constant Kn showed that the nanosilicate layers accelerate the overall crystallization rate greatly due to the nucleation effect, and the crystallization rate was increased with the increase in MMT content. Meanwhile, the crystallinity of PP in nanocomposites decreased with the increase in clay content which indicated the PP chains were confined by the nanosilicate layers during the crystallization process. Although the well-dispersed silicate layers did not have much influence on spherulites growth rate, the nucleation rate and the nuclei density increased significantly. Accordingly, the spherulite size decreased with the increase in MMT content. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2215–2225, 2009
Co-reporter:Huarong Nie, Aihua He, Jianfen Zheng, Shanshan Xu, Junxing Li and Charles C. Han
Biomacromolecules 2008 Volume 9(Issue 5) pp:
Publication Date(Web):April 24, 2008
DOI:10.1021/bm701349j
As a natural biopolymer, sodium alginate (SA) has been widely used in the biomedical field in the form of powder, liquid, gel, and compact solid, but not in the form of nanofiber. Electrospinning is an effective method to fabricate nanofibers. However, electrospinning of SA from its aqueous solution is still a challenge. In this study, an effort has been made to solve this problem and find the key reasons that hinder the electrospinning of alginate aqueous solution. Through this research, it was found that pure SA nanofibers could be fabricated successfully by introducing a strong polar cosolvent, glycerol, into the SA aqueous solutions. The study on the properties of the modified SA solution showed that increasing glycerol content increased the viscosity of the SA solution greatly and, meanwhile, decreased the surface tension and the conductivity of the SA solution. The rheological results indicated that the increase in glycerol content could result in the enhanced entanglements of SA chains. Two schematic molecular models were proposed to depict the change of SA chain conformation in aqueous solution with and without glycerol. The main contribution of glycerol to the electrospinning process is to improve the flexibility and entanglement of SA chains by disrupting the strong inter- and intramolecular hydrogen bondings among SA chains, then forming new hydrogen bondings with SA chains.
Co-reporter:Kai Du;Aihua H. He;Charles C. Han;Xin Liu
Macromolecular Rapid Communications 2007 Volume 28(Issue 24) pp:2294-2299
Publication Date(Web):2 NOV 2007
DOI:10.1002/marc.200700592
Highly exfoliated poly(propylene) (PP)/clay nanocomposites with obvious improvements in both the tensile strength and toughness have been prepared by a novel TiCl4/MgCl2/imidazolium-modified montmorillonite (IOHMMT) compound catalysts. Through this approach, in situ propylene polymerization can actually take place between the silicate layers and lead not only to PP with a high isotacticity and molecular weight, but also to a highly exfoliated structure even at high clay content levels (as high as 19 wt.-%).
Co-reporter:Jianfen Zheng;Junxing Li;Charles C. Han
Macromolecular Rapid Communications 2007 Volume 28(Issue 22) pp:
Publication Date(Web):8 OCT 2007
DOI:10.1002/marc.200700544
Polymorphism control of PVDF has been realized through electrospinning. PVDF fibrous membranes with fiber diameter in the range of 100 nm to several micrometers were produced by electrospinning and the crystal phase of electrospun PVDF fibers can be adjusted at the same time. Through the control of electrospinning parameters such as the solvent, electrospinning temperature, feeding rate, and tip-to-collector distance, PVDF fibrous membranes containing mainly α- or β- or γ-phase could be fabricated successfully.
Co-reporter:Junxing Li;Charles C. Han;Benjamin S. Hsiao;Benjamin Chu;Dufei Fang
Macromolecular Rapid Communications 2006 Volume 27(Issue 2) pp:114-120
Publication Date(Web):29 DEC 2005
DOI:10.1002/marc.200500726
Summary: In the present study, electrospinning of hyaluronic acid (HA) and hyaluronic acid/gelatin (HA-GE) blends in N,N-dimethylformamide (DMF)/water-mixed solvents have been investigated. When the volume ratio of DMF to water was in the range of 1.5–0.5, HA solutions could be electrospun into fibrous membranes successfully. The average diameter of HA fibers was about 200 nm. The HA-GE composite nanofibrous membranes with varied HA/GE weight ratio in the range of 100/20–100/100 have also been successfully fabricated. The average diameter of HA-GE fibers was in the range of 190–500 nm. The decrease in surface tension could promote fiber formation. Thus, an introduction of DMF that could decrease the surface tension distinctively, without significant change or increase in viscosity of the solution, could bypass the use of blowing-assisted electrospinning. Our postulated picture is that the lower surface tension could help the ejection of stream with relatively high viscosity and reduce or prevent the droplet formation during the spinning process.
Co-reporter:Baochen Huang;Wei Yao;Yaqin Huang;Shuke Jiao
Journal of Applied Polymer Science 2004 Volume 92(Issue 5) pp:2941-2948
Publication Date(Web):17 MAR 2004
DOI:10.1002/app.20256
A high-trans 1,4-butadiene/isoprene copolymer (TBIP) was synthesized in a 5-L autoclave with hydrogen as an effective molecular weight modifier. The effects of hydrogen on the catalyst efficiency and molecular weight of the copolymers were investigated. The processability and physicomechanical properties of TBIP and their relationship to the composition, composition distribution, and molecular weight of TBIP were examined in detail. Increasing the H2 pressure effectively reduced the molecular weight of TBIP. The optimum Mooney viscosity of TBIP and the 1,4-butadiene molar content in the feed were 30–50 and 5–25%, respectively. No cis–trans isomerization was observed during the roll processing procedure for TBIP. The vulcanization characteristics of TBIP were similar to those of general rubbers, and no reverse vulcanization was observed for TBIP. A high green strength was the typical characteristic of TBIP. Vulcanized TBIP (TBIR) with an optimum composition and molecular weight presented outstanding antifatigue properties and low heat buildup in comparison with general rubbers. Compared with general sidewall stock [natural rubber (NR)/butadiene rubber (BR) = 50/50], TBIR exhibited a greater than 15-fold increase in its crack-initiation resistance. The other mechanical properties of TBIR were similar to those of 50/50 NR/BR. The heat-aging mechanism of TBIR was crosslinking aging. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2941-2948, 2004
Co-reporter:Jiliang Ci, Hongliang Kang, Chenguang Liu, Aihua He, Ruigang Liu
Carbohydrate Polymers (10 February 2017) Volume 157() pp:
Publication Date(Web):10 February 2017
DOI:10.1016/j.carbpol.2016.10.051
•HPC-g-PMPC copolymers with comb structure were synthesized by ATRP.•LCST of HPC-g-PMPC copolymers was regulated by varying the graft density.•Above the LCST, the aggregates with core-shell structure were obtained.•The anti-adsorption of BSA on the aggregates depended on the side chain length.Zwitterionic graft copolymers, hydroxypropyl cellulose graft poly(2-(methacryloyloxy) ethyl phosphorylcholine) (HPC-g-PMPC) with well-defined architecture were synthesized by atom transfer radical polymerization (ATRP). The self-assembly behaviors and thermal sensitivity of HPC-g-PMPC copolymers and their correlations with graft density and side chain length were investigated in details. HPC-g-PMPC copolymers can self-assemble into spherical aggregate structure above the critical aggregation concentration (CAC) at room temperature. Meanwhile, the size of the aggregates mainly depended on the graft density. The obtained aggregates were thermal sensitive and their low critical solution temperature (LCST) was efficiently regulated by varying the graft density. Above the LCST, the aggregates were transferred into aggregates with core-shell structure, in which the HPC rich core was stabilized by the PMPC rich shell. The interaction between the HPC-g-PMPC aggregates and BSA was investigated. The results indicated that the anti-adsorption of BSA on the aggregates surface depended on the length and graft density of the PMPC zwitterionic side chains.
