Jian Yu | Chinese Academy Of Science (original) (raw)

Papers by Jian Yu

As a biorenewable resource, cellulose is widely used in our life in the form of films and fibers ... more As a biorenewable resource, cellulose is widely used in our life in the form of films and fibers after dissolution-regeneration process. In this paper, cellulose/Laponite nanocomposite films were prepared from microcrystalline cellulose (MCC) and Laponite via a solution blending process by using a green solvent, 1-allyl-3-methylimidazolium chloride ionic liquid, to dissolve MCC effectively and disperse Laponite layers homogeneously. The dispersion of layered Laponite nanoparticles up to 5 wt% in MCC matrix was investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The results showed that the best dispersion was obtained for 1 wt% content of Laponite. The optical properties, tensile strength, and thermal stability of regenerated MCC/Laponite composite films depended on the dispersion of Laponite in MCC matrix. The MCC/Laponite film up to 3 wt% Laponite showed increased tensile strength, elongation at break, and thermal stability, retaining high transmittance above 80 % at 800 nm.

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Monolithic cellulose aerogels was prepared via dissolution-regeneration route by dissolving cellu... more Monolithic cellulose aerogels was prepared via dissolution-regeneration route by dissolving cellulose in 1-allyl-3-methylimidazolium chloride (AMIMCl). Using a high
concentration aqueous AMIMCl solution as regeneration bath endowed cellulose aerogels with high flexibility and transparency. Possessing homogeneous nano-scale porous morphology, the strong cellulose aerogels have excellent compressive properties, low densities and low thermal conductivities.

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Poly(methyl methacrylate) (PMMA)/montmorillonite (MMT) nanocomposites were prepared by a new one-... more Poly(methyl methacrylate) (PMMA)/montmorillonite (MMT) nanocomposites were prepared by a new one-pot technique,
where the hydrophilic Na-MMT layerswere decorated with hydrophobic 1-dodecyl-3-methylimidazolium hexafluorophosphate (C12mimPF6) ionic liquid in situ duringmelt blending with PMMA and intercalation of polymer chains took place subsequently. The in situ modification and intercalation of Na-MMT were confirmed using X-ray diffraction and transmission electron microscopy. The combination of the compatible C12mimPF6 with PMMA and the good dispersion of MMT layers at the nanoscale rendered the resultant PMMA/MMT nanocomposites with improved optical transparency, thermal stability and mechanical properties.

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Monodisperse poly(methyl methacrylate) (PMMA) particles in the size range of 1-5 mu m were prepa... more Monodisperse poly(methyl methacrylate) (PMMA) particles in the size range of 1-5 mu m were prepared by unseeded dispersion polymerization in methanol-water media using ate-type initiator and poly(acrylic acid) (PAA) or poly(vinyl pyrrolidone) (PVP) as a steric dispersant. The influences of various polymerization parameters, such as polymerization temperature and time, concentration and type of initiator, concentration, type and molecular weight of dispersant, composition of the reaction media including dispersed medium and monomer, content of electrolyte and crosslinking agent on the particle size and particle size distribution were systematically investigated. (C) 2000 Elsevier Science S.A. All rights reserved.
Chemical Engineering Journal 08/2000; 78(2-3):211-215.

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A substituted glycolide, 3-benzyloxymethyl-1,4-dioxane-2,5-dione, was synthesized. It is a suitab... more A substituted glycolide, 3-benzyloxymethyl-1,4-dioxane-2,5-dione, was synthesized. It is a suitable precursor for the preparation of a new hydrophilic biodegradable poly(a-hydroxy acid). The polymerizations were carried out in bulk in the presence of Sn(Oct)(2) at 120-140 degreesC. The resulting polymers were subjected to hydrogenolysis with a Pd/C catalyst in a mixed solvent to remove the protecting benzyl groups. A novel poly(a-hydroxy acid) with pendant hydroxy groups was obtained. The hydrophilicity of the resulting polymer was evaluated preliminarily.
Chinese Journal of Polymer Science 09/2001; 19(5):509-516.

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The synthesis of a new cyclic ester, 3 - benzyloxymethyl - 1, 4 - dioxane - 2, 5 - dione (3 BMG),... more The synthesis of a new cyclic ester, 3 - benzyloxymethyl - 1, 4 - dioxane - 2, 5 - dione (3 BMG), was described, which is a precursor of a novel poly (a - hydroxy acid). As an important intermediate, 3 - benzyloxy - glyceric acid (3 - O - BGA) was obtained and first isolated as white needle crystal using 3 chloro - propandiol as starting material. Polymerization of 3 - BMG was carried out in bulk at 140 degreesC with stannous 2 - ethyl hexanoate [Sn(Oct)(2)] as catalyst. High molecular weight of polymer obtained indicates that the polymerization behavior of 3 - BMG is similar to that of common lactides or lactones. 3 - BMG can also be polymerized by the bimetallic (Al/Zn) alkoxide initiator. The resulting polymer undergoes hydrogenolysis at atmospheric pressure in the presence of a palladium on charcoal and the pendant benzyl group was removed completely. The glass transition temperature ( Tg) of the polymer decreases after deprotection. And the deprotective polymer has melting temperature around 120 degreesC. The data of water absorbing and contact angle determinations suggest that the hydrophility of the polymer was improved obviously after deprotection.
Acta Chimica Sinica -Chinese Edition- 10/2001; 59(10):1809-1812

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A route was proposed to synthesize 3-benzyl-glyceric acid (3-BGA) as an important intermediate f... more A route was proposed to synthesize 3-benzyl-glyceric acid (3-BGA) as an important intermediate for the synthesis of a novel six-membered cyclic ester monomer-3-benzyloxymethyl-1,4-dioxane-2,5-dione (3-BMG). According to this route, 3-BGA was obtained from ring-opening reaction of benzyl alcohol with methyl glycidate, which was prepared from the epoxidation of methyl acrylate using sodium hypochlorite as the oxidant.
Chinese Journal of Polymer Science 03/2002; 20(2):177-180

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The copolymerization of DL-LA and 3-BMG was carried out in bulk with stannous 2-ethythexanoate as... more The copolymerization of DL-LA and 3-BMG was carried out in bulk with stannous 2-ethythexanoate as the catalyst. A series of copolymers with pendant protected groups were obtained and characterized by H-1-NMR and GPC analysis. The monomer reactivity ratios were evaluated by the Fineman-Ross method and the Kelen-Tudos method and found to be r(BMG)=1.96 and r(LA)=0.37, respectively.
Chinese Journal of Polymer Science 09/2002; 20(5):413-417.

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The influences of the chemical composition and microstructure on the degradation behaviors of 3-s... more The influences of the chemical composition and microstructure on the degradation behaviors of 3-series cyclic olefin copolymers (COCs) were investigated by using non-isothermal thermogravimetric analysis (TGA). Kinetic parameters of degradation were evaluated by using the Flynn-Wall-Ozawa iso-conversional method and the pseudo first-order method. Compared with conventional polyolefins, e.g. HDPE, COCs have lower peak temperatures of degradation, narrower degradation temperature ranges and higher amount of residual weights at the end of the degradation, which should be attributed to the chemical structure and microstructure features of COCs including the branching effect and the steric effect. The values of the reaction order of COCs determined by the Kissinger method are close to I in the non-isothermal degradation process. Although the values of E-a in region 11 calculated by using the pseudo first-order method are much higher than those calculated by using the Flynn-Wall-Ozawa method, there is a similar change trend of E-a between these two methods. However, there is a good correlation between the E-a in region 11 and the peak temperature of degradation for COCs. The theoretical weight loss versus temperature curves, generated by using the estimated kinetic parameters, well fit the experimental data, which indicates that the analysis method used in this work is valid. (C) 2003 Elsevier Science Ltd. All rights reserved.
Polymer Degradation and Stability 08/2003; 81(2):197-205.

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Macromolecules 11/2004; 37(24):9279-9282.

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In different media in the range of approximately 160-240degreesC, the gamma form of syndiotactic ... more In different media in the range of approximately 160-240degreesC, the gamma form of syndiotactic polystyrene was transformed into different crystal forms having different stabilities. Compared with the transition to less stable forms in ambient air and gaseous CO2, the gamma form transformed into beta' form in supercritical CO2 at 240degreesC and 12 MPa, and into the more ordered beta'' form in supercritical CO2 and acetone at the same temperature and pressure.
Macromolecular Rapid Communications 01/2005; 26(2):112 - 115.

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The crystal transition behavior of δ form syndiotactic polystyrene (sPS) in supercritical CO2 was... more The crystal transition behavior of δ form syndiotactic polystyrene (sPS) in supercritical CO2 was investigated in detail by using Fourier transform infrared spectroscopy and differential scanning calorimetry. The empty δ, form sPS was obtained after treating the δ form in supercritical CO2 of 12 MPa in a range from 35 to 80&DEG; C. At higher temperatures, the δ form transformed into the δ(e) form transiently and then into the γ form. The existence of the intermediate δ(e) form lowered the temperature for the δ to γ transition. At 240&DEG; C, supercritical CO2 of 12 MPa transformed the δ crystal form into more stable β form without passing through the δ(e) form. Increasing the pressure of supercritical CO2 made the δ to δ(e). transition occur easily and decreased the temperature for the δ to β transition.
Macromolecules 05/2005; 38(11):4755-4760.

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Mechanism of solid phase transformation of α to β form crystal of syndiotactic polystyrene (sPS) ... more Mechanism of solid phase transformation of α to β form crystal of syndiotactic polystyrene (sPS) was investigated in supercritical CO2. The phase transformation occurred in the original pure α and mixed (α+β) form sPS in supercritical CO2 was traced as a function of temperature and pressure by means of wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC). At appropriate temperature and pressure, sPS underwent solid phase transitions from α to β form. Higher temperature or higher pressure favored this transformation. Compared to the original pure α form sample, the original β form crystal in the mixed (α+β) form sample acted as the nucleus of β form crystal, so that reduced the transition temperature and pressure.
Polymer 07/2005; 46(15):5789-5796.

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The formation of crystal forms of syndiotactic polystyrene having different stability was invest... more The formation of crystal forms of syndiotactic polystyrene having different stability was investigated in different media having different solubility parameters with the help of wide-angle X-ray diffraction, Fourier-transform infrared spectroscopy and differential scanning calorimetry. The starting sample was the gamma form of syndiotactic polystyrene, and the solubility parameter of the media was adjusted by changing the temperature, pressure, cosolvent of supercritical carbon dioxide. With increasing solubility parameter, the stability of the resultant crystal forms was increased in the order from gamma through alpha" and beta' to beta" form. (c) 2005 Elsevier Ltd. All rights reserved.
Polymer 11/2005; 46(24):11104-11111.

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Electrically conductive composites were prepared via the chemical oxidative polymerization of pyr... more Electrically conductive composites were prepared via the chemical oxidative polymerization of pyrrole monomer in polystyrene(PS) and zinc neutralized sulfonated polystyrene(Zn-SPS) films under supercritical carbon dioxide(SC-CO2) circumstance. The strong swelling effect of SC-CO2 made polypyrrole(PPy) particles not only formed on the surface, but also incorporated into the film, resulting in a homogenous structure and a relatively higher conductivity. By comparison, the composite prepared in aqueous solution shows a skin-core structure and a conductivity of 3 to 4 orders of magnitude lower than that of the former due to the diffusion controlled process of pyrrole monomer. The percolation thresholds of PS/PPy and Zn-SPS/PPy composites are 6.2% and 2.7% of volume fractions of PPy, respectively, much lower than a theoretically predicted value of 16%. Moreover, the conductive composites prepared under SC-CO2 Circumstance show higher thermal stabillty, especially in the high-temperature region.
Chemical Journal of Chinese Universities -Chinese Edition- 04/2006; 27(4):771-774

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Supercritical carbon dioxide (SC-CO2) has been used to assist the preparation of conductive polyp... more Supercritical carbon dioxide (SC-CO2) has been used to assist the preparation of conductive polypyrrole/cellulose diacetate (PPy/CDa) composites by in situ chemical oxidative polymerization. The morphology and conductivity of resulted composites were investigated with scanning electron microscopy and four-probe method, respectively. With the assistance of strong swelling effect of SC-CO2, composite films were obtained with a macroscopically homogeneous structure and conductivity up to 10−1 S cm−1 order of magnitude. Increasing the pressure of SC-CO2 increased conductivity, while increasing the temperature decreased conductivity. For comparison, PPy/CDa composite was also prepared with conventional oxidative method in aqueous solution. From the viewpoint of conductivity and environmental protection, the SC-CO2 method showed its superiority over the conventional one. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4575–4580, 2006
Journal of Applied Polymer Science 06/2006; 100(6):4575 - 4580.

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Microcellular polycarbonate/nano-silica nanocomposites (PCSN) were prepared by temperature rising... more Microcellular polycarbonate/nano-silica nanocomposites (PCSN) were prepared by temperature rising process using supercritical CO2 as the blowing agent. Neat PC foam showed a quite broad distribution of cell sizes. Under the same foaming conditions, the addition of nano-silica resulted in PCSN foams having uniform cell size distribution, reduced cell size of 0.3-0.5 mu m and increased cell density of 10(11)-10(13) cells/cm(3). The underlying nucleation mechanism was semi-quantitatively analyzed by the classical nucleation theory. The results indicate that the energy-barrier for heterogeneous nucleation was three orders of magnitude lower than that of homogeneous one. The heterogeneous nucleation of nano-silica aggregates dramatically increased the nucleation rate, decreased the nucleation time interval, and hence facilitated the almost instantaneous growth of cell size. Combined with the well-dispersed nucleation sites, resulted from the uniform dispersion of nano-silica aggregates, the narrow-distributed cell size was obtained in PCSN foams. (c) 2006 Elsevier Ltd. All rights reserved.
Polymer 10/2006; 47(21):7580-7589.

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The crystallization behavior of two long-chain branched bisphenol A polycarbonates (PC-Bs) was st... more The crystallization behavior of two long-chain branched bisphenol A polycarbonates (PC-Bs) was studied in supercritical CO(2) using differential scanning calorimetry (DSC), wide-angle X-diffraction, and atomic force microscopy (AFM), with a linear polycarbonate (PC-L) as reference. All the PCs had similar molecular weights and molecular weight distributions. Positron annihilation lifetime spectroscopy measurement indicated that the increase in free volume fraction of 13.1% (PC-B1) and 11.8% (PC-B2) was obtained with incorporating long-chain branches compared to PC-L. This increased segmental mobility decreased the energy barrier for PC crystallization and hence increased the crystallization kinetics for PC-Bs. Two melting peaks (T(m1) and T(m2)) observed during DSC heating scan were associated with the melting of secondary and primary crystallization, respectively. The T(m2) of PC-Bs was about 2-4 degrees C lower than that of PC-L of at the same treatment time, pressure, and temperature. These results, qualitatively consistent with AFM results, mean that the incorporation of long-chain branches decreased the perfection or increased the lattice disorder of primary crystallites. The T(m1) of crystallized PC-Bs was also much lower than that of PC-L under the same treatment conditions, which was attributed to the decrease in primary crystallization process and the resultant reduction in conformational constraints in the residual amorphous regions. AFM results also indicate that the branching structure might increase the crystallite density and sequentially the crystallinity degree of PC-Bs.
Macromolecules 01/2007; 40(1):73-80

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The form II of syndiotactic polypropylene (sPP) has been found more thermodynamically stable than... more The form II of syndiotactic polypropylene (sPP) has been found more thermodynamically stable than form I when melt crystallized at pressures above 150 MPa, while the reverse occurs below 150 MPa. In the present study, through the cold and melt crystallization in supercritical CO2 the stability of various polymorphic forms of sPP, especially form II, was confirmed by using Fourier-transform infrared spectroscopy and wide-angle X-ray diffraction. Compared with the formation of pure form I at high temperatures under ambient condition, a mixture of forms I and II was formed by both the cold and melt crystallization in supercritical CO2. This atmosphere changed the relative stability of forms I and II, and made the form II more thermodynamically stable than form I. The increased solubility parameters of the surroundings, at which the form II was formed, also confirmed the stability of form II over form I in supercritical CO2. The incubation pressure was the key factor affecting the formation and amount of form II. Supercritical CO2 provides a combining severe condition to obtain the form II crystal, although its pressure was much lower than the elevated pressures (> 150 MPa) reported before. (c) 2007 Elsevier Ltd. All rights reserved.
Polymer 03/2007; 48(6):1741-1748.

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Electrically conductive composites were prepared via the chemical oxidative polymerization of the... more Electrically conductive composites were prepared via the chemical oxidative polymerization of the pyrrole monomer in polystyrene (PS) and zinc neutralized sulfonated polystyrene (Zn-SPS) films under supercritical carbon dioxide (SC-CO2) conditions. The strong swelling effect of SC-CO2 made polypyrrole (PPy) particles not only form on the surface, but also become incorporated into the film, resulting in a homogeneous structure with a relatively higher conductivity. By comparison, the composite prepared in aqueous solutions shows a skin-core structure and a conductivity of 3 to 4 orders of magnitude lower than that of the former due to the diffusion-controlled process of the pyrrole monomer. The percolation thresholds of PS/PPy and Zn-SPS/PPy composites were 6.2% and 2.7% of the volume fraction of PPy, respectively, much lower than the theoretically predicted value of 16%. Moreover, the conductive composites prepared under SC-CO2 conditions showed higher thermal stability, especially in the high-temperature region.
Frontiers of Chemistry in China 03/2007; 2(2):118-122.

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Macromolecules 11/2004; 37(24):9279-9282.

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