Preparation of micron-size polystyrene particles in supercritical carbon dioxide

The dispersion polymerization of styrene in supercritical CO₂ utilizing poly(1,1-dihydroperfluorooctyl acrylate) (p-FOA) as a polymeric stabilizer was investigated as well as poly(1,1-dihydroperfluorooctyl methacrylate) (p-FOMA). The resulting high yield (>85%) of spherical and relatively uniform polystyrene (PS) particles with micron-size range (2.9–9.6 µm) was formed for 40 h at 370 bar using various amounts of p-FOA and p-FOMA as a stabilizer with good stability until the end of the reaction. The particle diameter was shown to be dependent on the weight percent of added stabilizer. Previously, we reported that p-FOA was not effective for the dispersion polymerization of styrene as a stabilizer. Here, we find that p-FOA can indeed be an effective stabilizer for the dispersion polymerization of styrene in supercritical CO₂, but the pressure necessary to achieve good stability is higher than pressure used by us previously. This study suggests the possibility that fluorinated acrylic homopolymers are effective for the dispersion polymerization of various kinds of monomers as a stabilizer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2429–2437, 1999     

Foaming behavior of polypropylene/polystyrene blends enhanced by improved interfacial compatibility

A series of polypropylene (PP)/polystyrene (PS) blends were prepared by solvent blending with PS‐grafted PP copolymers (PP‐g‐PS) having different PS graft chain length as compatibilizers. The interfacial compatibility was significantly improved with increasing PS graft chain length until the interface was saturated at PS graft chain length being 3.29 × 10³ g/mol. The blends were foamed by using pressure‐quenching process and supercritical CO₂ as the blowing agent. The cell preferentially formed at compatibilized interface because of low energy barrier for nucleation. Combining with the increased interfacial area, the compatibilized interface lead to the foams with increased cell density compared to the uncompatibilized one. The increase in interfacial compatibility also decreased the escape of gas, held more gas for cell growth, and facilitated the increase in expansion ratio of PP/PS blend foams. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1641–1651, 2008     

Controlling arrangement of multi‐layer microcellular materials by using supercritical fluids

A series of semicrystalline microcellular materials were prepared by the foaming technology using supercritical fluids. The distribution of multi‐size microcellulars and multi‐layer arrangement was observed by scanning electronic microscopy. By controlling the foaming condition accurately, the alternated arrangement of variable in cellular size may be tuned. One key point was discussed here to understand the phenomenon: the prior sequencing of the crystal nucleation and cellular nucleation. As the supporting experiments, the gravimetric desorption data of CO₂ were kinetically and thermodynamically evaluated by three diffusion equations. The concepts of local crystal nucleation and local cellular nucleation were introduced first, and the mechanism of multi‐layer arrangement was proved. Copyright © 2012 John Wiley & Sons, Ltd.     

Competitive influence of atactic polystyrene and supercritical carbon dioxide on the conformation of syndiotactic polystyrene

The crystallization behavior of miscible syndiotactic polystyrene (sPS) and atactic polystyrene (aPS) blends with different sPS/aPS weight ratios was investigated in supercritical CO₂ by using Fourier‐transform infrared spectroscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction. Supercritical CO₂ and aPS exhibited different effects on the conformational change of sPS and competed with each other. Increasing the content of amorphous aPS in the blends made its effect on the conformational change of sPS gradually surpass that of supercritical CO₂. Supercritical CO₂ favored the formation of the helical conformation of sPS in lower temperature range and the all trans planar conformation in higher temperature range, instead of forming the latter one only in higher temperature range in ambient atmosphere. However, increasing aPS content in the blends pushed the range for forming the helical conformation to lower temperature and made the all trans planar conformation dominant in aPS/sPS 25/75 blend after treating in supercritical CO₂ above 60 °C. The all trans planar zigzag conformation was more favorable than the helical conformation after mixing aPS in sPS in supercritical CO₂. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1755–1764, 2007     

Preparation of microcellular polypropylene/polystyrene blend foams with tunable cell structure

By using supercritical carbon dioxide (sc‐CO₂) as the physical foaming agent, microcellular foaming was carried out in a batch process from a wide range of immiscible polypropylene/polystyrene (PP/PS) blends with 10–70 wt% PS. The blends were prepared via melt processing in a twin‐screw extruder. The cell structure, cell size, and cell density of foamed PP/PS blends were investigated and explained by combining the blend phase morphology and morphological parameters with the foaming principle. It was demonstrated that all PP/PS blends exhibit much dramatically improved foamability than the PP, and significantly decreased cell size and obviously increased cell density than the PS. Moreover, the cell structure can be tunable via changing the blend composition. Foamed PP/PS blends with up to 30 wt% PS exhibit a closed‐cell structure. Among them, foamed PP/PS 90:10 and 80:20 blends have very small mean cell diameter (0.4 and 0.7 µm) and high cell density (8.3 × 10¹¹ and 6.4 × 10¹¹ cells/cm³). Both of blends exhibit nonuniform cell structure, in which most of small cells spread as “a string of beads.” Foamed PP/PS 70:30 blend shows the most uniform cell structure. Increase in the PS content to 50 wt% and especially 70 wt% transforms it to an irregular open‐cell structure. The cell structure of foamed PP/PS blends is strongly related to the blend phase morphology and the solubility of CO₂ in PP more than that in PS, which makes the PP serve as a CO₂ reservoir. Copyright © 2009 John Wiley & Sons, Ltd.     

Microcellular foaming of polylactide and poly(butylene adipate‐co‐terphathalate) blends and their CaCO3 reinforced nanocomposites using supercritical carbon dioxide

Foamed polylactide (PLA), PLA–PBAT (poly (butylene adipate‐co‐terphathalate)) blend and their composites with CaCO₃ were prepared in a batch process using supercritical carbon dioxide (CO₂) at 12 MPa and 45°C. The solubility of CO₂ and its diffusion patterns in different PLA samples was investigated. PLA systems had a relatively high CO₂ solubility related to the carboxyl groups. CO₂ desorption behaviors in PLA systems first followed the Fickian diffusion mechanism in short time and then decreased slowly to a plateau. The addition of both PBAT and CaCO₃ into PLA impeded the desorption of CO₂. In the presence of second phase PBAT, nanoparticles CaCO₃ and dissolved CO₂, the PLA crystallization behavior investigated by DSC technique was greatly changed. As the desorption time increased, the gas induced crystallinity slightly decreased in consequence of less CO₂ content in each system and thus less plasticization effect. The cell morphology of foamed PLA and PLA composites showed interesting microstructure patterns. The prepared pure PLA foam exhibits a typical bimodal structure because of the foaming in both the amorphous and crystalline zones. With PBAT and CaCO₃ into PLA, the composite foam presented significant increase in cell uniformity and cell density. With less CO₂ content in each PLA sample, the cell structure showed interesting variation. Pure PLA foam presented transition from bimodal structure to more uniform cell structure with decreased cell density. In contract, PLA–PBAT foam show unfoamed regions because of none CO₂ left in the separated PBAT phase. Copyright © 2016 John Wiley & Sons, Ltd.     

超临界CO2技术制备微孔聚合物中的基本问题

微发泡聚合物材料以环境友好的超临界CO₂为发泡剂, 具有优异的材料性能. 本文对本课题组的研究工作做了归纳总结, 对聚合物微发泡中CO₂的传质、微发泡过程中泡孔结构参数的变化以及多相/多组分聚合物体系的微发泡行为等内容做了针对性的综述. 结合对聚合物微发泡过程理论模拟研究工作的评述, 展望了超临界CO₂微发泡技术未来的发展方向.     

超临界CO_2技术制备微孔聚合物中的基本问题

微发泡聚合物材料以环境友好的超临界CO2为发泡剂,具有优异的材料性能.本文对本课题组的研究工作做了归纳总结,对聚合物微发泡中CO2的传质、微发泡过程中泡孔结构参数的变化以及多相/多组分聚合物体系的微发泡行为等内容做了针对性的综述.结合对聚合物微发泡过程理论模拟研究工作的评述,展望了超临界CO2微发泡技术未来的发展方向.     

Conformational changes of poly(ethylene oxide) in poly(ethylene oxide)/poly(methyl methacrylate) blends by supercritical carbon dioxide

The effects of supercritical carbon dioxide (SC CO₂) fluids on the morphology and/or conformation of poly(ethylene oxide) (PEO) in PEO/poly(methyl methacrylate) (PMMA) blends were investigated by means of differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and Fourier transform infrared (FTIR). According to DSC data for a given blend, the melting enthalpy and, therefore, degree of crystallinity of PEO were increased, whereas the melting temperature of PEO was decreased, with SC CO₂ treatment. The enhancement of PEO crystallization with SC CO₂ treatment, as demonstrated by DSC data, was supported by WAXD data. According to FTIR quantitative analyses, before SC CO₂ treatments, the conformation of PEO was transformed from helix to trans planar zigzag via blending with PMMA. This helix‐to‐trans transformation of PEO increased proportionally with increasing PMMA content, with around 0.7% helix‐to‐trans transformation per 1% PMMA incorporation into the blend. For a given blend upon SC CO₂ treatments, the conformation of PEO was transformed from trans to helix. This trans‐to‐helix transformation of PEO decreased with increasing PMMA contents in the blends because of the presence of interactions between the two polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2479–2489, 2004     

Analysis of polystyrene surface properties on thin film bonding under carbon dioxide pressure using nanoparticle embedding technique

A gold nanoparticle embedding technique is used to determine how vacuum and pressured carbon dioxide (CO₂) affect polystyrene (PS) thin film properties. The pressured CO₂ greatly increased the gold nanoparticle embedding depth, possibly due to a low cohesive energy density near the film surface. For the monodisperse PS used in this study (M_n = 214,000), two spin‐coated thin films with intimate contact can be bonded below the bulk glass transition temperature (T_g) under CO₂ pressure when the embedded depth is larger than half of the gyration radius of PS molecules. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1535–1542, 2009     

Copolymerization of vinylidene difluoride with hexafluoropropene in supercritical carbon dioxide

Vinylidene difluoride and hexafluoropropene are copolymerized in supercritical carbon dioxide at 280 bar and 50 °C by means of free radical copolymerization, initiated by diethyl peroxydicarbonate. The first stages of the reaction were monitored by turbidity measurements and the time/conversion curve was followed gravimetrically to measure the initial rates of polymerization. The obtained copolymers possessed bimodal molecular weight distributions, their average comonomer composition was well described by the Lewis‐Mayo equation with the copolymerization parameters r_VDF = 4.8 and r_HFP = 0. The glass transition and melting temperatures of the copolymers are similar to that of the materials resulting from aqueous emulsion polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1299–1316, 2006     

超临界二氧化碳介质中过渡金融催化反应研究进展

超临界介质中的化学反应研究是目前热点研究领域之一，对超临界CO2介质中 过渡金属催化反应研究进行了总结和述评，同时讨论了有关提高过渡金属催化剂在 超临界CO2中溶液度的方法。     

Preparation of silicone‐graft copolymers by homogeneous radical copolymerization in supercritical carbon dioxide

Copolymerizations of 1,1‐dihydroperfluorooctyl methacrylate (FOMA; M₁) and methacryloxypropyl‐terminated polydimethylsiloxane [M‐PDMS (M_n = 5.9 K); M₂] and homopolymerization of M‐PDMS in supercritical CO₂ are described. The homopolymerization of M‐PDMS proceeded homogeneously without difficulty to produce oligomers (M_n = 30 K). The copolymerizations of FOMA and M‐PDMS also proceeded homogeneously over a wide monomer feed ratio. The ratio of M‐PDMS incorporated into the copolymer obtained was almost equal to the monomer feed ratio even up to the high conversion. The reactivity ratio r₁ was determined to be 1.66. DSC examination of the copolymers indicated a microphase‐separated morphology consisting of poly‐FOMA (PFOMA) and PDMS domains for all copolymer compositions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1139–1145, 2000     

Preparation,characterization, and mechanical properties of microcellular poly(aryl ether ketone) foams

High‐performance microcellular closed‐cell foams were prepared by a two‐stage batch foaming process from fluorinated poly(ether ether ketone) and characterized by scanning electronic microscopy, tensile, and dynamic mechanical analysis (DMA). The effects of saturation pressure and temperature on the cell size, cell density, and bulk density of porous materials had been discussed. The resulting materials had average cell diameters in the range 3–17 μm, and cell densities (N_f) in the order of 0.6 × 10⁹–1.39 × 10¹⁰ cells/cm³. The porosity (V_f) was in the range of 0.2–0.85. In contrast, experimental values of Young's moduli were in good agreement with theoretically predicted values, but the relative strengths were somewhat lower than that predicted. The relaxation mechanism of microcellular was systematically investigated by DMA. The dynamic mechanical spectrometry showed that the storage modulus curve at high temperature region appeared a peak and the loss modulus was lower as compared to their solid counterparts. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 173–183, 2007     

Rheology of molten polystyrene with dissolved supercritical and near-critical gases

The viscosities of polystyrene melts containing three different dissolved gases, carbon dioxide, and the refrigerants R134a (1,1,1,2-tetrafluoroethane) and R152a (1,1-difluoroethane) are investigated at pressures up to 20 MPa. These pressures reach near-critical and supercritical conditions for the three gas components, and produce polymer–gas solutions containing up to 10 wt % gas. The measurements are performed in a sealed high-pressure capillary rheometer at 150 and 175°C, and at shear rates ranging from 1–2,000 s⁻¹. Very large reductions in melt viscosity are observed at high gas loading; at 150°C, 10 wt % R152a reduces the Newtonian viscosity by nearly three orders of magnitude relative to pure polystyrene. The viscosity data for all three polystyrene–gas systems follows ideal viscoelastic scaling, whereby the set of viscosity curves for a polymer-gas system can be scaled to a master curve of reduced viscosity vs. reduced shear rate identical to the viscosity curve for the pure polymer. The viscoelastic scaling factors representing the effect of dissolved gas content on rheological behavior are found to follow roughly the same variation with composition for all three polystyrene gas systems. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2771–2781, 1999     

Radical polymerizations of a silicone‐containing acrylic monomer in supercritical carbon dioxide

Radical homopolymerizations and copolymerizations of 3‐[tris(trimethylsilyloxy)silyl]propyl methacrylate (SiMA) in supercritical CO₂ were investigated. The homopolymer was obtained in CO₂ with a good yield. It was essentially insoluble in pure CO₂ at less than 500 bar at 65 °C but was soluble in a mixture of CO₂ and its monomer (10 w/v %) at 352 bar. The copolymerizations of SiMA with methyl methacrylate, 1,1‐dihydroperfluorooctyl methacrylate, and styrene with various monomer feed ratios were also examined in supercritical CO₂ and in bulk, and the reactivity ratios were determined. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3100–3105, 2000     

Rheology of polydimethylsiloxane swollen with supercritical carbon dioxide

Viscosity curves were measured for polydimethyl siloxane (PDMS) melts swollen with dissolved carbon dioxide at 50 and 80°C for shear rates ranging from 40 to 2300 s⁻¹, and for carbon dioxide contents ranging from 0 to 21 wt %. The measurements were performed with a capillary extrusion rheometer modified for sealed, high-pressure operation to prevent degassing of the melt during extrusion. The concentration-dependent viscosity curves for these systems are self-similar in shape, exhibiting low-shear rate Newtonian plateau regions followed by shear-thinning “power-law” regions. Considerable reduction of viscosity is observed as the carbon dioxide content is increased. Classical viscoelastic scaling methods, employing a composition-dependent shift factor to scale both viscosity and shear rate, were used to reduce the viscosity data to a master curve at each temperature. The dependence of the shift factors on polymer chain density and free volume were investigated by comparing the shift factors for PDMS-CO₂ systems to those obtained by iso-free volume dilutions of high molecular weight PDMS. This comparison suggests that the free volume added to PDMS upon swelling with dissolved carbon dioxide is the predominant mechanism for viscosity reduction in those systems. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 523–534, 1997     

Sorption and diffusion of carbon dioxide in single-phase polystyrene/poly(vinylmethylether) blends

The sorption and transport properties of CO₂ in miscible PS/PVME blends at 20°C are reported as a function of pressure from 1 to 15 atm. The complex shape of isotherms for glassy blends and the concentration-dependent diffusion coefficient for rubbery blends reveal a plasticization by sorbed CO₂. The significant depression in T_g has to be taken into account in the analysis of the sorption data. Diffusion coefficient for CO₂ passes through a minimum when plotted against the blend composition. Such a behavior can be quantitatively related to the negative volume mixing of the PS/PVME system in the framework of the theories based on unoccupied volume. © 1996 John Wiley & Sons, Inc.     

超临界水中煤与聚苯乙烯的共液化研究

在间歇式高压反应装置中,研究了兖州烟煤与塑料聚苯乙烯(PS)在超临界水中的共液化,考察了水/物料比(质量比10～30)、反应温度(360℃～430℃)和塑料添加量(10%～40%)对煤液化转化率及产物收率的影响.结果表明,随着水/物料比的增加,煤液化转化率先升高,之后变化不大;油气产率则呈上升的趋势.反应温度高于420...     

超临界CO_2溶胀聚合物的研究及其应用

本文介绍超临界CO2 溶胀聚合物的研究及其应用 ,包括聚合物与超临界CO2 相互作用 ,溶胀行为的理论模型以及溶胀后的聚合物的用途 ,如制备微孔聚合物材料、渗透小分子和超临界溶胀聚合等