超临界CO2在高分子合成与制备中的应用

介绍超临界二氧化碳流体作为介质在高分子合成与制备中的研究进展。文中表明，可在超临界二氧化碳中实施氟代单体的自由基溶液聚合、甲基丙烯酸甲酯的分散聚合、丙烯酸的沉淀聚合、丙烯酰胺的反相乳液聚合以及异丁基乙烯基醚的阳离子聚合等多种聚合反应，可用超临界二氧化碳溶胀聚合法制备梯度共混物。此外，超临界二氧化碳还可用于聚合物分级和聚合物微孔、微纤与微球材料的制备等，显示出超临界二氧化碳是一种对环境无污染且价廉的     

在超临界二氧化碳中制备超高分子量聚乙烯多孔微球

以超高分子量聚乙烯作为原料, 在超临界二氧化碳中通过热处理成功制备了聚合物微米球. 微球尺寸符合高斯分布, 并可以控制在较窄范围内, 微球表面多孔且内部中空. 微球的形成是恒温过程和超临界二氧化碳双重作用的结果. 降温过程导致聚合物溶解度降低, 超高分子量聚乙烯分子链析出结晶而形成微球, 内部包裹了少量二氧化碳; 温度进一步降低导致微球内外压力不平衡, 二氧化碳从空心球内部释放形成表面孔洞. 恒温结晶过程除了促使微球结晶度进一步提高外, 还可以使亚稳晶型单斜晶转化为稳定的正交晶.     

含C60聚苯乙烯微球的制备及光电导性能研究

目前,多功能、高性能聚合物微球的合成及应用已成为研究热点.制备聚合物微球的方法有乳液聚合法、分散聚合法、无皂乳液聚合法、超微乳液聚合法和悬浮聚合法等.制备微米级微球通常采用乳液聚合法和分散聚合法.     

聚合物微球的合成与应用进展(1)

本文综述了聚合物微(米)球和纳(米)球合成制备方法。重点评述了用悬浮聚合、乳液聚合、分散聚合、种子聚合和微流控聚合等方法合成制备聚合物微球的技术特点及存在的主要问题,并介绍了近年来的最新进展情况。     

乳液聚合的最新进展（上）

本文对近１０多年中发展起来的与乳液聚合相关的聚合技术，如无皂乳液聚合、细乳液聚合、微乳液聚合、分散聚合等，也对其实施方法、理论研究结果和应用作了介绍；还针对近年来已经成为热点的核壳乳液、单分散聚合物微球及表面官能化的乳液微球的制备方法及应用进行了综述。     

分散聚合研究

介绍了分散聚合制备聚合物微球的研究进展，对分散聚合的成核与稳定机理、聚合过程、动力学、反应参数对聚合物微球粒径及分散性的影响以及运用分散聚合制备功能性聚合物微球及聚合物－－磁性材料复合微球的研究现状进行了回顾。     

交联聚苯乙烯单分散微球的制备

微米级粒度均匀的聚合物微球作为功能高分子材料在分析化学、生物化学、标准计量以及某些高新技术领域中应用广泛。制备聚合物微球的传统方法有乳液和悬浮聚合法。乳液聚合只能制备粒径为0．1-0．7μm的颗粒，采用无皂或低皂乳液聚合法制成的单分散聚合物微球粒径接近1μm，但难于达到1μm以上，且后处理比较麻烦；悬浮聚合制备的聚合物微球粒径则一般在100-1000μm之间，且是多分散性的。而分散聚合获得的微球呈单分散性，是制备粒径为1-10μm的单分散聚合物微球的有效方法。     

分散聚合法制备PVP微球的研究

以N-乙烯基吡咯烷酮(NVP)为初始单体,乙酸乙酯为分散介质,采用分散聚合法制备了分散性能良好、粒径为3～4μm的聚乙烯基吡咯烷酮(PVP)微球.考察了单体、分散剂及引发剂浓度对PVP微球的粒径、单体转化率及分子量的影响,并对PVP的结构和性能进行研究.结果表明,单体浓度增加,PVP微球粒径和分子量增大,单体转化率升高;分散剂浓度增加,PVP微球粒径变小,分子量增大,单体转化率升高;引发剂浓度增加,PVP微球粒径变大,分子量减小,单体转化率升高.与溶液聚合法相比,分散聚合法制备的PVP分子量较小且具有一定的结晶性.     

超临界技术制备多孔聚合物微球及其应用

多孔聚合物微球被广泛应用在生物技术、医学工程、环境工程、食品安全、色谱填料等领域,因此受到材料科学家的广泛关注.超临界技术是一种廉价的绿色致孔技术,在多孔聚合物微球的制备方面具有广阔的发展前景.经悬浮聚合、乳液聚合、种子聚合、沉淀聚合等多种聚合方法合成聚合物微球,通过超临界干燥技术除去溶剂实现致孔,可得到高质量多孔聚合...     

聚苯乙烯单分散微球粒径可控性探讨

在系统研究分散聚合反应中的原料组成(分散稳定剂、单体、引发剂)和反应条件(反应介质极性、反应体系温度、搅拌速度)对所制备的聚合物微球的粒径大小及粒径分布和聚合反应速率影响的基础上,根据各因素的影响效应,优化设计分散聚合的反应条件,成功地制备出1μm~10μm粒径范围内不同粒径级别的微米级单分散聚合物微球,实现了不同粒径大小及粒径分布的微米级单分散聚合物微球制备的控制设计。     

超临界CO2中的高分子合成研究进展

本文介绍以超临界CO₂流体为介质的高分子合成的研究进展。说明可在超临界二氧化碳中实施氟代单体的自由基溶液聚合、甲基丙烯酸甲酯和苯乙烯的分散聚合、丙烯酸的沉淀聚合、丙烯酰胺的反相乳液聚合以及异丁基乙烯基醚的阳离子聚合等多种聚合反应。这显示出超临界CO₂是一种对环境无污染且价廉的替代溶剂。     

Preparation of polydivinylbenzene microspheres in supercritical carbon dioxide using acetone as cosolvent

Monodisperse polydivinylbenzene (PDVB) microspheres with clean surface were prepared by precipitation polymerization without stabilizer in supercritical carbon dioxide using acetone as cosolvent. Effects of the cosolvent, reaction time and pressure, and monomer concentration on the polymerization were studied. It was found that the conversions in all polymerization systems were above 95%. Examination by scanning electron microscopy showed that reaction pressure, divinylbenzene concentration, and level of the cosolvent had pronounced effects on the morphology of the microspheres. When 6?～?7 ml of acetone was used in a reactor of 50 ml, monodisperse PDVB microspheres of around 2.1 μm in diameter were obtained. Thermal gravimetrical analysis showed the products were of good thermostability up to about 400 °C.     

超临界二氧化碳中的高分子合成

近年来,超临界二氧化碳（sc-CO2）在聚合反应中的应用受到了越来越多的关注。本文主要综述了以sc-CO2为反应介质的自由基聚合、阳离子聚合、过渡金属催化聚合、热致开环聚合、溶胶-凝胶聚合以及氧化耦合聚合的研究概况。一系列研究结果表明sc-CO2是非常有前途的反应溶剂,在高分子合成领域将会有更加广阔的应用前景。     

Continuous precipitation polymerization of acrylic acid in supercritical carbon dioxide: The polymerization rate and the polymer molecular weight

The precipitation polymerization of acrylic acid in supercritical carbon dioxide was studied in a continuous stirred tank reactor with 2,2′‐azobis(2,4‐dimethylvaleronitrile) as the free‐radical initiator. The reactor temperature was between 50 and 90 °C, the pressure was 207 bar, and the average residence time was between 12 and 40 min. The product polymer was a white, dry, fine powder that dissolved in water. A wide range of polymer molecular weights (5–200 kg/mol) was obtained. The effects of the operating variables on the polymerization rate and on the polymer molecular weight were evaluated. The observed kinetics suggested that polymerization took place in both the supercritical fluid and the precipitated polymer particles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2546–2555, 2005     

聚乙二醇双丙烯酸酯在超临界二氧化碳中的光聚合研究

探索了聚乙二醇双丙烯酸酯在超临界二氧化碳中发生光聚合反应制备聚合物颗粒的过程.方法为向充满超临界二氧化碳的高压反应釜中,同时喷射二氧化碳与聚乙二醇双丙烯酸酯及光引发剂的溶液,溶液与二氧化碳形成均匀的喷雾并进一步通过反溶剂作用与超临界二氧化碳形成分散体系,当同步进行紫外光照射时,单体可以在超临界二氧化碳中发生光聚合.结果证明此方法是可行的,得到了聚合物微颗粒.研究了不同溶剂及反应原料用量对产物粒径分布的影响.采用不同溶剂,将改变反应原料及产物在超临界二氧化碳中的溶解度,进而改变产物的粒径分布;反应原料用量增加,其在超临界二氧化碳中的溶解度减小,导致产物粒径分布较宽。     

Raman spectroscopic investigation of the phase behavior and phase transitions in a poly(methyl methacrylate)‐carbon dioxide system

Laser Raman spectroscopy, in conjunction with an optical high‐pressure cell, was used to investigate the poly(methyl methacrylate)‐carbon dioxide system. The Raman shifts associated with carbon dioxide molecules in the gas phase and those dissolved in the polymer were used to derive sorption kinetics of carbon dioxide and the carbon dioxide‐induced phase changes in the polymer. Measurements were made in the temperature and pressure ranges in which this system is known to exhibit retrograde vitrification behavior. The Raman results on the sorption kinetics and on the onset of plasticization were in agreement with those obtained by gravimetric and calorimetric techniques, respectively. This technique provides a versatile and rapid way of characterizing polymer‐gas systems and information that so far has been obtainable only through painstaking and time‐consuming techniques. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2214–2217, 2003     

Polymerization of vinylidene fluoride with perfluoropolyether surfactants in supercritical carbon dioxide as a dispersing medium

The heterogeneous polymerization of vinylidene fluoride (VDF) was investigated at 50 °C with supercritical carbon dioxide (scCO₂) as a dispersing medium and diethylperoxidicarbonate as an initiator in the presence of different perfluoropolyether surfactants. When FLK 7004A ammonium carboxylate salts were used at a 5% (w/w) concentration with respect to VDF, with an initial pressure of 31–45 MPa and with an olefin concentration of about 5.5 mol/L, monomer conversions up to 63% were obtained, corresponding to a final solid content higher than 200 g/L, and the polymer was collected at the end of the process in the form of a white powder completely composed of microspheres. The effects of the density of the polymerization mixture, the monomer loading, and the surfactant concentration were studied. Collected experimental results suggest that Fluorolink ammonium perfluoropolyether carboxylic salts are the most effective surfactants yet tested in the dispersion polymerization of VDF in scCO₂. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2406–2418, 2006     

Liquid carbon dioxide as a solvent for the radiation polymerization of ethylene

The usefulness of liquid carbon dioxide as a solvent for polymerization of ethylene was studied. The effect of liquid carbon dioxide on the polymerization was investigated under conditions of the pressure of 400 kg./cm.² over the temperature range 20–45°C. by using γ-radiation and AIBN as initiators. The infrared spectrum of the polymers showed that carbon dioxide had little effect on the polymer structure. The polymers contained no combined carbon dioxide and only small amounts of vinylidene unsaturation. The methyl content of the polymers was 0.5–4.0 CH₃/1000C. The polymer yield and molecular weight were found to be decreased by the addition of carbon dioxide in both polymerization by γ-radiation and AIBN. The number of polymer molecules formed per unit time increased with the content of carbon dioxide in the γ-ray polymerization, and was constant in the case of AIBN. The advantages of the use of liquid carbon dioxide as a solvent in this polymerization were also considered from the viewpoints of the continuous process, the separation of polymer, the stability of carbon dioxide to radiation, and commercial applications.