超声波场下辅助引发苯乙烯分散聚合反应的研究

通过实验设计,对超声波场下辅助引发苯乙烯(St)分散聚合反应的可行性进行了研究。结果表明:利用超声波空化作用产生的热点效应,油溶性引发剂偶氮二异丁腈(AIBN)裂解生成自由基可引发St的分散聚合反应。超声波场的工作参数(超声波输出功率、作用时间)对聚苯乙烯(PS)粒子的性能影响很大,适宜的超声波场聚合反应条件为400W×3.0h。     

苯乙烯分散聚合反应

苯乙烯在乙醇／水混合溶液介质中,在偶氮二异丁腈引发作用下,以聚乙烯基吡咯烷酮为稳定剂进行分散聚合反应,采用溴加成双键分析方法研究了苯乙烯分散聚合反应过程中单体转化率的变化,并讨论了引发剂浓度和反应温度对单体转化率的影响。     

基于均匀设计的苯乙烯分散聚合反应研究

本文基于均匀设计方法对苯乙烯的分散聚合反应进行了试验设计,并通过回归分析,建立了聚苯乙烯粒子相关性能参数(聚苯乙烯粒子分子量、粒径大小及分布)和各变量(单体浓度、稳定剂用量、引发剂用量和反应介质溶度参数)之间的回归方程。根据回归方程进行了分散聚合反应的配方优化,得到了约束条件下的苯乙烯分散聚合反应配方,实测值与预测值比较结果表明,回归方程的预测值与优化配方制备的PS粒子的各项性能实测值存在一定的偏差(相对偏差在15%以内),但仍对试验配方设计有一定的指导作用。     

H2O2—FeSO4引发α—蒎烯与苯乙烯分散聚合

主要研究了通过采用散聚合的方法,以H2O2－FeSO4为引发剂体系,聚乙烯醇吡咯烷酮（PVP）作为分散剂,在无水乙醇溶液中使α－蒎烯与苯乙烯分散共聚,以石油醚为沉淀剂将产物分离出来,并对共聚物进行IR测试。初步探讨分散共聚反应的机理和共聚单体投料比,聚合时间,聚合反应温度,以及引发剂体系作用下,此共聚反应的最佳工艺条件：α－蒎烯：苯乙烯＝1：4,反应温度为80℃,反应时间为4h,引发剂：单体总量1：4。在此最佳条件下α－蒎烯的转化率约为90％。     

苯乙烯分散聚合工艺条件对转化率及微球尺寸的影响

以乙醇／水混合液为分散介质，聚乙烯基吡咯烷酮为稳定剂，研究了苯乙烯分散聚合过程中引发剂浓度，单体浓度及分散稳定剂用量对转化率和微球粒径及粒径分布的影响。实验表明，通过反应中期补加引发剂，后期升温的方法，可使聚合反应的转化率达到90％以上，微球粒径增大，粒度均匀。     

超声波场辅助引发MMA分散聚合反应

通过试验设计,对超声波场下辅助引发甲基丙烯酸甲酯分散聚合反应的可行性进行研究,研究结果表明:利用超声波空化作用产生的热点效应,油溶性引发剂AIBN裂解生成自由基可引发甲基丙烯酸甲酯的分散聚合反应.反应体系组成对甲基丙烯酸甲酯分散的聚合反应有较大的影响,较优化的配方为:w(MMA)=15%,w(AIBN)=0.20%,w(PVP)=1.50%,VMeOH/VH2O=2.0.     

超声波作用下反应体系组成对苯乙烯分散聚合反应规律的影响

研究了超声波作用下反应体系组成对苯乙烯(St)分散聚合反应规律的影响,表明超声波作用下的分散聚合反应并非一般的热引发分散聚合反应,超声波的空化作用可有效地、多途径地生成更多的自由基。掌握了聚合反应规律,可初步实现根据聚苯乙烯(PS)粒径及分布和聚合反应速率要求进行反应体系的配方设计。     

超声波场作用下苯乙烯的分散聚合反应机理研究

通过实验研究和理论分析,提出了超声波场作用下分散聚合的反应是分区域分阶段逐步进行的反应机理。在分散聚合反应过程中,成核机理为接枝共聚物聚结机理,稳定机理以接枝稳定机理为主,分散剂吸附为辅。聚合过程可分为5个阶段:自由基生成阶段、强化扩散阶段、均相溶液聚合阶段、聚结成核阶段和粒子增长阶段。     

油溶性氧化还原引发剂引发苯乙烯乳液聚合反应动力学的研究

本文详细地研究了过氧化月桂胺（ＬＰＯ）／Ｎ,Ｎ－二丁基苯胺（ＤＢＡＮ）引发苯乙烯乳液聚合反应的动力学行为。检测了聚合反应速率,聚合物粒子数,以及聚合物的分子量随引发剂ＤＢＡＮ／ＬＰＯ比率的变化。分析这些实验结果,从中发现聚合反应的极限转化率取决于ＤＢＡＮ／ＬＰＯ的比值,表观聚合反应速率是由发生在聚合物粒子中和在单体液滴中的聚合反应两部分组成。聚合反应总速率取决于ＤＢＡＮ／ＬＰＯ的比值。聚合物粒子数     

H2O2-FeSO4引发α-蒎烯与苯乙烯分散聚合

主要研究了通过采用散聚合的方法,以H2O2-FeSO4为引发剂体系,聚乙烯醇吡咯烷酮(PVP)作分散剂,在无水乙醇溶液中使α-蒎烯与苯乙烯分散共聚,以石油醚为沉淀剂将产物分离出来,并对共聚物进行IR测试.初步探讨分散共聚反应的机理和共聚单体投料比,聚合时间,聚合反应温度,以及引发剂体系作用下,此共聚反应的最佳工艺条件α-蒎烯苯乙烯=14;反应温度为80℃,反应时间为4 h,引发剂单体总量=14.在此最佳条件下α-蒎烯的转化率约为90%.     

氧化还原体系引发苯乙烯乳液聚合

以不同的过氧化物引发剂分别与硫酸亚铁组成氧化还原引发体系,引发苯乙烯的乳液聚合,研究反应温度和还原剂用量等对聚合的影响.采用气相色谱、三检测体积排除色谱、动态光散射对单体转化率、聚苯乙烯的相对分子质量及其分布和乳胶粒径进行了分析.结果表明:升高温度或增加还原剂用量均会使聚合物的相对分子质量增大,聚合反应速率加快,与常规...     

Ultrasonically initiated miniemulsion polymerization of styrene in the presence of Fe3O4 nanoparticles

Ultrasonically initiated miniemulsion polymerization of styrene was conducted in the presence of Fe₃O₄ nanoparticles. Stable polystyrene (PS)/Fe₃O₄ nanocomposite emulsions were prepared and magnetic PS/Fe₃O₄ composite particles were obtained through magnetic separation. The whole procedure comprised two steps. First, Fe₃O₄ nanoparticles were dispersed in the monomer phase with the aid of stabilizer Span‐80. Second, miniemulsion polymerization of styrene in the presence of Fe₃O₄ nanoparticles was carried out under an ultrasonic field in the absence of a chemical initiator. The affecting factors, including stabilizer concentration, surfactant concentration, hexadecane concentration and the amount of Fe₃O₄, were systematically studied. Stabilizer concentration, surfactant concentration and hexadecane concentration strongly affected the formation of the coagulation. The least amount of coagulation was formed at 2.5 wt% Span‐80 concentration. The addition of Fe₃O₄ nanoparticles drastically increased the polymerization rate owing to the fact that Fe₃O₄ nanoparticles increased the acoustic intensity and Fe²⁺ reacted with H₂O₂ to produce hydroxyl radicals and increase the number of radicals. The increase in cosurfactant concentration and power output also increased the polymerization rate. Copyright © 2005 Society of Chemical Industry     

Kinetics of polymerization and particle stabilization mechanism on dispersion copolymerization of styrene and divinylbenzene

Monodisperse highly crosslinked microspheres were prepared by dispersion copolymerization of styrene and divinylbenzene in an ethanol/water medium using poly(N‐vinylpyrrolidone) (PVP) as the stabilizer. The locus of polymerization and growth of particles were investigated. The polymerization kinetics, average particle diameter (D_n), polydispersity index (PDI), and numbers of particles (N_p) were presented. When the initial styrene concentration is below 20%, the results indicate that the polymerization occurs in the particles, and the particles grow to their final size by the diffusion of monomer and oligomer into the existing particles. The polymerization rate can be described by the equation R_p = k[l]^0.87 ([St]^1.91 + [DVB]^0.09) (1 + [PVP]^0.01) exp(? 45.35/RT). The data from infrared spectroscopy demonstrated that the graft stabilizer was present. The dissolution experiments show that the crosslinking reaction occurred irregularly in batch dispersion polymerization. Using the postaddition approach, up to 3% divenylbenzene (DVB) was successfully incorporated in the synthesis of coagulum‐free substance, and monodisperse crosslinked 5 μ m microspheres with a superior resistance to solvents have been prepared. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2230–2238, 2002     

Atom transfer radical polymerization of styrene initiated by bromoacetylated syndiotactic polystyrene macroinitiator

Atom transfer radical polymerization of styrene was conducted with bromoacetylated syndiotactic polystyrene as macroinitiator and copper bromide combined with N,N,N′,N′,N′‐pentamethyldiethylenetriamine as catalyst. A two‐stage process has been developed to synthesize the macroinitiator. First, syndiotactic polystyrene (sPS) was functionalized in the side phenyl rings with acetyl groups using the Friedel–Crafts reaction; second, the acetyl groups were converted to bromoacetyl groups by an acid‐catalyzed halogenation reaction. The initiator was found to be active in the polymerization of styrene, leading to the production of graft chains with well‐defined structure. The molecular weight and molecular weight distribution of the graft chains were determined using gel permeation chromatography after cleaving from the sPS backbone using peroxide acid oxidation followed by hydrazine‐catalyzed hydrolysis. The results indicated that the polymerization process was characteristic of a ‘living’ nature. Copyright © 2007 Society of Chemical Industry     

Solvent effect on TEMPO-mediated living free radical dispersion polymerization of styrene

Living free radical dispersion polymerization of styrene in the presence of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and 2,2-azobisisobutyronitrile (AIBN) was conducted in various glycol media having different solubility parameters. Genuine heterogeneous polymerization nature was observed from the initial stage of the reaction. The solubility parameter of the media was found to significantly influence the living characteristics of the polymerization including the polymerization kinetics and the molecular weight evolution at a fixed concentration of TEMPO. A grafting of stabilizer molecules onto monomer and a possible partitioning of TEMPO between the continuous medium and particle phase were postulated for the deviation of the experimentally obtained molecular weight from the calculated value. For a poor medium for styrene, such as diethylene glycol, the living nature was achieved by increasing the amount of TEMPO. The polystyrene (PS) microsphere was well obtained in all tested glycol media and the average size was increased with enhanced affinity of the media to styrene and with decreasing concentration of TEMPO.     

Polymerization in a magnetic field. 14. Possibilities to improve field effect during methyl acrylate polymerization

Magnetokinetic changes intervened in the radical polymerization of methyl acrylate in a continuous external magnetic field of 0.22 T was evidenced. The use of a matrix of polymerization, respectively, poly(ethylene glycol), was correlated with the obtained kinetic data. The occurring‐magnetokinetic changes were justified by the radical pair mechanism, Δg, which corresponds to the benzoyl peroxide decomposition into a magnetic field. The intervened magnetokinetic modifications during the reactions are correlated with the reaction conditions. The influence of the magnetic field is confirmed by the molecular weights of the obtained polymers, values interpreted from the viewpoint of the reaction conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1031–1036, 2004     

The influence of water on size of the monodisperse polystyrene microspheres prepared by dispersion polymerization

Polystyrene microspheres with uniform sizes have a wide range of applications in biomedical engineering. However, detailed and systematic investigations on the influence of water content on alcohol/water systems are relatively scarce. In this study, the impact of trace water content on microsphere size was comprehensively examined, and a systematic exploration of the varying effects of different hydration levels on particle nucleation and growth mechanisms was conducted. When the water content increased from 0.1% to 0.4%, the microsphere diameter rapidly decreases from 3.6 to 2.71 μm. Correspondingly, the molecular weight increased from 29,797 to 69,186. However, within the water content range of 0.5%–14.5%, alterations in water content induced only slight variations in the microsphere diameter. The microsphere size, molecular weight, conversion rate, and reaction rate were compared in two stages. It was observed that the diminishing influence of water on the system was due to the changes in the main polymerization sites. Subsequently, the addition of water content up to 33.5% revealed an exponential decrease in the microsphere size with increasing water content in ethanol. This pattern was also observed in methanol and isopropanol, demonstrating its universality and predictability, making it applicable for precise prediction of microsphere size in different solvents.     

Syndiotactic polymerization of styrene: Study of catalyst components and polymerization conditions

Syndiotactic polystyrene (s‐PS) was prepared using monotitanocene catalyst of cyclopentadienyl titanium trichloride (CpTiCl₃) activated by methylaluminoxane (MAO). Solution polymerization was carried out in toluene using different polymerization conditions. Syndiotacticity index (SI) between 68 and 91.6% was obtained. Increasing Al/Ti molar ratio shows an increase in both conversion percentage and SI. The conversion increased linearly with increasing Al/Ti molar ratio in the range studied. The conversion reached to an optimum value of about 65% at styrene/Al molar ratio of 2.83, while no regular behavior of SI was observed with changing the ratio. Effect of temperature of the range 50–80°C on polymerization was studied. The most favorable temperature for the polymerization regarding activity is 70°C; however SI decreased with temperature up to 80°C. H₂ value to 140 mL/100 mL solvent increased the productivity of the catalyst, however further increase of H₂ reduced the activity of the catalyst. Polymerization time of 15 to 125 min shows a decrease in activity. The decrease was sharper for about 30 min of polymerization than longer time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2216–2221, 2006     

Inhibitor radicals in styrene polymerization

Stable radicals derived from inhibitor molecules were detected in the process of styrene polymerization. N‐(1,4‐dimethylpentyl)‐4‐nitroso‐aniline and 2,4‐dinitrophenol inhibitors were shown to produce nitroxyl radicals. Phenoxyl radicals come from 4‐benzylidene‐2,6‐di‐tert‐butyl‐cyclohexa‐2,5‐dienone. The radical structures were determined. The kinetics of radical formation was studied. These radicals can participate in the process of living radical polymerization and significantly affect the kinetics of polymerization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1599–1603, 2004