共查询到19条相似文献,搜索用时 78 毫秒
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我们曾对丙烯酸丁酯(BA)与醋酸乙烯酯(VAc)一步法乳液共聚合机理进行过研究,并对其胶膜及胶乳性能进行了表征。结果表明一步法共聚乳胶粒具有类似于“核壳结构”的形态,其内核由BA含量高的共聚物组成,外壳基本是PVAc均聚物,对此用不同的方法进行了验证。在此基础上我们以VAc-BA进行了半连续法乳液共聚合,以与一步法相比较,从而探讨反应过程与胶粒结构及材料性能的关系。 相似文献
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在无机SiO2纳米粒子存在下的苯丙乳液共聚合 总被引:18,自引:0,他引:18
研究了在无机SiO2纳米粒子存在下的苯丙乳液共聚合.选择了能使苯丙乳液稳定存在的乳化剂体系,研究了温度和SiO2的加入对聚合过程转化率的影响,结果表明,SiO2的加入对聚合过程有阻聚作用,使单体的转化率降低.SEM照片证明SiO2粒子已经进入苯丙乳液粒子中,而且SiO2的加入对乳液制成的膜断面形态有一定影响.实验发现在无机SiO2纳米粒子存在下,苯丙乳液共聚合时有较多残渣出现,对此通过改进乳液聚合进行了有效地改善.同时对制成的复合材料进行了力学性能和热学性能的测定. 相似文献
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三元无皂乳液共聚合动力学及其模型的研究 总被引:6,自引:0,他引:6
以苯乙烯( St) 和甲基丙烯酸甲酯( M M A) 为主单体,以丙烯酸( A A) 为功能单体进行了无皂乳液批量共聚合.考察了功能单体浓度、引发剂过硫酸铵( A P S) 浓度及聚合温度对其动力学行为的影响.建立了转化率 时间关系曲线的模型函数——— Gam ma 积分函数,用它拟合了转化率 时间关系曲线,获得了聚合过程的重要特征参数,如平均成核速率( N V) ,聚合最大速率( M V) 和平稳期平均聚合速率( A V) 及成核结束和聚合进入完成期对应的转化率.同时对聚合速率与以上各聚合参数的关系数据进行了非线性拟合,得到了它们之间的关系式.研究发现拟合误差很小,成核结束时转化率在15 % 以内,成核及聚合速率均随以上参数增大而增大,引发剂过硫酸铵在聚合过程中起决定作用. 相似文献
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Shih‐Chang Hsu Wen‐Yen Chiu Chia‐Fen Lee Herng‐Show Chang 《Journal of polymer science. Part A, Polymer chemistry》2000,38(18):3253-3269
In this study, polymers of the MMA/Styrene/BMA three‐component system were synthesized through either soapless semibatch emulsion copolymerization or soapless batch emulsion copolymerization technique. The optimal monomer feed flow rate was determined from the interphase partition laws, monomer reactivity ratios, and three or four times of iterative experimental procedures through semibatch emulsion copolymerization. As a result, the instantaneous composition of polymers could also be effectively controlled to get the desired final products. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3253–3269, 2000 相似文献
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An experimental study of the bulk-free radical copolymerization of styrene (STY)/ethyl acrylate (EA) initiated by 2,2′-azobisisobutyronitrile was conducted. Reactivity ratios were evaluated using both nonlinear least-squares (NLLS) and error-in-variables model (EVM) techniques. A thorough study of the kinetics over the full conversion range was subsequently carried out at a variety of feed compositions, initiator concentrations, and temperatures, with and without added chain transfer agent (CTA). © 1996 John Wiley & Sons, Inc. 相似文献
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Shi-Yow Lin Ignac Capek Tien-Jung Hsu Chorng-Shyan Chern 《Journal of polymer science. Part A, Polymer chemistry》1999,37(23):4422-4431
The batch emulsion polymerization kinetics of styrene (St) initiated by a water-soluble peroxodisulfate in the presence of a nonionic emulsifier was investigated. The polymerization rate versus the conversion curves showed two nonstationary rate intervals, two rate maxima, and Smith–Ewart Interval 2 (nondistinct). The rate of polymerization and number of nucleated polymer particles were proportional to the 1.4th and 2.4th powers, respectively, of the emulsifier concentration. Deviation from the micellar nucleation model was attributed to the low water solubility of the emulsifier, the low level of the micellar emulsifier, and the mixed modes of particle nucleation. In emulsion polymerizations with a low emulsifier concentration, the number of radicals per particle and particle size increased with increasing conversion, and the increase was more pronounced at a low conversion. By contrast, in emulsion polymerizations with a high emulsifier concentration, the number of radicals per particle decreased with increasing conversion. This is discussed in terms of the mixed models of particle nucleation, the gel effect, and the pseudobulk kinetics. The formation of monodisperse latex particles was attributed to coagulative nucleation and droplet nucleation for the polymerizations with low and high emulsifier concentrations, respectively. The effects of the continuous release of the emulsifier from nonmicellar aggregates and monomer droplets, the close-packing structure of the droplet surface, and the hydrophobic nature of the emulsifier on the emulsion polymerization of St are discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4422–4431, 1999 相似文献
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Monique A. Mballa Mballa Ulrich S. Schubert Johan P. A. Heuts Alex M. van Herk 《Journal of polymer science. Part A, Polymer chemistry》2011,49(2):314-326
This article describes a method for carrying out emulsion copolymerization using an automated synthesizer. For this purpose, batch emulsion copolymerizations of styrene and butyl acrylate were investigated. The optimization of the polymerization system required tuning the liquid transfer method, sufficient oxygen removal from the reaction medium and setting a proper sampling procedure. The monomer conversion‐time plots obtained with gas chromatography revealed a good reproducibility of the automated reaction kinetics. Furthermore, the particle size distributions and the properties of the final products were found to be highly reproducible. The performance of the automated reactions was subsequently compared with the conventional ones: similar reproducibility of either synthetic method was observed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
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Particle formation and coagulation in the seeded semibatch emulsion polymerization of butyl acrylate
S. Sajjadi 《Journal of polymer science. Part A, Polymer chemistry》2000,38(19):3612-3630
Particle formation and coagulation in the seeded semibatch emulsion polymerization of butyl acrylate were studied under monomer‐starved conditions. To investigate the importance of the kinetics of the water phase in the nucleation process, the monomer feed rate was used as a variable to alter the monomer concentration in the aqueous phase. The emulsifier concentration in the feed was employed to alter the particle stability. Particle formation and coagulation were discussed in terms of critical surface coverage ratios. Particle coagulation occurred if the particle surface coverage dropped below θcr1 = 0.25 ± 0.05. The secondary nucleation occurred above a critical surface coverage of θcr2 = 0.55 ± 0.05. The number of particles remained approximately constant if the particle surface coverage was within θcr1 = 0.25 < θ < θcr2 = 0.55. This surface coverage band is equivalent to the surface tension band of 42.50 ± 5.0 dyne/cm that is required to avoid particle formation and coagulation in the course of polymerization. The kinetics of the water phase was shown to play an important role during homogeneous and micellar nucleations. For any fixed emulsifier concentration in the feed and above θcr2, the number of secondary particles increased with monomer concentration in the aqueous phase. Moreover, the presence of micelles in the reaction vessel is not the only perquisite for micellar nucleation to occur, a sufficient amount of monomer should be present in the aqueous phase to enhance the radical capture by partially monomer‐swollen micelles. The rate of polymerization increased with the surfactant concentration in the aqueous phase. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3612–3630, 2000 相似文献
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J. H. Kim M. Chainey M. S. El-Aasser J. W. Vanderhoff 《Journal of polymer science. Part A, Polymer chemistry》1992,30(2):171-183
The kinetics of the emulsifier-free emulsion copolymerization of styrene and sodium styrene sulfonate have been examined over a range of comonomer compositions. The rate of polymerization was found to increase dramatically in the presence of small amounts of sodium styrene sulfonate. This increase is attributed to the increased number of particles formed when sodium styrene sulfonate was present and to a gel effect enhanced by ion association. At low concentrations of functional comonomer, where a monodisperse product was obtained, a homogeneous nucleation mechanism of particle generation is proposed. At higher concentrations, broader and then bimodal size distributions were obtained, and this is ascribed to significant aqueous phase polymerization of sodium styrene sulfonate. The water-soluble homopolymer is supposed to act as a locus of polymerization. The occurrence of this aqueous phase side reaction and the generation of secondary particles makes impossible the preparation of highly sulfonated polystyrene latexes by batch or seeded batch emulsion copolymerization. 相似文献
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Unseeded semibatch emulsion polymerization of butyl acrylate (BA) using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator was carried out at the conditions where secondary nucleation was probable. This was achieved by using no emulsifier in the initial reactor charge. The effects of changes in monomer emulsion feed rate, initiator concentration and distribution, emulsifier concentration in the feed, and temperature on the evolution of particle size averages and distribution were investigated. Bimodal particle size distributions (PSD) were obtained for most of the latexes. Inhibition effects were found to be important in the development of PSD. Primary particle formation occurred through micellar nucleation, whereas secondary nucleation probably occurred through homogenous nucleation. The polydispersity index (PDI) of the latexes increased with the decreasing monomer emulsion feed rate. The application of a larger amount of initiator to the reactor charge or using a higher temperature, reduced the formation of secondary particles and resulted in a formation of an unimodal PSD. The overall steady‐state rate of polymerization was found to approach the rate of monomer addition (Rp ≈ Ra ), if the emulsifier concentration in the aqueous phase was appreciable. This is different from the correlation 1/Rp = 1/K + 1/Ra obtained for the BA semibatch process with neat monomer feed. This suggests that different rate expressions can be used for BA semibatch emulsion polymerization at different conditions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 528–545, 2000 相似文献
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M. Nomura H. Ichikawa K. Fujita T. Okaya 《Journal of polymer science. Part A, Polymer chemistry》1997,35(13):2689-2695
The seeded emulsion copolymerizations of styrene and acrylamide were carried out at 50°C using polystyrene latex particles as the seed and potassium persulfate as the initiator, respectively. It was found that the change in the number of seed particles initially charged causes a drastic change in the kinetic behavior of this seeded emulsion copolymerization system: when the number of seed particles initially charged was less than a certain critical value, both styrene and acrylamide started polymerization from the beginning of the reaction. However, when the number of seed particles was higher than this critical value, an apparent induction period suddenly emerged only for acrylamide polymerization, that is, acrylamide did not start polymerization until the styrene conversion exceeded around 75%, while the styrene polymerization started and continued very smoothly from the beginning of the reaction. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2689–2695, 1997 相似文献
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M. Fernndez‐García M. Fernndez‐Sanz E. L. Madruga 《Journal of polymer science. Part A, Polymer chemistry》2004,42(1):130-136
The free‐radical copolymerization of styrene and butyl acrylate has been carried out in benzene at 50 °C. The lumped k p/k parameter (where k p and k t are the average copolymerization propagation and termination rate constants, respectively) has been determined. Applying the implicit penultimate unit model for the overall copolymerization propagation rate coefficient and the terminal unit effect for the overall copolymerization termination rate coefficient and using the homopolymerization kinetic coefficients, we have found good qualitative agreement between the experimental and theoretical k p/k values. The variation of the copolymerization rate in solution with respect to the values previously found in bulk has been ascribed to a chain length effect on the copolymerization termination rate coefficient. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 130–136, 2004 相似文献