超声均质微悬浮聚合制备亚微米级聚苯乙烯胶粒

以苯乙烯St为代表性单体,以聚乙烯醇PVA为分散剂,以十六烷HD为助稳定剂,以亚硝酸钠NaNO2为水相阻聚剂,通过基于超声均质化的微悬浮聚合制得了一系列亚微米级聚苯乙烯胶粒。对亚微米级单体液滴的均质化产生及后续聚合过程中分散相尺寸的变化进行了考察。发现超声均质化和高分子分散剂的结合有利于制备粒径小、分布窄的稳定微悬浮液滴,而吸附于液滴表面的高分子分散剂、油相内的助稳定剂及水相中的阻聚剂的协同作用能使聚合过程较好地保持分散相原有的粒径大小及分布。因而通过改变超声均质强度,可较容易地在0.5~3.5μm范围内自由调节胶粒的平均粒径。相对于常规的剪切均质微悬浮聚合,超声均质微悬浮聚合可更好地填补(细)乳液聚合与悬浮聚合在粒径分布范围上的间隙,有望高效、高容量地微胶囊化包裹亚微米级目标内容物。     

微悬浮法制备有机颜料微胶囊中的粒径调控

为调控有机颜料微胶囊的粒径及其分布,在分析微悬浮聚合过程粒径变化的基础上,系统研究了微悬浮聚合工艺(均质化剪切速率、搅拌速率)和配方(有机颜料、分散剂含量)对颜料微胶囊粒径的影响。发现当搅拌速率为250 r·min^-1时,单体液滴的融合和乳胶粒的粘并现象均较少,聚合体系可较稳定地保持均质化单体液滴的尺寸。分散剂磷酸三钙TCP用量对体系稳定性影响明显,但其粒径调控能力有限。均质化强度对微胶囊粒径影响明显,具有较好的调控能力,而颜料含量对微胶囊粒径的影响较少。因而通过聚合工艺和配方的综合调节,可制得一系列颜料含量高、粒径分布窄、粒径可调范围较大的"石榴状"有机颜料微胶囊。     

氯乙烯微悬浮聚合成粒机制探讨

以不同均化方式得到微悬浮分散液,再经微悬浮聚合制备了PVC糊树脂。首先以三氯乙烯为氯乙烯单体的模拟液,研究了十二烷基硫酸钠乳化剂/十六、十八混合醇助稳定剂复合胶束和单体亚微液滴的形成过程,发现复合胶束的形成过程和三氯乙烯溶胀进入复合胶束形成亚微液滴的过程均受扩散动力学控制,延长溶胀时间及施加高速剪切分散可以强化溶胀过程,复合胶束对单体具有"超级溶胀"能力。然后采用搅拌溶胀和高速剪切微悬浮聚合得到PVC乳胶粒子,发现两者形貌相同,而前者粒径略大、分布略宽;延长搅拌溶胀时间,可使粒度分布更接近高速剪切均化微悬浮聚合得到的PVC乳胶粒子的粒度分布。     

化妆品用PMMA微球的制备及应用研究

采用悬浮聚合制备了平均粒径分别为~6μm,~10μm以及~15μm的聚甲基丙烯酸甲酯微球。分别考察了单体用量、均质条件、分散剂用量等因素对聚合稳定性及微球粒径的影响。结果表明单体用量会极大的影响聚合稳定性,单体用量不超过20%时聚合过程稳定。均质条件会影响微球粒径。均质机转速越大,微球粒径越小。分散剂用量对微球粒径影响较小将制备的不同粒径微球进行肤感评价,结果表明粒径为10μm的微球肤感最好。     

氯乙烯SET-DT悬浮聚合动力学和成粒过程的相互关系

以碘仿为引发剂、连二亚硫酸钠/碳酸氢钠为催化体系、聚乙烯醇(PVA)和/或纤维素衍生物(MC)为分散体系,进行氯乙烯单电子转移-蜕化链转移(SET-DT)活性自由基悬浮聚合,采用在线示踪气相色谱法和激光粒度分析系统研究分散剂种类和浓度、搅拌转速等对聚合动力学和单体液滴/聚合物颗粒粒径分布的影响。发现在相同搅拌转速下,以MC为分散剂的氯乙烯聚合速率最大,以PVA为分散剂时反应速率最小;分散剂种类固定时,聚合速率随分散剂浓度增大而增大。SET-DT悬浮聚合过程中,水相连二亚硫酸钠分解产生的自由基向单体液滴的扩散速率与液滴粒径分布和皮膜结构有关,因此聚合成粒过程影响聚合动力学。尽管不同条件下的聚合均经历液-液分散、液滴黏并、树脂颗粒稳定(转化率>30%)等成粒阶段,但各阶段的液滴/颗粒平均尺寸随分散体系和搅拌转速的变化而变化,引起聚合速率变化;采用MC为分散剂得到的PVC树脂皮膜少,有利于水相产生的自由基向单体相的扩散,聚合速率大。     

聚甲基丙烯酸酯高分子微球的研究

通过分散聚合法制各了微米级单分散聚甲基丙烯酸甲酯微球.考察了不同聚合单体浓度、引发剂、稳定剂浓度和分散介质等因素对聚合体系的稳定性、微球粒径及分布的影响.通过研究发现,粒径随着聚合温度、引发剂浓度、单体用量的增加而增加;而随着稳定剂(PVP)的浓度的增大而减小.     

微悬浮法PVC糊树脂的合成研究

采用三氯乙烯作为氯乙烯模拟液,研究主/助乳化剂结构、用量和比例等对分散液滴粒径及粒度分布的影响。采用5 L高压夹套釜进行氯乙烯微悬浮聚合,研究主/助乳化剂结构、用量、比例和水油比对PVC初级粒子平均粒径和粒度分布的影响。发现以十二烷基硫酸钠(SDS)为主乳化剂时分散液滴的尺寸最小,PVC胶乳稳定,粒度分布窄;随着脂肪醇助乳化剂链长的增加,分散液滴尺寸明显减小,十六醇、十八醇或两者的混合醇是氯乙烯微悬浮聚合适宜的助乳化剂;随着十六醇或十六~十八混合醇与SDS用量比的增加,分散液滴和PVC胶乳粒子的尺寸逐渐减小,粒度分布趋窄。微悬浮聚合PVC糊树脂包含粒径范围较宽但呈连续分布的初级粒子,通过主/助乳化剂用量比的改变,可调节PVC初级粒子的平均粒径及粒度分布。     

单分散亚微米级聚合物微球的研究进展

本文综述了单分散亚微米级聚合物微球的自由基聚合主要制备方法,包括分散聚合、RAFT分散聚合、乳液聚合和无皂乳液聚合,讨论了溶剂、引发剂、单体、分散剂、乳化剂、搅拌和温度的选择及其对聚合物微球粒径和单分散性的影响以及粒径控制机理.     

丙烯酰胺反相细乳液聚合

采用反相细乳液法,以白油为连续相,失水山梨醇单油酸酯/聚氧乙烯失水山梨醇单油酸酯为乳化剂,一种聚合物型乳化剂(聚异丁烯琥珀酸酯与山梨醇油酸酯的混合物)作为助稳定剂,通过正交实验确立了基本乳液体系,考察了微乳化工艺中转速变化、乳化剂体系组成、浓度及单体含量对聚合产物稳定性的影响,并研究了不同单体浓度和聚合时间等聚合工艺对微球粒径及分布的影响。结果表明,复合乳化剂含量为3.0%,转速为10 000 r/min下乳化20 min,在单体浓度55%,亲水疏水平衡值(HLB值)为5.5,采用氧化还原引发体系,聚合时间为6 h时,可以得到固含量35%以上、粒径数百纳米的长期稳定的亚微米级聚丙烯酰胺微球乳液。     

棉花球状树脂试制情况

氯乙烯悬浮聚合中,在主分散剂之外,添加一些助分散剂能得到性能良好的树脂。 报告认为,邻苯二甲酸二辛酯是优良的增塑剂,加到聚合体系中,可以改善树脂的增塑性能;硬脂酸盐是稳定剂,对树脂有热稳定效果,而且在聚合过程中有整粒作用。同时添加邻苯二甲酸二辛酯和硬脂酸钡时,硬脂酸钡将复盖在氯乙烯单体液滴的表面,硬脂酸烃基的“围栅效应”促使聚氯乙烯颗粒表     

悬浮聚合法制备磁性微球的粒度分布特性

本文研究了含有微细铁黑颗粒的混合单体悬浮聚合产物的粒度分布特性。分析了分散剂、超声预分散和无机铁黑颗粒对形成粒度多峰分布的影响。结果表明,分散剂是体系中形成小颗粒的主要因素;超声波的预分散作用使悬浮体系的液滴破裂以“腐蚀破碎（erosive breakage)”为主;无机铁黑颗粒由于其表面亲水性,倾向于分布在油性单体液表面,不仅有利于悬浮液滴的“磨蚀破碎”,同时也对分散液滴具有良好的稳定作用。上述因素的共同作用使得聚合产物的粒度呈三峰分布。     

在无机分散剂存在下苯乙烯悬浮聚合宏观成粒的特征

以苯乙烯悬浮聚合为体系,考察羟基磷酸钙(HAP)或HAP与聚乙烯醇(PVA)复合为分散剂体系时,各种因素如分散剂浓度、油水比、搅拌速度等与瞬时液滴大小及分布之间的关系,并分析讨论瞬时液滴分散、合并的过程特征.结果表明,悬浮苯乙烯液滴聚合宏观成粒的特征与分散剂的分散机理无关,仅体现液滴分散、合并的过程特点.当采用分批加分散剂时,实验观察到瞬时液滴大小分布呈由单峰过渡到双峰,再发展成单峰分布的特征,从而找出了以分批加分散剂方式制备窄分布聚合物颗粒的理论依据.     

Facile synthesis of one‐to‐one copy of monomer droplet to latex particle via equilibrium stabilized miniemulsion polymerization

Miniemulsion polymerization has been traditionally used to synthesize latex particles with a high homogenization energy to prepare an oil/water miniemulsion followed by further polymerizations. However, the exact copy of monomer droplets to latex particles depends critically on emulsion formulation, homogenization condition as well as the stability of the miniemulsified droplets after homogenization. In this study, we demonstrated experimentally for the first time that one‐to‐one copy of monomer droplets to latex particles can be synthesized via polymerization of a miniemulsion prepared from a less stringent preparation process including formulation without costabilizer and low homogenization energy. The criterion to obtain narrow size distribution of monomer droplets was established by equilibration of a low energy homogenized emulsion for different keeping time and the bulk homogenized emulsion subsequently phase separated into two layers. Top layer is the polydispersed monomer‐rich phase. The bottom layer is the equilibrium‐stabilized monomer droplet emulsion, in which the size distribution of droplets is narrow. The equilibrium‐stabilized emulsion is stable for days and subsequent polymerization exhibits nearly 100% droplet nucleation. Furthermore, the effect of surfactant/costabilizer and initiator on the one‐to‐one feature for the synthesis of latex particles was investigated in details. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Emulsion polymerization of an epoxy–acrylate emulsion stabilized with polyacrylate. II. Using the results of statistically designed experiments to deduce a possible polymerization mechanism

Epoxy–acrylate composite emulsions such as the one in this study can be used as metal coatings, etc. Many factors can influence the final quality of the product, and it is the aim of this study to highlight some of these factors. Statistically designed experiments were performed to investigate the influence of monomer level, the polymeric dispersant level, epoxy level, and the initiator level on particle size (light scattering), particle size distribution, and fractional conversion. It was found that the monomer level significantly influenced particle size and particle size distribution. The epoxy level and the monomer level influenced fractional conversion significantly. A qualitative model based on these observations is put forward to describe the mechanism of particle formation and polymerization. This model states that the high internal viscosity of the initial dispersed epoxy phase inhibits the formation of smaller particles and accelerates the polymerization rate during the first few minutes of polymerization by inducing a gel effect that inhibits termination and chain transfers of radical species. The addition of a monomer lowers the internal viscosity of the particles and causes them to break up into droplets containing dissolved epoxy, polyacrylate, and monomer. At the same time, radical species inside the smaller droplets can now undergo termination and chain transfer reactions. To confirm this model, polyacrylates of varying molecular masses were synthesized. Variation of the molecular masses of these polyacrylates resulted in variation in the viscosity of the dispersed phase. Polymerizations conducted with the polyacrylates confirmed the model observations. A dispersed phase with a high viscosity results in an increased polymerization rate, larger overall particle size, and a higher mass average molecular mass copolymer compared to lower molecular mass polyacrylates. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 368–381, 2000     

Encapsulation of magnetic particles via miniemulsion polymerization of styrene. II. Effect of some parameters on the polymerization of styrene

Effects of some parameters on the polymerization of Styrene (St) during encapsulation of iron oxide particles via miniemulsion polymerization have been investigated. At the early stage of reaction, polymerization rate increased slightly with the increase of sonicating time, and then it leveled off. The polymerization rate increased with the increase of KPS at the early stage of polymerization, which tendency is analogous to the result of polymerization of St in miniemulsion without the presence of iron oxide particles. The increase of iron oxide not only decreased the polymerization rate but also resulted in poorer monodisperse of the particles when keeping the amount of dispersant constant. The dispersant played an important role in the encapsulation of magnetic particles via miniemulsion polymerization of St. It not only made the iron oxide disperse well in monomer droplets but also led to a much faster polymerization than that of no dispersant in system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Study of the preparation and mechanism of formation of hollow monodisperse polystyrene microspheres by SPG (Shirasu Porous Glass) emulsification technique

In a previous study, it was found that monodisperse polystyrene (PSt) hollow particles can be prepared under special conditions by combining a Shirasu Porous Glass (SPG) emulsification technique and subsequent suspension polymerization process. That is, a mixture of styrene (St), N,N‐dimethylamino ethyl methacrylate (DMAEMA), hexadecane (HD), and initiator N, N′‐azobis(2,4‐dimethylvaleronitrile) (ADVN) was used as the dispersed phase in an aqueous phase containing poly(vinyl pyrrolidone) (PVP), sodium lauryl sulfate (SLS), and water‐soluble inhibitor. The dispersed phase was created by pushing the oil phase through the uniform pores of an SPG membrane into the continuous phase to form uniform droplets. Then, the droplets were polymerized at 70°C. It has been puzzling that hollow microspheres were obtained only when sodium nitrite (NaNO₂) was used as a water‐soluble inhibitor, while one‐hole particles were formed when hydroquinone (HQ) or diaminophenylene (DAP) was used. In this study, the mechanism of formation of the hollow microspheres was verified by measuring the variation of diameter, molecular weight distribution, and monomer conversion, and by observing morphological changes during the polymerization, as well as by changing the type and amount of hydrophilic monomer, and initiator. It was found that the diameter of the oil droplets decreased, and a large amount of secondary new particles formed immediately after polymerization started in the case of NaNO₂. However, there was no such apparent behavior to be observed when HQ or DAP was used. It was determined that the hollow particles formed due to the rapid phase separation between PSt and HD, and as a consequence, a large amount of monomer diffused into the aqueous phase to form the secondary particles. Rapid phase separation confined the HD inside the droplets, a nonequilibrium morphology. On the other hand, one‐hole particles, representing an equilibrium morphology, formed when the phase separation occurred slowly because a lot of monomer existed inside of the droplets to allow mobility of the PSt. The addition of DMAEMA allowed the hollow particles to be formed more easily by decreasing the interfacial tension between the copolymer and aqueous phase. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1530–1543, 2002     

Mechanism of suspension polymerization of uniform monomer droplets prepared by glass membrane (Shirasu Porous Glass) emulsification technique

The mechanism of the unique suspension polymerization of uniform monomer droplets, without coalescence and breakup during the polymerization, was investigated using styrene (S) as a monomer mixed with water‐insoluble hexadecane (HD). The glass membrane (Shirasu Porous Glass, SPG) emulsification technique was employed for the preparation of uniform droplets. Depending on the pore sizes of the SPG membranes (1.0, 1.4, and 2.9 μm), polymer particles of an average diameter ranging from 5.6 to 20.9 μm were obtained with the coefficient of variation (CV) being close to 10%. The role of HD was to prevent the degradation of the droplets by the molecular diffusion process. Sodium nitrite was added in the aqueous phase to kill the radicals desorbed from the droplets (polymer particles), thereby suppressing the secondary nucleation of smaller particles. Each droplet behaved as an isolated locus of polymerization. With the presence of HD, the initial polymerization rate was proportional to 0.24th power of the benzoil peroxide (BPO) concentration. This peculiar behavior as compared with the ordinary suspension polymerization was explained by introducing the assumption that each droplet was composed of isolated compartments (cells) in which active polymeric radicals were dissolved in an S‐rich phase and surrounded by a rather incompatible S/HD (continuous) phase. The average number of radicals in the droplet increased initially due to the separate existence of polymeric radicals in compartments. As the polymerization progressed, the HD‐rich phase gradually separated, eventually forming macrodomains, which were visible by an optical microscope. The phase separation allowed polystyrene chains to dissolve in a more favorable S phase, and the homogeneous bulk polymerization kinetics took over, resulting in a gradual decrease of the average number of radicals in the droplet until the increase of viscosity induced the gel effect. When no HD was present in the droplets, the polymerization proceeded in accordance with the bulk mechanism except for the initial retardation by the entry of inhibiting radicals generated from sodium nitrite in the aqueous phase. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1025–1043, 2000     

Preparation of uniform hollow polystyrene particles with large voids by a glass‐membrane emulsification technique and a subsequent suspension polymerization

Hollow polymer particles with large voids were prepared with styrene (St) as the main component and in the presence of a small amount of N,N′‐dimethylaminoethyl methacrylate (DMAEMA) via a glass‐membrane emulsification technique and a subsequent suspension polymerization. A mixture of the monomer, hexadecane (HD), and N,N′‐azobis(2,4‐dimethylvaleronitrile) as an initiator was used as a dispersed phase (oil phase). By the careful pushing of the dispersed phase through the pores of the glass membrane into the aqueous phase, an emulsion of fairly monodisperse monomer droplets was formed. Then, the polymerization was performed by temperature being elevated to 70°C. The aqueous phase (continuous phase) contained poly(N‐vinyl pyrrolidone) as a stabilizer, sodium lauryl sulfate as a surfactant, Na₂SO₄ as an electrolyte, and sodium nitrite (NaNO₂) as a water‐soluble inhibitor. Results related to the effects of the HD content, DMAEMA, and the composition of the comonomer, including the crosslinker and flexible segment, on the features of the hollow particles were investigated. When the content of DMAEMA was higher than 1.0 wt % based on the total monomer, small, secondary particles were generated in the aqueous phase, but the generation was effectively prevented when DMAEMA was limited to 0.5 wt %. Hollow particles, with an average diameter of around 7 μm, were obtained with an St–DMAEMA system. The void size of the hollow particles was controlled by the HD content. When the HD content was lower (<25 wt % based on the oil phase), unbroken hollow particles were easily obtained. However, they tended to break into halves after drying when the HD content was increased to 50 wt %. A soft segment, lauryl acrylate, and a crosslinker, ethylene glycol dimethacrylate, were added to overcome this problem. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 244–251, 2003