【作者】 曹志海；

【导师】 单国荣；

【作者基本信息】 浙江大学 ， 化学工艺， 2008， 博士

【摘要】 以细乳液聚合技术为基础,通过伴有水解-缩合反应的甲基丙烯酸3-三甲氧基硅丙酯(MPS)/苯乙烯(St)的共聚反应制备了有机-无机杂化纳米胶囊。该杂化材料兼具高分子和无机材料的优点,且具有囊化的特点,拓宽了材料的应用领域。本论文首先研究了MPS/St细乳液共聚体系中MPS的水解-缩合反应,及MPS对自由基共聚反应、胶乳性能和杂化聚合物微结构的影响;其次,通过研究液核为模板的St细乳液聚合体系,提出界面聚合制备纳米胶囊的机理;最后,将上述研究结果应用于以液核为模板的MPS/St细乳液共聚体系,成功制备胶囊分率高、结构规整的有机-无机杂化纳米胶囊。深入研究了MPS/St细乳液聚合过程中MPS的水解-缩合反应,发现细乳液聚合体系中,水解反应无法避免,主要发生在液滴/水及乳胶粒/水界面上,但MPS的缩合反应能被有效抑制。pH是影响MPS水解-缩合反应的重要因素,pH为3.9的体系,所有MPS参与水解-缩合反应;pH为9.2的体系,MPS的水解-缩合程度高,但有少量MPS未参与水解-缩合反应。水解-缩合产物在乳胶粒表面聚集,形成静电立构层,影响水相和乳胶粒相自由基的交换。过硫酸钾(KPS)引发的体系,在反应中后期,共聚速率及St消耗速率均随MPS质量分率增加而下降;偶氮二异丁腈(AIBN)体系,动力学受静电立构层影响较小。pH值也会影响自由基共聚反应,pH为3.9的体系,硅羟基电离程度低,对自由基的吸附速率影响小;pH为9.2的体系,硅羟基电离程度高,使自由基吸附速率下降。MPS/St细乳液共聚体系乳胶性能受pH值、MPS质量分率、引发剂种类及乳化剂浓度影响。中性条件下,AIBN引发体系的乳胶粒稳定性好,KPS引发体系的乳胶粒稳定性稍差;MPS质量分率增加,乳胶粒稳定性下降;pH=3.9和9.2的体系,乳胶粒易聚并,但所得产品仍为乳液。乳化剂在乳胶粒表面吸附面积随MPS用量增加而增加,随十二烷基硫酸钠(SDS)用量增加下降,AIBN引发得到的乳胶粒表面的吸附面积小于KPS引发得到的乳胶粒。FTIR及DSC结果证实MPS以自由基共聚方式接入聚合物链。从热力学角度预测聚苯乙烯-正辛烷-乳化剂水溶液三相体系的热力学平衡形态,结果显示,不含乳化剂的体系纳米胶囊为热力学稳定形态,而含乳化剂的体系以聚合物为核、油相为壳的粒子形态成为热力学稳定形态。向以液核为模板的St细乳液聚合体系引入N-异丙基丙烯酰胺(NIPAM)和二乙烯基苯(DVB),使齐聚物自由基锚定在油水界面,实现界面聚合,能得到胶囊结构完整、分率高的产品。并研究了NIPAM用量、DVB用量和油相单体质量分率对乳胶粒最终形态的影响。发现只有同时添加适量NIPAM和DVB才能显著提高纳米胶囊分率。热力学分析发现,MPS/St共聚物-HD-乳化剂水溶液三元体系,随共聚组成及乳化剂浓度变化可形成“油包聚合物型”核-壳粒子或半球形粒子等形态。因此仍需采用界面细乳液聚合制备有机-无机杂化纳米胶囊。详细研究了以液态烃为模板,MPS/St细乳液聚合体系液滴形成机理、成核方式、外加交联剂体系和pH控制体系纳米胶囊形成机理及影响因素。初始液滴尺寸分布宽的体系,因部分模板化合物流失,降低芯材包覆效率。采用水溶性低的模板化合物、提高油相单体分率、增加乳化剂浓度及加入NIPAM均能改善初始液滴尺寸分布。本实验采用的5～10 mmol/L的乳化剂浓度范围内,不会出现胶束成核。单体质量分率超过50%的体系,才会出现均相成核。通过调节体系pH值,用MPS水解-缩合反应量调控乳胶粒形态。弱酸或弱碱体系、碱性条件下提高MPS质量分率、添加适量DVB和NIPAM均能提高纳米胶囊分率。改变SDS用量和油相单体质量分率可调节纳米胶囊尺寸及尺寸分布。更多还原

【Abstract】 The organic-inorganic hybrid nanoparticles and nanocapsules were elaborated via miniemulsion copolymenzation of styrene （St） andγ-methacryloxypropyltrimethoxysilane （MPS） in which the free radical copolymenzation of vinyl groups is accompanied with the hydrolysis and condensation of MPS. The hybrid materials embody the excellent properties of polymers and inorganic materials, and therefore the applications of this kind of materials are extended in more and more fields, such as coating, catalyst, biology, medicine and cosmetics. In this thesis, the kinetics, the reaction mechanism, the colloidal properties of latex particles, and the microstructure of hybrid copolymers in the miniemulsion copolymerization of MPS and St were investigated, as well as the formation mechanism and determining factors for the synthesis of polymeric or organic-inorganic hybrid nanocapsules via interfacial copolymerization in miniemulsion by using an oily template.Kinetic experiments were carried out to analyze the effects of the MPS weight content, the nature and amount of initiator, and the surfactant concentration on the copolymerization rate. At low conversions, an increase in the MPS concentration led to an increase in the copolymerization rate due to the higher MPS propagation rate coefficient and its higher water solubility, compared to St. The copolymerization rate and the St polymerization rates decreased at higher conversions presumably due to the formation of a silane-rich interface near the particle surface which decreased the rate at which oligomers could undergo entry. The kinetics of the miniemulsion polymerization reaction performed in the presence of 2, 2’-azobis（isobutyronitrile） （AIBN） supports this hypothesis. As the radicals were mainly produced in the oil phase, the overall kinetic process was no longer influenced by the presence of the silane monomer. In the case of potassium persulfate （KPS）, the copolymerization rate was found to be nearly independent of the amount of initiator while it was strongly influenced by the surfactant concentration.Increasing the surfactant concentration led to an increase in the rate of hydrolysis indicating that hydrolysis was taking place at the particles/water interface. The rate of hydrolysis was moderate under neutral conditions but increased rapidly at high and low pH. The siloxane oligomers formed under basic or neutral conditions had an influence on the kinetics process which is presumably related to differences in oligomers architecture. Premature crosslinking could be avoided under neutral conditions and minimized in basic conditions even for a high initial MPS weight content.The properties of latex particles were investigated in terms of the suspension pH, the MPS weight content, the nature of initiator, and the sodium dodecyl sulfate （SDS） concentration. In contrast to neutral conditions, the initial miniemulsion with a smaller droplet size was obtained under basic and acidic conditions. As the polymerization proceeded, the particle size showed a much rapider increase under acidic and basic conditions than that of neutral conditions. Under neutral conditions, the latex particles in the system initiated by AIBN showed a better colloidal stability than that of the system initiated by KPS. The results of FTIR and DSC indicated that the incorporation of MPS in the polymer chains was mainly via free radical copolymerization.According to the thermodynamic analysis, the morphology of nanocapsules is not the favorite for the ternary system of polystyrene/octane/aqueous solution of SDS. However, polymeric nanocapsules with crosslinked shells could be elaborated by interfacial miniemulsion copolymerization of styrene, N-isopropylacrylamide （NIPAM）, and divinylbenzene （DVB） through encapsulation of a hydrocarbon in one step. In this process, NIPAM and DVB played key roles in inducing the interfaces of the nanodroplets to be the loci of polymerization. FTIR and solid-state ¹³CNMR spectroscopic analyses have confirmed that NIPAM molecules were incorporated into the shell copolymers. An investigation of the influence of the amount of DVB on the formation of nanocapsules in the presence of NIPAM has further confirmed that the nanocapsules are formed by an interfacial miniemulsion polymerization mechanism. An increase in the monomer content of the oil phase is detrimental to the formation of nanocapsules.Although the morphology of nanocapsules was not the most favorable state for the ternary system of poly（MPS-co-PS）/Hexadecane （HD）/aqueous solution of SDS, the organic-inorganic hybrid nanocapsules were elaborated by interfacial copolymerization of St, MPS, NIPAM and DVB （optional） in miniemulsion under different pH conditions. It has been shown that the droplet size and droplet size distribution of the miniemulsion were extremely influenced by the water solubility of the oil phase, the monomer content, surfactant concentration and NIPAM amount. Smaller droplets with a relatively narrow size distribution could be prepared by introducing a higher amount of monomer, by using HD as template or by increasing the surfactant concentration.According to DLS analysis, most of the large droplets originally present in the octane and （to a lesser extent） n-Hexadecane （HD） miniemulsions disappeared during polymerization leading to nanocapsules with a relatively narrow size distribution. We indeed showed that micellar nucleation could be neglected in our systems with 5～10 mmol/L aqueous solution of SDS. Homogenous nucleation only appeared in the system with high monomer contents.The morphology of latex particles could be controlled by manipulating the hydrolysis and condensation degree of MPS via changing the pH value of suspension. The portion of nanocapsules could be improved by increasing or decreasing pH value from the neutral condition, increasing the MPS weight content under basic condition, and introducing a suitable amount of crosslinker and NIPAM. The size of nanocapsules could be tuned by changing the SDS concentrations and monomer weight content in oil phase.更多还原