迷你乳化聚合製備奈米複合乳膠顆粒PS/Fe3O4，P(AA-SA)/ZnO 及PMMA-b-PBA — 成核機制，形態控制及動力分析

Abstract

複合材料是指將兩種不同性質的材料結合在一起，形成一種性質更好的新材料，已經被廣泛使用在軍事、航空、建築、運動器材等相關領域。本論文為研究以迷你乳化聚合合成奈米複合乳膠顆粒及高分子團聯共聚物，並探討反應機制及其功能應用。論文內容共分為三大部分。第一部份使用oil in water (O/W) 迷你乳化聚合製備 聚(苯乙烯)/四氧化三鐵 複合乳膠顆粒。第二部份使用water in oil (W/O) 迷你乳化聚合製備 聚(丙烯酸-丙烯酸鈉)/氧化鋅 複合乳膠顆粒。第三部分以活性自由基聚合製備 聚(甲基丙烯酸甲酯)-聚(丙烯酸丁酯) 團聯共聚物。 第一部份包含第二、三章。第二章中的合成方法分兩步驟。首先使用共沈澱法合成四氧化三鐵奈米粒子，再以月桂酸進行表面處理，使得改質後的四氧化三鐵表面為疏水。在第二步驟，將含四氧化三鐵及共同安定劑的單體液滴以均質乳化程序分散於水相後，再藉著水溶性的起始劑(KPS)或油溶性的起始劑(AIBN)起始反應，進行迷你乳化聚合反應，最後得到一磁性複合顆粒。過程中將討論反應組成對反應動力、複合顆粒粒徑分佈、成核機制及形態的影響。 第三章的合成方法分成三步驟。先利用共沈澱法合成四氧化三鐵奈米粒子，接著進行月桂酸與十二烷基硫酸鈉的雙重處理，以得到帶負電的穩定的四氧化三鐵懸浮水溶液。在第二步驟則是先以低均質能量製備不安定的迷你乳液，靜置一天使單體的交換到達平衡。再取下層較安定的迷你乳液進行反應，此時得到的乳膠粒子將完全是從單體液滴原位聚合而來，且其粒徑分佈相當狹窄。最後一步驟將上述四氧化三鐵懸浮水溶液與乳膠顆粒混合，利用異質凝聚法即可得到磁性複合顆粒。過程中將討論各項反應組成，對此種此種新型迷你乳液之成核機制及粒徑分佈的影響。除此，也將使用全分子模擬探討有機、無機粒子大小及其表面電性對複合顆粒形態的影響，並與實驗結果相互驗證。 第二部份包含第四、五章。第四章中以W/O迷你乳化聚合法，利用環己烷為溶劑。過硫酸銨(APS)和偏亞硫酸鈉(SMBS)當作氧化還原起始劑在0-5oC下進行聚合反應合成 聚(丙烯酸-丙烯酸鈉) 乳膠顆粒，以減少單體溶在環己烷的比例。並探討共同介面安定劑的種類及量對迷你乳液的安定性、乳膠顆粒形態、乳膠顆粒成核機制的影響。所合成乳膠顆粒的pKa及其在酸鹼緩衝上的應用也在此研究中做深度探討。第五章則是第四章的延續實驗，引入了經油酸改質的奈米氧化鋅粒子，使其與聚(丙烯酸-丙烯酸鈉)形成複合顆粒。氧化鋅不但是兩性物質也具有光觸媒及紫外光遮蔽的效果，除了原本的酸鹼緩衝功能，此複合顆粒的應用面將更加廣泛。本章中探討了聚(丙烯酸-丙烯酸鈉)/氧化鋅 的合成機制、形態、酸鹼緩衝及紫外光吸收性質。 第三部份包含第六章。1,1-二苯基乙烯(DPE) 被利用來控制甲基丙烯酸甲酯的活性自由基聚合，但是不論改變1,1-二苯基乙烯的量、起始劑的量、反應溫度(但小於95oC)，分子量都不隨單體轉化率提高而增加，反而都幾乎維持著定值。於是我們提出了一個活性聚合反應動力模型嘗試去解釋此種現象，並與實驗數據比較以估計相關的速率常數，發現這是因為k2的速率常數太小，也就是DPE capped dormant chains重新活化的反應速率太慢，造成分子量無法繼續成長。為了增加k2，聚合反應溫度提高至135oC，證實了高分子鏈的分子量可以隨轉化率增加而繼續成長，表現出活性聚合反應的特性，再輔以預熱處理，讓所有的起始劑都在預熱階段分解，就可以成功製備窄分子量分佈的高分子，並在反應的過程中都只觀察到單峰的分子量分佈，而不會有過渡的雙峰分子量分佈GPC圖譜。最後利用DPE-containing PMMA當巨起始劑，成功的用兩種聚合方法(均相聚合及迷你乳化聚合)製備 聚(甲基丙烯酸甲酯)-聚(丙烯酸丁酯) 團聯共聚物，並探討引入溶劑的量及聚合方法對反應速率、活性自由基聚合控制效果、分子量及其分佈之影響。

Composite materials were made from two or more constituent materials with different chemical or physical properties and have been demonstrated an enhanced performance. It has been widely applied in many fields, such as military hardware, aviation, architecture and fitness equipment. In this work, composite latex particles and block copolymers were synthesized via miniemulsion polymerization. The reaction mechanisms and related applications were investigated. This research was divided into three parts. The objective of the first part was to prepare PS/Fe3O4 composite latex particles by oil in water (O/W) miniemulsion polymerization. The objective of the second part was to prepare P(AA-SA)/ZnO composite latex particles by water in oil (W/O) miniemulsion polymerization. The objective of the third part was to synthesize PMMA-b-PBA block copolymers via controlled/living radical polymerization. In the first part, there were two synthesis pathways to prepare PS/Fe3O4 nano composite latex particles. The first pathway contained a two-step process. First, the Fe3O4 nanoparticles were prepared by a coprecipitation method followed by the surface treatment with lauric acid. Hence, the surface modified Fe3O4 was hydrophobic in nature. In the second step, the monomer droplets containing Fe3O4 and costabilizer were dispersed in water with surfactant by ultrasonication. As the miniemulsion polymerization was initiated by water-soluble initiator, potassium persulfate (KPS), or oil-soluble initiator, 2,2'-azobisisobutyronitrile (AIBN), magnetic composite latex particles could be obtained. The influences of initial formulation on the monomer conversion, size distributions of monomer droplets and latex particles, nucleation mechanism, and morphology of composite particles were investigated in depth. Another synthesis pathway contained a three-step process. On the first step, the Fe3O4 dispersion was prepared by a coprecipitation method followed by the surface treatment with lauric acid and sodium dodecyl sulfate (SDS). On the Second step, the one-to-one copy of monomer droplets to latex particles could be synthesized via polymerization of an equilibrium stabilized miniemulsion prepared from a less stringent preparation process. The size distribution of obtained latex particles was relatively narrow. On the third step, by mixing the Fe3O4 dispersion with latex particles, the magnetic composite latex particles could be fabricated from heterocoagulation. Moreover, an all-atom molecular dynamics simulations were employed to explore the influences of sizes and surface polarity of polymer and inorganic particles on the morphology of composite latex particles. The simulation results were in agreement with our experimental results. In the second part, P(AA-SA) latex particles were synthesized via W/O miniemulsion polymerization. In order to minimize the monomer dissolving in continuous phase, cyclohexane, the polymerization was carried out in the presence of ammonium persulfate/sodium metabisulfite (APS/SMBS) redox initiators at 0-5oC. The influences of costabilizer on the stability of miniemulsion, its morphology and nucleation mechanism were studied. The pKa and pH regulation capacity of P(AA-SA) latex particles synthesized in this work were investigated in depth. Furthermore, the ZnO nanoparticles were fabricated by a hydrothermal synthesis method in ethanol followed by oleic acid surface modification for dispersing the nanoparticles in cyclohexane. Based on our previous experimental procedure of synthesizing P(AA-SA) latex particles, P(AA-SA)/ZnO composite particles could be fabricated by introducing modified ZnO nanoparticles into continuous phase. ZnO was not only amphoteric substance but also owned an excellent performance in photocatalyst and UV shielding. The applications of P(AA-SA)/ZnO composite particles were various besides pH regulation. The reaction mechanism, morphology, pH regulation capacity and UV/Vis absorbance properties of composite latex particles were examined. In the third part of this work, 1,1-diphenylethene (DPE) was employed to control the living free radical polymerization of MMA. When the reaction temperature was low (less than 95oC), the molecular weight of synthesized polymer remained almost a constant throughout the reaction time regardless of changing the amounts of DPE and initiator. A living polymerization kinetic model was established and compared with our experimental results. The kinetic rate constants involved in the DPE mechanism were estimated. The rate constant k2, corresponding to the reactivation reaction of the DPE- capped-dormant chains, was found to be very small, that accounted for the result of a constant molecular weight of polymer synthesized throughout the polymerization. In order to increase k2, the polymerization temperature was increased to 135oC, and the molecular weight of polymers increases with conversion, demonstrating the living nature of DPE mechanism. In addition, by using a preheating treatment, all the initiators dissociated into radicals at the very beginning of the polymerization. Then the synthesized polymers with narrow molecular weight distribution could be prepared successfully. From the trace of GPC diagram, a unimodal rather than bimodal molecular weight distribution was observed throughout the polymerization. Finally, PMMA-b-PBA block copolymers were synthesized by two polymerization methods (homogeneous polymerization and miniemulsion polymerization) using DPE-containing PMMA as a macroinitiator. The influences of solvent and polymerization methods on the polymerization rate, controlled living character, molecular weight (Mn) and molecular weight distribution (PDI) throughout the polymerization were studied and discussed.