聚苯乙烯/黏土奈米複合材料熱性質之研究

Abstract

蒙托土應用於高分子奈米複合材料上，改善了高分子的物理性質，例如：熱穩定性、機械性質、阻氣性，尺寸安定性等。這些物理性質改善的程度取決於蒙托土在高分子基材中分散的程度，分散的程度愈好性質提升愈顯著，反之則不然。本篇論文分成三部份，主要探討不同插層劑對於奈米複合材料熱性質的影響。 1. 我們使用乳化聚合的方法製備聚苯乙烯/黏土奈米複合材料，奈米複合材料在3wt％的黏土含量下達到脫層結構。我們使用兩種不同的插層劑改質黏土：POSS（Polyhedral Oligomeric Silsesquioxane）與CPC（Cetylpyridinium chloride）。插層劑預先插層到分散於水中的黏土後再進行乳化聚合反應，雖然POSS插層後黏土的層間距離較CPC插層後的層間距離小，但聚苯乙烯與POSS互容性較佳，所以易使黏土達到脫層結構，而CPC則反之。紅外線光譜儀分析進一步確認POSS成功插層進入黏土層間，X光繞射儀（XRD）與穿透式電子顯微鏡（TEM）觀察黏土在高分子基材中分散的程度，POSS改質黏土之奈米複合材料達到脫層結構（exfoliated），CPC改質黏土之奈米複合材料達到插層結構（intercalated）。在相同的聚合條件下奈米複合材料之聚苯乙烯分子量較純的聚苯乙烯分子量小，有添加黏土的聚苯乙烯之玻璃轉移溫度（Tg）較純的聚苯乙烯高8℃且熱裂解溫度高21℃。POSS分子的存在於黏土中增加其高分子的的熱穩定性。 2. 我們合成APB插層劑並且使用乳化聚合的方法製備聚聚苯乙烯/黏土奈米複合材料。我們使用兩種不同的插層劑改質黏土：磷鹽（APP）與胺鹽（APB）。將黏土預先在水中分散後再用插層劑進行插層。我們預期APB插層劑具有金剛烷官能基會比具有磷官能基有較佳的熱穩定性，我們使用X光繞射儀與穿透式電子顯微鏡觀察奈米複合材料的結構與分散情形。APB與APP改質黏土之奈米複合材料其結構均達到脫層。在相同的聚合條件下奈米複合材料的分子量比純的聚苯乙烯些微低。使用熱機械分析儀所測之熱膨脹係數（CTE），APB與APP改質黏土之奈米複合材料之熱膨脹係數較純的聚苯乙烯低44~45％。在奈米複合材料中之聚苯乙烯的玻璃轉移溫度較純的聚苯乙烯高並且熱裂解溫度也有提升的趨勢。所以，黏土存在於聚苯乙烯中增加其聚苯乙烯之熱穩定性。 3. 我們使用乳化聚合的方法製備聚苯乙烯/黏土奈米複合材料。奈米複合材料在3wt％的黏土含量下達到脫層的結構，我們使用兩種插層劑來改質黏土：CPC（cetylpyridinium chloride）與CPC套上環糊精錯合物，聚合反應前將每種插層劑預先在水中進行插層於黏土層間。使用X光繞射儀、13C 核磁共振光譜儀、1H核磁共振光譜儀與熱重量損失儀來描述其CPC套上α-環糊精錯合物結構與性質。CPC套上α-環糊精錯合物用X光繞射光譜指出α-環糊精存在於黏土層間。錯合物之13C 核磁共振光譜儀指出CPC鏈段藉由α-環糊精在黏土間形成通道，錯合物之1H 共振光譜儀測得之光譜指出錯合物之化學計量比為1：2（一個CPC分子套兩個α-環糊精）。熱重量損失儀所測得之結果指出CPC套上α-環糊精相較於CPC具有較高的熱穩定性，我們使用X光繞射光譜儀（X-ray diffraction）與穿透式電子顯微鏡（transmission electron microscopy）觀察奈米複合材料的結構與分佈情形。在奈米複合材料中的聚苯乙烯之玻璃轉化溫度較純的聚苯乙烯高6℃，其熱裂解溫度高33℃。CPC套上α-環糊精改質黏土其增加聚苯乙烯之熱穩定性之效率比CPC改質黏土高。

Nanoclay-filled polymeric systems offer the prospect of greatly improving many of the properties of their mother polymers. In the recent literature, there have been reports of nanoclay-filled polymeric systems that display significant improvements in tensile and thermal properties, heat distortion temperature, and resistance to flammability and reduced permeability to small molecules and reduced solvent uptake. A common observation emerging from these studies is that the magnitude of improvement depends strongly on the state of dispersion of the clay layers in the polymer matrix. The experiment work in this dissertation was divided into three areas： 1. We have prepared polystyrene/clay nanocomposites using an emulsion polymerization technique. The nanocomposites were exfoliated at up to a 3 wt % content of pristine clay relative to the amount of polystyrene (PS). We used two different surfactants for the montmorillonite: the aminopropylisobutyl polyhedral oligomeric silsesquioxane (POSS) and the ammonium salt of cetylpyridinium chloride (CPC). Both surfactants can intercalate into the layers of the pristine clay dispersed in water prior to polymerization. Although the d spacing of the POSS-intercalated clay is relatively smaller than that of the CPC-intercalated clay, PS more easily intercalates and exfoliates the POSS-treated clay than the CPC-treated clay. IR spectroscopic analysis further confirms the intercalation of POSS within the clay layers. We used X-ray diffraction (XRD) and transmission electron microscopy (TEM) to characterize the structures of the nanocomposites. The nanocomposite prepared from the clay treated with the POSS containing surfactant is exfoliated, while an intercalated clay was obtained from the CPC-treated surfactant. The molecular weights of polystyrene (PS) obtained from the nanocomposite is slightly lower than the virgin PS formed under similar polymerization conditions. The value of Tg of the PS component in the nanocomposite is 8 °C higher than the virgin PS and its thermal decomposition temperature (21 °C) is also higher significantly. The presence of the POSS unit in the MMT enhances the thermal stability of the polystyrene. 2. We synthesized intercalation agent APB and prepared polystyrene/clay nanocomposites using an emulsion polymerization technique. We used two different intercalation agents to treat clay：the phosphonium salt（APP）and the ammonium salt（APB）.We expected that the intercalation agent APB containing rigid adamantane group also has high thermal stability besides phosphonium group. The molecular weights of polystyrene（PS） obtained from the nanocomposites is slightly lower than the virgin PS formed under similar polymerization conditions. The coefficient of thermal expansion（CTE） was obtained from thermomechanical analysis. A 44~55 ％ decrease of CTE is observed for APB- and APP-intercalated clay nanocomposites relative to pure PS. 3. We have prepared polystyrene/clay nanocomposites using an emulsion polymerization technique. The nanocomposites were exfoliated at 3wt% content of pristine clay relative to the amount of polystyrene (PS). We employed two surfactants for the montmorillonite: cetylpyridinium chloride (CPC) and the CPC/α-CD inclusion complex. Prior to polymerization, each surfactant intercalates into the layers of the pristine clay dispersed in water. The inclusion complex was characterized by X-ray diffraction, 13C CP/MAS NMR spectra, and 1H NMR spectroscopy, and TGA. X-Ray powder patterns of the CPC/α-CD complex indicate that the α-CDs units form channels. The 13C CP/MAS NMR spectrum of the complex suggests that a CPC chain is included in the channel formed by the α-CDs. The 1H NMR spectra of the complexes indicate that the stoichiometry of the complexes is 1:2 (i.e.,one CPC molecule and two α-CD units). The TGA reveals that the inclusion complex has higher thermal stability relative to the virgin CPC. We employed both X-ray diffraction (XRD) and transmission electron microscopy (TEM) to characterize the structures of the nanocomposites. The value of Tg of the PS component in the nanocomposite is 6 °C higher than that of the virgin PS and its thermal decomposition temperature is 33 °C higher. The CPC/α-CD-treated clay is more effective than is virgin CPC-treated clay at enhancing the thermal stability of polystyrene.