混合官能基之pH敏感型高分子的電荷密度及膨潤行為

Abstract

近年來，pH敏感型材料因為在生物科技、藥學及製藥科技等方面有廣泛的應用而逐漸受到重視。一般來說，這種材料使用了酸性或鹼性官能基團。舉弱酸性pH敏感型高分子為例子，在高pH值的環境下，它們丟出質子，形成帶負電荷的高分子鏈，進而使整體結構膨潤，甚至可以使原本嵌入在內的物質釋放出來；在低pH值的環境下，它們接受質子，形成不帶電的高分子鏈，留住原本嵌入在內的物質。換句話說，電荷密度的改變是pH敏感程度的關鍵。若可以在特定的pH值任意地調控電荷密度並促使膨潤行為產生，將會是一個值得研究的方向。透過混合不同比例的酸性和鹼性官能基團，由於它們會互相抵銷電荷，所以就可以製作出可調控電荷的表面。本研究中，利用這個概念，將含有羧基的甲基丙烯酸 (MAA) 和含有三級胺的N-(3-二甲氨基丙基)甲基丙烯醯胺 (DMAPMA) 藉由自由基聚合法合成出可調控電荷的pH敏感型高分子。使用核磁共振頻譜儀 (NMR) 及X射線光電子光譜儀 (XPS) 鑑定官能基團的比例，並使用靜態光散射 (SLS) 技術中的Debye plot計算出分子量。藉由動態光散射 (DLS) 技術，量測不同pH值下的界面電位及平均水合半徑來代表不同比例官能基團高分子的電荷密度及膨潤行為。根據實驗結果發現，隨著界面電位的數值增加，水合半徑也跟著增加，代表高分子所帶電荷控制其膨潤行為。此外，當環境pH值接近於等電位點時，會觀察到最小的水合半徑。總結來說，透過調控酸性及鹼性官能基團比例，可以製備出可調控電荷的pH敏感型高分子，並可以針對不同的應用去調控可促使膨潤行為的某特定pH值。

In recent years, pH-sensitive materials have drawn attentions owing to their comprehensive applications in biotechnology, medicine and pharmaceutical technology. In general, acidic or basic functional groups are employed in these materials. For instance, weak polyacids, they release protons at higher pH, forming a negatively charged polymer chain which in turn causes the structure to swell and can release cargos embedded within. At lower pH, they accept protons, leading to an uncharged polymer chain and can retain cargos. In other words, the change in charge density is the key to its pH sensitivity and it is desirable to be able to tailor the charge density at a given pH hence the swelling can be triggered at will. By mixing variable ratio of acidic and basic functional groups that cancel the charge of each other, charge-tunable surfaces can be realized. Using this concept, charge-tunable pH-sensitive polymers were synthesized by free-radical polymerization of methacrylic acid (MAA) containing carboxylic group and N-[3-(dimethylamino)propyl] methacrylamide (DMAPMA) containing tertiary amine group in this work. The ratio of functional groups in the synthesized pH-sensitive polymers were determined using Nuclear Magnetic Resonance (NMR) and X-ray Photoelectron Spectrometer (XPS), and the molecular weight was determined using Static Light Scattering (SLS) with Debye plot. The charge density and the swelling behavior of pH-sensitive polymers with different ratios of functional groups were characterized by measuring the surface zeta-potential and mean hydrodynamic radius as a function of pH using Dynamic Light Scattering (DLS). It was found that the hydrodynamic radius increased with the zeta-potential, which indicated the charge of polymer controlled its swelling behavior. Furthermore, when environmental pH was close to the iso-electric point (IEP), minimal hydrodynamic radius was observed. In conclusion, through adjusting the ratio of acidic and basic functional groups, charge-tunable pH-sensitive polymers were prepared and the pH that triggered the swelling can be tailored for desired applications.