Charge Density and Swelling Behavior of pH-sensitive Polymers with Mixed Functional Groups

• Main Authors: Shu-Min Yang, 楊舒閔
• Other Authors: 薛景中
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/p7s2z6

碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 107 === 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.