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 polyelectrolytes 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 polyelectrolytes were determined using Nuclear Magnetic Resonance (NMR) and the molecular weight was determined using Static Light Scattering (SLS) with Debye plot. The charge density and the swelling behavior of polyelectrolytes 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, with increasing loading of methacrylic acid, the pH where the polymer swelled systematically increased and the surface showed more negative zeta-potential at a given pH. On the other hand, increasing loading of amine groups let the polymer swell at lower pH and higher iso-electric point. In other words, through adjusting the ratio of acidic and basic functional groups, charge-tunable polyelectrolytes were prepared and the pH that triggered the swelling can be tailored for desired applications.

Charge density and swelling behavior of pH-sensitive polymers with mixed functional groups

2019 Spring National Meeting

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