Tan Beng H, Ravi P, Tan Lie N, Tam Kam C
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798.
J Colloid Interface Sci. 2007 May 15;309(2):453-63. doi: 10.1016/j.jcis.2007.01.019. Epub 2007 Feb 16.
Emulsion copolymerization of poly(methacrylic acid) and poly(2-(diethylamino)ethyl methacrylate) (PMAA/PDEA) yielded pH-responsive polyampholyte microgels of 200-300 nm in diameter. These microgels showed enhanced hydrophilic behavior in aqueous medium at low and high pH, but formed large aggregates of approximately 2500 nm at intermediate pH. To achieve colloidal stability at intermediate pH, a second batch of microgels of identical monomer composition were synthesized, where monomethoxy-capped poly(ethylene glycol)methacrylate (PEGMA) was grafted onto the surface of these particles. Dynamic light-scattering measurements showed that the hydrodynamic radius, Rh, of sterically stabilized microgels was approximately 100 nm at intermediate pH and increased to 120 and 200 nm at pH 2 and 10, respectively. Between pH 4 and 6, these microgels possessed mobility close to zero and a negative second virial coefficient, A2, due to overall charge neutralization near the isoelectric pH. From the Rh, mobility, and A2, cross-linked MAA-DEA microgels with and without PEGMA retained their polyampholytic properties in solution. By varying the composition of MAA and DEA in the microgel, it is possible to vary the isoelectric point of the colloidal particles. These new microgels are being explored for use in the delivery of DNA and proteins.
聚（甲基丙烯酸）和聚（甲基丙烯酸2-（二乙氨基）乙酯）（PMAA/PDEA）的乳液共聚产生了直径为200 - 300 nm的pH响应型聚两性电解质微凝胶。这些微凝胶在低pH和高pH的水性介质中表现出增强的亲水性行为，但在中间pH时形成了直径约为2500 nm的大聚集体。为了在中间pH实现胶体稳定性，合成了第二批具有相同单体组成的微凝胶，其中单甲氧基封端的聚（乙二醇）甲基丙烯酸酯（PEGMA）接枝到这些颗粒的表面。动态光散射测量表明，空间稳定的微凝胶在中间pH时的流体力学半径Rh约为100 nm，在pH 2和10时分别增加到120和200 nm。在pH 4至6之间，由于在等电点pH附近的整体电荷中和，这些微凝胶的迁移率接近零且第二维里系数A2为负。从Rh、迁移率和A2来看，有和没有PEGMA的交联MAA - DEA微凝胶在溶液中都保留了它们的聚两性性质。通过改变微凝胶中MAA和DEA的组成，可以改变胶体颗粒的等电点。这些新型微凝胶正在被探索用于DNA和蛋白质的递送。
