ABSTRACT

We prepared nano/microgels by precipitation copolymerization of N-isopropylacrylamide (NIPAAm), and one of three different carboxyalkyl methacrylamides [methacryloylamido hexanoic acid (M₅), 8-methacryloylamido octanoic acid (M₇), and 11-methacryloylamido undecanoic acid (M₁₀)], either in the acid forms or as carboxylates (potassium salts). The hydrodynamic diameter (Dh) of the nano/microgels prepared with the carboxylates was smaller (≈100 nm for M₁₀ copolymers), compared to the size of homopolymeric NIPAAm microgels prepared by dispersion polymerization (around 600 nm), indicating that the carboxylates act as surfactants reducing the size of the seeds during the polymerization process. These materials presented a swollen-shrunken transition temperature (T _tr) similar to the T _tr of the homopolymeric NIPAAm microgels, without pH sensitivity. On the other hand, the copolymeric microgels prepared from the acid form of the comonomers have a similar or bigger size than NIPAAm microgels. For these copolymers, the T _tr can be tuned by the type and proportion of acid comonomer used and present pH sensitivity. This is important for biomedical applications such as positive temperature control release. Polyelectrolyte titration demonstrates that the nano/microgels prepared with the carboxylates behave as hard spheres, while the microgels prepared with the weak acid behave as porous materials.

摘要

我们通过沉淀共聚N-异丙基丙烯酰胺（NIPAAm）和三种不同的羧基烷基甲基丙烯酰胺[甲基丙烯酰胺基己酸（M ₅），8-甲基丙烯酰胺基辛酸（M ₇）和11-甲基丙烯酰胺基十一酸（M ₁₀）]，可以是酸形式，也可以是羧酸盐形式（钾盐）。用羧酸盐制备的纳米/微凝胶的流体动力学直径（Dh）较小（对于M ₁₀约为100 nm与通过分散聚合制备的均聚物NIPAAm微凝胶的尺寸（约600 nm）相比，表明羧酸盐充当表面活性剂，可在聚合过程中减小种子的尺寸。这些材料呈现溶胀-收缩转变温度（Ť _TR）类似于Ť _TR的均聚的NIPAAm微凝胶的，不进行pH敏感性。另一方面，由共聚单体的酸形式制备的共聚微凝胶具有与NIPAAm微凝胶相似或更大的尺寸。对于这些共聚物，T _tr可以通过使用的酸共聚单体的类型和比例以及目前的pH敏感性来调整。这对于生物医学应用（例如正温度控制释放）非常重要。聚电解质滴定表明，用羧酸盐制备的纳米/微凝胶表现为硬球，而用弱酸制备的微凝胶表现为多孔材料。