Poly(methacrylic acid)-poly(2-hydroxypropyl methacrylate) (PMAA₅₀-PHPMA₂₃₇) diblock copolymer nanoparticles are synthesized via reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization, which is an example of polymerization-induced self-assembly (PISA). These nanoparticles exhibit complex stimulus-responsive behavior in dilute aqueous solution. They undergo macroscopic precipitation at low pH owing to protonation of the PMAA steric stabilizer. However, adjusting the solution pH above the pK_a of 6.3 for the PMAA block ensures colloidal stability and confers thermoresponsive behavior. The degree of ionization of these anionic stabilizer chains increases at high pH, which leads to increasingly negative zeta potentials as judged by aqueous electrophoresis. Variable temperature dynamic light scattering (DLS) studies indicate the formation of progressively larger nanoparticles at higher temperatures, with TEM images providing evidence for weakly anisotropic nanoparticles at 50 °C. These observations are consistent with variable temperature ¹H NMR spectroscopy studies, which indicate gradual dehydration of the structure-directing PHPMA block. Rheology measurements on a 20% w/w copolymer dispersion indicate a critical gelation temperature of around 10 °C and a gel modulus (G′) of approximately 1000 Pa at 25 °C. Shear-induced polarized light imaging (SIPLI) studies confirm the presence of weakly anisotropic worm-like particles under such conditions.

中文翻译：

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刺激响应的聚（甲基丙烯酸）-聚（甲基丙烯酸2-羟丙酯）二嵌段共聚物纳米粒子的水溶液行为

聚（甲基丙烯酸）-聚（甲基丙烯酸2-羟丙酯）（PMAA ₅₀ -PHPMA ₂₃₇）二嵌段共聚物纳米粒子是通过可逆加成-断裂链转移（RAFT）水分散聚合法合成的，这是聚合诱导自组装的一个例子（PISA）。这些纳米颗粒在稀水溶液中表现出复杂的刺激响应行为。由于PMAA空间稳定剂的质子化作用，它们在低pH下会发生宏观沉淀。但是，将溶液的pH值调整到p K _a以上PMAA嵌段的6.3可以确保胶体稳定性并赋予热响应性。这些阴离子稳定剂链的离子化程度在高pH下会增加，这导致越来越多的zeta负电势（通过水相电泳判断）。可变温度动态光散射（DLS）研究表明，在较高温度下会形成逐渐变大的纳米粒子，而TEM图像可为50°C的弱各向异性纳米粒子提供证据。这些观察结果与可变温度¹ H NMR光谱学研究一致，该研究表明结构导向的PHPMA嵌段逐渐脱水。对20％w / w共聚物分散体的流变学测量表明，临界胶凝温度约为10°C，凝胶模量（G′）在25°C时约为1000 Pa。剪切诱导偏振光成像（SIPLI）研究证实了在这种条件下弱各向异性蠕虫样颗粒的存在。