We report the synthesis of poly(N-(2-acryloyloxyethyl)pyrrolidone)-poly(4-hydroxybutyl acrylate) (PNAEP₈₅-PHBA_x) diblock copolymer nano-objects via reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 4-hydroxybutyl acrylate (HBA) at 30 °C using an efficient two-step one-pot protocol. Given the relatively low glass transition temperature of the PHBA block, these nano-objects required covalent stabilization prior to transmission electron microscopy (TEM) studies. This was achieved by core crosslinking using glutaraldehyde. TEM analysis of the glutaraldehyde-fixed nano-objects combined with small-angle X-ray scattering (SAXS) studies of linear nano-objects confirmed that pure spheres, worms or vesicles could be obtained at 20 °C in an acidic aqueous solution by simply varying the mean degree of polymerization (x) of the PHBA block. Aqueous electrophoresis, dynamic light scattering and TEM studies indicated that raising the dispersion pH above the pK_a of the terminal carboxylic acid group located on each PNAEP chain induced a vesicle-to-sphere transition. ¹H NMR studies of linear PNAEP₈₅-PHBA_x nano-objects indicated a concomitant increase in the degree of partial hydration of PHBA chains on switching from pH 2-3 to pH 7-8, which is interpreted in terms of a surface plasticization mechanism. Rheological and SAXS studies confirmed that the critical temperature corresponding to the maximum worm gel viscosity could be tuned from 2 to 50 °C by adjusting the PHBA DP. Such tunability is expected to be useful for potential biomedical applications of these worm gels.

中文翻译：

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变形刺激响应双嵌段共聚物纳米物体的合成及水溶液性质

我们报告了聚（N-（2-丙烯酰氧基乙基）吡咯烷酮）-聚（丙烯酸4-羟基丁酯）（PNAEP ₈₅ -PHBA _x) 使用高效的两步一锅法，在 30°C 下通过丙烯酸 4-羟基丁酯 (HBA) 的可逆加成-断裂链转移 (RAFT) 水分散聚合制备二嵌段共聚物纳米物体。鉴于 PHBA 块的玻璃化转变温度相对较低，这些纳米物体在透射电子显微镜 (TEM) 研究之前需要共价稳定。这是通过使用戊二醛的核心交联来实现的。戊二醛固定纳米物体的 TEM 分析结合线性纳米物体的小角 X 射线散射 (SAXS) 研究证实，可以在 20 °C 的酸性水溶液中通过简单地获得纯球体、蠕虫或囊泡改变平均聚合度 ( x) 的 PHBA 块。水性电泳、动态光散射和 TEM 研究表明，将分散体 pH 值提高到位于每个 PNAEP 链上的末端羧酸基团的 p K _a以上会诱导囊泡到球体的转变。线性 PNAEP ₈₅ -PHBA _{x 的}¹ H NMR 研究纳米物体表明 PHBA 链的部分水合程度在从 pH 2-3 切换到 pH 7-8 时随之增加，这被解释为表面增塑机制。流变学和 SAXS 研究证实，通过调整 PHBA DP，可以将对应于最大蠕虫凝胶粘度的临界温度从 2 调整到 50°C。这种可调性有望用于这些蠕虫凝胶的潜在生物医学应用。