Block copolymers having stimuli-responsive properties are gaining impetus in the design of drug and gene delivery systems for therapeutic purposes. Thermoresponsive polymers are particularly interesting due to the ease of control over their solution behavior in aqueous media. The fine tuning of the lower critical solution temperature (LCST) of such polymers is necessary to achieve a successful drug delivery. In this work, the thermoresponsive properties of block copolymers based on a bile acid are studied in aqueous media to determine the factors affecting the LCST. Poly(allyl glycidyl ether) (PAGE) and poly(ethylene glycol) (PEG) blocks were grafted from a cholic acid (CA) core to yield star-shaped block copolymers with 4 arms. The PAGE block was further functionalized to bear pendant amine groups. The addition of amine groups may be expected to improve the hydrophilicty of the polymers, but the functionalized polymers showed pronounced thermoresponsive properties and aggregation under physiological conditions. It is thus necessary to understand the changes of their solution properties for a better design of such polymers for drug delivery applications. In this work, we studied the effects of PEG length and of the amine groups on the LCST behavior in water at various salt concentrations. A shorter PEG chain of 21 repeat units shows a LCST of 16 °C, whereas a longer PEG of 41 repeat units failed to show thermoresponsiveness up to 80 °C and at concentrations up to 50 mg/mL. Functionalizing the allyl groups increased the LCST of the polymers. A salting-out effect was observed by a decrease in LCST and the presence of salt also promoted precipitation of the nanoparticles.

具有刺激响应特性的嵌段共聚物在用于治疗目的的药物和基因递送系统的设计中获得了推动力。由于在水性介质中易于控制它们的溶液行为，热响应聚合物特别令人感兴趣。此类聚合物的较低临界溶解温度 (LCST) 的微调对于实现成功的药物递送是必要的。在这项工作中，研究了基于胆汁酸的嵌段共聚物在水性介质中的热响应特性，以确定影响 LCST 的因素。聚（烯丙基缩水甘油醚）（PAGE）和聚（乙二醇）（PEG）嵌段从胆酸（CA）核接枝得到具有 4 个臂的星形嵌段共聚物。PAGE 嵌段被进一步官能化以带有侧链胺基团。胺基团的加入有望提高聚合物的亲水性，但功能化聚合物在生理条件下表现出明显的热响应特性和聚集。因此，有必要了解其溶液特性的变化，以便更好地设计用于药物输送应用的此类聚合物。在这项工作中，我们研究了 PEG 长度和胺基团对不同盐浓度下水中 LCST 行为的影响。21 个重复单元的较短 PEG 链显示 16 °C 的 LCST，而 41 个重复单元的较长 PEG 在高达 80 °C 和高达 50 mg/mL 的浓度下未能显示热响应性。使烯丙基官能化增加了聚合物的LCST。