Cationic Temperature-Responsive Poly( N -isopropyl acrylamide) Graft Copolymers: from Triggered Association to Gelation
Cationic Temperature-Responsive Poly( N -isopropyl acrylamide) Graft Copolymers: from Triggered Association to Gelation
复制标题
阳离子温度响应型聚（N-异丙基丙烯酰胺）接枝共聚物：从触发缔合到凝胶化
作者：
Liu R
在这项工作中，研究了新型阳离子聚（N-异丙基丙烯酰胺）（PNIPAm）接枝共聚物的水溶液中温度引发的缔合和凝胶形成。使用水性原子转移自由基聚合 (ATRP) 合成了五种共聚物，其中涉及基于季铵化甲基丙烯酸 N,N-二甲氨基乙酯单元 (DMA+) 的大分子引发剂。 PDMA+x-g-(PNIPAmn)y共聚物具有源自大分子引发剂的xandy值； n 的值对应于 PNIPAm 臂长。共聚物溶液在浊点温度（33−34°C）下表现出温度触发的纳米尺寸聚集体的形成。使用变温浊度、流体动力学直径和电泳迁移率测量来研究聚集体。使用 SEM 可以清楚地看到聚集体，并且观察到花状或球形形态。变温电泳迁移率测量表明，聚集体的 zeta 电位随着 DMA+ 含量的增加而增加。对添加 NaNO3 影响的研究表明静电相互作用控制聚集体的尺寸。当共聚物浓度超过 5 wt% 时，浓缩的接枝共聚物溶液表现出温度引发的凝胶化，构建了流体-凝胶相图。研究发现静电相互作用也控制凝胶化温度。发现聚集体尺寸和形成凝胶所需的最小共聚物浓度之间存在相关性。提出了一种温度触发的结构变化导致聚集体（在稀溶液中）或凝胶（在浓溶液中）形成的机制。
In this work temperature-triggered association and gel formation within aqueous solutions of a new family of cationic poly(N-isopropyl acrylamide) (PNIPAm) graft copolymers have been investigated. Five copolymers were synthesized using aqueous atom transfer radical polymerization (ATRP) involving a macroinitiator based on quaternarizedN,N-dimethylaminoethyl methacrylate units (DMA+). The PDMA+x-g-(PNIPAmn)ycopolymers havexandyvalues that originate from the macroinitiator; values forncorrespond to the PNIPAm arm length. The copolymer solutions exhibited temperature-triggered formation of nanometer-sized aggregates at the cloud point temperature, which was 33−34 °C. The aggregates were investigated using variable-temperature turbidity, hydrodynamic diameter, and electrophoretic mobility measurements. The aggregates were clearly evident using SEM and flowerlike or spherical morphologies were observed. Variable-temperature electrophoretic mobility measurements revealed that the zeta potentials of the aggregates increased with DMA+content. A study of the effect of added NaNO3showed that electrostatic interactions controlled the size of the aggregates. The concentrated graft copolymer solutions showed temperature-triggered gelation when the copolymer concentrations exceeded 5 wt %, Fluid-to-gel phase diagrams were constructed. It was found that electrostatic interactions also controlled the gelation temperature. A correlation was found between aggregate size and the minimum copolymer concentration needed to form a gel. A mechanism for the temperature-triggered structural changes leading to the formation of aggregates (in dilute solution) or gels (in concentrated solutions) is proposed.