Programmed thermodynamic formation and structure analysis of star-like nanogels with core cross-linked by thermally exchangeable dynamic covalent bonds
Programmed thermodynamic formation and structure analysis of star-like nanogels with core cross-linked by thermally exchangeable dynamic covalent bonds
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DOI：
10.1021/ja075447n
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发表时间：
2007-10-31
影响因子：
15
通讯作者：
Takahara, Atsushi
中科院分区：
文献类型：
--
作者：
Amamoto, Yoshifumi;Higaki, Yuji;Takahara, Atsushi
对侧链中具有可热交换动态共价键的设计二嵌段共聚物进行了星状纳米凝胶的程序热力学形成，并对纳米凝胶进行了结构分析。通过原子转移自由基聚合（ATRP）制备了由聚甲基丙烯酸甲酯嵌段和甲基丙烯酸甲酯（MMA）与带有烷氧基胺部分的甲基丙烯酸酯的无规共聚物嵌段组成的线性二嵌段共聚物。通过在苯甲醚中加热二嵌段共聚物，由于烷氧基胺部分的自由基交叉反应而发生交联反应，从而提供星状纳米凝胶。动力学研究表明，交联行为在给定的反应时间内达到平衡，并观察到热力学反应的特征反应行为。星状纳米凝胶的平衡结构由二嵌段共聚物的初始浓度及其组成和分子量控制。此外，通过用过量的烷氧基胺加热星状纳米凝胶，线性聚合物成功再生。分别通过凝胶渗透色谱-多角度激光光散射（GPC-MALLS）和小角X射线散射（SAXS）测量评估纳米凝胶的分子量和尺寸，并通过扫描力显微镜（SFM）直接观察纳米凝胶的形貌。
Programmed thermodynamic formation of star-like nanogels from designed diblock copolymers with thermally exchangeable dynamic covalent bonds in their side chains and structure analysis of the nanogels were performed. Linear diblock copolymers that consist of poly(methyl methacrylate) block and random copolymer block of methyl methacrylate (MMA) and methacrylic esters with alkoxyamine moiety were prepared by atom transfer radical polymerization (ATRP). By heating the diblock copolymers in anisole, a cross-linking reaction occurred as a result of the radical crossover reaction of alkoxyamine moieties to afford star-like nanogels. Kinetic studies have revealed that the cross-linking behavior reaches equilibrium at a given reaction time, with characteristic reaction behaviors for thermodynamic reactions being observed. The equilibrium structures of the star-like nanogels were controlled by the initial concentrations of diblock copolymers as well as their compositions and molecular weights. Furthermore, by heating the star-like nanogels with excess alkoxyamine, linear polymers were successfully regenerated. The molecular weights and sizes of the nanogels were evaluated by gel permeation chromatography-multiangle laser light scattering (GPC-MALLS) and small-angle X-ray scattering (SAXS) measurements, respectively, and the morphologies of the nanogels were directly observed by scanning force microscopy (SFM).