School of Materials and Chemical Engineering, Ningbo Key Laboratory of Specialty Polymers, Ningbo University, Ningbo, 315211, China and Department of Chemistry, University of Connecticut, Storrs, CT 06269, USA.
Department of Chemistry, University of Connecticut, Storrs, CT 06269, USA.
Soft Matter. 2017 Jul 26;13(29):5028-5037. doi: 10.1039/c7sm00825b.
Cross-linking that defines the three-dimensional networks in hydrogels has a significant impact on their physiochemical properties. The cross-linking of hydrophilic polymers via post-polymerization reactions is an ideal way to manufacture hydrogels with high reproducibility and without monomer residuals. We herein report the use of Ag(i)-catalyzed oxidative decarboxylation to cross-link poly(acrylic acid) (PAA) and a family of COOH-containing hydrophilic polymers. Our method is based on the radical-mediated elimination reaction to remove COOH group(s) and generate alkyl radical(s) simultaneously, in the presence of AgNO and persulfates. The further intermolecular radical coupling is demonstrated to be very effective in inducing cross-linking and gelation of COOH-containing hydrophilic polymers. The cross-linking reaction can be readily achieved by simply mixing a small amount of AgNO (as low as 0.03 wt%) and persulfates with polymers at room temperature in air. Rheological measurements show that the gelation occurs in 20-30 min. The applications of oxidative decarboxylation in the preparation of hydrogels of COOH-containing hydrophilic copolymers and their interpenetrating polymer network (IPN) hydrogels are further validated. Finally, the residual Ag(i) ions in hydrogels are discussed in terms of how Ag(i) ions further change the mechanical and optical properties of hydrogels by photoreduction of Ag(i) to Ag nanoparticles. We expect that this Ag(i)-catalyzed oxidative decarboxylation chemistry can not only serve as a facile and general strategy to produce hydrogels through post-polymerization, but also enrich the toolbox of cross-linking chemistries of COOH-containing polymers in all forms (e.g. films, colloids and dispersions).
交联作用决定了水凝胶的三维网络，对其物理化学性质有重大影响。通过聚合后反应将亲水性聚合物交联是制造具有高重现性且无单体残留的水凝胶的理想方法。在此，我们报告了使用 Ag(i)-催化的氧化脱羧反应来交联聚丙烯酸 (PAA) 和一系列含有 COOH 的亲水性聚合物。我们的方法基于自由基介导的消除反应，在 AgNO 和过硫酸盐的存在下，同时去除 COOH 基团并生成烷基自由基。进一步的分子间自由基偶联被证明在诱导含有 COOH 的亲水性聚合物的交联和胶凝方面非常有效。交联反应可以通过简单地将少量的 AgNO（低至 0.03wt%）和过硫酸盐与聚合物在室温下在空气中混合来实现。流变学测量表明凝胶化发生在 20-30 分钟内。氧化脱羧反应在制备含有 COOH 的亲水性共聚物的水凝胶及其互穿聚合物网络 (IPN) 水凝胶中的应用进一步得到了验证。最后，讨论了水凝胶中残留的 Ag(i)离子如何通过 Ag(i)离子的光还原将 Ag(i)还原为 Ag 纳米颗粒来进一步改变水凝胶的机械和光学性质。我们期望这种 Ag(i)-催化的氧化脱羧化学不仅可以作为通过聚合后反应生产水凝胶的简便通用策略，而且可以丰富各种形式（例如膜、胶体和分散体）的含有 COOH 的聚合物的交联化学工具箱。
