Copolymer gels are a class of hydrogels that possess at least two different monomers within the same polymer chain. A common method for synthesizing copolymer gels is the one-pot free radical polymerization reaction. In charged copolymer gels, however, this fabrication method has previously led to anomalous, and often unexplained, material properties. In this paper, we report on the anomalous, enhanced swelling of anionic poly (3-sulfopropylmethacrylate-co-2-hydroxyethylmethacrylate) (P(SPMA-co-HEMA)) hydrogels, whereby we provide experimental results and a theoretical framework to explain this swelling behavior. The swelling ratio of our copolymer gels exhibits a local optimum at ∼ 25 mol% SPMA before transiting into a linear trend between charge density and gel swelling. A kinetic study of P(SPMA-co-HEMA) copolymerization reactions revealed that a transition in copolymer architecture is taking place, from a gradient (0–50 mol%) to a random (50–100 mol%) chain character with increasing SPMA content. With Flory–Rehner’s theoretical framework, we investigate why this change in copolymer architecture leads to enhanced swelling. For gradient copolymer gels, the difference in charge distribution likely enhances the local ionic driving force, and herewith the swelling. With the ability to tune the swelling behavior by controlling the copolymer architecture, we open further possibilities to study architecture-dependent properties, such as visco-elastic and stimuli-responsive behavior, or pH- and salt-dependent swelling.

中文翻译：

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带电共聚物凝胶的异常增强溶胀


共聚物凝胶是一类水凝胶，在同一聚合物链中至少具有两种不同的单体。合成共聚物凝胶的常用方法是一锅法自由基聚合反应。然而，在带电共聚物凝胶中，这种制造方法以前导致了异常的、通常无法解释的材料特性。在本文中，我们报道了阴离子聚（3-磺基丙基甲基丙烯酸酯-co-2-羟乙基甲基丙烯酸酯）（P（SPMA-co-HEMA））水凝胶的异常、增强溶胀，从而提供了实验结果和理论框架来解释这种溶胀行为。我们的共聚物凝胶的溶胀率在 25 mol% SPMA 时 $\sim$ 表现出局部最佳，然后过渡到电荷密度和凝胶溶胀之间的线性趋势。对 P（SPMA-co-HEMA） 共聚反应的动力学研究表明，随着 SPMA 含量的增加，共聚物结构正在发生转变，从梯度 （0–50 mol%） 转变为随机 （50–100 mol%） 链状。利用 Flory-Rehner 的理论框架，我们研究了为什么共聚物结构的这种变化会导致溶胀加剧。对于梯度共聚物凝胶，电荷分布的差异可能会增强局部离子驱动力，从而增强溶胀。凭借通过控制共聚物结构来调节溶胀行为的能力，我们为研究结构依赖性特性提供了更多可能性，例如粘弹性和刺激响应行为，或 pH 和盐依赖性溶胀。