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Abstract：
This study investigates the crosslinking dynamics and swelling properties of pH-responsive poly(ethylene glycol) (PEG)/poly(acrylic acid) (PAA) interpenetrating polymer network (IPN) hydrogels. These hydrogels feature denser crosslinked networks compared to PEG single network (SN) hydrogels. Fabrication involved a two-step UV curing process: First, forming PEG-SN hydrogels using poly(ethylene glycol) diacrylate (PEGDA) through UV-induced free radical polymerization and crosslinking reactions, then immersing them in PAA solutions with two different molar ratios of acrylic acid (AA) monomer and poly(ethylene glycol) dimethacrylate (PEGDMA) crosslinker. A subsequent UV curing step created PAA networks within the pre-fabricated PEG hydrogels. The incorporation of AA with ionizable functional groups imparted pH sensitivity to the hydrogels, allowing the swelling ratio to respond to environmental pH changes. Rheological analysis showed that PEG/PAA IPN hydrogels had a higher storage modulus (G\') than PEG-SN hydrogels, with PEG/PAA-IPN5 exhibiting the highest modulus. Thermal analysis via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicated increased thermal stability for PEG/PAA-IPN5 compared to PEG/PAA-IPN1, due to higher crosslinking density from increased PEGDMA content. Consistent with the storage modulus trend, PEG/PAA-IPN hydrogels demonstrated superior mechanical properties compared to PEG-SN hydrogels. The tighter network structure led to reduced water uptake and a higher gel modulus in swollen IPN hydrogels, attributed to the increased density of active network strands. Below the pKa (4.3) of acrylic acid, hydrogen bonds between PEG and PAA chains caused the IPN hydrogels to contract. Above the pKa, ionization of PAA chains induced electrostatic repulsion and osmotic forces, increasing water absorption. Adjusting the crosslinking density of the PAA network enabled fine-tuning of the IPN hydrogels\' properties, allowing comprehensive comparison of single network and IPN characteristics.
摘要：
本研究研究了pH响应性聚（乙二醇）（PEG）/聚（丙烯酸）（PAA）互穿聚合物网络（IPN）水凝胶的交联动力学和溶胀性能。与PEG单网络(SN)水凝胶相比,这些水凝胶以更致密的交联网络为特征。制造涉及两步UV固化过程:首先,使用聚（乙二醇）二丙烯酸酯（PEGDA）通过紫外线诱导的自由基聚合和交联反应形成PEG-SN水凝胶，然后将它们浸入具有两种不同摩尔比的丙烯酸（AA）单体和聚（乙二醇）二甲基丙烯酸酯（PEGDMA）交联剂的PAA溶液中。随后的UV固化步骤在预制的PEG水凝胶内产生PAA网络。含有可电离官能团的AA的掺入赋予了水凝胶的pH敏感性，允许溶胀率响应环境pH值的变化。流变分析表明，PEG/PAAIPN水凝胶比PEG-SN水凝胶具有更高的储能模量(G')，PEG/PAA-IPN5表现出最高的模量。通过热重分析(TGA)和差示扫描量热法(DSC)的热分析表明,与PEG/PAA-IPN1相比,PEG/PAA-IPN5的热稳定性增加,这是由于来自增加的PEGDMA含量的更高的交联密度。与储能模量趋势一致，与PEG-SN水凝胶相比,PEG/PAA-IPN水凝胶表现出优异的机械性能。在溶胀的IPN水凝胶中，更紧密的网络结构导致吸水率降低和更高的凝胶模量，归因于活性网络链的密度增加。低于丙烯酸的pKa(4.3)，PEG和PAA链之间的氢键导致IPN水凝胶收缩。在pKa之上，PAA链的电离引起的静电斥力和渗透力，增加吸水性。调节PAA网络的交联密度能够微调IPN水凝胶的性能，允许对单个网络和IPN特性进行全面比较。
