Equilibrium swelling of copolymerized acrylic acid- methacrylated dextran networks: Effects of pH and neutral salt
Equilibrium swelling of copolymerized acrylic acid- methacrylated dextran networks: Effects of pH and neutral salt
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DOI：
10.1021/ma0122021
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发表时间：
2002-06-18
期刊：
影响因子：
5.5
通讯作者：
Hung, SH
中科院分区：
文献类型：
--
作者：
Chiu, HC;Lin, YF;Hung, SH
本研究以过硫酸铵为引发剂，N，N，N‘，N’-四甲基乙二胺为引发剂，甲基丙烯酸化葡聚糖(MA-葡聚糖)和丙烯酸(AAc)为引发剂，在水溶液中进行自由基共聚合，制备了pH响应型葡聚糖凝胶。用傅里叶变换红外光谱定量测定了水凝胶中AAc的含量。根据Donnan平衡理论，通过定量评价离子渗透性能来表征水凝胶对pH/盐浓度变化的溶胀响应，同时考虑了Donnan平衡理论对AAc基团表观酸性常数的Debai-Huckel效应以及水凝胶中丙烯酸酯阴离子与反离子的离子结合。水凝胶的平衡溶胀与pH诱导的离子渗透压之间存在着接近线性的关系。聚合物-溶剂相互作用参数的伴随变化由离子渗透压、弹性伸缩力和聚合物网络与水分子的相互作用(混合贡献)之间的自由能平衡得到，并由水凝胶中固定的电离AAc单元的浓度决定。对于不同AAc含量的水凝胶，相同渗透压下溶胀度的差异是由于水凝胶的有效网络密度不同造成的。中性盐对同一水凝胶pH诱导的溶胀的影响遵循德拜-休克尔理论中AAc单元的离子渗透压和离解程度的变化。AAc单元的离解程度随离子强度效应的变化决定了水凝胶的溶胀行为对离子渗透压的敏感性。
In this study, pH-responsive dextran hydrogels were prepared by radical copolymerization of methacrylated dextran (MA-dextran) with acrylic acid (AAc) in aqueous solution, using ammonium peroxydisulfate and N,N,N',N'-tetramethylethylenediamine as an initiation system. The AAc content in hydrogels was determined quantitatively by FTIR. The swelling response of hydrogels to changes in pH/ salt concentration was characterized by quantitative evaluation of ionic osmotic performance according to the Donnan equilibrium theory, taking account of the Debye-Huckel effect on the apparent acidity constant of AAc groups and the ionic binding of acrylate anions with counterions within hydrogel. A close-to-linear relation between the equilibrium swelling of hydrogels and the pH-induced ionic osmotic pressure is observed. The accompanied change of the polymer-solvent interaction parameter (chi) is obtained from free energy balance between ionic osmotic pressure, the elastic retractile force, and the interaction of polymer network with water molecules (the mixing contribution) and is governed by the concentration of fixed ionized AAc units within hydrogels. For hydrogels having varying AAc contents, the difference in swelling under identical osmotic pressure results from the variation in the effective network density of hydrogels. The neutral salt effect on the pH-induced swelling of the same hydrogel follows changes in the ionic osmotic pressure and the degree of dissociation of AAc units associated with the Debye-Huckel theory. The change of the degree of dissociation of AAc units in response to the ionic strength effect dominates and describes well the sensitivity of the swelling behavior of hydrogels to the ionic osmotic pressure.