聚(4-乙酰基丙烯酰乙酸乙酯-co-丙烯酸)水凝胶的溶胀动力学以及温度敏感性研究

通过分子结构设计, 合成了疏水性单体4-乙酰基丙烯酰乙酸乙酯(AAEA), 并以该单体与丙烯酸(AA)进行自由基溶液共聚, 制备了P(AAEA-co-AA)新型温度敏感性水凝胶. AAEA的¹H NMR及FT-IR分析表明, 该单体主要以烯醇式结构存在; P(AAEA-co-AA)的FT-IR分析发现, PAAEA与PAA之间存在较强烈的氢键作用, 使得AAEA烯醇异构体中的C—O伸缩振动吸收峰移向了低波数处. 对冷冻干燥后凝胶的电镜分析发现, 当AAEA用量较高时, 由于凝胶内部分子链段的疏水聚集, 各部分溶胀度以及溶胀速度不均一而使得凝胶表面粗糙不平. 采用DSC对凝胶的体积相转变进行了研究, 结果表明, 该水凝胶的体积相转变温度(VPTT)在48.2至61.8 ℃之间, 并且随着AAEA用量的减小, 凝胶的VPTT逐渐增加. 对该新型温度敏感性水凝胶在去离子水中的溶胀动力学研究发现, 当AAEA用量高于4.6 g时, 凝胶属于Fick凝胶; 反之凝胶则属于非Fick凝胶. 该水凝胶在去离子水中具有良好的温度敏感性, 当外界温度低于VPTT时, 凝胶能保持溶胀状态; 而当外界温度高于VPTT时, 凝胶的平衡溶胀度迅速下降, 表现为温度敏感性. 进一步研究发现, 凝胶组成不仅会影响凝胶的VPTT, 而且会影响凝胶温度敏感性的强弱.

Study on Swelling Kinetics and Temperature Sensitivity of Poly(4-acetyl acryloyl ethyl acetate-co-acrylic acid) Hydrogels

A novel monomer called 4-acetyl acryloyl ethyl acetate (AAEA) was designed and synthesized, and a series of P(AAEA-co-AA) temperature sensitive hydrogels were obtained via free radical solution co- polymerization between AAEA and acrylic acid (AA). The novel monomer and the hydrogel were characterized using 1H NMR and FT-IR spectra. The results showed that AAEA mainly existed as enol forms. In the IR spectrum of P(AAEA-co-AA), the peak of C-O stretching from enol forms of AAEA shifted to low wave numbers. This is attributed to the formation of strong hydrogen bond between PAAEA and PAA. SEM micrographs revealed that when the dosage of AAEA was high, the hydrophobic aggregation of PAAEA induced an inhomogeneous swelling of the hydrogels, and the hydrogels exhibited coarse morphology. The volume phase transition temperature (VPTT) of the hydrogels was determined by their respective DSC thermograms of swollen hydrogel specimens. The results showed that the VPTT of the hydrogels ranged from 48.2 to 61.8 ℃, and increased significantly with the decreasing dosage of AAEA. The swelling kinetics of the hydrogels was studied. The results indicate that when the dosage of AAEA was higher than 4.6 g, the hydrogel was Fick hydrogel; contrarily, the hydrogel became non-Fick hydrogel. This series of hydrogels exhibited excellent temperature sensitivity, when the temperature was lower than VPTT, the hydrogels kept at a swollen state, but when the temperature was higher than VPTT, the hydrogels deswelled significantly. Further investigation showed that the components of the hydrogels not only influenced the VPTT of the hydrogels but also influenced the temperature sensitivity of the hydrogels.