Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005, India.
Langmuir. 2010 May 4;26(9):6775-82. doi: 10.1021/la9041259.
Macroporous poly(N-isopropylacrylamide) (PNIPAM) hydrogels have been prepared in methanol-water (1:1, v/v) mixture in the presence of 0, 0.05, 0.1, 0.15, and 0.2 M Y(OTf)(3) Lewis acid concentrations. Synthesis of the corresponding linear PNIPAM homopolymers in the absence of a cross-linker keeping all other conditions the same shows that the isotacticity (meso dyad, %) and the cloud point temperature of the resulted in polymers increases and decreases, respectively, with the increase in the concentration of the Lewis acid. SEM micrographs reveal that the resulted hydrogels are highly porous. Swelling ratios of all the hydrogels in water decrease with the increase in the temperature. Moreover, swelling ratios of all the hydrogels in different methanol-water mixtures pass through a minimum in the co-nonsolvency zone, and the co-nonsolvency zone shifts toward the lower methanol-content solvent mixture with gradual increase in the Lewis acid concentration. Deswelling rate of the hydrogel prepared in methanol-water (1:1, v/v) mixture is much faster than that of the conventional hydrogel prepared in water. Moreover, the deswelling rate slightly increases with the hydrogels prepared with the increasing concentrations of Lewis acid. But, the reswelling rate of the hydrogels follows almost the reverse order. All these results have been explained on the basis of the formation of highly porous hydrogels with higher isotactic PNIPAM chain segment owing to the faster polymerization rate in the methanol-water mixture in the presence of Lewis acid and the co-nonsolvency behavior of the methanol-water (1:1, v/v) mixture toward PNIPAM chain segment in the PNIPAM hydrogel.
大孔聚（N-异丙基丙烯酰胺）（PNIPAM）水凝胶已在甲醇-水（1：1，v/v）混合物中制备，存在 0、0.05、0.1、0.15 和 0.2 M Y（OTf）（3）路易斯酸浓度。在不存在交联剂的情况下，在保持所有其他条件相同的情况下合成相应的线性 PNIPAM 均聚物表明，得到的聚合物的立构规整度（间规二单元，%）和浊点温度分别随着路易斯酸浓度的增加而增加和降低。SEM 显微照片显示所得水凝胶具有高度多孔性。所有水凝胶在水中的溶胀比随温度升高而降低。此外，所有水凝胶在不同甲醇-水混合物中的溶胀比在共非溶剂区通过最小值，并且随着路易斯酸浓度的逐渐增加，共非溶剂区向低甲醇含量溶剂混合物移动。在甲醇-水（1：1，v/v）混合物中制备的水凝胶的解吸速率远快于在水中制备的常规水凝胶。此外，随着路易斯酸浓度的增加，水凝胶的解吸速率略有增加。但是，水凝胶的再溶胀率几乎遵循相反的顺序。所有这些结果都基于在路易斯酸存在下甲醇-水混合物中更快的聚合速率和甲醇-水（1：1，v/v）混合物对 PNIPAM 链段的共非溶剂行为形成具有更高立构规整 PNIPAM 链段的高度多孔水凝胶来解释。
