采用傅立叶变换红外光谱仪测试了由聚(N-异丙基丙烯酰胺)(PNIPA)和聚丙烯酸(PAA)两种聚合物网络形成的具有互穿聚合物网络结构(IPN)的pH/温度双重敏感性微凝胶D2O分散液,通过差谱技术对不同pH值和温度条件下的红外吸收光谱进行处理,研究微凝胶相转变过程中分子链微环境的变化.结果表明,随着D2O介质的pH值增大,微凝胶中PAA分子链上的羧酸基团离解为羧酸根离子,导致微凝胶发生响应pH值变化的相转变.PNIPA分子链的微环境随pH值变化较小,说明PNIPA网络保持了相对独立性.微凝胶响应温度变化发生相转变后,PNIPA组分中的酰胺Ⅰ谱峰位置发生了蓝移,而酰胺Ⅱ潜峰位置发生了红移,表明PNIPA分子链上酰胺基团与水分子之间的氢键被破坏,游离态的酰胺基团数量增加.PNIPA分子链上异丙基的C-H伸缩振动谱峰发生红移的原因可能是因相转变过程中其周围的水笼结构被破坏.%The microenvironment change of macromolecular chains of pH/temperature dually responsive microgels with interpenetrating polymer network (IPN) structure, based on poly (N-isopropylacrylamide) (PNIPA) network and poly(acrylic acid) (PAA) network in D2O dispersion during their phase transition, were investigated by Fourier transform infrared (FTIR) spectra and IR difference spectra at different temperatures and pH values. With the increase of pH value of D2O, the intensity of the symmetric C=O stretch IR band from carboxylate anions (1 568 cm-1) was increased, and the intensity of the C=O stretch band from COOH groups ( 1 705 cm-1 ) was decreased, which indicated that the COOH groups of PAA chains in the microgels dissociated into COO- leading to the phase transition induced by pH variation. However, IR bands of main characteristic peaks of PNIPA were hardly changed, which indicated the microenvironment of PNIPA chains was not evidently changed with the pH variation, and the PNIPA network within the microgels holds relative independence. The appearance of both positive peak( 1 650 cm-1 and 1 448 cm-1 ) and negative peak( 1 625cm-1 and 1 479 cm-1 ) with the redshift of the amide Ⅱ bands and the blueshift of the amide I bands of PNIPA component after temperature induced phase transition of the microgels exhibited that the hydrogen bonds between amide groups and waters were damaged, and the number of free amide groups were increased. In addition, the appearances of both positive peak (2 970 cm-1) and negative peak (2 990 cm-1 ) with redshift of the C-H stretching bands for the isopropyl groups of PNIPA component may be due to breakdown of water cage structure around the groups.
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