Koyama Misao, Hirano Tomohiro, Ohno Keiichi, Katsumoto Yukiteru
Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan.
J Phys Chem B. 2008 Sep 4;112(35):10854-60. doi: 10.1021/jp800759w. Epub 2008 Aug 8.
The upper critical solution temperature (UCST)-type phase separation of an isotactic-rich poly( N-isopropylacrylamide) (PNiPA) in bis(2-methoxyethyl) ether (diglyme) has been investigated by turbidity measurement and infrared (IR) spectroscopy. The IR spectra of stereocontrolled PNiPAs in various solvents have clearly indicated that the amide I bands do not directly reflect the tacticity of the polymer. The relative intensity of the amide I bands changes depending upon the molecular environment around the amide groups of PNiPA, which is influenced by the tacticity. During the UCST-type phase separation of the isotactic-rich PNiPA in diglyme, the amide I band at around 1625 cm (-1) changes. To link the IR spectral change with the molecular information, quantum chemical calculations have been carried out for NiPA n-mers ( n = 1-4) with an isotactic stereosequence. The result has suggested that the amide I band at around 1625 cm (-1) arises from a helical structure formed by the isotactic stereosequences in the PNiPA main chain with the aid of intramolecular CO...H-N hydrogen bonding. The experimental IR spectra have revealed that the helical structures are unfolded as the temperature rises. The folding and unfolding of the isotactic sequences in the main chain may induce the thermal change in the solubility of the isotactic rich PNiPA in diglyme, resulting in the UCST-type phase separation of the solution.
通过浊度测量和红外（IR）光谱研究了等规度较高的聚（N-异丙基丙烯酰胺）（PNiPA）在双（2-甲氧基乙基）醚（二甘醇二甲醚）中的上临界溶液温度（UCST）型相分离。立体规整的PNiPA在各种溶剂中的红外光谱清楚地表明，酰胺I带并不直接反映聚合物的立构规整度。酰胺I带的相对强度随PNiPA酰胺基团周围的分子环境而变化，而立构规整度会影响该分子环境。在等规度较高的PNiPA在二甘醇二甲醚中的UCST型相分离过程中，1625 cm（-1）附近的酰胺I带发生变化。为了将红外光谱变化与分子信息联系起来，对具有等规立构序列的NiPA n聚体（n = 1-4）进行了量子化学计算。结果表明，1625 cm（-1）附近的酰胺I带源于PNiPA主链中等规立构序列借助分子内CO...H-N氢键形成的螺旋结构。实验红外光谱表明，随着温度升高，螺旋结构展开。主链中等规序列的折叠和展开可能会引起等规度较高的PNiPA在二甘醇二甲醚中溶解度的热变化，从而导致溶液的UCST型相分离。
