Xue Bai, Zhang Junhua, Zhou Tao
State Key Laboratory of Polymer Materials Engineering of China, Polymer Research Institute, Sichuan University, Chengdu, 610065, China.
Anal Bioanal Chem. 2015 Nov;407(29):8765-71. doi: 10.1007/s00216-015-9035-1. Epub 2015 Oct 14.
In this paper, the dissolution process of fully hydrolyzed polyvinyl alcohol (PVA) was investigated by temperature-dependent Fourier transform infrared spectroscopy (FTIR) combined with moving-window two-dimensional (MW2D) correlation infrared spectroscopy (IR). The results show that the FTIR spectra of PVA in OH stretching and bending regions exceed the measuring range of the spectrometer because of the presence of abundant water. The OH stretching and bending peaks reveal that the water mainly diffuses into amorphous region below 45 °C, and water molecules mainly diffuse into crystalline region above 45 °C. The peak at 1141 cm(-1) has ever been thought as the indication of crystallinity of PVA in solid state, but in solution, the peak does not decrease with the dissolution of crystalline region and finally increases when PVA is dissolved completely. The hydrogen bonds between hydroxyl groups in PVA chains are broken by water molecules but abundant new hydrogen bonds between hydroxyl groups in PVA chains and water molecules are formed during the dissolving process. In the 2D correlation analysis of the FTIR spectra, only the correlation movements of hydroxyl groups, including stretching and bending mode, can be observed. The correlation range and intensity are larger than that of PVA in solid state because the dissolution is the interaction process of water molecules diffusing into PVA chains.
本文采用变温傅里叶变换红外光谱（FTIR）结合移动窗口二维（MW2D）相关红外光谱（IR）研究了完全水解聚乙烯醇（PVA）的溶解过程。结果表明，由于存在大量水，PVA在OH伸缩和弯曲区域的FTIR光谱超出了光谱仪的测量范围。OH伸缩峰和弯曲峰表明，水在45℃以下主要扩散到非晶区，在45℃以上水分子主要扩散到结晶区。1141 cm(-1)处的峰曾被认为是固态PVA结晶度的指示，但在溶液中，该峰并不随结晶区的溶解而降低，最终在PVA完全溶解时升高。PVA链中羟基之间的氢键被水分子破坏，但在溶解过程中PVA链中羟基与水分子之间形成了大量新的氢键。在FTIR光谱的二维相关分析中，只能观察到羟基的相关运动，包括伸缩和弯曲模式。相关范围和强度比固态PVA的大，因为溶解是水分子扩散到PVA链中的相互作用过程。
