Sato Harumi, Morisawa Yusuke, Takaya Satoshi, Ozaki Yukihiro
Graduate School of Human Development and Environment, 12885Kobe University, Kobe, Japan.
Molecular Photoscience Research Center, Kobe University, Kobe, Japan.
Appl Spectrosc. 2022 Jul;76(7):831-840. doi: 10.1177/00037028221086913. Epub 2022 Apr 21.
Inter- and intramolecular hydrogen bonding and their temperature-dependent changes in a poly(4-vinylphenol)/poly(methyl methacrylate)(PVPh 30%/PMMA 70%) blend were investigated using near-infrared (NIR) and infrared (IR) spectroscopy. Band assignments of the fundamentals and first overtones of the OH stretching mode of a free OH group and OH groups in C=O···HO and OH···OH (dimer, trimer, and oligomer) hydrogen bonding of PVPh 30%/PMMA 70% were carried out by comparison between its NIR and IR spectra and comparison with NIR and IR spectra of phenol. The comparison of the NIR spectra of the PVPh 30%/PMMA 70% blend (hereafter, we denote it as PVPh30%) with the corresponding IR spectra reveals that to observe bands arising from the free OH and OH···OH dimer, which is a weaker hydrogen bonding, NIR is better while to investigate bands originating from OH groups in the OH···O=C and OH···OH (oligomer) hydrogen bonds, which are stronger hydrogen bonding, IR is better. Thus, a combination of IR and NIR spectroscopy has provided convincing results for the hydrogen bonding of PVPh30%. The relative intensity of the two bands at 7058 and 6921 cm (I/I) due to the first overtones of the OH stretching modes of the free OH group and the OH group in the dimer, respectively, increases significantly above 90 °C, which is close to Tg of PVPh. In concomitance with the intensity increase in the relative intensity of the free OH band, the intensity of a band at 1706 cm due to the C=O stretching mode of the C=O···HO hydrogen bond of PVPh30% decreases above 90°C. These results suggest that above the Tg of PVPh the C=O···HO hydrogen bond is broken gradually and that the free OH increases. Of note is that below Tg the intensities of NIR bands due to the OH first overtones of free OH group and OH groups in the OH···OH dimer gain intensity in parallel with temperature increase, and above Tg the intensity of the band derived from the OH···OH group increases linearly much slower than that of the band due to the free OH. Moreover, a band due to an OH···OH oligomer decreases linearly. Hence, it is very likely that the OH···OH oligomers dissociate into free OH groups. Anharmonicity of O-H bonds, which is sensitive to a hydrogen bond, was estimated for the free OH and OH bonds in the C=O···HO and OH···OH (dimer, trimer, and oligomer) hydrogen bonding by comparison between the NIR and IR spectra in the OH stretching band regions.
使用近红外（NIR）和红外（IR）光谱研究了聚（4-乙烯基苯酚）/聚（甲基丙烯酸甲酯）（PVPh 30%/PMMA 70%）共混物中的分子间和分子内氢键及其随温度的变化。通过比较其NIR和IR光谱，并与苯酚的NIR和IR光谱进行比较，对PVPh 30%/PMMA 70%中游离OH基团以及C=O···HO和OH···OH（二聚体、三聚体和低聚物）氢键中OH基团的OH伸缩模式的基频和第一泛音进行了谱带归属。PVPh 30%/PMMA 70%共混物（以下简称PVPh30%）的NIR光谱与相应IR光谱的比较表明，要观察来自游离OH和OH···OH二聚体（较弱的氢键）的谱带，NIR更好；而要研究来自OH···O=C和OH···OH（低聚物）氢键中OH基团（较强的氢键）的谱带，IR更好。因此，IR和NIR光谱的结合为PVPh30%的氢键提供了令人信服的结果。分别由游离OH基团和二聚体中OH基团的OH伸缩模式的第一泛音引起的7058和6921 cm处两条谱带的相对强度（I/I）在90°C以上显著增加，这接近PVPh的玻璃化转变温度（Tg）。随着游离OH谱带相对强度的增加，PVPh30%中C=O···HO氢键的C=O伸缩模式在1706 cm处的谱带强度在90°C以上降低。这些结果表明，在PVPh的Tg以上，C=O···HO氢键逐渐断裂，游离OH增加。值得注意的是，在Tg以下，由游离OH基团和OH···OH二聚体中OH基团的OH第一泛音引起的NIR谱带强度随温度升高而平行增加，而在Tg以上，由OH···OH基团产生的谱带强度的线性增加比由游离OH产生的谱带慢得多。此外，由OH···OH低聚物引起的谱带呈线性下降。因此，OH···OH低聚物很可能解离成游离OH基团。通过比较OH伸缩带区域的NIR和IR光谱，估算了C=O···HO和OH···OH（二聚体、三聚体和低聚物）氢键中游离OH和OH键对氢键敏感的O-H键非谐性。
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