A Study of C-O•••HO and OH•••OH (Dimer, Trimer, and Oligomer) Hydrogen Bonding in a Poly(4-vinylphenol) 30%/Poly(methyl methacrylate) 70% Blend and its Thermal Behavior Using Near-Infrared Spectroscopy and Infrared Spectroscopy

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 center dot center dot center dot HO and OH center dot center dot center dot 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%/PM MA 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 center dot center dot center dot OH dimer, which is a weaker hydrogen bonding, NIR is better while to investigate bands originating from OH groups in the OH center dot center dot center dot O=C and OH center dot center dot center dot 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(-1) (I-7058/I-6921) 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 degrees 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(-1) due to the C=O stretching mode of the C=O center dot center dot center dot HO hydrogen bond of PVPh30% decreases above 90 degrees C. These results suggest that above the Tg of PVPh the C=O center dot center dot center dot 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 center dot center dot center dot OH dimer gain intensity in parallel with temperature increase, and above Tg the intensity of the band derived from the OH center dot center dot center dot OH group increases linearly much slower than that of the band due to the free OH. Moreover, a band due to an OH center dot center dot center dot OH oligomer decreases linearly. Hence, it is very likely that the OH center dot center dot center dot 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 center dot center dot center dot HO and OH center dot center dot center dot OH (dimer, trimer, and oligomer) hydrogen bonding by comparison between the NIR and IR spectra in the OH stretching band regions.

Automated summary

Inter- and intramolecular hydrogen bonding in a PVPh 30%/PMMA 70% blend were investigated using near-infrared (NIR) and infrared (IR) spectroscopy, revealing temperature-dependent changes in the hydrogen bonding. The study demonstrated that different types of hydrogen bonding exhibit distinct spectral features at different temperatures.