Two types of C[dbnd]O⋯HO hydrogen bonds and OH⋯OH (dimer, trimer, oligomer) hydrogen bonds in PVA with 88% saponification/PMMA and PVA with 99% saponification/PMMA blends and their thermal behavior studied by infrared spectroscopy

Abstract

In this study, polyvinyl alcohol (PVA) with 88% and 99% degrees of saponification was blended with polymethyl methacrylate (PMMA) to investigate the intramolecular hydrogen bonding in PVA and the intermolecular hydrogen bonding between PVA and PMMA. Differential scanning calorimetry (DSC) results confirmed the miscibility of the PVA/PMMA blends. Temperature-dependent ATR-IR spectra revealed that in PVA with an 88% saponification degree, some CO groups were free while the others were involved in CO···HO hydrogen bonding. In the blends with 88% saponified PVA, two types of CO···HO hydrogen bonds formed: CO(PVA)···HO(PVA) and CO(PMMA)···HO(PVA). Since the glass transition temperature of PVA is lower than that of PMMA, CO(PVA)···HO(PVA) can be broken at a lower temperature than CO(PMMA)···HO(PVA). In the blends with 99% saponified PVA, peaks derived from the CO stretching modes of CO(PMMA)···HO(PVA) were observed for PVA:PMMA = 60:40 and 40:60. In the OH stretching region of PVA and the blends, a broad band was observed in the 3700–3000 cm−1 region, where in OH bands arising from OH···OH (dimer, trimer, oligomer) hydrogen bonds and from the two types of CO···HO hydrogen bonds were expected to appear. In the PVA/PMMA blends with 88% saponified PVA, two types of CO⋯HO hydrogen bonds, CO(PVA)···HO(PVA) and CO(PMMA)···HO(PVA), yielded an OH stretching band at around 3370 cm−1. By contrast, the PVA/PMMA blends with 99% saponified PVA showed only a band corresponding to CO(PMMA)···HO(PVA) hydrogen bonding.