Acetalization of poly(vinyl alcohol) by a fatty aldehyde in water medium: Model study, kinetics, and structure analysis

Abstract

Acid catalyzed poly(vinyl alcohol) (PVA) acetalization was investigated in aqueous medium at 80 8C for a PVA concentration of 8 wt %. The reactant, 10-undecenal, was composed of a long alkyl chain with a vinyl end group, and the functionalization reaction was studied in heterogeneous media for low reactant concentrations (from 0.33 to 2.0 mol % compared with PVA hydroxyl groups concentration). First, the reaction was scrutinized with pentane-2,4-diol, as a model compound of PVA. Besides the expected reaction, the oxidation of the aldehyde into 10-undecenoic acid in the presence of water was evidenced. This carboxylic acid appeared unreactive toward esterification of pentane-2,4-diol and PVA in water. Characterization of acetal stereochemical structure formed on the PVA backbone was performed by NMR spectroscopy in accordance to the model approach. A protocol based on 1 H NMR analysis was developed to quantify grafted aldehyde, residual aldehyde, and created carboxylic acid through direct sampling of the reaction medium. Conversions and reaction rate constants were calculated for pH ranging from 1 to 3. Finally, the acetalization yield was found to be enhanced at low pH and, in such conditions, the oxidation reaction contribution was limited.

Improvement of Thermal Conductivities for Epoxy Composites via Incorporating Poly(vinyl benzal)-Coated h-BN Fillers and Solvent-Assisted Dispersion

“…From this formula, we found that the average acetalization degree in aqueous solution was only about 36.3%, but the acetalization can achieve more than 90% in DMSO solvent because it belongs to homogeneous reaction and hydroxyl can be reacted more completely. Also, it is worth noting that the acetalization degree can be adjusted according to reaction time, temperature, pH, and the concentration of reaction medium . Furthermore, using different aldehydes to react with PVA to modify inorganic particles may achieve different performances …”