Sustainable polyvinyl acetals from bioaromatic aldehydes

Abstract

A series of polyvinyl aromatic acetals was obtained from the condesation of commercially available polyvinyl alcohol (PVA) and sustainable aromatic aldehydes: 4-hydroxybenzaldehyde, vanillin, syringaldehyde, ethylvanillin, ortho-vanillin, isovanillin, salicylaldehyde, ortho-anisaldehyde, para-anisaldehyde, benzaldehyde, cinnamaldehyde, cuminaldehyde, and hydroxymethylfurfural. The degree of acetalization was determined by ¹H NMR and found to range from 54 to 75%, resulting in calculated number average molecular weights of 38 200 to 46 000 Da. The glass transition temperature (T_g) of PVA (75 °C) was increased to substantially excel over that of polystyrene (PS, 100 °C), with polyvinyl aromatic acetal T_g values ranging from 114 to 157 °C. Heterogeneous degradation studies of polyvinyl vanillin acetal at room temperature indicated nearly complete hydrolysis over 24 hours in acidic aqueous media. For example, at pH = 1, the initial acetalization of 54% dropped to 0.8%, generating benign aromatic small molecules and water-soluble, biodegradable PVA.