Sustainable polyvinyl acetals from bioaromatic aldehydes

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 H-1 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 degrees C) was increased to substantially excel over that of polystyrene (PS, 100 degrees C), with polyvinyl aromatic acetal T-g values ranging from 114 to 157 degrees 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.