Grafting of phosphonate groups onto PVA by acetalyzation. Evaluation of the anti-corrosive properties for the acetalyzed PVA coatings

One novel aldehyde bearing a phosphonate group, ca. (3-diethylphosphonate)propanal, was successfully synthesized and characterized by means of NMR. Then phosphonic acid ester groups were chemically grafted onto poly(vinyl acetal) pre-made polymers, and especially poly(vinyl butyral) (PVB). Four acetalyzed PVA were then synthesized with different molar contents of either butyral or (3-diethylphosphonate)propanal groups. Only PVAP4 was composed of both groups, i.e. 80 mol% of butyral and 20 mol% of phosphonate. TGA of acetalyzed PVA showed a clear improvement of the PVA thermal stability. Furthermore, for PVAP3, having 50 mol% of phosphonate groups, 40% of weight remained after 600 °C under air. This high thermostability was attributed to stable anhydride bonds. Finally, the coatings were subject to the salt spray test for duration up to 120 h. The results indicate that PVAP3 coating shows an excellent resistance to corrosion, thus excellent adhesive properties, as no corrosion was observed until 100 h subject to the salt spray test.