Substitution Reactions of Poly vinyl alcohol

There are many practical uses for products from reactions of poly(vinyl alcohol). Among them are commercial preparations of poly(vinyl acetal)s formed through condensations with aldehydes. Two materials that are currently being marketed are poly(vinyl formal) and poly(vinyl butyral). The first is formed from partially hydrolyzed poly(vinyl acetate) that is dissolved in aqueous acetic acid and excess formaldehyde. The mixture is heated, sulhiric acid is added, and the reaction is allowed to proceed at 70-90 °C for 6 hours. Sulfuric acid is then neutralized and the formal precipitates out (see also Chapter 5). 

Two different industrial processes are used for preparations of the butyral. In both of them acetate-free poly(vinyl alcohol) is used. In the first one, 10% solutions of the starting material are treated with butyraldehyde and sulfuric acid. The mixtures are heated to 90 °C for one and a half hours and the products precipitate. They are neutralized, washed, and dried. In the second one poly(vinyl alcohol) is suspended in ethanol/ethyl acetate, and butyraldehyde together with a strong mineral acid are added. The solutions are then neutralized. The butyrals separate out. They are neutralized and the resin washed and dried. 

If poly(vinyl alcohol) films are reacted with formaldehyde in water containing salt and an acid catalyst (heterogeneous formalization), crosslinking occurs. The number of the crosslinks increases with decreasing acid concentration and fixed amounts of formaldehyde and salt.  

Direct reactions of poly(vinyl alcohol) with aldehydes in the Komblwn reaction result in formations of acetals that also contain residual hydroxyl group and often acetate groups. The acetate groups can be there from incomplete hydrolysis of the parent poly(vinyl acetate) that was used to form the poly (vinyl alcohol). Reactions of poly (vinyl alcohol) with ketones yield similar ketals. At present no ketals are offered commercially. 

Alkyl etherifications of poly(vinyl alcohol) occur when the polymer is combined with n-alkyl halides in dimethylsulfoxide combined with pyridine. It was suggested that the alkyl halides convert to aldehydes and acids and then act as intermediates in the dimethylsulfoxide-pyridine solution  

---