Chemistry Reference
In-Depth Information
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 1½ h 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 is added.
The solutions are then neutralized. The butyrals separate out. They are neutralized and the resin are
washed and dried.
If poly(vinyl alcohol) films are reacted with formaldehyde in water containing salt and an acid
catalyst (heterogeneous formalization), cross-linking occurs. The number of the cross-links increases
with decreasing acid concentration and fixed amounts of formaldehyde and salt [
257
].
Direct reactions of poly(vinyl alcohol) with aldehydes in the
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 etherification of poly(vinyl alcohol) occurs when the polymer is combined with
Kornblum reaction
-alkyl
halides in dimethylsulfoxide combined with pyridine [
258
,
259
]. It was suggested that the alkyl
halides convert to aldehydes and acids and then act as intermediates in the dimethylsulfoxide-
pyridine solution [
258
,
259
]:
n
N
RCH
2
Br
+
HBr
+
OH
O
O
S
R
Many modifications of poly(vinyl alcohol) were carried out to form photosensitive materials.
Thus, unsaturation was introduced into the pendant groups for photocross-linking. One example is a
condensation with pyridinium and quinolinium salts [
260
]:
+
OO
OH
OH
N
N
