Chemical experiments and carbon nuclear magnetic resonance studies showed that there were two addition manners

l

2-and l

4-additions when α-butenal (crotonaldehyde)

as an unsaturated aldehyde

conducted an acetalization reaction with polyvinyl alcohol．This mechanism is different from that for the acetalization reaction of polyvinyl alcohol with saturated aldehydes

which has only 1

2-addition．Crosslinking in polyvinyl butenal was mainly resulted from the 1

4-addition．Methods for calculating the acetalization degree and the ratio of 1

2-and 1

4-additions according to the results of chemical analysis have also been suggested．