Poly(vinyl alcohol) (PVA) Sloviol R was modified to different degrees by acetalization reactions with aldehyde (formaldehyde, acetaldehyde, propionaldehyde and n-butyraldehyde) for 6 h at 60 degrees C in the presence of HCl as catalyst. Samples of the modified PVA were tested as dispersants in vinyl chloride suspension polymerization. The grains of poly(vinyl chloride) (PVC) powder produced are more compact, not very porous, have a higher bulk density and lower plasticizer absorption. By increasing the degree of acetalization, the bulk density of the PVC produced decreases. Using a mixture of commercial PVA Alcotex 72.5 (which produces porous PVC with a low bulk density) and acetalized PVA, PVC with a grain morphology can be obtained.