Lactones and ester derivatives thereof

Polyvinyl chloride plastic compositions containing amounts sufficient to impart plasticizing properties of the cyclic keto esters of spirodilactones from alkenyl or alkyl bis(succinic anhydride) having the formula ##STR5## in which R is alkyl or alkenyl of 2 to 28 carbon atoms and R' groups, which may be the same or different, are hydrogen or alkyl groups of 1 to 8 carbon atoms each.