Polymers having a sequential structure of the following formula--A--X--B].sub.r (I)with r=1 to 20, in which --A-- is a polymer of a cyclic carbonate, --B-- is a polymer of a lactone and --X-- is a link, with a decreasing concentration of residues of the cyclic carbonate in the --B-- direction and a decreasing concentration of residues of the lactone in the --A-- direction, and the use of the these products as molding compositions.