Z???(OOCNH???X???NHCOO???(R-A)nR???OOCNH???X???NCO)m wherein Z is a group derived from a multifunctional compound; X is an aliphatic or aromatic group; A is a group derived from an aliphatic diacid; R can be the same or different at each occurrence and is a group derived from a dihydroxy compound; n is 1 to 10; and m is 2 to 6.