Process for stabilizing plastics containing ester groups

A process for stabilizing polyester-containing plastics against thermal and/or hydrolytic degradation comprising reacting a polyester having hydroxyl, amine, or hydrazide functional groups or a combination of said functional groups and an incorporable, sterically hindered carbodiimide corresponding to the formula ##STR4## wherein A and D are the same or different substituted C.sub.6-20 aromatic or araliphatic hydrocarbon groups wherein in each group A and D

• (1) the carbodiimide group is attached to an aromatic ring carbon atom of said C.sub.6-20 aromatic or araliphatic hydrocarbon group,
• (2) one or two aromatic ring positions of said C.sub.6-20 aromatic or araliphatic hydrocarbon group ortho to the carbodiimide group are substituted with an aromatic substituent containing 6 to 15 carbon atoms, an aliphatic substituent containing 2 to 20 carbon atoms, or a cycloaliphatic substituent containing 5 to 20 carbon atoms, or a combination thereof, and
• (3) an NCO group is attached to an aromatic ring carbon atom of said C.sub.6-20 aromatic or araliphatic hydrocarbon group;
• is a substituted C.sub.6-20 aromatic or araliphatic hydrocarbon group wherein in each group B
• (1) each carbodiimide group is attached to an aromatic ring carbon atom of said C.sub.6-20 aromatic or araliphatic hydrocarbon group, and
• (2) one or two aromatic ring positions of said C.sub.6-20 aromatic or araliphatic hydrocarbon group ortho to either or both carbodiimide groups are substituted with an aromatic substituent containing 6 to 15 carbon atoms, an aliphatic substituent containing 2 to 20 carbon atoms, or a cycloaliphatic substituent containing 5 to 20 carbon atoms, or a combination thereof;
• and
• n is 0 to 3 (on average).