Stabilized ethylene/chlorotrifluoroethylene copolymer composition

A copolymer composition having improved thermal stability which comprises an admixture of an ethylene/chlorotrifluoroethylene copolymer containing about 40 to about 60 mol percent of ethylene units and about 40 to about 60 mol percent of chlorotrifluoroethylene units, and

• (a) 0.01 percent to 3 percent by weight of the polymer of a transesterified reaction product obtained from an organic polyhydric phenol selected from the group consisting of 1,1,3-tri(2-methyl-4-hydroxy-5-tert-butyl phenyl)butane and the phenol of the formula ##STR4## wherein X is selected from the group consisting of oxygen, sulfur, alkylene, alicyclidene, arylidene and mixed alkylene-arylidene and alkylene-alicyclidene groups, wherein the aliphatic or cycloaliphatic portion of the molecule may be straight chain or branched chain, having from 1 to about 18 carbon atoms;
• wherein the R substituents, which may be the same or different, are independently selected from the group consisting of hydrogen and alkyl, straight or branched chain, having from 1 to about 18 carbon atoms;
• and wherein m and n are integers from 1 to 5, and o and p are integers from 0 to 4, with the proviso that the sums of m+o, and n+p may not exceed 5, and an organic phosphite triester free from phenolic hydroxyl groups having up to about 60 carbon atoms obtained by transesterification of the phenol and phosphite at an elevated temperature sufficient to form a homogeneous mixture;
• (b) 0.01 percent to 10.0 percent by weight of the polymer of a salt of a monocarboxylic acid having from 6 to about 24 carbon atoms and a metal of Group II of the Periodic Table;
• and
• (c) 0.01 percent to 3.0 percent by weight of the polymer of the ester of a (4-hydroxy-5-alkylphenyl)alkanoic acid, the ester having the formula:
• ##STR5## wherein R.sub.1 is methyl, ethyl or an alpha-branched group of from 3 to 10 carbon atoms;
• R.sub.2 is hydrogen, methyl, ethyl or an alpha-branched alkyl group of from 3 to 10 carbon atoms;
• v has a value of from 1 to 6;
• w has a value of from 2 to 6;
• and
• Z is an aliphatic hydrocarbon of the formula:
• C.sub.y H.sub.2y+2-w
• in which y has a value of from 2 to 18 when w is 2 and a value of from 3 to 6 when w is greater than 2, the value of y in all cases being equal to or greater than that of w.