Combination of an organothio compound and a zinc mercapto ester as a heat stabilizer in PVC processing

A polymer composition comprising a halogen-containing polymer and a stabilizer composition consisting essentially of:

• (A) an organothio compound selected from the group consisting of dithiodiglycol, polyformals and polyacetals of said dithiodiglycol, and a mercaptoalkanol having the formula:
• 2
• wherein R1 and R2 are the same or different and are hydrogen or C1 to C18 alkyl;
• and i is 0 or an integer from 1 to 6 inclusive;
• (B) at least one zinc mercaptoester selected from the group consisting of:
• (B1) a zinc mercaptoacid ester having the formula:
• Zn-}S(CH2)x-C(=O)OR]2 wherein R is a hydrocarbyl radical having from 2 to about 22 carbon atoms and x is 1 or 2;
• (B2) a zinc mercaptoacid ester having the formula:
• Zn-[S(CHR)a(CH2)b-[C(=O)OR′]2, wherein:
• R′ is methyl or C(=O)OR″;
• R″ is [(CH2-[C-(R*(R2*)]yCH2O)2R3*];
• R* is H, alkyl, or hydroxyalkyl;
• R2* is OH, hydroxy-substituted alkyl, or O(O=)C-R4*;
• R3* is H, (O=)C-R4*, or alkyl;
• R4* is alkyl or alkenyl;
• A=0 or 1;
• b=1 or 2, y=0 or 1;
• and z=1 to 4;
• (B3) a zinc mercaptoalkyl carboxylic acid ester having the formula:
• Zn [SCH2(CH2)qO-C(=O)R5*]2;
• wherein
• R5* is an alkyl or alkenyl group havng from 1 to 18 carbon atoms or an aryl group having from 6 to 12 carbon atoms, and q is from 1 to 6;
• (C) from 0 to 40% by weight of a basic alkali or alkaline earth metal compound;
• and
• (D) from 0 to 40% by weight of a substituted dihydropyridine.