Alkyltin sulfanyl mercaptocarboxylates having terminal thiol groups

1. An alkyltin compound of Formula 1:

(R) x —Sn[—S—(CH 2 ) y —COO—CH 2 —CH 2 —OOC—(CH 2 ) y —SH] 4-x

wherein:

R is a methyl group;

x is 2;

y is 2; and

wherein the alkyltin compound of Formula 1 when added to a halogen-containing resin is effective to provide improved color stabilization in both initial color hold and long term heat stability relative to a halogen-containing resin having an added alkyltin compound derived from glycols with a divalent hydrocarbon radical containing more than two carbon atoms or relative to a halogen-containing resin having an added alkyltin compound without terminal thiol groups.

2. The compound of claim 1 , wherein said compound is selected from the group consisting of dimethyltin bis(1,2-ethane dithioglycolate), monomethyltin tris(1,2-ethanedithioglycolate), dimethyltin bis(1,2-ethane dimercaptopropionate), monomethyltin tris(1,2-ethanedimercaptopropionate) and mixtures thereof.

3. A composition comprising a halogen-containing resin and an alkyltin compound of claim 1 in an amount effective to stabilize the resin against elevated temperatures.

4. The composition of claim 3 , wherein said halogen-containing resin is a member of the group consisting of polyvinyl chloride, polyvinyl bromide, polyvinylidene chloride, copolymers of vinyl chloride and vinyl acetate, copolymers of vinyl chloride and vinylidene chloride, copolymers of vinyl chloride and acrylonitrile, copolymers of vinyl chloride and maleic or fumaric esters and copolymers of vinyl chloride and styrene.

5. The composition of claim 3 , wherein said effective amount is within a range of from 0.5 to 1.80 parts stabilizer per hundred parts resin.

6. The composition of claim 5 , wherein said range is from 0.8 to 1.2 parts stabilizer per hundred parts resin.

7. The composition of claim 4 , further comprising at least one additive selected from the group consisting of lubricants, fillers, pigments, flame retardants, UV absorbers, impact modifiers and processing aids.

8. The composition of claim 7 , wherein said lubricants are selected from the group consisting of calcium stearate, montan wax, fatty acid esters, polyethylene waxes, chlorinated hydrocarbons, glycerol esters and combinations thereof.

9. The composition of claim 8 , wherein said fillers are selected from the group consisting of titanium oxide, calcium carbonate, kaolin, glass beads, glass fibers, talc, wood flour and mixtures thereof.

10. The composition of claim 7 , wherein said pigments are selected from the group consisting of azo pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, diketopyrrolopyrrole pigments and anthraquinone pigments.

11. The composition of claim 7 , wherein said flame retardants are selected from the group consisting of antimony oxide, molybdates, borates and hydroxystannates.

12. A method for preparation of the alkyltin compound of claim 1 , comprising

I) esterifying ethylene glycol with a thioacid in a molar ratio of 1:2 in the presence of a suitable catalyst to produce a dithiol ester; and

II) reacting said dithiol ester with a tin-containing reactant at the following molar ratios: for dialkyltin derivatives S:Sn>1.5 and for monoalkyltin derivatives S:Sn>1.0.

13. The method of claim 12 , wherein said tin-containing reactant is an alkyltin chloride or alkyltin oxide.

14. A method of stabilizing initial color of PVC consisting of adding to the PVC 1.12 phr of dimethyltin bis(1,2-ethane dithioglycolate), wherein the PVC has a yellow index of 3.59 at 3 minutes.

15. The method of claim 14 , wherein the PVC has a yellow index of 5.99 at 6 minutes, and 7.93 at 9 minutes.