Stabilization of methylmethacrylate-butadiene-styrene graft copolymers against thermal oxidation
The instant invention relates to a stabilized composition of methylmethacrylate-butadiene-styrene graft copolymers with selected sterically hindered phenolic antioxidants and thioethers. Further subjects of the invention are a process for the stabilization of methylmethacrylate-butadiene-styrene graft copolymers and the use of selected sterically hindered phenolic antioxidants together with a thioether for the thermal stabilization of said graft copolymer.
1 . A stabilized polymer composition comprising
a) a polymer, which is a graft copolymer of methylmethacrylate and styrene on polybutadiene or on polybutadiene-styrene (methylmethacrylate-styrene-butadiene graft copolymer, MBS);
b) a sterically hindered phenolic antioxidant of formula (I), (II) or (III) or a mixture thereof
wherein n is from 1-10;
and
c) a thioether differing from that of formula (II);
with the proviso that other styrene/polybutadiene graft copolymers are not present.
2 . A stabilized polymer composition according to claim 1 , which is in the solid state.
3 . A stabilized polymer composition according to claim 2 , which is in the form of a powder or granulate.
4 . A stabilized polymer composition according to claim 1 wherein the thioether is a compound of formula (IV) or (V)
wherein the R 1 are independently C 8 -C 20 alkyl.
5 . A stabilized polymer composition according to claim 1 wherein the sterically hindered phenolic antioxidant is present in an amount of 0.05 to 1% based on the weight of the dry graft copolymer, component a).
6 . A stabilized polymer composition according to claim 1 wherein the thioether is present in an amount of 0.1 to 5% based on the weight of the dry graft copolymer, component a).
7 . A stabilized polymer composition according to claim 1 wherein the ratio of sterically hindered phenolic antioxidant to thioether is from 1:1 to 1:5.
8 . A stabilized polymer composition according to claim 1 additionally comprising a further sterically hindered phenolic antioxidant different from that of claim 1 , a phosphite process stabilizer, a UV-absorber, a sterically hindered amine light stabilizer, a metal deactivator, an acid scavenger, a metal salt of a fatty acid, a fluorescent whitening agent, a biocide or a surfactant.
9 . A process for the stabilization of a graft copolymer of methylmethacrylate and styrene on polybutadiene or polybutadiene-styrene (methylmethacrylate-styrene-butadiene graft copolymer, MBS) where no other styrene polymer or copolymer, which is not a graft copolymer on butadiene is present, comprising the steps
a) adding to a MBS latex a sterically hindered phenolic antioxidant of formula (I), (II) or (III);
wherein n is from 1-10;
and a thioether differing from that of formula (II);
b) coagulating the MBS latex and
c) drying the MBS latex at elevated temperature.
10 . A process according to claim 9 wherein the drying step is carried out at a temperature of 40° C. to 150° C.