Impact modified monovinylidene aromatic polymer having low rubber crosslinking
View Patent ↗The ductility/stiffness balance of a rubber-modified monovinylidene aromatic polymer, e.g., HIPS, is increased without increasing the rubber content of the polymer and/or changing the size of the average rubber particle by a process comprising the step of crosslinking the rubber such that the rubber-modified polymer has an optical crosslink index (OCLI) of <0.5 and an injection molded/compression molded (IM/CM) modulus ratio ≧1.3.
1. A mass-polymerized, rubber-modified monovinylidene aromatic polymer in which the rubber is crosslinked such that the modified polymer has an optical crosslink index (OCLI) of <0.5 and an injection molded/compression molded (IM/CM) modulus ratio of ≧1.3, wherein the polymer is HIPS.
2. The polymer of claim 1 in which the OCLI is <0.45.
3. The polymer of claim 1 in which the OCLI is <0.4.
4. The polymer of claim 2 in which the IM/CM modulus ratio is ≧1.32.
5. The polymer of claim 3 in which the IM/CM modulus ratio is ≧1.35.
6. An article comprising the polymer of claim 1 .
7. A process of modifying the ductility/stiffness balance of a rubber-modified monovinylidene, mass-polymerized aromatic polymer, the process comprising the step of crosslinking the rubber such that the rubber-modified polymer has an OCLI of <0.5 and an IM/CM modulus ratio of ≧1.3, wherein the polymer is HIPS.
8. The process of claim 7 in which the rubber of the rubber-modified monovinylidene aromatic polymer is crosslinked during a finishing step of a process in which the rubber-modified monovinylidene aromatic polymer is made.
9. The process of claim 8 in which the rubber is crosslinked by controlling at least one of the finishing step temperature or residence time of the rubber-modified monovinylidene aromatic polymer in the finishing step.
10. The process of claim 8 in which the rubber is crosslinked either by controlling the structure of the rubber or by diluting the polymer with one or more oils that exhibit a preference for the rubber phase of the polymer.
11. The process of claim 7 in which the finishing step comprises passing the rubber-modified monovinylidene aromatic polymer through a devolatization unit operated at a temperature between 235° C. and 245° C.
12. The process of claim 7 in which the rubber-modified monovinylidene aromatic polymer comprises a poly-a-olefin oil.
13. A mass-polymerized, rubber-modified monovinylidene aromatic polymer in which the rubber is crosslinked such that the modified polymer has an optical crosslink index (OCLI) of <0.5 and an injection molded/compression molded (IM/CM) modulus ratio of ≧1.3, wherein the polymer is HIPS, wherein the rubber-modified monovinylidene aromatic polymer further comprises poly-a-olefin oil.
14. The polymer of claim 13 in which the OCLI is <0.45.
15. The polymer of claim 13 in which the OCLI is <0.4.
16. The polymer of claim 14 in which the IM/CM modulus ratio is ≧1.32.
17. The polymer of claim 15 in which the IM/CM modulus ratio is ≧1.35.
18. An article comprising the polymer of claim 13 .
19. The process of claim 12 in which the rubber of the rubber-modified monovinylidene aromatic polymer is crosslinked during a finishing step of a process in which the rubber-modified monovinylidene aromatic polymer is made.
20. The process of claim 19 in which the rubber is crosslinked by controlling at least one of the finishing step temperature or residence time of the rubber-modified monovinylidene aromatic polymer in the finishing step.
21. The process of claim 19 in which the rubber is crosslinked either by controlling the structure of the rubber or by diluting the polymer with one or more oils that exhibit a preference for the rubber phase of the polymer.