Co-agents for the preparation of thermoplastic elastomeric blends of rubber and polyolefins
A thermoplastic elastomer with increased oil resistance and decreased compression set compared to conventionally cured thermoplastic elastomers may be made from a dynamically vulcanized blend of propylene resin and ethylene/alpha-olefin/non-conjugated diene elastomers via a curing system containing a free radical initiator, a first co-agent including diene-containing polymers with a 1,2-vinyl content greater than 50% by weight, and a second co-agent including multifunctional acrylates containing at least two acrylate groups, multifunctional maleimides containing at least two imide groups, or mixtures of both, where the elastomer gel content in the modified blend is at least 97%.
1. A reactively modified thermoplastic elastomeric blend comprising at least one propylene resin and at least one ethylene/alpha-olefin/non-conjugated diene elastomer wherein the blend is dynamically vulcanized via a curing system comprising:
a free radical initiator;
a first co-agent comprising diene-containing polymers with a 1,2-vinyl content greater than about 50% by weight; and
a second co-agent comprising multifunctional acrylates containing at least two acrylate groups, multifunctional maleimides containing at least two imide groups, or mixtures thereof;
wherein the free radical initiator and the co-agents are collectively present in an amount sufficient to provide a gel content of the elastomer of at least 97% and to provide blends of the invention having a shore A durometer hardness of at least 70 with an oil swell of less than about 90% by weight, and blends having a shore A durometer hardness of no greater than 70 with an oil swell of less than about 100% by weight.
2. The modified blend of claim 1 , wherein the modified blend comprises about 10 to 70% by weight propylene resin and about 5 to 60% by weight ethylene/alpha-olefin/non-conjugated diene elastomer.
3. The modified blend of claim 1 , wherein the first co-agent is present in an amount of greater than 1% to about 10 % by weight of the modified blend.
4. The modified blend of claim 3 , wherein the first co-agent comprises syndiotactic 1,2-polybutadiene, atactic 1,2-polybutadiene, high vinyl solution styrene-butadiene elastomer, or mixtures thereof.
5. The modified blend of claim 4 , wherein the syndiotactic 1,2-polybutadiene has a melting point of at least about 60° C.
6. The modified blend of claim 1 , wherein the first co-agent or the second co-agent, or both, are each present in an amount of about 0.1 to 10% by weight of the modified blend.
7. The modified blend of claim 6 , wherein the second co-agent comprises trimethylolpropane triacrylate.
8. The modified blend of claim 6 , wherein the second co-agent comprises N,N′-m-phenylene dimaleimide.
9. The modified blend of claim 1 , wherein the free radical initiator is present in an amount of about 0.001 to 2% by weight of the modified blend.
10. The modified blend of claim 9 , wherein the free radical initiator comprises at least one organic peroxide and the blend is essentially free of moisture sensitivity.
11. The modified blend of claim 1 , further comprising about 5 to 65% by weight of at least one extender oil.
12. The modified blend of claim 1 , further comprising a filler present in an amount of about 0.001 to 20% by weight.
13. The modified blend of claim 1 , wherein the ethylene/alpha-olefin/non-conjugated diene elastomer comprises ethylene/propylene/diene elastomer.
14. The modified blend of claim 1 , wherein the ethylene/alpha-olefin/non-conjugated diene elastomer without oil has a Mooney viscosity [ML (1+4) @ 125° C.] of at least about 100.
15. The modified blend of claim 1 , further comprising one or more of organic and inorganic pigments, heat stabilizers, antioxidants, ultraviolet absorbers, photostabilizers, flame retardants, antiblocking agents, foaming agents, antistatic agents or antibacterial agents, or any combination thereof.
16. An article comprising the reactively modified blend of claim 1 .
17. The blend of claim 1 , wherein the blend has a yellowness index of less than 30.
18. A process for preparing a dynamically vulcanized thermoplastic elastomer composition comprising:
blending a mixture of at least one polypropylene resin and at least one ethylene/alpha-olefin/non-conjugated diene elastomer at a temperature above the melting point of the at least one polypropylene resin;
adding a free radical initiator, at least one co-agent comprising diene-containing polymers with a 1,2-vinyl content greater than about 50% by weight, and at least one co-agent comprising multifunctional acrylates containing at least two acrylate groups or multifunctional maleimides containing at least two imide groups; and
then mixing and shearing the blend sufficiently at a temperature to effect crosslink formation such that the elastomer has a gel content of at least 97%, wherein the free radical initiator and the co-agents are collectively present in an amount sufficient to provide blends of the invention having a shore A durometer hardness of at least 70 with an oil swell of less than about 90% by weight, and blends having a shore A durometer hardness of no greater than 70 with an oil swell of less than about 100% by weight.
19. A process according to claim 18 , wherein the mixing device comprises a twin screw extruder.
20. A thermoplastic elastomer curing system comprising:
a free radical initiator comprising at least one organic peroxide;
a first co-agent comprising diene-containing polymers with a 1,2-vinyl content greater than about 50% by weight; and
a second co-agent comprising multifunctional acrylates containing at least two acrylate groups, multifunctional maleimides containing at least two imide groups, or mixtures thereof;
wherein the curing system includes sufficient amounts of the free radical initiator and the co-agents, when combined with at least one polypropylene resin and at least one additional ethylene-containing material, to form a reactively modified thermoplastic elastomer blend having a gel content of the elastomer of at least 97% and to provide blends of the invention having a shore A durometer hardness of at least 70 with an oil swell of less than about 90% by weight, and blends having a shore A durometer hardness of no greater than 70 with an oil swell of less than about 100% by weight.
21. A thermoplastic elastomer-based reaction mixture comprising:
at least one propylene resin and at least one ethylene/alpha-olefin/non-conjugated diene elastomer; and
the thermoplastic elastomer curing system of claim 20 .
22. The modified blend of claim 1 , wherein the curing system is at least substantially free of TMPTMA-containing co-agents.
23. The modified blend of claim 1 , wherein the curing system is at least substantially free of methacrylate-containing co-agents.