Thermally reversibile crosslinked polyolefins and related polymers, and related methods
The disclosure relates to thermally reversibly crosslinked polyolefins (TRC-PO) and methods for making the same. A TRC-PO can be formed by reactive melt-processing a mixture including (i) a polyolefin, (ii) an initiator, and (iii) a reversible crosslinker. The reversible crosslinker includes (A) a grafting agent moiety selected from unsaturated cyclic anhydrides, unsaturated cyclic imides, cyclic nitroxides, and ring-opened analogs thereof, and (B) a crosslinking moiety bound to the cyclic grafting agent moiety. This reactive melt-processing, for example including reactive extrusion, forms a thermally reversibly crosslinked (TRC) polyolefin with polyolefin chains reversibly crosslinked via the reversible crosslinkers, which provide dynamic covalent bonds, such as siloxanes and esters, that are amenable to melt re-processing to re-from or otherwise re-use the TRC-PO while still retaining the reversible crosslinks after re-processing. Catalysts and additives such as rheology modifiers can be added to the melt-processing mixture.
1. A method for forming a thermally reversibly crosslinked (TRC) polyolefin, the method comprising:
reactive melt-processing a mixture comprising (i) a polyolefin, (ii) an initiator, and (iii) a reversible crosslinker comprising (A) a grafting agent moiety selected from the group consisting of unsaturated cyclic anhydrides, unsaturated cyclic imides, cyclic nitroxides, and ring-opened analogs thereof, and (B) a crosslinking moiety bound to the grafting agent moiety, the crosslinking moiety comprising at least one of a silyl ether group and an ester group, thereby forming a thermally reversibly crosslinked (TRC) polyolefin comprising polyolefin chains crosslinked via crosslinking moieties therebetween.
2. The method of claim 1 , wherein the polyolefin comprises polyethylene.
3. The method of claim 1 , wherein the polyolefin comprises polypropylene.
4. The method of claim 1 , wherein the initiator comprises a peroxide free-radical initiator.
5. The method of claim 1 , wherein the grafting agent moiety comprises a 5-membered ring structure, a 6-membered ring structure, or a ring-opened analog thereof.
6. The method of claim 1 , wherein the grafting agent moiety comprises an unsaturated cyclic anhydride moiety.
7. The method of claim 1 , wherein the grafting agent moiety comprises an unsaturated cyclic imide moiety.
8. The method of claim 1 , wherein the grafting agent moiety comprises a cyclic nitroxide.
9. The method of claim 1 , wherein the crosslinking moiety comprises the silyl ether group.
10. The method of claim 9 , wherein the crosslinking moiety further comprises a secondary amino group.
11. The method of claim 9 , wherein the mixture being melt-processed further comprises at least one of a Lewis acid catalyst and a Brønsted acid catalyst.
12. The method of claim 9 , wherein the mixture being melt-processed further comprises a boronic compound.
13. The method of claim 1 , wherein the crosslinking moiety comprises the ester group.
14. The method of claim 13 , wherein the crosslinking moiety further comprises an internal transesterification acid catalyst.
15. The method of claim 13 , wherein the mixture being melt-processed further comprises an external transesterification acid catalyst.
16. The method of claim 1 , wherein the mixture being melt-processed contains the reversible crosslinker in a range from 0.5 mol. % to 40 mol. % relative to the polyolefin.
17. The method of claim 1 , wherein the TRC polyolefin has a crosslinking density in a range from 0.5 mol. % to 40 mol. %.
18. The method of claim 1 , wherein the TRC polyolefin is gel-free.
19. The method of claim 1 , wherein the mixture being melt-processed further comprises an additive selected from the group consisting of rheology modifiers, co-agents, and combinations thereof.
20. The method of claim 1 , wherein reactive melt-processing the mixture comprises:
reactively extruding the mixture.
21. The method of claim 1 , comprising:
prior to reactive melt-processing, adding to the mixture the reversible crosslinker comprising the grafting agent moiety and the crosslinking moiety bound thereto.
22. The method of claim 1 , comprising:
prior to reactive melt-processing, adding to the mixture a grafting agent comprising the grafting agent moiety and a crosslinker, thereby forming the reversible crosslinker as a product between the grafting agent and the crosslinker in situ during reactive melt-processing of the mixture.
23. A method for forming a thermally reversibly crosslinked (TRC) polyolefin, the method comprising:
reactive melt-processing a mixture comprising (i) a polyolefin, (ii) an initiator, and (iii) a reversible crosslinker comprising (A) a grafting agent moiety comprising at least one of an unsaturated cyclic anhydride moiety and an unsaturated cyclic imide moiety, and (B) a crosslinking moiety bound to the grafting agent moiety, thereby forming a thermally reversibly crosslinked (TRC) polyolefin comprising polyolefin chains crosslinked via crosslinking moieties therebetween.
24. The method of claim 23 , wherein the polyolefin comprises polyethylene.
25. The method of claim 23 , wherein the polyolefin comprises polypropylene.
26. The method of claim 23 , wherein the initiator comprises a peroxide free-radical initiator.
27. The method of claim 23 , wherein the grafting agent moiety comprises the unsaturated cyclic anhydride moiety.
28. The method of claim 23 , wherein the grafting agent moiety comprises the unsaturated cyclic imide moiety.
29. The method of claim 23 , wherein the crosslinking moiety comprises a silyl ether group.
30. The method of claim 23 , wherein the crosslinking moiety comprises an ester group.
31. The method of claim 23 , wherein the mixture being melt-processed contains the reversible crosslinker in a range from 0.5 mol. % to 40 mol. % relative to the polyolefin.
32. The method of claim 23 , comprising:
prior to reactive melt-processing, adding to the mixture the reversible crosslinker comprising the grafting agent moiety and the crosslinking moiety bound thereto.
33. The method of claim 23 , comprising:
prior to reactive melt-processing, adding to the mixture a grafting agent comprising the grafting agent moiety and a crosslinker, thereby forming the reversible crosslinker as a product between the grafting agent and the crosslinker in situ during reactive melt-processing of the mixture.
34. A method for forming a thermally reversibly crosslinked (TRC) polyolefin, the method comprising:
reactive melt-processing a mixture comprising (i) a polyolefin, (ii) an initiator, and (iii) a reversible crosslinker comprising (A) a grafting agent moiety selected from the group consisting of unsaturated cyclic anhydrides, unsaturated cyclic imides, cyclic nitroxides, and ring-opened analogs thereof, and (B) a crosslinking moiety bound to the grafting agent moiety, thereby forming a thermally reversibly crosslinked (TRC) polyolefin comprising polyolefin chains crosslinked via crosslinking moieties therebetween;
wherein the TRC polyolefin has at least one of properties (I) and (II):
(I) the TRC polyolefin has a crosslinking density in a range from 0.5 mol. % to 40 mol. %; and
(II) the TRC polyolefin is gel-free.
35. The method of claim 34 , wherein the polyolefin comprises polyethylene.
36. The method of claim 34 , wherein the polyolefin comprises polypropylene.
37. The method of claim 34 , wherein the initiator comprises a peroxide free-radical initiator.
38. The method of claim 34 , wherein the grafting agent moiety comprises a 5-membered ring structure, a 6-membered ring structure, or a ring-opened analog thereof.
39. The method of claim 34 , wherein the grafting agent moiety comprises an unsaturated cyclic anhydride moiety.
40. The method of claim 34 , wherein the grafting agent moiety comprises an unsaturated cyclic imide moiety.
41. The method of claim 34 , wherein the grafting agent moiety comprises a cyclic nitroxide.
42. The method of claim 34 , wherein the crosslinking moiety comprises a silyl ether group.
43. The method of claim 34 , wherein the crosslinking moiety comprises an ester group.
44. The method of claim 34 , wherein the mixture being melt-processed contains the reversible crosslinker in a range from 0.5 mol. % to 40 mol. % relative to the polyolefin.
45. The method of claim 34 , wherein the TRC polyolefin has the property (I) that the TRC polyolefin has a crosslinking density in a range from 0.5 mol. % to 40 mol. %.
46. The method of claim 34 , wherein the TRC polyolefin has the property (II) that the TRC polyolefin is gel-free.
47. The method of claim 34 , comprising:
prior to reactive melt-processing, adding to the mixture the reversible crosslinker comprising the grafting agent moiety and the crosslinking moiety bound thereto.
48. The method of claim 34 , comprising:
prior to reactive melt-processing, adding to the mixture a grafting agent comprising the grafting agent moiety and a crosslinker, thereby forming the reversible crosslinker as a product between the grafting agent and the crosslinker in situ during reactive melt-processing of the mixture.
49. A method for forming a thermally reversibly crosslinked (TRC) polyolefin, the method comprising:
reactive melt-processing a mixture comprising (i) a polyolefin comprising polyproplyene, (ii) an initiator, and (iii) a reversible crosslinker comprising (A) a grafting agent moiety selected from the group consisting of unsaturated cyclic anhydrides, unsaturated cyclic imides, cyclic nitroxides, and ring-opened analogs thereof, and (B) a crosslinking moiety bound to the grafting agent moiety, thereby forming a thermally reversibly crosslinked (TRC) polyolefin comprising polyolefin chains crosslinked via crosslinking moieties therebetween.
50. The method of claim 49 , wherein the initiator comprises a peroxide free-radical initiator.
51. The method of claim 49 , wherein the grafting agent moiety comprises a 5-membered ring structure, a 6-membered ring structure, or a ring-opened analog thereof.
52. The method of claim 49 , wherein the grafting agent moiety comprises an unsaturated cyclic anhydride moiety.
53. The method of claim 49 , wherein the grafting agent moiety comprises an unsaturated cyclic imide moiety.
54. The method of claim 49 , wherein the grafting agent moiety comprises a cyclic nitroxide.
55. The method of claim 49 , wherein the crosslinking moiety comprises a silyl ether group.
56. The method of claim 49 , wherein the crosslinking moiety comprises an ester group.
57. The method of claim 49 , wherein the mixture being melt-processed contains the reversible crosslinker in a range from 0.5 mol. % to 40 mol. % relative to the polyolefin.
58. The method of claim 49 , comprising:
prior to reactive melt-processing, adding to the mixture the reversible crosslinker comprising the grafting agent moiety and the crosslinking moiety bound thereto.
59. The method of claim 49 , comprising:
prior to reactive melt-processing, adding to the mixture a grafting agent comprising the grafting agent moiety and a crosslinker, thereby forming the reversible crosslinker as a product between the grafting agent and the crosslinker in situ during reactive melt-processing of the mixture.