Crosslinked polyolefins for biomedical applications and method of making same
The invention relates to a polymer composition that includes a branched alkene which is cationically polymerizable as well as a glass-forming comonomer and/or a vinyl comonomer containing benzocyclobutene as the pendant group. The structure of the polymer composition can take various forms: linear random copolymer, linear block copolymer, star random copolymer, star block copolymer, and other hyperbranched polymers. The copolymer composition can undergoes crosslinking at elevated temperatures (preferably above 180° C.).
1. A method of preparing a thermoset copolymer comprising:
cationic polymerizing a mixture including i) at least one branched alkene monomer, ii) at least one olefin monomer having a pendant benzocyclobutene (BCB) group, and iii) at least one initiator suitable for cationic polymerization of the mixture to form the thermoset copolymer;
wherein the thermoset copolymer formed by cationic polymerization of the mixture is a block copolymer having a random distribution of a plurality of constitutional units that include constitutional units corresponding to the at least one branched alkene monomer of i) and constitutional units corresponding to the at least one olefin monomer having a pendant benzocyclobutene (BCB) group of ii); and
wherein the branched alkene monomer of i) is an isoolefin selected from the group consisting of isobutylene, 2-methyl-1-butene, 2-methyl-1-pentene, 2-methyl-1-hexene, and combinations thereof.
2. A method according to claim 1 , wherein:
the isoolefin is isobutylene.
3. A method according to claim 1 , wherein:
the at least one olefin monomer having a pendant BCB group includes a monomer having the formula
wherein R is hydrogen or an alkyl group and n is 0.
4. A method according to claim 3 , wherein:
the at least one olefin monomer having a pendant BCB group includes 4-vinylbenzocyclobutene or 2-(4-benzocyclobutenyl)-propene.
5. A method according to claim 1 , wherein:
the at least one olefin monomer having a pendant BCB group includes a monomer having the formula
wherein R is alkyl group and n is an integer ranging from 0-3.
6. A method according to claim 5 , wherein:
the at least one olefin monomer having a pendant BCB group includes 2-methyl-3-(4-benzocyclobutenyl)-propene.
7. A method according to claim 1 , wherein:
the mixture further includes iv) a glass-forming monomer selected from the group consisting of styrene, indene, α-methylstyrene, p-tert-butylstyrene, p-chlorostyrene, norbornene, and combinations thereof.
8. A method according to claim 1 , wherein:
the branched alkene monomer is isobutylene, the at least one olefin monomer having a pendant BCB group consists of 4-vinylbenzocyclobutene, and the mixture further includes iv) a glass-forming monomer consisting of styrene.
9. A method according to claim 1 , wherein:
said block copolymer is a triblock copolymer having a center segment and two end segments, wherein the triblock copolymer comprises (a) a random distribution of a plurality of constitutional units corresponding to both the branched alkene monomer and the olefin monomer having a pendant BCB group as the center segment, and the polymerized glass-forming monomer as the end segments; or (b) a random distribution of a plurality of constitutional units corresponding to both the branched alkene monomer and the olefin monomer having a pendant BCB group as the center segment, and a random distribution of a plurality of constitutional units corresponding to both the olefin monomer having a pendant BCB group and the glass-forming monomer as the end segments.
10. A method according to claim 1 , wherein:
said block copolymer is a star block copolymer having at least one arm having an inner segment and an outer segment, wherein the star block copolymer comprises (a) a random distribution of a plurality of constitutional units corresponding to both the branched alkene monomer and the olefin monomer having a pendant BCB group as the inner segment, and the polymerized glass-forming monomer as the outer segment; or (b) a random distribution of a plurality of constitutional units corresponding to both the branched alkene monomer and the olefin monomer having a pendant BCB group as the inner segment, and a random distribution of a plurality of constitutional units corresponding to both the olefin monomer having a pendant BCB group and the glass-forming monomer as the outer segment.
11. A method according to claim 1 , wherein:
the at least one olefin monomer having a pendant BCB group is present in amount ranging from 0.01 to 60 mol % of the monomeric units of the thermoset polymer.
12. A method according to claim 1 , wherein:
the cationic polymerizing involves living cationic polymerization.
13. A method according to claim 1 , wherein:
the thermoset polymer undergoes crosslinking when exposed to temperatures of at least 180° C.
14. A method according to claim 1 , wherein:
the at least one initiator comprises a Lewis acid initiator.
15. A method according to claim 1 , wherein:
a combination of the at least one branched alkene monomer of i) and the at least one olefin monomer having a pendant benzocyclobutene (BCB) group of ii) is added to the mixture during the cationic polymerizing of the mixture.
16. A method according to claim 7 , wherein:
the random distribution of the plurality of constitutional units comprises a random distribution of constitutional units corresponding to both the olefin monomer having a pendant BCB group of ii) and the glass-forming monomer of iv).
17. A method according to claim 7 , wherein:
a combination of the at least one olefin monomer having a pendant benzocyclobutene (BCB) group of ii) and the glass-forming monomer of iv) is added to the mixture during the cationic polymerizing of the mixture.
18. A method according to claim 1 , wherein:
the cationic polymerizing involves sequential monomer addition involving the branched alkene monomer of i) and the at least one olefin monomer having a pendant benzocyclobutene (BCB) group of ii).
19. A method of preparing a thermoset polymer comprising:
processing a thermoset copolymer prepared according to claim 1 to form a resultant polymer, wherein the processing includes heating the thermoset copolymer such that the thermoset copolymer undergoes crosslinking to form the resultant polymer.
20. A method of preparing an implantable medical device comprising:
processing a thermoset copolymer prepared according to claim 1 to form at least part of the implantable medical device, wherein the processing includes heating the thermoset copolymer such that the thermoset copolymer undergoes crosslinking to form a resultant polymer that is part of the implantable medical device.
21. A method according to claim 20 , wherein:
the implantable medical device comprises an intraocular lens.