Shape memory polymers and methods of making and use thereof
Described are shape memory polymers and methods of making shape memory polymers and actuators from the shape memory polymers.
1. A method of making a shape memory polymer, comprising:
partially crosslinking a prepolymer to form a partially crosslinked polymer, wherein the prepolymer comprises a semi-crystalline polymer;
stretching the partially crosslinked polymer to form a stretched, partially crosslinked polymer; and
crosslinking the stretched, partially crosslinked polymer, thereby making the shape memory polymer.
2. The method of claim 1 , wherein the semi-crystalline polymer comprises a polyethylene, polyethylene terephthalate, polytetrafluoroethylene, isotactic polypropylene, polyphenylene sulfide, polyetherketone, polyetheretherketone, polyphthalamide, polyetherketoneketone, thermoplastic polyimide, polybutylene terephthalate, polyoxymethylene, nylon, polyester, polyether, poly(caprolactone), or a copolymer thereof.
3. The method of claim 1 , wherein the prepolymer comprises acrylate end groups and partially crosslinking the prepolymer comprises base-catalyzed Michael addition of at least a portion of the acrylate end groups of the polymer and a multifunctional thiol.
4. The method of claim 1 , wherein the partially crosslinked polymer has a pre-stretched length; the stretched, partially crosslinked polymer has a post-stretched length; and the post-stretched length is from greater than 0% to 1000% longer than the pre-stretched length.
5. The method of claim 4 , wherein the post-stretched length is 100% or more longer than the pre-stretched length.
6. The method of claim 1 , wherein crosslinking the stretched, partially crosslinked polymer comprises a photocrosslinking reaction.
7. The method of claim 6 , wherein the photocrosslinking reaction comprises photocuring with UV irradiation in the presence of a photoinitiator.
8. The method of claim 1 , wherein the method occurs at a temperature above the melting temperature of the shape memory polymer.
9. The method of claim 1 , wherein stretching the partially crosslinked polymer comprises applying a load to the partially crosslinked polymer, and the method further comprises removing the load from the shape memory polymer, thereby making an actuator with a loadless length.
10. The method of claim 9 , wherein the partially crosslinked polymer has a pre-stretched length; the stretched, partially crosslinked polymer has a post-stretched length; and the loadless length is between the pre-stretched length and the post-stretched length.
11. The method of claim 9 , further comprising cooling the actuator to a temperature below the melting temperature of the shape memory polymer, thereby elongating the actuator along the direction to an elongated length.
12. The method of claim 10 , wherein the elongated length is from greater than 0% to 50% longer than the loadless length.
13. The method of claim 10 , further comprising heating the actuator to a temperature above the melting temperature of the shape memory polymer, thereby contracting the actuator along the direction to the loadless length.
14. The method of claim 11 , further comprising cooling the actuator to a temperature below the melting temperature of the shape memory polymer, thereby elongating the actuator along the direction to the elongated length.
15. A method of making a shape memory polymer, comprising:
providing a semi-crystalline polymer with photosensitive crosslinks and permanent crosslinks;
stretching and heating the semi-crystalline polymer; and
irradiating the stretched and heated semi-crystalline polymer, to thereby reshuffle the photosensitive crosslinks.