Post polymerization cure shape memory polymers
This invention relates to chemical polymer compositions, methods of synthesis, and fabrication methods for devices regarding polymers capable of displaying shape memory behavior (SMPs) and which can first be polymerized to a linear or branched polymeric structure, having thermoplastic properties, subsequently processed into a device through processes typical of polymer melts, solutions, and dispersions and then crossed linked to a shape memory thermoset polymer retaining the processed shape.
1. A method comprising:
forming a polymer composition comprising a thermoplastic polymer: (a) having shape memory properties and crosslinkable sites substantially regularly spaced from each other, (b) which comprises at least one of a back bone and a side chain having an electron withdrawing group with alpha and beta positions, a methyne carbon in the alpha position, and an unsaturated carbon-carbon double bond in the beta position;
forming the polymer composition into a shape;
crosslinking the shaped thermoplastic polymer to form a thermoset polymer having shape memory properties;
wherein the thermoplastic polymer is a polyurethane.
2. The method of claim 1 , wherein the thermoplastic polymer includes crosslinkable sites that are double bonds.
3. The method of claim 1 , wherein the crosslinking includes crosslinking by at least one of heat and electron beam radiation.
4. The method of claim 1 , wherein the thermoplastic polymer has the side chain comprising the electron withdrawing group, the methyne carbon in the alpha position, and the unsaturated carbon-carbon double bond in the beta position.
5. The method of claim 1 comprising forming the thermoplastic polymer into a foam by at least one process selected from the group comprising freeze drying, high inverse phase emulsion foaming, physical blowing, pore templating, solution spinning, stereolithographic patterning, micro-extrusion, ink pen printing, 3D microdot based printing, and laser machining.
6. The method of claim 1 , wherein crosslinking the thermoplastic polymer includes a curing mechanism selected from the group consisting of thermally or radiatively initiated radical crosslinking of vinyl groups, peroxide or sulfur based crosslinking of vinyl groups, thiol addition to vinyl, reaction of isocyanate containing curing agents with hydroxyl, carboxylic acid, amine, or other functionality on the polymer chains; condensation of ester linkages, epoxy chemistry, silane and siloxane coupling reactions.
7. The method of claim 1 , wherein the thermoplastic polymer is derived from alkene diol monomers and the crosslinking includes crosslinking by e-beam radiation.
8. The method of claim 1 , wherein the thermoplastic polymer comprises at least one radiation sensitizer.
9. The method of claim 8 , wherein the radiation sensitizer comprises at least one tris[2-(acryloyloxy)ethyl]isocyanurate (TAcIc) and pentaerithol triacrylate (PETA).
10. The method of claim 1 comprising forming the thermoplastic polymer into a foam, and subsequently crosslinking the thermoplastic polymer into the thermoset polymer.
11. The method of claim 10 , wherein both of the thermoplastic and thermoset polymers are amorphous.
12. The method of claim 10 , wherein both of the thermoplastic and thermoset polymers are aliphatic.
13. The method of claim 10 , wherein the thermoplastic polymer is extruded.
14. The method of claim 10 comprising forming the thermoplastic polymer from trimethylhexamethylene diisocyanate.
15. An article of construction made by the method of claim 10 .