Light activated shape memory co-polymers
The present discovery uses monomers which contain reversible photo-crosslinkable groups in addition to primary polymerizable groups. The mechanical properties of these materials and the reversibility of the photo-activated shape memory effect demonstrate the effectiveness of using photo-irradiation to effect change in modulus and shape memory effect. In the preferred embodiment the reaction mixture includes a photo-reactive monomer comprising a photo reactive group and a polymerizable group; a second monomer, which is more preferably a mixture of monomers, which are acrylate based; a multi-functional crosslinking agent, preferably 1,6 hexanediol diacrylate (HDODA); an initiator, preferably a free radical initiator; and a fifth, optional, component which is a modifying polymer. The mixture of the second monomer, crosslinking agent, and initiator comprise the base polymer matrix into which the photo-reactive monomer is incorporated. The polymeriziable group of the photo reactive monomer allows the photo reactive monomer to polymerize with the base polymer matrix.
1. A thermoset cross-linked polymer network comprising polymerized units of (a) 30-70% by weight of a coumarin derivative photo reactive monomer, (b) 30-70% by weight of at least one additional monomer, and (c) more than 0% by weight less than 5% by weight of a crosslinking agent; said thermoset polymer network having a first initial crosslink density due to (c) the crosslinking agent and a second, photo-reversible crosslink density created upon exposure to a predetermined wavelength of light, and wherein the coumarin derivatives have the form:
wherein R1 is C1-C12 alkylene, arylene, or a bond, wherein R3 can be H, C1-C12 alkyl or aryl, wherein X can be O, S, HN, or a bond, and wherein R2 is a residue of a polymerizable group which copolymerizes with the (b) at least one additional monomer to form the thermoset cross-linked polymer network, wherein the thermoset cross-linked polymer network is an epoxy resin, oxetane resin, or polyurethane resin.
2. A thermoset cross-linked polymer network as recited in claim 1 wherein said thermoset cross-linked polymer network is a light activated shape memory polymer and said coumarin photo reactive monomer is a photo-reversible crosslinking monomer.
3. A thermoset cross-linked polymer network as recited in claim 1 wherein said polymerizable group is either glycidyl ether or hydroxy.
4. A thermoset cross-linked polymer network as recited in claim 1 wherein said polymerizable group is either a hydroxyl, carboxylic acid, acyl chloride, isocyanate, amine, or amide group.
5. A thermoset cross-linked polymer network as recited in claim 1 wherein said polymerizable group is either a hydroxyl, thiol, or amine group.
6. A thermoset cross-linked polymer network as recited in claim 1 wherein the coumarin photo reactive monomer (a) is a monomer that undergoes reversible photodimerization in the ultra violet range.
7. A thermoset cross-linked polymer network as recited in claim 1 wherein said cross-linking agent (c) is 1,6 hexanediol diacrylate (HDODA).
8. A polymer mixture comprising:
(1) the thermoset cross-linked polymer network of claim 1 ;
(2) a thermoplastic polymer;
wherein the thermoset polymer has a first initial crosslink density and a second, photo-reversible crosslink density created upon exposure to a predetermined wavelength of light.
9. A polymer mixture as recited in claim 8 wherein said (a) photo reactive monomer is a photo-reversible crosslinking monomer.
10. A polymer mixture as recited in claim 9 wherein said thermoset polymer and said thermoplastic polymer exist in the mixture as distinct polymers.
11. A polymer mixture as recited in claim 8 wherein said (c) cross-linking agent is 1,6 hexanediol diacrylate (HDODA).
12. A polymer mixture as recited in claim 8 wherein said thermoplastic polymer is polystyrene.