Method to produce colorless, high porosity, transparent polymer aerogels
A method to produce a polymer gel includes dissolving precursors in a solvent to form a precursor solution, the precursors including polymer precursors, a stable free radical, one or more initiating radicals, and one or more stable free radical control agents, and heating the precursor solution to a temperature of polymerization to produce a cross-linked gel. A dried polymer aerogel has a Brunauer-Emmett Teller (BET) surface area over 100 m2/g, porosity of greater than 10%, visible transparency greater than 20%, color rendering index of over 20%, and average pore size of less than 100 nm.
1. A method to produce a cross-linked, polymer gel, comprising:
dissolving precursors in a solvent to form a precursor solution, the precursors including polymer precursors, a stable free radical, one or more initiating radicals, and one or more stable free radical control agents; and
heating the precursor solution to a temperature of polymerization to produce the cross-linked, polymer gel.
2. The method of claim 1 , wherein the one or more stable free radical control agents comprises one or more reducing agents.
3. The method of claim 1 , wherein the one or more stable free radical control agents comprises one or more time-controlled decomposing initiators.
4. The method of claim 1 , wherein the one or more stable free radical control agents comprises a mixture of one or more reducing agents and one or more time-controlled decomposing initiators.
5. The method of claim 1 , further comprising mixing and deoxygenating the precursors in solvent.
6. The method of claim 1 , wherein the polymer precursors comprise from at least one selected from a first group consisting of: difunctional monomers with two vinyl groups; crosslinkers with three or more vinyl groups; divinylbenzene, tricyclodecane dimethanol diacrylate; hexanediol diacrylate; butanediol diacrylate; hexanediol dimethacrylate; butanediol dimethacrylate; trimethacryl adamantine; dipentaerythritol pentacrylate; either alone or in combination with at least one selected from a second group consisting of: monomers with one vinyl group, styrene, and methylmethacrylate.
7. The method of claim 6 , wherein the polymer precursors comprise 0.1-60% of the precursor solution.
8. The method of claim 1 , wherein the stable free radical comprises one of the group consisting of: a nitroxide species added directly, a nitroxide species derived from the decomposition of an alkoxyamine, 4-hydroxy-TEMPO, TEMPO, TIPNO, chlorobenzyl-TIPNO, SG1, and an alkoxyamine based on SG1 nitroxide joined to a methacrylic acid radical.
9. The method of claim 1 , wherein the stable free radical comprises 0.001-10 wt % of the precursor solution.
10. The method of claim 1 , wherein the one or more initiating radicals comprises an initiating radical derived from one of a conventional thermal initiator, a photoinitiator, or from decomposition of an alkoxyamine species.
11. The method of claim 1 , wherein the one or more initiating radicals has a decomposition half-life of less than 1 hour at the temperature of polymerization, and in the solvent of polymerization.
12. The method of claim 1 , wherein the one or more initiating radicals comprises 0.001-10 wt % of the precursor solution.
13. A method to produce a cross-linked, polymer gel, comprising:
dissolving precursors in a solvent to form a precursor solution, the precursors including polymer precursors, a stable free radical, one or more initiating radicals, and a stable free radical control agent comprising a reducing agent; and
heating the precursor solution to a temperature of polymerization to produce the cross-linked, polymer gel.
14. The method of claim 13 , wherein the reducing agent comprises one selected from the group consisting of: reducing sugars, reagents containing hemiacetal groups, glucose, hydroxyacetone, and reagents capable of forming enediol species.
15. The method of claim 13 , wherein the reducing agent comprises 0.001-20 wt % of the precursor solution.
16. The method of claim 13 , wherein the precursor also includes a time-controlled decomposing initiator.
17. A method to produce a cross-linked, polymer gel, comprising:
dissolving precursors in a solvent to form a precursor solution, the precursors including polymer precursors, a stable free radical, one or more initiating radicals, and a stable free radical control agent comprising a time-controlled decomposing initiator; and
heating the precursor solution to a temperature of polymerization to produce the cross-linked, polymer gel.
18. The method of claim 17 , wherein the time-controlled decomposing initiator is one of either a thermally-decomposing radical initiator or a mixture of thermally-decomposing initiators with half-life greater than 1 hour at the temperature of polymerization, and in the solvent of the polymerization.
19. The method of claim 17 , wherein the time-controlled decomposing initiator is one or more of the group consisting of: dicumyl peroxide, di-tert-butylperoxide, 2,2-bis(tert-butylperoxy)butane, 1,1-bis(tert-butylperoxy)cyclohexane, 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, 2,5-bis(tert-butylperoxy)2,5-dimethyl-3-hexyne, tert-butyl hydroperoxide, cumene hydroperoxide, or 2,4-pentanedione peroxide.
20. The method of claim 17 , wherein the time-controlled decomposing initiator comprises 0.001 to 10 wt % of the precursor solution.
21. The method of claim 17 , wherein the precursors also include a reducing agent.
22. The method of claim 1 , wherein the solvent comprises one or more selected from the group consisting of: acetophenone, xylenes, toluene, dimethylsulfoxide, dimethylformamide, n-methylpyrrolidone, and organic solvents with boiling points over 80° C. that dissolve the precursors.
23. The method of claim 1 , wherein the solvent comprises 40-99.9 wt % of the precursor solution.
24. The method of claim 1 , further comprising removing the solvent from the cross-linked, polymer gel to produce an aerogel.
25. The method of claim 24 , wherein removing solvent from the cross-linked, polymer gel comprises performing one or more solvent exchanges.
26. The method of claim 25 , wherein performing one or more solvent exchanges comprises:
performing one or more solvent exchanges with a first solvent that is compatible with the polymer precursors, such that the polymer precursors dissolve entirely in the solvent; and
performing one or more solvent exchanges with a second solvent that is only partially compatible with the polymer network such that linear polymers made from same components as the polymer network do not fully dissolve in the solvent.
27. The method of claim 26 , wherein the first solvent comprises one of:
tetrahydrofuran, toluene, xylenes, n-methylpyrrolidone, dimethylformamide, dimethylsulfoxide, or acetophenone, and the second solvent comprises one of: acetone, heptane, hexane, octane, water, or alcohols.
28. The method of claim 25 , wherein performing one or more solvent exchanges comprises performing one of either static solvent exchange or flow solvent exchange.
29. The method of claim 24 , wherein removing solvent from the cross-linked, polymer gel comprises drying the cross-linked, polymer gel after one of either heating the precursor solution to a temperature of polymerization or removing the solvent, by one of either ambient drying or supercritical CO 2 drying.