Method to create gradient index in a polymer
Novel photo-writable and thermally switchable polymeric materials exhibit a refractive index change of Δn≧1.0 when exposed to UV light or heat. For example, lithography can be used to convert a non-conjugated precursor polymer to a conjugated polymer having a higher index-of-refraction. Further, two-photon lithography can be used to pattern high-spatial frequency structures.
1. A method to create a gradient index in a polymer, comprising:
providing a low-index non-conjugated precursor polymer having a photocleavable leaving group; and
photoexposing the precursor polymer to eliminate the photocleavable leaving group, thereby providing a conjugated polymer having a higher index-of-refraction than the precursor polymer, wherein the non-conjugated precursor polymer is exposed to different doses of photons in different regions to create a graded index material.
2. The method of claim 1 , wherein the non-conjugated precursor polymer comprises a precursor to poly(phenylene vinylene).
3. The method of claim 1 , wherein the non-conjugated precursor polymer comprises a precursor to polyacetylene, poly(p-phenylene), poly(thiophene vinylene), poly(pyrrole vinylene), poly(1,4-naphthylene vinylene), poly(p-pyridine vinylene), or a substituted version thereof.
4. The method of claim 1 , wherein the photocleavable leaving group comprises a xanthate.
5. The method of claim 1 , wherein the photocleavable leaving group comprises an acetate, dithiocarbamate, sulfinyl, sulfonium, or halogen.
6. The method of claim 1 , wherein the precursor polymer further comprises at least one alkoxysilane end group to enable crosslinking of the precursor polymer.
7. The method of claim 1 , wherein the photoexposing comprises photopatterning.
8. The method of claim 7 , wherein the photopatterning is accomplished using contact lithography.
9. The method of claim 7 , wherein the photopatterning is accomplished using multiphoton lithography.
10. A method to create a gradient index in a polymer, comprising:
providing a low-index non-conjugated precursor polymer comprising a thermally activated leaving group; and
locally heating the precursor polymer to eliminate the leaving group, thereby providing a conjugated polymer having a higher index-of-refraction than the precursor polymer, wherein the non-conjugated precursor polymer is exposed to different amounts of local heating in different regions to create a graded index material.
11. The method of claim 10 , wherein the non-conjugated precursor polymer comprises a precursor to poly(phenylene vinylene).
12. The method of claim 10 , wherein the non-conjugated precursor polymer comprises a precursor to polyacetylene, poly(p-phenylene), poly(thiophene vinylene), poly(pyrrole vinylene), poly(1,4-naphthylene vinylene), poly(p-pyridine vinylene), or a substituted version thereof.
13. The method of claim 10 , wherein the thermally activated leaving group comprises a xanthate.
14. The method of claim 10 , wherein the thermally activated leaving group comprises an acetate, dithiocarbamate, sulfinyl, sulfonium, or halogen.
15. The method of claim 10 , wherein the precursor polymer further comprises at least one alkoxysilane end group to enable crosslinking of the precursor polymer.
16. The method of claim 10 , wherein the locally heating is accomplished using an atomic force microscope.
17. The method of claim 10 , wherein the locally heating is achieved by exposure to photons.