High refractive index materials

Abstract

In some cases, fabricating a high refractive index polymer composite may include combining a thiol monomer and an ene monomer to yield a composite mixture, heating the composite mixture to yield a homogenous composite mixture, and curing the homogeneous composite mixture to yield a polymer composite, wherein the ene monomer comprises zirconium oxo (meth)acrylate clusters. The refractive index of the high refractive index polymer composite may be at least 1.70. In certain cases, fabricating a high reactive index polymer composite includes combining a vinyl (ene) monomer, a thiol monomer, and zirconium oxo (meth)acrylate clusters to yield a composite mixture, heating the composite mixture to yield a homogenous composite mixture, and curing the homogeneous composite mixture to yield a polymer composite. The refractive index of the high refractive index polymer composite may be at least 1.75.

Claims

1. A method of fabricating a high refractive index polymer composite, the method comprising: combining a thiol monomer and an ene monomer to yield a composite mixture; heating the composite mixture to yield a homogenous composite mixture; and curing the homogeneous composite mixture to yield a polymer composite, wherein the ene monomer comprises zirconium oxo (meth)acrylate clusters, and the zirconium oxo (meth)acrylate clusters provide 50 wt % to 100 wt % of the ene monomer in the composite mixture.

2. The method of claim 1, wherein the zirconium oxo (meth)acrylate clusters comprise Zr.sub.6(OH).sub.4O.sub.4(O.sub.2C(CH.sub.3)CH.sub.2).sub.12, Zr.sub.4O.sub.2(O.sub.2C(CH.sub.3)CH.sub.2).sub.12, Zr.sub.6(OH).sub.4O.sub.4(O.sub.2CHCH.sub.2).sub.12, Zr.sub.4O.sub.2(O.sub.2CHCH.sub.2).sub.12, or a combination thereof.

3. The method of claim 1, wherein the thiol monomer comprises 1,2-ethanedithiol, 1,5-pentanedithiol, 1,3-benzenedithiol, or a combination thereof.

4. The method of claim 1, wherein the refractive index of the polymer composite is at least 1.70.

5. The method of claim 1, wherein the zirconium oxo (meth)acrylate clusters provide a majority of the ene monomers by wt % in the composite mixture.

6. The method of claim 1, wherein the zirconium oxo (meth)acrylate clusters provide 75 wt % to 100 wt % of the ene monomer in the composite mixture.

7. A polymer composite formed by the method of claim 4.

8. An optical element comprising the polymer composite of claim 7.

9. The optical element of claim 8, wherein the optical element comprises a lens.

10. The method of claim 6, wherein the zirconium oxo (meth)acrylate clusters provide 90 wt % to 100 wt % of the ene monomer in the composite mixture.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts a first process for fabricating high refractive index materials.

(2) FIG. 2 depicts a second process for fabricating high refractive index materials.

(3) FIGS. 3-5 depict repeat units for high refractive index materials.

DETAILED DESCRIPTION

(4) High refractive index materials typically include constituent elements with high molecular polarizability. Constituent elements with higher molecular polarizability generally lead to materials with higher refractive indices. Elements with higher molecular polarizability include S, P, Ge, Zr, Ti, Si, and the like, as well as certain organic compounds such as those containing aromatic structures (e.g., benzene rings). In some cases, highly polarizable elements are doped into a host polymer matrix. Higher amounts of these elements enhance the refractive indices of the host materials to even higher values. In one example, high refractive index polymers are fabricated through incorporation of Zr-oxo-clusters (ZOCs) into a thiol-ene matrix. ZOCs generally refer to zirconium oxo (meth)acrylate clusters. Zirconium oxo and oxo zirconium are used interchangeably herein, and zirconium oxo (meth)acrylate clusters include zirconium oxo acrylate clusters, zirconium oxo acrylate clusters, and any combination thereof. Polymer composites based on thiol-ene and Zr-oxo-clusters (ZOCs) have been prepared via a process that includes dissolving ZOCs in ene (vinyl) monomer at room temperature, filtering the excess ZOCs from the ene monomer, and then adding thiol monomer to achieve polymerization, thereby forming a polymer composite. This process, and thus the refractive index of the resulting polymer composite, is limited by the solubility of ZOCs (typically up to 1 wt %) in the vinyl (ene) monomer.

(5) FIG. 1 depicts a process 100 for fabricating high refractive index materials. This process achieves a higher loading of ZOCs in the host material, thereby yielding polymer composites with refractive indices exceeding 1.75. In 102, a vinyl (ene) monomer, a thiol monomer, and zirconium oxo(methacrylate) clusters are combined to yield a composite mixture. In some cases, the vinyl (ene) monomer, ZOCs, and thiol monomer are combined sequentially to yield a composite mixture. In one example, the ZOCs are combined with the vinyl (ene) monomer, and the thiol monomer is then added to yield the composite mixture. However, the order of addition may be varied (e.g., the vinyl (ene) monomer and the thiol monomer may be combined first to yield a monomer mixture, and the ZOCs added to the monomer mixture; or the ZOCs may be combined with the thiol monomer, to which the vinyl (ene) monomer is subsequently added). The vinyl monomer and thiol monomer are typically combined in molar ratio such that number of vinyl groups equals number of thiol groups in the final monomer solution. ZOCs are typically added in an amount between 1 wt % and 15 wt % of the mixture (e.g., between 5 wt % and 15 wt %, or between 10 wt % and 15 wt %).

(6) Suitable vinyl monomers include, for example, trivinyl, trialyl, tetravinyl, and tetra-allyl monomers such as those depicted below, where M is Si, Ge, Sn, or the like.

(7) ##STR00002##

(8) Suitable thiol monomers include, for example, 1,2-ethanedithiol, 1,5-pentanedithiol, and 1,3-benzenedithiol, depicted below.

(9) ##STR00003##

(10) Suitable ZOCs include zirconium oxo acrylate or methacrylate clusters, such as Zr.sub.6(OH).sub.4O.sub.4(O.sub.2C(CH.sub.3)CH.sub.2).sub.12, Zr.sub.4O.sub.2(O.sub.2C(CH.sub.3)CH.sub.2).sub.12, Zr.sub.6(OH).sub.4O.sub.4(O.sub.2CHCH.sub.2).sub.12, Zr.sub.4O.sub.2(O.sub.2CHCH.sub.2).sub.12], and the like. The composite mixture may include any combination of one or more vinyl (ene) monomers and one or more thiol monomers.

(11) One or more components of the mixture (e.g., the vinyl monomer, the thiol monomer, or both) may be heated prior to forming the composite mixture.

(12) In 104, the composite mixture is heated (e.g., in a closed container) to dissolve the ZOCs in the composite mixture, thereby yielding a homogenous composite mixture. The homogeneous composite mixture is typically transparent. The monomers, the composite mixture, or any combination thereof may be heated (e.g., above room temperature) to dissolve the ZOCs. In some examples, the composite mixture is heated a temperature exceeding 25 C. (e.g., at least 50 C., at least 75 C., at least 100 C., or at least 125 C.) to yield a viscous, homogenous composite mixture free of undissolved ZOCs. In one example, the composite mixture is heated for about 30 minutes at 125 C. Excess ZOCs are not obtained upon filtration of the homogeneous composite mixture. As such, filtration to remove excess ZOCs is unnecessary, thereby streamlining the fabrication process while allowing a higher loading of ZOCs.

(13) Polymerization begins during heating of the mixture, thereby promoting solution of ZOCs as the reaction proceeds. In 106, the homogeneous composite mixture is cured to yield a polymer composite. In some cases, the homogenous composite mixture is cured in an air atmosphere for a length of time (e.g., at least 12 hours) to yield a high refractive index polymer composite. Polymer composites prepared by the process described in FIG. 1 may have refractive indices greater than 1.75, greater than 1.76, greater than 1.77, or greater than 1.78, and typically less than 1.80 (e.g., less than 1.79). Polymer composites prepared by the process described in FIG. 1 may have refractive indices greater than 1.75, greater than 1.76, greater than 1.77, or greater than 1.78.

(14) FIG. 2 depicts a process 200 for preparing high refractive index materials by crosslinking ZOCs with thiol monomers to yield polymer composites with enhanced optical properties. These free-standing polymer compositesmore glass-like that doped polymer compositesare rigid, highly transparent optical polymers with high inorganic content and high crystallinity. They demonstrate advantageous optical and mechanical properties, and can exhibit refractive indices above 1.70.

(15) In 202, an thiol monomer and an ene monomer including ZOCs are combined to yield a composite mixture. In 204, the composite mixture is heated to yield a homogeneous composite mixture. In 206, the homogeneous composite mixture is cured to yield a polymer composite. Process 200 includes crosslinking ZOCs with thiol monomers. Suitable ZOCs function as ene monomers, and include Zr.sub.6(OH).sub.4O.sub.4(O.sub.2C(CH.sub.3)CH.sub.2).sub.12, Zr.sub.4O.sub.2(O.sub.2C(CH.sub.3)CH.sub.2).sub.12, Zr.sub.6(OH).sub.4O.sub.4(O.sub.2CHCH.sub.2).sub.12, Zr.sub.4O.sub.2(O.sub.2CHCH.sub.2).sub.12, and the like. Suitable thiol monomers typically have at least two thiol functional groups, and include 1,2-ethanedithiol, 1,5-pentanedithiol, and 1,3-benzenedithiol, shown below.

(16) ##STR00004##
One or more suitable ZOCs may be reacted with one or more suitable thiol groups to yield a polymer composite with a high refractive index. The ZOCs and the thiol monomer are typically combined in a molar ratio such that number of vinyl groups equals number of thiol groups in the composite mixture.

(17) Polymer composites formed as described may include one or more of the repeating units shown in FIGS. 3-5, in which Oxo-Zr-Cluster may be one or more of Zr.sub.6(OH).sub.4O.sub.4(O.sub.2C(CH.sub.3)CH.sub.2).sub.12, Zr.sub.4O.sub.2(O.sub.2C(CH.sub.3)CH.sub.2).sub.12, Zr.sub.6(OH).sub.4O.sub.4(O.sub.2CHCH.sub.2).sub.12, Zr.sub.4O.sub.2(O.sub.2CHCH.sub.2).sub.12, and the like. The zirconium oxo clusters (ZOCs) provideene (vinyl) functionalities to form polymers through crosslinking with thiol monomers. Unlike polymer composites in which ZOCs are included as dopants, these polymer composites are formed with a majority of the ene reactant in the form of ZOCs.

(18) ZOCs may provide 1-100 wt % of the ene monomer in the composite mixture (e.g., 5-100 wt %, 10-100 wt %, 15-100 wt %, 20-100 wt %, 25-100 wt %, 50-100 wt %, 75-100 wt %, or 90-100 wt %). In certain cases, ZOCs provide a majority of ene monomer in the composite mixture. The ene monomer may consist essentially of ZOCs. That is, the ZOCs may provide all or substantially all the ene functionality in the composite mixture. Examples of other ene monomers suitable for use in combination with ZOCs are shown below, where M is Si, Ge, or Sn:

(19) ##STR00005##

(20) The reactant monomers (e.g., ene monomer and thiol monomer) can be combined in a stoichiometric ratio, with the number of available ene groups equal to the number of thiol groups, or any molar ratio (e.g., less than or greater than the stoichiometric ratio) effective to yield a polymer composite in the form of a free-standing polymer.

(21) Polymer composites described herein are suitable for use as optical elements, such as lenses.

(22) A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure.