Polymer composites and films comprising reactive additives having thiol groups for improved quantum dot dispersion and barrier properties

Abstract

The present invention provides polymer composites, such as films, having dispersed therein quantum dots, wherein the polymer comprises (b) polymerized units of a first compound comprising from one to 6 thiol groups, the compound having a molecular weight from 300 to 20,000 and having at least one continuous acyclic hydrocarbyl chain of at least three carbon atoms, or, preferably, at least 5 carbon atoms; and (c) polymerized units of a second compound having a molecular weight from 100 to 750 and comprising at least two polymerizable vinyl groups as part of a (meth)acrylate ester group or attached directly to an aromatic ring and, wherein the molecular weight of the first compound minus the molecular weight of the second compound is at least 100. The polymer composites provide more stably dispersed and durable quantum dot compositions for use in, for example, display devices.

Claims

1. A polymer composite having dispersed therein quantum dots, the polymer composite comprising: (a) quantum dots; (b) polymerized units of a first compound comprising from one to 6 thiol groups and having a molecular weight from 300 to 20,000 and having at least one continuous acyclic hydrocarbyl chain of at least three carbon atoms; and (c) polymerized units of a second compound having a molecular weight from 100 to 750 and comprising at least two polymerizable vinyl groups as part of a (meth)acrylate ester group or attached directly to an aromatic ring and, wherein the molecular weight of the first compound minus the molecular weight of the second compound is at least 100.

2. The polymer composite as claimed in claim 1 in which the (a) quantum dots are cadmium-free quantum dots.

3. The polymer composite as claimed in claim 1 in which the first compound used to make the polymerized units (b) comprises at least one continuous acyclic hydrocarbyl chain of at least five carbon atoms.

4. The polymer composite as claimed in claim 1 in which the first compound used to make the polymerized units (b) further comprises at least one hydroxyl group.

5. The polymer composite as claimed in claim 1 in which the first compound used to make the polymerized units (b) comprises any of an oligomeric or polymeric adduct of an N-alkylamine thiol or a thiol group containing amino acid with a C.sub.12-C.sub.26 aliphatic hydroxycarboxylic acid; an adduct of an N-alkylamine thiol or a thiol group containing amino acid with a C.sub.12-C.sub.26 aliphatic carboxylic acid; an adduct of a thio alkylcarboxylic acid with a C.sub.12-C.sub.26 aliphatic diol or triol; or an adducts of a thio alkylcarboxylic acid with oligomers of one or more C.sub.4 to C.sub.16 hydroxyalkyl (meth)acrylates.

6. The polymer composite as claimed in claim 4 in which the first compound used to make the polymerized units (b) is an oligo (hydroxy fatty acid) amide having a terminal thiol group, wherein the fatty acid chain contains a hydroxyl group located three or more carbons from the end of the fatty acid chain.

7. The polymer composite as claimed in claim 6 in which the first compound used to make the polymerized units (b) is the thiolethylamide of 12-hydroxystearic acid or the thiolethylamide of oligo(12-hydroxystearic acid).

8. The polymer composite as claimed in claim 1 in which the second compound used to make the polymerized units (c) comprises a monomer chosen from one having (meth)acrylate ester groups attached to an aromatic ring or a cycloaliphatic group, one having vinyl groups directly attached to an aromatic ring or a cycloaliphatic group, or mixtures thereof.

9. The polymer composite as claimed in claim 1 in which the second compound used to make the polymerized units (c) is chosen from tricyclodecane dimethanol diacrylate, isobornyl dimethacrylate, divinyl benzene, or mixtures thereof.

10. The polymer composite as claimed in claim 1 in which the polymer composite comprises (a) from 0.001 to 5 wt. % of quantum dots, (b) from 0.5 to 40 wt. % of polymerized units of the first compound, and (c) from 55 to 94.999 wt. % of polymerized units of the second compound.

Description

EXAMPLES

(1) The following examples illustrate the present invention. Unless otherwise indicated, all units of temperature are room temperature and all units of pressure are standard pressure or 101 kPa.

(2) The following test methods were used:

(3) O.sub.2 permeability (cc/m/day/atm) of the indicated polymeric films was measured using a Mocon OX-TRAN model 2/21 device (Mocon, Inc., Minneapolis, Minn.). The method details are outlined in ASTM Method D3985 (Standard Test Method for Oxygen Gas Transmission Rate through a Plastic Film and Sheeting Using a Coulometric Sensor, Jan. 30, 1981) using a test gas of 3% O.sub.2 and 97% N.sub.2 at 23 C. The measurements were taken from films made in the manner disclosed below and having a 10 wt. % loading of the indicated first compound.

(4) Film thicknesses were determined by measurement of the cured films with a micrometer and then subtracting out the thickness of any barrier film thickness.

(5) Photoluminescent Quantum Yield (PLQY) was measured with a custom integrating sphere using a 450 nm excitation LED light source and a Hamamatsu Absolute PL quantum yield spectrometer (Hamamatsu Photonics KK, Shizuoka, Japan). For each reported example a total of three (3) measurements were taken from three (3) randomly selected points in each analyte substrate and the indicated PLQY represents an average of the measurements taken.

(6) Peak emission wavelength (PWL) was determined using a Hamamatsu integrating sphere; for green QD in the examples, below, the target wavelength is from 520 to 540 nm; for red QD, the target wavelength is from 620 to 640 nm.

(7) Abbreviations used in Examples:

(8) OHS is oligo(12-hydroxystearic acid), Mw=1,500; OHS-SH is oligo(12-hydroxystearic acid) containing a single thiol group, Mw=1,500; C is cysteine; IBOA is isobornyl acrylate; SR833 is tricyclo [5.2.1.0.sup.2,6] decane dimethanol diacrylate; I-819 and I-651 are IRGACURE photoactive polymerization initiators (BASF AG, Leverkusen, Del.); Finex zinc oxide particles (Sakai Chemical Industry co., LTD., Japan); and CFQD stands for cadmium free quantum dots. Green CFQD comprise core-shell QDs having Indium containing cores and exhibit an 73.9% QY (PLOY), 44.1 nm FWHM, and a 534.4 nm PWL (at absorbance=0.3). All quantum dots further comprise a non-polar ligand.

(9) The OHS with one carboxyl acid group and one hydroxyl group is modified by the incorporation of thiol group through cysteine via a peptide reaction. To prepare OHS-SH, the OHS (9.115 g, 6.2 mmol) and N-hydroxysuccinimide (NHS, 1.8 g, 15.5 mmol, 2.5 molar eq.) were mixed together in 40 mL of anhydrous toluene under an N.sub.2 atmosphere. A solution of disodium ethylenediamine tetraacetate dihydrate (EDTA disodium salt, 3 g, 15.5 mmol, 2.5 molar eq.) in dimethylformamide (DMF) (60 mL) was slowly added using a pressure-equalized addition funnel. The solution was maintained at 20 C. for 24 h to complete the activation of all carboxyl groups. 3.8 g cysteine (31 mmol, 5 molar eq.) was dissolved in anhydrous DMF (120 ml) and then mixed with trimethylamine (1.6 g, 15.5 mmol, 2.5 molar eq.). The resulting mixture was slowly charged into the NHS-activated polymer solution under N.sub.2 and further stirred for 24 h. The DMF was then removed and the final product was extracted using toluene, and washed with a saturated NaCl solution. Finally, toluene was removed under N.sub.2 purge and the product was dried in vacuum oven at RT overnight.

Example 1

(10) All indicated polymer composites were films that were prepared by lamination of the indicated resin formulations between two i-Component PET barrier films. Approximately 2 mL of resin was dispensed on the bottom film and was drawn down with a gap coating bar having a 250 to 300 (10 mil-12 mil) gap to insure the desired film thickness. All formulations were cured using a DRS-10/12 QNH at, 500 mJ/cm.sup.2 UV curing intensity (Fusion UV Systems, Inc., Gaithersburg, Md.).

(11) Formulations are indicated in Table 1, below. Such formulations were made by blending the indicated second compound monomer and a photoinitiator together, followed by mixing the first compound or a comparative compound not containing a thiol group with the second compound monomer and heating the resulting mixture to 50 C. for 15 mins. A second compound monomer IBOA (Isobornyl acrylate) was then blended with the indicated QD into the mixture. The mixture was formed or poured into the film, as disclosed in the prior paragraph, and then cured under UV light for about 3 s. Quantum yield results are shown in Table 2, below.

Example 3 and Comparative Example 3A

(12) In each example, oxygen permeability was determined for each of two films made using the formulation in Table 1, below, and in the manner disclosed in Example 1, above, except that the film was formulated with a 10 wt. % loading of the first compound or indicated comparative compound. The results reported are the average of the two films. Oxygen permeability results are shown in Table 3, below.

(13) TABLE-US-00001 TABLE 1 Formulations PHS PHS-SH PI-819 SR833 IBOA Green CFQD Finex EXAMPLE (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) 1A* 6 1.5 85.5 5 0.5 2 1B*- 1.5 91.5 5 0.5 2 Control 2 6 1.5 85.5 5 0.5 2 *Denotes Comparative Example.

(14) TABLE-US-00002 TABLE 2 Quantum Yield Results EXAMPLE PLQY (%) Abs PWL (nm) 1B* Control 38 0.46 544 1A* 6 wt. % OHS 45 0.42 534 2 6 wt. % OHS-SH 43 0.43 534 *Denotes Comparative Example.

(15) As shown in Table 2, above, the quantum yield of the inventive polymer films in Examples 2 is superior to the control. The peak wavelengths are similar in Examples 2 and 1A, indicating a reasonably low red-shift in the compositions of the present invention. Further, the peak Absorbance of the film of inventive Example 2 is superior to that of the Comparative Example 1A, indicating that the QDs are better dispersed in Example 2 than Example 1B.

(16) TABLE-US-00003 TABLE 3 Oxygen Permeability Example 3 - O.sub.2 Comparative Example 3A* - O.sub.2 permeability (cc/m/day/atm) permeability (cc/m/day/atm) of film with 10% OHS-SH of film with 10% OHS 0.021 0.002 0.030 0.003 *Denotes Comparative Example.

(17) As shown in Table 3, above, the oxygen permeability of films made in accordance with the present invention is dramatically lower than a film of the same compositions having a hydroxyl fatty acid first compound without a thiol group. The results indicate that the QD composition is well-dispersed in the cured polymer composite and is more reliable than the composition of Comparative Example 3A.