REACTIVE MESOGEN BASED POLYMER PARTICLES

Abstract

This invention relates to a process for the preparation of monodisperse optical and shape anisotropic polymer particles comprising monomer units of at least one reactive mesogen, such particles per se, the use of these particles for the preparation of optical, electrooptical, electronic electrochemical, electrophotographic, electrowetting and electrophoretic displays and/or devices and security, cosmetic, decorative, and diagnostic applications, and electrophoretic fluids and displays.

Claims

1. A process for the preparation of polymer particles with optical anisotropy and shape anisotropy by dispersion polymerisation comprising a) forming a solution comprising at least one reactive mesogen having a molecular structure providing non-covalent interactions in the polymer particles, at least one solvent, at least one initiator, optionally at least one surfactant, and optionally at least one co-monomer b) polymerising the solution, and optionally c) separating, washing and/or drying the polymer particles.

2. Process according to claim 1, characterised in that the reactive mesogen has a molecular structure providing -interactions, hydrogen-bondings, and/or halogen-halogen interactions in the polymer particles.

3. Process according to claim 1, characterised in that the reactive mesogen comprises at least one diphenylacetylene group.

4. Process according to claim 1, characterised in that the reactive mesogen is a compound of Formula I ##STR00013## Wherein P=a polymerisable group; Sp.sup.1 and Sp.sup.2=independently of one another a spacer group; L, L, and L=independently of one another P-Sp-, F, Cl, Br, I, CN, NO.sub.2, NCO, NCS, OCN, SCN, C(O)NR.sup.00R.sup.000, C(O)X.sup.0, C(O)OR.sup.00, C(O)R.sup.0, NR.sup.00R.sup.000, SF.sub.5, optionally substituted silyl, aryl or heteroaryl with 1 to 12, preferably 1 to 6 C atoms, and straight chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy with 1 to 12, preferably 1 to 6 C atoms, wherein one or more H atoms are optionally replaced by F or Cl; R.sup.1=H, alkyl with 1 to 12 C-atoms or OR.sup.2 with R.sup.2=H or alkyl with 1 to 12 C-atoms; R.sup.0, R.sup.00, and R.sup.000=independently of each other denote H or alkyl with 1 to 12 C-atoms; and r=independently of one another, 0, 1, 2, 3 or 4.

5. Process according to claim 1, characterised in that, at least one reactive mesogen selected from compounds of Formula II-V is used ##STR00014##

6. Process according to claim 1, characterised in that, at least one co-monomer is selected from polymerisable dyes, reactive mesogens other than according to Formula I, ionic co-monomers, and polymerisable stabilisers, wherein the co-monomers comprise one or more ethylenically unsaturated groups.

7. Process according to claim 1, characterised in that the polymerisation is a thermal polymerisation.

8. Process according to claim 1, characterised in that the surfactant is PVP.

9. Process according to claim 1, characterised in that at least one polar solvent selected from water, toluene, ethylene glycol, glycine, ethanol, 3-pentanol, and butanol is used.

10. Polymer particles with optical anisotropy and shape anisotropy prepared by a process according to claim 1.

11. Polymer particles with optical anisotropy and shape anisotropy comprising at least one reactive mesogen of Formula I wherein Sp.sup.2=COO.

12. Polymer particles according to claim 11, characterised in that, at least one reactive mesogen selected from compounds of Formula II-IV is used.

13. Polymer particles according to claim 11, characterised in that, at least one co-monomer is used selected from polymerisable dyes, reactive mesogens other than according to Formula I, ionic co-monomers, and polymerisable stabilisers, wherein the co-monomers comprise one or more ethylenically unsaturated groups.

14. Use of polymer particles according to claim 10, electrooptical, electronic electrochemical, electrophotographic, electrowetting and electrophoretic displays and/or devices, and in security, cosmetic, decorative, and diagnostic applications.

15. Use according to claim 14, characterised in that the polymer particles are used for the preparation of a mono, bi or polychromal electrophoretic device.

16. Electrophoretic fluid comprising polymer particles according to claim 10.

17. Electrophoretic display device comprising an electrophoretic fluid according to claim 16.

18. Electrophoretic display device according to claim 17, characterised in that the electrophoretic fluid is applied by a technique selected from inkjet printing, slot die spraying, nozzle spraying, and flexographic printing, or any other contact or contactless printing or deposition technique.

Description

EXAMPLES

List of Abbreviations

[0103] RM520: 4-(6-acryloxy-hexyloxy) benzoic acid-2-chloro-4-(4-methyoxy phenyl ethinyl) phenylester
RM257: 2-methyl-1,4-phenylene-bis[4-(3-acryloyloxypropyloxy)benzoate]

PVP: Polyvinylpyrrolidone

[0104] V-59: 2,2-Azobis(2-methylbutyronitrile)
BDH1281: chiral dopant
MR3:N,N-bis-(2-Methacryloyloxyethyl)-4-(4-nitrophenylazo)-aniline
TiO.sub.2 nanoparticles: R960

[0105] Reactive mesogens and chiral dopant are purchased from Merck KGaA, Darmstadt, Germany. V-59 is purchased from Wako. MR3 is prepared according to example 16 of WO 2012/019704. Titania nanoparticles are obtained from Du Pont. All other chemicals are sourced from Sigma-Aldrich at the highest grade possible and are used without further purification unless otherwise stated.

[0106] The following examples are synthesised via dispersion polymerisation. Reactive mesogens (RMs), surfactant and other chemical are dissolved in ethanol. Then, the thermal initiator (which is soluble in the solvent) is added and the reaction is left to polymerise under nitrogen. The particles show internal director orientation, shape anisotropy, respond under very low electric and magnetic fields and they exhibit fluorescent properties.

[0107] The characterisation of the formulations is performed using a Malvern NanoZS particle analyser. This instrument measures the size of particles in dispersion and the zeta potential of an electrophoretic fluid. The Zeta potential (ZP) is derived from the real-time measurement of the electrophoretic mobility and thus is an indicator of the suitability of the fluid for use in electrophoretic applications.

Example 1

Preparation of a Particle Dispersion of RM520

[0108] 2.5 g of RM520, 250 mg of PVP and 70 mL of ethanol are added into a 100 mL round bottomed flask. The reaction mixture is heated at 80 C. under nitrogen atmosphere and stirred at 500 rpm. Once all the components are solved 200 mg of Vazo 59 (thermal initiator) is added into the reaction and the reaction is left to polymerise for 2 hours. After the two hours the reaction is cooled down to room temperature and the reaction mixture is filtered through a 50 micrometer cloth.

[0109] Highly oblate spheroidal particles result from this reaction (FIG. 2). The particles are monodisperse with a size of 1.1 microns and they exhibit a smartie-like shape with an (A/B) ratio of 2.05 and the flattening or oblateness (f) is 0.51.

[0110] Particles show the characteristic twinkling of bipolar colloids which results from the changing the director orientation during the Brownian motion. The particles rotate under low electric fields (30 mVpp, 100 Hz, ITO cells with 20 m spacers) and they aligned parallel to the magnetic field at very low field value (0.1-0.5 T) (FIG. 3).

Example 2

Preparation of a Particle Dispersion of RM520 with High Flattening or Oblateness

[0111] 5 g of RM520, 500 mg of PVP and 70 mL of ethanol are added into a 100 mL round bottomed flask. The reaction mixture is heated at 80 C. under nitrogen atmosphere and stirred at 500 rpm. Once all the components are solved 200 mg of Vazo 59 (thermal initiator) is added into the reaction and the reaction is left to polymerise for 2 hours. After the two hours the reaction is cooled down to room temperature and the reaction mixture is filtered through a 50 micrometer cloth.

[0112] Highly oblate spheroidal particles with a bipolar orientation of the molecular director result from this reaction. The size is 1.8 microns and compared to the particles described in example 1, they exhibit a flatter smartie-like shape what yields to an (A/B) ratio of 1.4 and the flattening or oblateness (f) is 0.76 (FIG. 4).

Example 3

Preparation of a Particle Dispersion of RM520 with Prolate Shape

[0113] 5 g of RM520, 500 mg of PVP, 235.5 mg BDH1281 and 70 mL of ethanol are added into a 100 mL round bottomed flask. The reaction mixture is heated at 85 C. under nitrogen atmosphere and stirred at 500 rpm. Once all the components are solved 100 mg of Vazo 59 (thermal initiator) is added into the reaction and the reaction is left to polymerise for 2 hours. After the two hours the reaction is cooled down to room temperature and the reaction mixture is filtered through a 50 micrometer cloth.

[0114] Flat-prolate particles with a bipolar orientation of the molecular director and with a perpendicular alignment respect to the magnetic field (0.5 T) are obtained (FIG. 5). The size is around 1.6 microns and the (C/D) ratio is 1.33, respectively. Birefringence vs magnetic field of a dispersion of the particles according to Example 3 is shown in FIG. 6.

Example 4

Preparation of a Particle Dispersion of RM520 with Diamond Shape

[0115] 5 g of RM520, 500 mg of PVP, 235.5 mg BDH1281 and 70 mL of ethanol are added into a 100 mL round bottomed flask. The reaction mixture is heated at 85 C. under nitrogen atmosphere and stirred at 500 rpm. Once all the components are solved 200 mg of Vazo 59 (thermal initiator) is added into the reaction and the reaction is left to polymerise for 2 hours. After the two hours the reaction is cooled down to room temperature and the reaction mixture is filtered through a 50 micrometer cloth.

[0116] Diamond-like anisotropic particles with a bipolar orientation of the molecular director result from this reaction. The dimensions of the particles are given by a (C/D) ratio of 1.68, (C/B) ratio is 2.28 and a B value of 0.7 microns (flattening of 0.8) (FIG. 7a/b).

[0117] A reversible self-assembly process is observed under low frequency electric field (30 mVpp, 100 Hz, 20 microns). The particles redisperse again when the electric field is removed. Additionally, the particles align parallel to the magnetic field (1 T) (FIG. 8a/b).

Example 5

Preparation of a Particle Dispersion of Reactive Mesogen Mixture I (Monoacrylate+Diacrylate)

[0118] 2.5 g of RM520, 250 mg of PVP, 12.5 mg RM257 and 70 mL of ethanol are added into a 100 mL round bottomed flask. The reaction mixture is heated at 85 C. under nitrogen atmosphere and stirred at 500 rpm. Once all the components are solved 200 mg of Vazo 59 (thermal initiator) is added into the reaction and the reaction is left to polymerise for 2 hours. After the two hours the reaction is cooled down to room temperature and the reaction mixture is filtered through a 50 micrometer cloth.

[0119] Oblate spheriodal particles with a size of 1.3 microns,

(A/B) ratio=2.02, f=0.54 and bipolar orientation of the molecular director result from this reaction.

Example 6

Preparation of a Particle Dispersion of Reactive Mesogen Mixture II (Monoacrylate+Monoacrylate)

[0120] 2.5 g of RM520, 250 mg of PVP, 125 mg of 4-(6-Acryloyloxy-n-hex-1-yloxy)benzoic acid and 70 mL of ethanol are added into a 100 mL round bottomed flask. The reaction mixture is heated at 85 C. under nitrogen atmosphere and stirred at 500 rpm. Once all the components are solved 200 mg of Vazo 59 (thermal initiator) is added into the reaction and the reaction is left to polymerise for 2 hours. After the two hours the reaction is cooled down to room temperature and the reaction mixture is filtered through a 50 micrometer cloth.

[0121] Highly oblate spheriodal particles with a size around 1.3 microns,

(A/B) ratio=1.93, f=0.63 and bipolar orientation of the molecular director result from this reaction.

Example 7

Preparation of a Particle Dispersion of RM520 Containing Titanium Dioxide Nanoparticles

[0122] 2.5 g of RM520, 250 mg of PVP, 250 mg of TiO.sub.2 nanoparticles (R960) and 70 mL of ethanol are added into a 100 mL round bottomed flask. The reaction mixture is heated at 85 C. under nitrogen atmosphere and stirred at 500 rpm. Once all the components are solved 200 mg of Vazo 59 (thermal initiator) is added into the reaction and the reaction is left to polymerise for 2 hours. After the two hours the reaction is cooled down to room temperature and the reaction mixture is filtered through a 50 micrometer cloth. Oblate spheriodal particles with a size around 1.1 microns, (A/B) ratio=2.07, f=0.52 and bipolar orientation of the molecular director result from this reaction.

Example 8

Preparation of a Red Coloured Particle Dispersion of RM520 and Merck Red 1

[0123] 2.5 g of RM520, 250 mg of PVP, 12.5 mg of Methacrylated Disperse Red 1 (MR3) and 70 mL of ethanol are added into a 100 mL round bottomed flask. The reaction mixture is heated at 85 C. under nitrogen atmosphere and stirred at 500 rpm. Once all the components are solved 200 mg of Vazo 59 (thermal initiator) is added into the reaction and the reaction is left to polymerise for 2 hours. After the two hours the reaction is cooled down to room temperature and the reaction mixture is filtered through a 50 micrometer cloth. Oblate spheriodal particles with a size around 1.1 microns, (A/B) ratio=1.70, f=0.40 and bipolar orientation of the molecular director result from this reaction.

FIGURES

[0124] FIG. 1: Schematic representation of the different shapes described in the present invention. (Left: top-view; Right: side-view).

[0125] FIG. 2: Oblate spheroidal particles made of RM520 in ethanol according to Example 1

[0126] FIG. 3: Representation of the birefringence vs magnetic field of a dispersion of the particles according to Example 1.

[0127] FIG. 4: Oblate spheroidal particles made of RM520 in ethanol with a high flattening value according to Example 2

[0128] FIG. 5: Flat-prolate particles made of RM520 in ethanol according to Example 3

[0129] FIG. 6: Representation of the birefringence vs magnetic field of a dispersion of the particles according to Example 3

[0130] FIG. 7a: Diamond-shape particles made of RM520 in ethanol according to Example 4

[0131] FIG. 7b: Diamond-shape particles made of RM520 in ethanol according to Example 4

[0132] FIG. 8a: Representation of the birefringence vs magnetic field of a dispersion of the particles according to Example 4

[0133] FIG. 8b: Self-assembly of the particles according to Example 4 under electric field