POLYMERS GRAFTED ONTO A METAL OXIDE SURFACE, METHOD OF GRAFTING POLYMERS ONTO A METAL OXIDE SURFACE, GRAFT POLYMER SUITABLE FOR THE METHOD

Abstract

Metal oxide having a surface onto which a multitude of individual polymers are grafted, each polymer comprising an addition polymer having a first and a second end, and a first moiety comprising a terminal phosphonate group, which first moiety is bonded to the first end, which phosphonate group attaches to the metal oxide surface in such a way that the multitude of the grafted polymers comprises at least one group of adjacent polymers that have a stretched chain conformation wherein the adjacent stretched chains have a substantially parallel orientation, such that the polymers within said group together form a brush structure. Method of grafting a multitude of individual polymers onto a surface of a metal oxide.

Claims

1. Metal oxide having a surface onto which a multitude of individual polymers are grafted, each polymer comprising an addition polymer having a first and a second end, and a first moiety comprising a terminal phosphonate group, which first moiety is bonded to the first end, which phosphonate group attaches to the metal oxide surface in such a way that the multitude of the grafted polymers comprises at least one group of adjacent polymers that have a stretched chain conformation wherein the adjacent stretched chains have a substantially parallel orientation, such that the polymers within said group together form a brush structure.

2. Metal oxide according to claim 1, wherein the group of polymers forming a brush structure, are grafted onto a non-spherical metal oxide surface.

3. Metal oxide according to claim 1, wherein the metal oxide is diamagnetic.

4. Metal oxide according to claim 1, wherein the group of polymers forming a brush structure, have an average distance D on the metal oxide surface between adjacent polymers, wherein D/2 is smaller than the average radius of gyration Rg of a random coil conformation of the individual grafted polymers.

5. Metal oxide according to claim 1, wherein the grafted polymers have a small polydispersity index (PDI) which is the ratio of the weight average molecular weight (Mw) and is the number average molecular weight (Mn), the PDI value being between 1 and 2.

6. Metal oxide according to claim 1, wherein each of the grafted polymers has a second moiety comprising a terminal aliphatic group, which second moiety is bonded to the second end via a thiocarbonylthio (SC(S)) group.

7. Metal oxide according to claim 1, wherein the addition polymer comprises a linear chain of carbon atoms, which comprises 10 to 50 carbon atoms.

8. Metal oxide according to claim 1, wherein the addition polymer is a polystyrene, polyisoprene, polyacrylonitrile, polyacrylate, polymethacrylate, ABS, SAN, or a combination thereof.

9. Metal oxide according to claim 6, wherein the terminal aliphatic group is a linear alkyl group chosen from n-butyl up to n-dodecyl.

10. Metal oxide according to claim 1, wherein the phosphor atom P of phosphonate group is bonded to the first end via a carboxylate group.

11. Metal oxide according to claim 10, wherein the carboxylate group is bonded to the first end via a C(CH3)(CH3)- group

12. Metal oxide according to claim 1, wherein the metal oxide is in the form of a particle in the range of 20 to 200 nm.

13. Metal oxide according to claim 1, wherein the metal oxide is in the form of a macroscopic sheet, such that the grafted polymers form a coating layer.

14. Polymer material containing a polymer medium in which a multitude of metal oxide particles according to claim 12 are dispersed, and wherein the polymer medium is compatible with the polymers grafted onto the metal oxides.

15. Dielectric article comprising a polymer material according to claim 14, having a relative permittivity .sub.r of 3 or higher.

16. Method of grafting a multitude of individual polymers onto a surface of a metal oxide, wherein each polymer comprises an addition polymer having a first and a second end, and a first moiety comprising a terminal phosphonate group, which first moiety is bonded to the first end, comprising the steps of: dissolving the individual polymers in an appropriate solvent; applying the formed solution onto the surface of the metal oxide; allowing the individual polymers to attach to the surface, wherein the phosphonate group attaches to the metal oxide surface during the method in such a way that the obtained multitude of grafted polymers onto the surface of the metal oxide comprises at least one group of adjacent polymers that have a stretched chain conformation wherein the adjacent stretched chains have a substantially parallel orientation, such that the polymers within said group together form a brush structure.

17. Method according to claim 16, wherein the group of polymers forming a brush structure, have an average distance D on the metal oxide surface between adjacent polymers, wherein D/2 is smaller than the average radius of gyration Rg of a random coil conformation of the individual grafted polymers.

18. Graft polymer suitable for grafting onto a metal oxide surface according to the method of claim 16, wherein the polymer comprises an addition polymer having a first and a second end, and a first moiety comprising a terminal phosphonate group, which first moiety is bonded to the first end, wherein the polymer has a second moiety comprising a terminal aliphatic group, which second moiety is bonded to the second end via a tristhiocarbonate (SC(S)S) group, wherein the phosphor atom P of the phosphonate group is bonded to the first end via a methylene carboxylate group (PCH2-O(O)C).

19. Graft polymer according to claim 18, wherein the addition polymer comprises a linear chain of carbon atoms, which comprises 10 to 50 carbon atoms.

20. Metal oxide according to claim 4, wherein D/2 is 70% of the average radius of gyration Rg or smaller.

Description

EXAMPLE

[0079] The invention is further illustrated by the below example, together with appended drawings, wherein:

[0080] FIG. 1 shows a reaction scheme for producing a graft polymer according to the invention;

[0081] FIG. 2 shows schematically two adjacent grafted polymers attached to a flat metal oxide surface;

[0082] FIGS. 3a and 3b show two different conformations of two different polymers grafted onto a flat metal oxide surface;

[0083] FIG. 4 shows a metal oxide particle of rutile that is preferably used in the invention.

[0084] FIG. 1 shows a reaction scheme wherein a pre-polymer IV is prepared, which has the functionality of a RAFT reagent. The pre-polymer IV is allowed to react with styrene in AIBN and DMF, thus forming a polymer V, which is a graft polymer according to the invention. The graft polymer V was prepared in three batches with three different numbers of repeating styrene units, wherein n=18, 23 or 42.

[0085] Pre-polymer IV is prepared by allowing compound I to react with oxalyl chloride in DMF and DCM, thus obtaining compound II. Compound II is reacted with a dimethyl phosphonate IIa to obtain compound III. Compound III is reacted in SiMe3Br, DCM, and MeOH, to obtain compound IV.

[0086] The graft polymer V (having n=18, 23 or 42) was dissolved in an appropriate solvent such as DMF and brought in a reactor containing rutile nanoparticles. The solution of graft polymer V was allowed to react with the rutile nanoparticles under ambient conditions for 24 hours. Subsequently the particles grafted with polymer V were separated by centrifuge and dried at 60 C. under reduced pressure.

[0087] FIG. 2 shows schematically two adjacent graft polymers 1 that are attached to a flat titanium dioxide surface 3. The distance D on the titanium dioxide surface between the two adjacent graft polymers 1 is indicated, as well as the average radius of gyration Rg of a random coil conformation of the individual grafted polymers (the polymers are not visualized as a random coil, but simply as rods perpendicular to the surface). When D/2 is equal or larger than Rg, the conformation of a random coil is preferred for reasons of entropy.

[0088] FIG. 3a resp. 3b show two conformations of two different polymers 4, resp. 5, that are grafted onto a flat titanium dioxide surface 3. The polymers 4, resp. 5, were grafted onto the surface 3 by applying a solution of the respective polymers onto rutile nanoparticles according to above outlined procedure.

[0089] FIG. 3a shows three adjacent grafted polymers 4, which are almost equal to graft polymer V, with the exception that the terminal attaching group is not a phosphonate group but a carboxyl group instead. Each graft polymer 4 has 23 styrene units. The distance D between adjacent polymers is such that D/2 is larger than Rg (the average radius of gyration Rg of a random coil conformation). [0090] From FIG. 3a it follows that when grafting onto a metal oxide a polymer having as a terminal attaching group a carboxyl group, a random coil conformation is achieved.

[0091] FIG. 3b shows eight adjacent grafted polymers 5, which are exactly equal to graft polymer V. Each graft polymer 5 has 23 styrene units. The distance D between adjacent polymers is such that D/2 is smaller than Rg (the average radius of gyration Rg of a random coil conformation). [0092] FIG. 3b shows that when grafting onto a metal oxide a polymer having a phosphonate group as a terminal attaching group, a stretched chain conformation is achieved wherein the adjacent stretched chains have a substantially parallel orientation, such that the polymers within said group together form a brush structure.

[0093] The above qualitative difference is supported by the below measurement of the distance D between adjacent polymers grafted onto a flat titanium dioxide surface:

TABLE-US-00001 Attaching group of graft polymer, number of styrene Conformation units D/2 (nm) Rg (nm) of polymer chain Carboxylate, 23 1.55 1.51 Random coil Phosphonate, 18 0.74 1.30 Stretched chain Phosphonate, 23 0.79 1.51 Stretched chain Phosphonate, 42 0.92 2.17 Stretched chain

[0094] From the above results, it follows that the graft polymer according to the invention allows for a grafting onto a metal oxide, wherein D/2 for adjacent polymers is substantially smaller than the Rg value of the individual polymers. Accordingly, the adjacent polymers are forced by their mutual steric hindrance to adopt a stretched chain conformation. Consequently, the adjacent graft polymers according to the invention together form a brush structure with the concomitant advantages such as a better shielding of the metal oxide surface.

[0095] FIG. 4 shows a metal oxide particle 40 of rutile, which is a type of TiO2 crystal that is preferably used in the invention. The length of the particle is approximately 140 to 180 nm. The width and height of the particle is approximately 30 to 35 nm. The larger flat surfaces 42 are especially suitable for grafting polymers onto according to the invention. When grafted onto surfaces 42, the free tail ends of adjacent grafted polymers have a limited distance to each other which forces them to adapt a stretched chain conformation, as long as the relationship is fulfilled that D/2 is smaller than Rg.