FR2721937A1 - Crosslinked NLO active polymers useful in optical communications - Google Patents

Abstract

Crosslinked nonlinear optical (NLO) polymers contain an NLO-active component which is covalently bonded to an amino resin. Also claimed an NLO-active amino resin precondensate; a process for the production of the amino resin; the use of the resins as a coating; and the use of the polymers as optical communications.

Description

Crosslinked ONL polymers, process for their preparation and their use
The present invention relates to polymers for nonlinear optics (ONL polymers), which are suitable, for example, for use in optical transmission elements of information.

 It has been suggested in recent years to replace known mineral single crystals with organic materials having nonlinear optical properties. These are finding more and more opportunities for use, for example in the rapidly growing field of telecommunications. It has been found in particular that organic materials having extended electron systems Ir exhibit nonlinear optical effects of considerable magnitude.

Two different strategies for the provision of materials of this kind have developed so far. The first is to dope polymers using (relatively small amounts) chromophores. Such systems are referred to by the term Guest-Host polymer. "Poly (methylmethacrylate) has been used as a polymeric matrix since the dye used has been an azo dye, which is disadvantageous in such systems. the fact that the basic chromophore elements can not be optimally oriented and that the dyes are partially exposed to diffusion processes, in addition to an increase in the proportion by mass of the dyestuff contained therein. It is possible only in a restricted way (not more than 10%), so that no sufficient electro-optical coefficient can be reached (R. Loucif-Saibi et al.
Chem. Mater. 1993, 5, 229-236).

Another "Guest-Host" system consists of polyvinyl cinnamate as "Host" and an azo dye having Cinnamoyl moieties as "Guest".

Although this system may undergo subsequent crosslinking by a [2 + 2] cycloaddition, it nevertheless remains the disadvantage of the fact that, in principle, in the Guest-Host systems, the density of the chromophoric groups remains insufficient because of their limited miscibility in the polymer.

The second strategy exploits the production of copolymers, consisting of a main polymer chain with chromophoric base elements chemically bonded thereto. Strohriegl et al (Makromol Chem, 194, 363-387, 1993) and Müller et al (Makromol Chem., Rapid Commun 13, 289, 198, 1992) describe polymethacrylate systems having active ONL side groups. It is thus possible to proceed to the synthesis of copolymers by an esterification, analogous to a polymerization, of poly (methacryloyl chloride) or of copolymers, consisting of methacryloyl chloride and methacrylate, with active azo dyes in ONL, the groups chromophores being located in the side chain. The radical polymerization of the corresponding methacrylates with ONL active side groups is a known synthetic strategy for the preparation of materials having nonlinear optical properties (Mahlmann, G.R., Synthetic Metals 37, 207-221, 1990).

By means of a cationic polymerization technique, the p-nitrophenyl B-vinyloxyethyl ether monomer can be polymerized with the S-vinyloxyethyl cinnamate monomer, an ONL-active material also obtainable (see Hashidate et al., Polymers). for Advanced Technologies, 3, 145-149, 1992).

The classes of substances known at present, for a low optical damping and for a sufficiently large electro-optical coefficient, only reach glass transition temperatures of up to 2000 ° C.

However, relaxation mechanisms already play a role, well below this temperature. In the system described by Wedel et al. (Acta
Polymer., 44, 302-306, 1993) having a temperature of about 900 ° C., much more than half of the orientation is lost in the course of 140 days, the loss during the first hours being the stronger (about 50% in 1000 minutes). It is for this reason that polymers of this type are unsuitable for long-term uses, as they are necessary for use in, for example, telecommunications.

The object of the present invention is to provide ONL polymers which have, on the one hand, excellent optical and electrical properties, which, on the other hand, have however in comparison with known ONL polymers up to significant improvement in their long-term stability. In addition, ONL polymers must be such that films or films can be made from them that can be used in optical systems.

It has surprisingly been found that the object according to the invention is solved by the provision of a new class of ONL substances, which incorporates an amino resin (crosslinked) and at least one active component in ONL having groups oriented chromophores, which component is covalently bound to the resin through at least one functional group accessible by amino resin reactions.

The cross-linked ONL polymers according to the invention can be prepared among other things in the form of layers or films. In one embodiment of the invention, they are deposited in this form on optical articles. They exhibit defined reflection and absorption properties, a high electro-optical coefficient and a long-term stability, respectively a defined thermal stability.

They can also be prepared in a cost-effective manner, not harmful to the environment and by a simple process technology.

The polymers according to the invention are manufactured in most cases, after forming, preferably as a thin layer on a suitable substrate, by a thermally activated polycondensation of precondensates of amino active resin in ONL, soluble in water, respectively soluble in organic components.

The water-soluble amino resin components used, respectively soluble in organic components, can be prepared in this case from usual amino resins or also from, for example, amino resins specially synthesized from the aldehyde and amine monomer components. multifunctional. As the usual water-soluble amino resins soluble in organic components, respectively, all transparent materials, melamine-formaldehyde-lacquer resins soluble in organic components and soluble melamine-formaldehyde adhesive resins can be used. water being particularly suitable.

Especially synthesized precondensate aldehyde components may be formaldehyde and acetaldehyde as well as glyoxal or glutardialdehyde or mixtures of these aldehydes. As components containing amino groups, it is possible to use all the substances known from the chemistry of amino resins, for example melanin, urea, dicyandiamide or urethanes, or mixtures thereof.

The introduction of the active component in ONL is done through the addition and condensation reactions typical of the amino resins on the reactive groups of the component
ONL, the amino groups being preferred reactive groups of the resin component. It is thus possible to use, according to the invention, for the preparation of crosslinked active polymers in ONL, all active compounds in ONL, which have reactive groups typical of amino resins. The classes of active substances in ONL suitable for the process are, for example, nitroaromatic compounds, nitroazobenzenes and nitro-stilbenes or nitro derivatives of aromatic heterocycles.

The active ingredient in ONL can be a single substance or a mixture of various active substances in ONL. In the case of ONL active substances containing amino groups, these compounds can provide by themselves the component containing amino groups of the precondensate. However, they are usually a part of other resin components and are used in amounts of 5-60% by weight, based on the amino group-containing component of the amino resin.

According to the invention, the active precondensate can be synthesized in ONL as a function of the chemical structure of the amino resin component in the aqueous phase or in the organic phase. Suitable organic solvents are aliphatic and aromatic hydrocarbons, higher alcohols, amide solvents (dimethylformamide, N-methylpyrrolidone, etc.) or ketone type.

Preferred solvents are n-butanol and xylene. In the case of preparation of the precondensate in an aqueous medium, it is possible, with a view to improving the solubility of the active component in ONL with water, to add water-miscible organic solvents such as alcohols, dimethylsulfoxide or solvents. amide solvents.

The preparation of the active amino resin precondensates in ONL from the starting components, aldehyde, ONL active component and, if appropriate, amino compound is possible according to the invention both in a one-step process, but also in a two-step process with separate synthesis of the resin component and subsequent bonding by incorporation of the active component into ONL.

In the case of a two-step process with separate preparation of the resin component, the reaction time, the monomer ratio and the pH value are used for the reaction temperature. the preparation of precondensates of amino resin soluble in water or soluble in organic components. Advantageous in this case is the synthesis of products having a high content of hydroxyl groups for precondensates of amino resin which are soluble in water, and having a high content of ether on precondensates which are soluble in organic components. They are obtained for a corresponding excess of aldehyde (amine: aldehyde = 1: 2 to 1: 3) and slightly basic medium (pH value: 7.5 - 10). The subsequent reaction of the resin component with the active compound in ONL is then done according to the chemical structure of the amino resin in the aqueous phase, respectively in the organic phase at temperatures of 50.degree.-100.degree. C., preferably 70.degree.-1000.degree. reaction conditions which are otherwise customary for the formation of amino resin precondensates. With regard to the precondensates of amino resin soluble in organic components, analogous to the manner of proceeding for the usual products, also for those synthesized especially, the organic solvents already mentioned, such as n-butanol or xylene. If aqueous solutions of precondensate are used as the resin component, the reaction is carried out with the active component in ONL in a weakly basic medium (pH value: 7.5-10) at temperatures preferably of 70-900C.

In the case of a one-step process, the resin components and the active components in water phase ONL, respectively in the organic phase, are synthesized directly from the monomers at temperatures of 50 - 900 ° C and at molar ratio of 1: 2 to 1: 3 (amino component plus active ingredient in ONL: aldehyde), the reaction being carried out in aqueous phase, by analogy with the two-step process, at pH values of 7.5-10. In both cases, adjustment of the pH value is suitably done with aqueous caustic soda. It is of course also possible to use all other suitable basic substances as well as buffer solutions working in this field.

The precondensates active in soluble ONL in the organic components are preferably synthesized without regulators additional to the pH value.

The appropriate shaping of aqueous ANO-active solutions of precondensates of aqueous amino resin is preferably carried out before crosslinking.
respectively organic, obtained during the pre
condensation, respectively active solids
in ONL again put in solution.

If the crosslinked ONL polymer according to the invention is to be present in the form of a layer or a film, by
For example, on a substrate, the polymer solution can be applied in a thin layer to a substrate, for example using the centrifugal coating method or the dipping or immersion coating method or any other method. another usual way. A preferred layer thickness of the polymer
ONL is from 100 nm to 20 microns, particularly preferably from 500 nm to 5 microns. The layer may for example be applied to optical articles, such as glasses, indium-tin oxide glasses, silicon, silicon dioxide, mineral crystals or surfaces of synthetic materials. Then follows a heat treatment, for example in the range of 100 to 2000C and preferably between 130 and 1600C. This is how the final crosslinking occurs to form a rigid three-dimensional structure of the ONL polymer.

To orient the chromophore groups stably, polarization in the electric field is necessary.

To do this, the polymer is preferably placed in the electric field of a corona discharge.

The crosslinking and polarization of the chromophoric groups can occur simultaneously; However, it is also possible to bias the chromophore groups of the already crosslinked product. The polarization must then be at a temperature, which is in the vicinity of the crosslinking temperature.

The active groups in ONL are oriented in both cases under the effect of the electric field. The degree of orientation achieved is, depending on the structure of the active resin in ONL and the conditions of synthesis and crosslinking, between 0.12 and 0.20. The degree of orientation of these crosslinked materials and prepared according to the invention is stable vis-à-vis time and temperature.

Examples of realization
A. Preparation of Precondensates
Example 1
Preparation of an active amino resin precondensate
Water-soluble ONL from the monomers and an ONL active compound (2-step process).

A. Preparation of unmodified amino resin precondensate:
First heated 55 g of a solution of
aqueous formaldehyde 30% by weight (0.55
mole) at a temperature of 900C and adjust the
pH value using a soda solution
1 N aqueous caustic at a pH of 7. Occurs
then the stirring addition of 31.5 g
(0.25 moles) melamine. After adjusting the
pH value using aqueous NaOH 1N to
7.5 - 9.0, the solution is stirred at room temperature
at 900C for about 30 minutes.

B. Binding by incorporation of the active component into
ONL (preparation of a modified precondensate of amino resin):
12.5 g of the precursor solution are reacted
densat (solids content 6.9 g
55.9%) with 0.874 g (3.61 mol-3 moles) of 4
amino-4'-nitroazobenzene dissolved in 80 ml
ethanol. The solution is then heated
reaction for 60 minutes under reflux at a
pH value of 8.5 - 9.0. We then leave the
solution cool to room temperature.

Example 2
Preparation of an active amino resin precondensate
Water soluble ONL from a melamine formaldehyde resin and an ONL active compound.

The mixture is heated to 90 ° C., until the azo dye is completely dissolved, 150 ml of an aqueous solution of a PIAMID resin at a rate of 50%, soluble in water (the products PIAMID is a melamine-ne-formaldehyde resin). ) with 8.75 g of 4-amino-4'-nitroazobenzene. The reaction is then allowed to continue for another hour at the same temperature until completion of the conversion. The pH value of the reaction mixture is maintained with 1N NaOH at pH = 8.5.

Example 3
Preparation of an active amino resin precondensate
ONL soluble in organic components.

100 ml of xylene are diluted with 30 ml of a solution of a MELADUROL resin (the product MELADUROL is a butyl-ethereal melamine-formaldehyde resin) and 5 g of 4-amino-4 are added to this solution. '-nitroazoben zen. The reaction mixture is heated with stirring for 5 hours at 900C. After cooling to room temperature, the subsequent treatment of this xylene solution can be carried out directly, for example in accordance with Example 4. view of the isolation of an active solid resin in ONL. The solid substance which precipitates is soluble in hexane and can be formed into films from this solution.

B. Layer formation and characterization of
active resins in polarized and crosslinked ONLs.

Example 4
The aqueous solution synthesized in Example 1 of the active amino resin precondensate in ONL is applied using the dipping method on an indium tin oxide (ITO) glass support. To do this, the solution is poured into a small cuvette and the layer is applied by immersing the substrate at a speed of 100 mm / minute. The layer is then dried at a temperature of 1300 ° C. in an oven.

Example 5
The aqueous solution of the active amino resin precondensate in ONL prepared in accordance with Example 2 is applied using the spin-coating process in thin layer on an ITO glass support. For a regime of 1400 rpm, a layer with a thickness of about 900 nm is obtained with the solution prepared according to Example 2 for a centrifugation time of 40 seconds.

Example 6
The active amino resin precondensate in precipitated ONL described in Example 3 is dissolved in xylene. The 10% solution is centrifuged at 2100 rpm on an ITO glass support. The prepared amino resin thin films can be subjected to dipping or dip coating (Example 4) respectively by spin coating (Examples 5 and 6) directly to the polarization and crosslinking operations.

Example 7
For activation in order to produce an optically active material, it is necessary to convert the optically active groups of the active amino resin precondensate into ONL into a non-centrosymmetric molecular structure. The thin layers prepared according to Examples 4 - 6 are exposed to a Corona discharge with voltages of 6 to 10 kV for peak intervals of 10 - 16 mm. This gives a stable orientation of the chromophore groups within the layer.

The orientation of the chromophore groups is determined by means of absorption measurements before and after the polarization. The degree of orientation of the chromophore moieties is used for the absorption bands in the visible range of the spectrum. The degrees of orientation and their stability are summarized in Table 1.

The orientation is not only stable in the long term, but also thermally stable as a result of the crosslinking of the material. Thus even heating the material for one hour at 2000C does not lead to any change in the permanent orientation.

Table 1. Orientation of active materials in reticulated ONL based on precondensates of amino resin soluble in water or soluble in organic components

<tb> Example <SEP><SEP> Degree of Orientation <SEP> Orientation <SEP> Degree
<tb><SEP> after <SEP> polarization <SEP> after <SEP> 150 <SEP> days
<tb> 1 <SEP> 0.20 <SEP> 0.18
<tb> 2 <SEP> 0.18 <SEP> 0.17
<tb> 3 <SEP> 0.15 <SEP> 0.14
<Tb>

Claims (20)

 amino resin reactions.  least one functional group accessible by  resin covalently via  of at least one active component in ONL which is linked to the  1. Cross-linked ONL polymer, consisting of an amino resin and 2. The crosslinked ONL polymer according to claim 1, wherein  form of an applied layer or a self-supporting film. 3. crosslinked ONL polymer according to claim 2,  characterized in that  the layer or film has a thickness ranging from  100 nm to 20 microns. 4. Cross-linked ONL polymer according to any one of  preceding claims,  characterized in that  the amino component of the amino resin is selected from  melamine, urea, urea derivatives or their  mixtures. Cross-linked ONL polymer according to any one of the claims  previous cations,  characterized in that  the aldehyde component of the amino resin is selected from  formaldehyde and acetaldehyde, glyoxal, glutar  dialdehyde or mixtures of these aldehydes. 6. Crosslinked ONL polymer according to any one of the claims  previous cations,  characterized in that  the active component in ONt is chosen from the compounds  nitro-aromatics, aromatic nitro-heterocycles, azobenzenes,  stilbenes or their mixtures. 7. Cross-linked ONL polymer according to any one of  preceding claims,  characterized in that  the functional groups of the active component in ONL  accessible by amino resin reactions are  chosen from amino, imino and hydroxyl groups,  aldehyde or combinations of these groups  tional. Cross-linked ONL polymer according to claim 6,  characterized in that  the active component in ONL is chosen from p-nitro  aniline, 4-amino-4'-nitroazobenzene, 1,4- (4'-  aminophenyl-41-nitrophenyl) -diazobenzene, 4-amino-4'-  nitrostilbene or mixtures thereof. 9. Cross-linked ONL polymer according to any one of  preceding claims,  characterized in that  the active component in ONL is contained in a quantity  from 5 to 60% by weight, based on the component of the  amino resin containing amino groups. 10. Precondensate of active amino resin in ONL, comprising the  following constituents:  - active components in ONL having at least one  functional group accessible by reac-  amino resins  a precondensate of soluble amino resin in  water or soluble in organic components  and or  monomeric components of the amino resin. 11. Process for preparing an amino resin precondensate  active in ONL,  characterized in that  reactive active components in ONL, having at  least one functional group accessible by  reactions of amino resins, with precondensates of  amino resin and / or mono amino resin components  mothers, soluble in water or soluble in  organic posers. 12. Process for preparing an amino resin precondensate  active in ONL according to claim 11,  characterized in that  the soluble amino resin precondensates are prepared  in water or soluble in organic components to  from an aldehyde component chosen preferably  formaldehyde and acetaldehyde, glyoxal,  glutardialdehyde or mixtures of these aldehydes, and  from an amino component, preferably selected from  nitroaromatic compounds, aromatic nitro-heterocycles,  azobenzenes, stilbene or their mixtures. 13. Process for preparing a crosslinked polymer ONL according to  any one of claims 1 to 9,  characterized in that  - we put in the desired form a solution  aqueous, respectively organic precondensate  of active amino resin in ONL  - it is submitted in this form to a treatment  thermal and  - it is exposed to a field polarization  efficient electric. 14. Process for preparing a crosslinked polymer ONL according to  claim 2 or 3, characterized in that  - it is applied as a layer on a sub  strat an aqueous solution, respectively organ  precondensate of active amino resin in  ONL,  - it is submitted in this form to a treatment  thermal and  - it is exposed to a field polarization  efficient electric. 15. Use for the preparation of a crosslinked polymer  ONL according to claim 14,  characterized in that  the application of the aqueous solution is carried out,  respectively organic, of precondensate of amino resin  active in ONL on the substrate using a method of  coating by centrifugal application or coating by dipping or  by immersion. 16. Process for preparing a crosslinked polymer ONL according to  any of claims 13-15,  characterized in that  the effective electric field polarization is realized  using a corona discharge. 17. Use of a crosslinked polymer ONL according to one  any of claims 1 to 9, in processes  optical transmission of information. 18. Use of the crosslinked polymer ONL according to the claim  17 in the form of a layer on an optical substrate. 19. Use of a crosslinked polymer ONL according to the claimed  cation 18,  characterized in that  the substrate is selected from the group consisting of  glasses, indium-tin oxide glasses, silicon,  silicon dioxide, organic crystals and minerals  and synthetic materials. 20. The use according to claim 17, in  multilayer structures or building elements  optics.