JP2950521B2 - Polyimide optical material for optical waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention particularly relates to a polyimide optical material for an optical waveguide having an extremely small birefringence and capable of controlling the value, which is used for an optoelectronic component or the like.

[0002]

2. Description of the Related Art Organic polymer materials (plastics) have features such as lighter weight, superior impact resistance and workability, and easier handling than inorganic materials.
Previously also optical fiber and the optical disc board has been used in a variety of optical applications such as optical lenses. Further, in recent years, with the demand for establishment of various optical waveguide technologies with the practical use of optical communication systems, plastic optical materials that can be used as waveguide components of optical circuits or optoelectronic circuits have been proposed. (For example, Japanese Patent Application No. Hei 2-
317913). Among them, fluorine-containing aromatic polyimides in which fluorine atoms are introduced into the molecular structure are known to satisfy many properties required for optical components, such as high heat resistance and low water absorption, as well as good optical properties (transparency). (For example, Japanese Patent Application No. 2-110500) and is currently regarded as the most promising as a next-generation plastic optical material.

By the way, plastics having a benzene ring or a heterocyclic ring in a molecular structure such as a polyimide or a polycarbonate used for an optical disk substrate often have anisotropy of polarizability inherent in these ring structures, and thus are often used in plastics. It is known to exhibit anisotropy of refractive index, that is, birefringence. On the other hand, when a plastic material is applied to an optical waveguide component, precise control of the refractive index is required in order to satisfy waveguide conditions suitable for each waveguide structure.

In particular, in an optical circuit or an optoelectronic circuit, it is essential to control the refractive index of the core portion and the clad portion with an accuracy of 10 ^-3 or less in order to satisfy a condition called a single mode. In a polarization-maintaining waveguide that is kept constant, the refractive index difference (birefringence) in the vertical and horizontal directions must be kept at a constant value of about 10 ⁻³ . The presence of large birefringence in optical materials not only makes precise control of the refractive index difficult, but also complicates waveguide design. In particular, what is more problematic in a thin film or an optical waveguide is the birefringence between the in-plane direction and the direction perpendicular to the surface (optical birefringence (difference in refractive index due to the difference in the direction in which light is guided)) (The refractive index difference in the plane perpendicular to the plane) and the technique for reducing and controlling the birefringence are key technologies in developing a plastic optical waveguide.

In a quartz optical waveguide which is already being put to practical use, it is possible to suppress this birefringence to about 5 × 10 ^−4, and to optimize the conditions at the time of thermoforming even for the above-mentioned polycarbonate optical disk. By doing so, one having a small birefringence is obtained. However, since polyimide often starts to decompose below the glass transition point, it is difficult to control birefringence by heat treatment. There have already been some reports on the birefringence of polyimide films [for example, T.I. P. Russell (TP Russe)
1, Journal of Polymer Science (Polymer Physics), vol. 21, p. 1745 (1983)
Year)), 8 × 10 ^-2 for conventional polyimide, and 3.4 × 10 for fluorine-containing polyimide with low birefringence.
It is known that a birefringence of ^-3 exists and cannot be applied to precision optical components or optoelectronic components as it is.
In addition, a polyimide optical material exhibiting a birefringence of 1 × 10 ⁻³ or less has not yet been obtained, and examples of controlling the birefringence of a thin film or an optical waveguide using the polyimide optical material have not been known.

[0006]

As described above, when applying a polyimide optical material to an optical component, an optoelectronic component , especially an optical waveguide , first, a polyimide optical material having a very small birefringence is developed, and then the birefringence is controlled. It is indispensable to develop technologies to do this. The present invention has been made in view of such a situation, and an object thereof is to provide a polyimide optical material for an optical waveguide having very small birefringence and a polyimide optical material for an optical waveguide capable of controlling birefringence. Is to do.

[0007]

SUMMARY OF THE INVENTION In general, the present invention relates to the reduction of birefringence and control of birefringence of a polyimide optical material for an optical waveguide.

Embedded image (Wherein R ₁ is a tetravalent organic group, and R ₂ is

Embedded image An optical waveguide polyimide optical material comprising a polyimide having a repeating unit represented by a divalent organic group) selected from, R ₂ is

Embedded image In the case where a halogen atom, an alkyl group, or a fluorinated alkyl group is introduced at a position other than the para position of the benzene ring bonded to the nitrogen atom of the imide ring (provided that R ₁ , R ₂ , and the benzene ring Bound halogen atoms
Others as a chemical bond between carbon and monovalent elements contained in the fluorinated alkyl group, a carbon - except those containing fluorine bonds only), R ₂ is

Embedded image If it is, the both of ortho positions of the benzene ring bonded to the nitrogen atom of the imide ring, by introducing a halogen atom or an alkyl group or a fluorinated alkyl group, the meta position of the benzene ring
Has a hydrogen atom, a halogen atom, an alkyl group or
Represents that a fluorinated alkyl group is bonded (provided that R ₁ , R ₂ , and the ortho position of the benzene ring are
Hydrogen atom, halogen atom, or fluorine atom
As a chemical bond between carbon and monovalent element contained in the alkyl group ,
Excluding those containing only carbon-fluorine bonds).

The present inventors have measured the birefringence of various existing plastic optical materials, and have intensively studied the causes of the birefringence in the plastic optical materials by referring to the examples reported so far. As a result, the first cause of birefringence is the orientation of functional groups with large refractive index anisotropy, such as aromatic rings, heterocycles, carbonyl groups, and cyano groups, which occur during thermoforming or thin film formation of samples. It was clear that In particular, since aromatic polyimide has both a benzene ring and an imide ring in the molecule, if many of these ring structures are oriented with the same plane when forming a thin film, large birefringence will result. Of particular concern is the mutual rotation of the imide ring and the benzene ring bonded to its nitrogen. For example, in a typical polyimide represented by the following structural formula [II], the two ring structures are the same. Taking a plane, inevitably five ring structures exist on the same plane.

Embedded image On the other hand, when the two ring structures have mutually twisted orientations, the plane directions of the benzene ring and the imide ring are averaged over the entire molecular chain, and as a result, birefringence is expected to be reduced.

[0009] The rotation angle of the bond between the imide ring and the adjacent benzene ring in the polyimide; θ (0 in the case of being in the same plane;
°, 90 ° when orthogonal)), there are some reports from X-ray diffraction and theoretical calculations, but they do not show uniform results, and it is difficult to determine which angle is most stable in the solid state. Not revealed. However, G. Results of Conte et al. (Θ = 13 °, GC Conte, Journal of Polymer Science, Vol. 14, p. 1553 (1
976)) and S.M. Kafafi results (θ = 30 °,
S. According to Kafafi, Polymer Preprint (American Chemical Society), vol. 31, p. 565 (1990), etc., in conventional polyimide, the imide ring and the adjacent benzene ring are not orthogonal to each other, but are slightly twisted but almost the same. It is considered to be facing the direction.

Based on the above considerations, the present inventors have found that in order to reduce the birefringence of the polyimide optical material, the benzene ring adjacent to the imide ring shown in the following structural formula [III] is formed. Introducing a halogen atom, an alkyl group, or a fluoroalkyl group at the ortho position as viewed from the imide ring causes steric hindrance, and making the imide ring and the adjacent benzene ring more orthogonal to each other reduces birefringence. They predicted it would work.

Embedded image (Where X ₁ and Y ₁ represent a halogen atom, an alkyl group or a fluorinated alkyl group) To theoretically support this prediction, calculation of rotational energy by molecular force field method (MMP2 method) for two model compounds 1 and 2 show the results obtained. In the conventional polyimide model (FIG. 1) in which both X ₁ and Y ₁ in the structural formula [III] are hydrogen, the energy is averaged at all rotation angles, and the imide ring and the adjacent benzene ring are orthogonal. Has the same steric energy as that of the planar structure, while X
_The calculation clearly shows that when both ₁ and Y ₁ are fluorine (FIG. 2), the planar structure is greatly destabilized and the imide ring and the adjacent benzene ring are close to being orthogonal.

Therefore, the polyimide optical material according to the present invention is characterized in that, in the above-mentioned structural formula [III] appearing in the repeating unit of the polyimide, the imide ring side site (X ₁ and Y ₁ ) of the benzene group adjacent to the imide ring is The essence is that a halogen atom, an alkyl group or a fluorinated alkyl group is bonded to both. Thereby, the stereochemical structure of the polyimide is controlled, and the birefringence of the polyimide optical material can be reduced or controlled.

The following are mentioned as acid anhydrides, acid chlorides and esterified compounds as tetracarboxylic acids or derivatives thereof used in producing the polyimide optical material of the present invention. Here, an example of tetracarboxylic acid will be given. Pyromellitic acid, (trifluoromethyl) pyromellitic acid, di (trifluoromethyl) pyromellitic acid, di (heptafluoropropyl) pyromellitic acid, pentafluoroethylpyromellitic acid, bis {3,5-di (trifluoro) Methyl) phenoxy dipyromellitic acid, 2,3,3 ', 4'-biphenyltetracarboxylic acid, 3,3', 4,4'-tetracarboxydiphenyl ether, 2,3 ', 3,4'-tetracarboxydiphenyl ether 3,3 ', 4,4'-benzophenonetetracarboxylic acid, 2,3,6,7-tetracarboxynaphthalene, 1,4,5,7-tetracarboxynaphthalene, 1,4,5,6-tetracarboxy Naphthalene, 3,3 ', 4,4'-tetracarboxydiphenylmethane, 3,3', 4,4'-tetraca Boxoxydiphenyl sulfone, 2,2-bis (3,4-dicarboxyphenyl) propane, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane, 5,5'-bis (trifluoromethyl) -3,3 ', 4,4'-tetracarboxydiphenyl, 2,2', 5,5'-tetrakis (trifluoromethyl) -3,3 ', 4,4'-tetracarboxybiphenyl, 5,5' -Bis (trifluoromethyl) -3,3 ', 4,4'-tetracarboxybiphenyl ether,

5,5'-bis (trifluoromethyl)-
3,3 ', 4,4'-tetracarboxybenzophenone, bis {(trifluoromethyl) dicarboxyphenoxy} benzene, bis {(trifluoromethyl) dicarboxyphenoxy} (trifluoromethyl) benzene,
Bis (dicarboxyphenoxy) (trifluoromethyl) benzene, bis (dicarboxyphenoxy) bis (trifluoromethyl) benzene, bis (dicarboxyphenoxy) tetrakis (trifluoromethyl) benzene, 3,4,9,10-tetra Carboxyperylene,
2,2-bis {4- (3,4-dicarboxyphenoxy) phenyl} propane, butanetetracarboxylic acid, cyclopentanetetracarboxylic acid, 2,2-bis {4-
(3,4-dicarboxyphenoxy) phenyl {hexafluoropropane, bis (trifluoromethyl) dicarboxyphenoxy} biphenyl, bis {(trifluoromethyl) dicarboxyphenoxy} bis (trifluoromethyl) biphenyl, bis} ( Trifluoromethyl)
Dicarboxyphenoxy diphenyl ether, bis (dicarboxyphenoxy) bis (trifluoromethyl) biphenyl and the like.

The diamine is preferably a halogen atom or an alkyl group at both ortho positions as viewed from the two amino groups.
Alternatively, any compound having a fluorinated alkyl group bonded thereto may be used. However, as described above, the use of a fluorinated compound improves light transmittance, heat resistance, water absorption, dielectric constant, and the like. It is desirable to use a diamine. Hereinafter, examples of diamines suitable for this purpose include tetrafluoro-p-phenylenediamine and tetrafluoro-m
-Phenylenediamine, tetramethyl-p-phenylenediamine, tetramethyl-m-phenylenediamine, tetra (trifluoromethyl) -p-phenylenediamine, tetra (trifluoromethyl) -m-phenylenediamine, 3,3 ', 5 , 5'-tetrafluorobenzidine, 3,3 ', 5,5'-tetrafluoro-4,4'-
Diaminodiphenyl ether, 3,3 ', 5,5'-tetrafluoro-4,4'-diaminodiphenylmethane,
3,3 ', 5,5'-tetramethylbenzidine, 3,
3 ', 5,5'-tetramethyl-4,4'-diaminodiphenyl ether, 3,3', 5,5'-tetramethyl-4,4'-diaminodiphenylmethane, 3,3 ',
5,5'-tetra (trifluoromethyl) -4,4'-
Diaminodiphenyl, 3,3 ', 5,5'-tetra (trifluoromethyl) -4,4'-diaminodiphenyl ether,

3,3 ', 5,5'-tetra (trifluoromethyl) -4,4'-diaminodiphenylmethane, octafluorobenzidine, octafluoro-4,4'-
Diaminodiphenyl ether, octafluoro-4,
4'-diaminodiphenylmethane, octamethylbenzidine, octamethyl-4,4'-diaminodiphenylether, octamethyl-4,4'-diaminodiphenylmethane, octa (trifluoromethyl) benzidine, octa (trifluoromethyl) -4,4'- Diaminodiphenyl ether, octa (trifluoromethyl) -4,
4'-diaminodiphenylmethane and the like.

The method for producing the polyamic acid which is a precursor of the polyimide used in the present invention may be the same as the ordinary production conditions for polyamic acid, and is generally N-methyl-2-pyrrolidone, N, N-dimethyl. The reaction is performed in a polar organic solvent such as acetamide and N, N-dimethylformamide.
In the present invention, not only a diamine and a tetracarboxylic dianhydride are used as a single compound, but also a mixture of a plurality of diamines and tetracarboxylic dianhydrides may be used. In such a case, the total number of moles of a plurality or a single diamine and the total number of moles of a plurality or a single tetracarboxylic dianhydride are equal or almost equal.
In the above-mentioned polymerization solution such as polyamic acid, the concentration of the solution is 5 to 40% by weight, preferably 10 to 25% by weight.
The rotational viscosity (25 ° C.) of the polymer solution is preferably 50 to 5000 poise.

As a method for producing a film of the polyimide optical material of the present invention, an ordinary method for producing a polyimide film can be used. For example, a polyamic acid solution is spin-coated on an aluminum plate and heated stepwise from 70 ° C. to 350 ° C. in a nitrogen atmosphere (70 ° C. for 2 hours, 160 ° C. for 1 hour, 2 hours).
(50 ° C for 30 minutes, 350 ° C for 1 hour) and solidify. Thereafter, the aluminum plate is immersed in an aqueous solution of an acid such as 10% hydrochloric acid to dissolve the aluminum plate, thereby obtaining a polyimide optical material film.

In the present invention, in order to control the birefringence of the polyimide optical material, a method of copolymerizing a plurality of diamines with tetracarboxylic acid or a method of obtaining a plurality of polyamic acids using a plurality of diamines and mixing these are used. There are ways to do that.
This makes it possible to control the birefringence to a very low level and to a predetermined value.

[0019]

EXAMPLES Hereinafter, the polyimide optical material of the present invention will be described in detail with reference to examples. In each of the following examples, the imidation was confirmed from the characteristic absorption of the carbonyl group in the infrared absorption spectrum due to symmetric and asymmetric stretching vibrations.
The birefringence of the polyimide film was measured using an Abbe refractometer with a polarizer (measuring wavelength: 589.3 nm, measuring temperature: 23).
° C), the refractive index in the film plane and in the film thickness direction were measured, and the difference was determined. In the following examples, the in-plane birefringence was 1 × 10 ⁻⁴ or less. The thickness of the polyimide film subjected to the measurement was in the range of 10 μm to 20 μm, and the measured value of birefringence did not depend on the thickness.

Example 1 An Erlenmeyer flask was charged with 2,2'-bis (3,4-dicarboxyphenyl) -hexafluoropropane dianhydride (6FD
A) 8.885 g (0.02 mol) of tetrafluoro-p-phenylenediamine (FP) represented by the following structure
P)

Embedded image 3.60 g (0.02 mol) and 100 g of N-methyl-2-pyrrolidone (NMP) were added, and the mixture was stirred under a nitrogen atmosphere at room temperature for 3 days to obtain an NMP solution of polyamic acid. This was spin-coated on an aluminum plate and completely imidized by heating at 70 ° C. for 2 hours, 160 ° C. for 1 hour, 250 ° C. for 30 minutes and further at 350 ° C. for 1 hour in a nitrogen atmosphere. This aluminum plate was immersed and dissolved in a 10% HCl solution to obtain a polyimide film. The measured birefringence of the polyimide film was 0.0018.

Reference Example In place of FPP in Example 1, tetrafluoro-m-phenylenediamine (FM) represented by the following structural formula was used.
P)

Embedded image Synthesis was performed in the same manner as in Example 1 except that the amount was changed to 3.60 g (0.02 mol), and the same heat treatment was performed to obtain a polyimide film. When the birefringence of this film was measured, 0.0
008.

Example 2 In place of FPP in Example 1, tetramethyl-p-phenylenediamine (MP
P),

Embedded image Synthesis was performed in the same manner as in Example 1 except that the amount was changed to 3.28 g (0.02 mol), and the same heat treatment was performed to obtain a polyimide film. When the birefringence of this film was measured, 0.0
016.

Examples 3 to 5 In place of 6FDA in Examples 1 and 2 and Reference Example , 4.36 g of pyromellitic dianhydride (PMDA) (0.0
2 mol), and synthesized in the same manner as in Example 1, and subjected to the same heat treatment to obtain a polyimide film. Example 1
2. Table 1 summarizes the measured birefringence along with Reference Examples .

Example 6 Instead of FPP in Example 1, 1.80 g of FPP
(0.01 mol) and 1.80 g (0.01 mol) of MPP were replaced with each other to synthesize in the same manner as in Example 1, and subjected to the same heat treatment to obtain a copolymerized polyimide film composed of two kinds of diamines. The birefringence of this film was 0.0013 when measured.

Example 7 An NMP solution of polyamic acid of 6FDA and FPP obtained in Example 1 and an NMP solution of polyamic acid of 6FDA and FMP obtained in Reference Example were accurately weighed and measured at room temperature for 1 hour. Stirred. This NMP solution was similarly subjected to a heat treatment to obtain a film composed of a mixture of two kinds of polyimides.
The measured birefringence of the film was 0.0014.

Comparative Example 1 Instead of FPP in Example 1, 4,4'-diaminodiphenyl ether (OD
A)

Embedded image Synthesis was performed in the same manner as in Example 1 except that the amount was changed to 4.00 g (0.02 mol), and the same heat treatment was performed to obtain a polyimide film. When the birefringence of this film was measured, 0.0
080.

Comparative Example 2 Instead of FPP in Example 1, 2,2'-bis (trifluoromethyl) -4, represented by the following structural formula:
4'-diaminobiphenyl (TFDB)

Embedded image Synthesis was performed in the same manner as in Example 1 except that the amount was changed to 6.40 g (0.02 mol), and the same heat treatment was performed to obtain a polyimide film. When the birefringence of this film was measured, 0.0
057.

Comparative Examples 3 and 4 The 6FDA in Comparative Examples 1 and 2 was replaced by 4.36 g of PMDA.
(0.02 mol), and synthesized in the same manner as in the example.
The same heat treatment was performed to obtain a polyimide film. Table 2 summarizes the measured birefringence along with Comparative Examples 1 and 2.

[0029]

[Table 1]

[0030]

[Table 2]

The abbreviations in Tables 1 and 2 are as follows. 6FDA: 2,2'-bis (3,4-dicarboxyphenyl) -hexafluoropropane dianhydride PMDA: pyromellitic dianhydride FFP: tetrafluoro-p-phenylenediamine FMP: tetrafluoro-m-phenylenediamine MPP : tetramethyl-p-phenylenediamine ODA: 4,4'-diaminodiphenyl ether TFDB: 2,2'-bis (trifluoromethyl)-
4,4'-diaminobiphenyl

As is clear from the above results, when a polyimide film is prepared from the same acid anhydride, the value of birefringence is greatly reduced by using the diamine shown in the present invention. It was also confirmed that the birefringence can be controlled by mixing a plurality of diamines at the stage of copolymerization or polyamic acid.

[0033]

As described above, the polyimide optical material of the present invention is a polyimide optical material for an optical waveguide comprising a polyimide having a repeating unit represented by the general formula [I], wherein the nitrogen atom of the imide ring is A specific atom or group at a specific position on the benzene ring
Since the stereochemical structure of the imide is controlled, a polyimide optical material for an optical waveguide having extremely low birefringence and capable of controlling the value is obtained, which is suitable for optical components and optoelectronic components.

[Brief description of the drawings]

FIG. 1 is a calculation result of steric energy of a conventional polyimide model compound.

FIG. 2 is a calculation result of steric energy of a model compound of a polyimide optical material according to the present invention.

Claims (1)

(57) [Claims] 1. A compound represented by the following general formula [I] (Wherein R ₁ is a tetravalent organic group, and R ₂ is An optical waveguide polyimide optical material comprising a polyimide having a repeating unit represented by a divalent organic group) selected from, R ₂ is ## STR3 ## In the case where a halogen atom, an alkyl group, or a fluorinated alkyl group is introduced at a position other than the para position of the benzene ring bonded to the nitrogen atom of the imide ring (provided that R ₁ , R ₂ , and the benzene ring Bound halogen atoms
Or a compound containing only a carbon-fluorine bond as a chemical bond between carbon and a monovalent element contained in a fluorinated alkyl group ), and R ₂ is If it is, the both of ortho positions of the benzene ring bonded to the nitrogen atom of the imide ring, by introducing a halogen atom or an alkyl group or a fluorinated alkyl group, the meta position of the benzene ring
Has a hydrogen atom, a halogen atom, an alkyl group or
Represents that a fluorinated alkyl group is bonded (provided that R ₁ , R ₂ , and the ortho position of the benzene ring are
Hydrogen atom, halogen atom, or fluorine atom
As a chemical bond between carbon and monovalent element contained in the alkyl group ,
Excluding those containing only carbon-fluorine bonds).