JP3550641B2 - Novel maleimide-based copolymer, production method thereof, and second-order nonlinear optical material using the same - Google Patents

Description

で表わされる構成単位及び（Ｂ）式
【化９】

（式中のＲは水素原子又はメチル基である）
で表わされる構成単位からなり、重量平均分子量５，０００〜１５，０００を有するマレイミド−ノルボルネン共重合体を提供するものである。
【０００９】
このマレイミド−ノルボルネン共重合体は、文献未載の新規化合物であって、例えばＮ‐（４‐ヒドロキシフェニル）マレイミドと２‐ノルボルネンとをラジカル重合開始剤の存在下で共重合させ、次いでこのようにして得た共重合体に、一般式
【化１０】

（式中のＲは水素原子又はメチル基である）
で表わされる赤色染料を反応させることにより製造することができる。
また、このマレイミド−ノルボルネン共重合体は、電場配向により良好な二次ＮＬＯ特性を付与することができ、二次非線形光学材料として好適に用いることができる。
【００１０】
【発明の実施の形態】
本発明のマレイミド−ノルボルネン共重合体は、例えば次の反応式に従い、Ｎ‐（４‐ヒドロキシフェニル）マレイミドと２‐ノルボルネンとをラジカル共重合させてＮ‐（４‐ヒドロキシフェニル）マレイミドと２‐ノルボルネンとの共重合体（ＩＶ）を製造する第一工程と、この共重合体（ＩＶ）に前記一般式（ＩＩＩ）の赤色染料を反応させて、前記構成単位（Ｉ）及び（ＩＩ）からなる共重合体（Ｖ）を製造する第二工程を順次行うことにより製造される。
【００１１】
【化１１】

（式中のｘ、ｙ及びｚは１以上の整数であり、Ｒは前記と同じ意味をもつ）
【００１２】
この第一工程の共重合反応は、Ｎ‐（４‐ヒドロキシフェニル）マレイミドと２‐ノルボルネンとの混合物を、重合溶媒中、ラジカル重合開始剤の存在下で加熱することにより行われる。
この際のＮ‐（４‐ヒドロキシフェニル）マレイミドと２‐ノルボルネンとの使用割合は、モル比で５：１ないし１：２、好ましくは１．２：１ないし１：１の範囲内で選ばれる。これよりも２‐ノルボルネンの量が少ないと所望の物性を有する共重合体が得られないし、またこれよりもＮ‐（４‐ヒドロキシフェニル）マレイミドの量が少ないと、高温における配向構造の緩和を防止することができない上、後続工程における赤色染料の導入量が低くなり、所望の二次非線形光学活性が得られない。
【００１３】
この共重合反応は、溶液重合、乳化重合、懸濁重合のいずれでもよいが、第二工程を連続して行いうるという点で溶液重合が好ましい。この場合、重合溶媒を使用しないで行うこともできるが、重合溶媒を用いる場合には、テトラヒドロフラン、ジメチルホルムアミド、ジメチルアセトアミド、ジメチルスルホキシド、ジエチルスルホキシドなどが好適である。そのほか、ベンゼン、ニトロベンゼンなどの炭化水素類、第三ブチルアルコールのようなアルコール類も用いられる。
【００１４】
また、ラジカル重合開始剤としては、過酸化アセチル、過酸化ベンゾイル、過酸化ラウロイル、過酸化ｔ‐ジブチルのような過酸化物系重合開始剤や、アゾビスイソブチロニトリル、アゾビスシアノ吉草酸、アゾビスシクロヘキサンカルボニトリル、アゾビスイソブチルアミジン塩酸塩のようなアゾ系重合開始剤が用いられる。このラジカル重合開始剤の使用量は、通常、単量体全重量に基づき０．０５〜５．０重量％の範囲内で選ばれる。
【００１５】
次に、この共重合反応の温度としては、５０〜１００℃、好ましくは６０〜８０℃の範囲が好ましい。これよりも低い温度では、反応速度が遅く実用的でないし、またこれよりも高い温度では、副反応を生じ、最終的に得られる共重合体の品質低下の原因になる。この温度における重合時間は通常１０〜５０時間である。
このようにして得られる、Ｎ‐（４‐ヒドロキシフェニル）マレイミドと２‐ノルボルネンとの共重合体（ＩＶ）は、重量平均分子量３，５００〜１２，０００、数平均分子量５，０００〜２０，０００、多分散度（Ｍｗ／Ｍｎ）１．３〜３．０の白色固体であり、３００℃付近のガラス転移温度を有する。
【００１６】
次に、第二工程においては、このようにして得た共重合体に、前記一般式（ＩＩＩ）の赤色染料を反応させる。この際、縮合剤として、トリフェニルホスフィンとアゾジカルボン酸ジエチルエステルとを用いるのが好ましい。
この赤色染料としては、一般式（ＩＩＩ）においてＲが水素原子のもの、Ｒがメチル基でアゾ基に対し、オルト位に結合しているもの、及びニトロ基がアゾ基に対し、オルト位又はパラ位に結合しているものがある。
これらの赤色染料は高分子化合物の側鎖に導入して二次非線形光学材料を形成させるクロモフォアとしてよく知られているものである。
【００１７】
上記の赤色染料の導入率は、生成する共重合体の二次非線形光学特性に応じて選択される。この導入率は、赤色染料の使用量、反応時間により左右されるが、通常５０〜９５モル％、好ましくは７０〜９０モル％の範囲である。例えば、共重合体中のヒドロキシル基当量よりもやや過剰に使用し、４０〜５０時間反応させた場合、ヒドロキシル基の約７０モル％以上に、この赤色染料を導入することができる。
【００１８】
この第二工程は、反応溶媒としてテトラヒドロフラン、ジメチルホルムアミド、ジメチルアセトアミド、ジメチルスルホキシド、ジエチルスルホキシドなどを用いて行われる。
このようにして得られる本発明のマレイミド−ノルボルネン共重合体は、重量平均分子量７，０００〜１５，０００、数平均分子量５，０００〜１０，０００、多分散度（Ｍｗ／Ｍｎ）１．２５〜２．０、ガラス転移温度１９５〜２００℃の赤褐色固体であり、塩化メチレン、クロロホルム、テトラヒドロフランなどの有機溶媒に可溶で、製膜性を有する化合物である。また、このものの最適ポーリング温度は１３０〜１６０℃の範囲にある。
【００１９】
【実施例】
次に、実施例により本発明をさらに詳細に説明する。
【００２０】
実施例１
蒸留して精製した２‐ノルボルネン０．５ｇ（５．３２ミリモル）とヒドロキシフェニルマレイミド１．０ｇ（５．３２ミリモル）、２，２′‐アゾビスイソブチロニトリル０．０２ｇ（０．１２ミリモル）を蒸留により精製したテトラヒドロフラン３ミリリットルとともに５ミリリットル容量アンプル管に詰め、脱気後封管したのち、６５〜７０℃の温度で、２４時間ラジカル共重合させた。
次いで、生成物を取り出し、エーテルを用いて２回再沈殿することにより、淡黄色固体の共重合体１．１ｇ（収率７２％）を得た。
このものについて、ゲルパーミエーションクロマトグラフィー法により分子量を測定した結果、数平均分子量５，１００、重量平均分子量７，７００、多分散度１．５であった。また、ＤＳＣで測定したガラス転移温度は３００℃であった。
このものの^１Ｈ−ＮＭＲのチャートを図１に示す。
【００２１】
次に、前記のようにして得た共重合体０．５６３ｇ（１．２ミリモル）に、トリフェニルホスフィン０．８６８ｇ（３．３２ミリモル）と、前記一般式（ＩＩＩ）におけるＲが水素原子で、ニトロ基がアゾ基に対しパラ位に結合している化合物に相当する赤色染料ＤＲ−１ ０．７４８ｇ（２．３８ミリモル）を、蒸留により精製したテトラヒドロフラン２０ミリリットルに溶解し、アルゴン雰囲気中において、この中へアゾジカルボン酸ジエチルエステル０．５８ｇ（３．３２ミリモル）を滴下した。室温において４８時間反応させたのち、生成物を回収した。この生成物をメタノールで２回再沈殿して精製後、１２時間減圧乾燥することにより、２‐ノルボルネンと式
【化１２】

で表わされるＮ‐置換無水マレイミドとの共重合体（以下ＰＨＮＤと略す）１．１ｇ（収率７７％）を赤褐色固体として得た。
このものは、数平均分子量６，７００、重量平均分子量９，７００、多分散度１．３４であり、ガラス転移温度は１９７℃であった。
このものの^１Ｈ−ＮＭＲチャートを図２に示す。
【００２２】
実施例２
実施例１で得た共重合体ＰＨＮＤをテトラヒドロフランに溶解し、１重量％溶液を調製し、これをスピンコート法（７００ｒｐｍ、３０ｓｅｃ）によりガラス基板上で製膜した。
このようにして得たフィルムにコロナポーリングを用いて配向処理を施し、非線形型光学材料を作製した。すなわち、この共重合体のガラス転移温度が１９７℃であることを考慮し、１１０℃、１４０℃、１５５℃、１７０℃及び２００℃をポーリング温度として選び、これらのポーリング温度まで昇温したのち、この状態で５ｋＶ／ｃｍの電界を２０分印加し、このまま室温まで降温することによって行った。
ポリマーの屈折度をエリプソメータ（測定波長λ ６３２．８ｎｍ、Ｈｅ−Ｎｅレーザー、入射角７０°）で測定したところ、１．６７であった。
このようにして測定したｄ_３３値のポーリング依存性を図３に示す。
この結果、最適ポーリング温度は１４０℃であることが分った。
【００２３】
実施例３
実施例１で得た共重合体ＰＨＮＤをテトラヒドロフランに溶解し、２重量％溶液を調製し、これを用いて実施例２と同様に製膜することによりフィルムを作製した。
このフィルムについて最適ポーリング温度、すなわち１４０℃でポーリングし、８０℃の恒温槽に入れ、所定時間ごとにこれを取り出し、その第二高調波発生（ＳＨＧ）を測定することによりｄ_３３値の経時安定性を調べた。
この結果を図４に示す。
この図から分るように測定初期においては、わずかな緩和が認められたが、３０時間後緩和は認められなくなり、２５０時間後においても初期値（２９０×１０^−９ｅｓｕ）の８０％が保持されている。
【００２４】
【発明の効果】
本発明の共重合体は、二次非線形光学特性を有する新規化合物であって、しかも長時間にわたって、高温における二次非線形光学特性の緩和に対して、優れた抑制効果を示す。
【図面の簡単な説明】
【図１】２‐ノルボルネンとヒドロキシフェニルマレイミドとの共重合体のＮＭＲチャート。
【図２】ＰＨＮＤのＮＭＲチャート。
【図３】ＰＨＮＤのｄ_３３値のポーリング依存性を示すグラフ。
【図４】ＰＨＮＤのｄ_３３値の経時安定性を示すグラフ。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a novel maleimide-norbornene copolymer exhibiting second-order nonlinear optical characteristics, a method for producing the same, and an organic second-order nonlinear optical material using the same.
[0002]
[Prior art]
In the advanced information society in the future, it is necessary to transmit large-capacity and precise information at high speed, high density and high efficiency. Light is expected to play an important role in this field in addition to electronic technology because it has properties such as parallel progression, spatial processing, large operability, and high density. Meanwhile, an organic nonlinear optical material has recently been receiving attention as one of the materials necessary for utilizing this light.
[0003]
The nonlinear effects of inorganic materials known so far are caused by lattice vibration absorption, whereas the nonlinear effects of organic materials are due to the dipole moment caused by the dislocation of the delocalized π electron system by the substituent. And fundamentally does not involve lattice vibration, so that a faster response is possible.
[0004]
By the way, in order to generate a second-order nonlinear effect, it is necessary to orient the induced dipole moment in the same direction. Although the approach using poling is known, the approach using poling can obtain an oriented structure by a simpler process than other methods, and there are relatively few restrictions in molecular design. There is an advantage that a non-linear effect can be generated.
[0005]
However, the second-order nonlinear optical effect obtained in this manner tends to decrease with time because the active group in the molecule that causes it is relaxed by thermal motion or electrical repulsion of the molecule.
As one of the methods for suppressing such a time-dependent decrease of the second-order nonlinear optical effect and maintaining the long-term stability of the second-order NLO characteristic, a rigid aromatic ring is introduced into the main chain of a polymer material. It has been proposed to increase the glass transition temperature. However, when the glass transition temperature is increased in this way, the solubility of the polymer material in the solvent is reduced, so that there is a problem that the processability is reduced.
[0006]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a polymer material which can maintain nonlinear characteristics stably for a long period of time and has good processability.
[0007]
[Means for Solving the Problems]
The present inventors have conducted various studies on the second-order nonlinear optical material, and as a result, by allowing a specific dye as a nonlinear optically active group to be pendant on the side chain of the copolymer of maleimide and norbornene, the second-order NLO characteristic is improved. It has been found that a polymer material having long-term stability and good processability can be obtained, and the present invention has been accomplished based on this finding.
[0008]
That is, the present invention provides a compound represented by the formula (A):

And a structural unit represented by the formula (B):

(R in the formula is a hydrogen atom or a methyl group)
And a maleimide-norbornene copolymer having a weight average molecular weight of 5,000 to 15,000.
[0009]
This maleimide-norbornene copolymer is a novel compound which has not been described in the literature. For example, N- (4-hydroxyphenyl) maleimide and 2-norbornene are copolymerized in the presence of a radical polymerization initiator. To the copolymer obtained in the above,

(R in the formula is a hydrogen atom or a methyl group)
By reacting a red dye represented by the following formula:
In addition, the maleimide-norbornene copolymer can impart good secondary NLO characteristics by electric field orientation, and can be suitably used as a secondary nonlinear optical material.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The maleimide-norbornene copolymer of the present invention can be obtained by, for example, radically copolymerizing N- (4-hydroxyphenyl) maleimide and 2-norbornene according to the following reaction formula to form N- (4-hydroxyphenyl) maleimide with 2-norbornene. A first step of producing a copolymer (IV) with norbornene; and reacting the copolymer (IV) with a red dye of the general formula (III) to convert the copolymer (IV) from the structural units (I) and (II). The copolymer (V) is produced by sequentially performing the second step of producing the copolymer (V).
[0011]
Embedded image

(Where x, y and z in the formula are integers of 1 or more, and R has the same meaning as described above)
[0012]
The copolymerization reaction in the first step is performed by heating a mixture of N- (4-hydroxyphenyl) maleimide and 2-norbornene in a polymerization solvent in the presence of a radical polymerization initiator.
At this time, the ratio of N- (4-hydroxyphenyl) maleimide to 2-norbornene is selected in a molar ratio of 5: 1 to 1: 2, preferably 1.2: 1 to 1: 1. . If the amount of 2-norbornene is smaller than this, a copolymer having desired physical properties will not be obtained, and if the amount of N- (4-hydroxyphenyl) maleimide is smaller than this, relaxation of the orientation structure at high temperatures will be reduced. In addition to this, the amount of the red dye introduced in the subsequent step is low, and the desired second-order nonlinear optical activity cannot be obtained.
[0013]
This copolymerization reaction may be any of solution polymerization, emulsion polymerization and suspension polymerization, but solution polymerization is preferred in that the second step can be performed continuously. In this case, the reaction can be carried out without using a polymerization solvent, but when a polymerization solvent is used, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethylsulfoxide, diethylsulfoxide and the like are preferable. In addition, hydrocarbons such as benzene and nitrobenzene, and alcohols such as tert-butyl alcohol are also used.
[0014]
Examples of the radical polymerization initiator include peroxide polymerization initiators such as acetyl peroxide, benzoyl peroxide, lauroyl peroxide, and t-dibutyl peroxide, azobisisobutyronitrile, azobiscyanovaleric acid, An azo polymerization initiator such as biscyclohexanecarbonitrile or azobisisobutylamidine hydrochloride is used. The amount of the radical polymerization initiator used is usually selected in the range of 0.05 to 5.0% by weight based on the total weight of the monomers.
[0015]
Next, the temperature of the copolymerization reaction is preferably in the range of 50 to 100C, more preferably 60 to 80C. If the temperature is lower than this, the reaction rate is too slow to be practical, and if it is higher than this, a side reaction occurs, which causes deterioration in the quality of the finally obtained copolymer. The polymerization time at this temperature is usually 10 to 50 hours.
The copolymer (IV) of N- (4-hydroxyphenyl) maleimide and 2-norbornene thus obtained has a weight average molecular weight of 3,500 to 12,000 and a number average molecular weight of 5,000 to 20, 000, a white solid having a polydispersity (Mw / Mn) of 1.3 to 3.0 and a glass transition temperature of around 300 ° C.
[0016]
Next, in the second step, the thus obtained copolymer is reacted with the red dye of the general formula (III). At this time, it is preferable to use triphenylphosphine and diethyl azodicarboxylate as the condensing agent.
As the red dye, those represented by the general formula (III) in which R is a hydrogen atom, R is a methyl group bonded to the ortho position relative to the azo group, and a nitro group is in the ortho position or the azo group. Some are attached to the para position.
These red dyes are well known as chromophores that are introduced into the side chain of a polymer compound to form a second-order nonlinear optical material.
[0017]
The rate of introduction of the red dye is selected according to the second-order nonlinear optical characteristics of the copolymer to be produced. The introduction rate depends on the amount of the red dye used and the reaction time, but is usually in the range of 50 to 95 mol%, preferably 70 to 90 mol%. For example, when used in a slight excess of the hydroxyl group equivalent in the copolymer and allowed to react for 40 to 50 hours, the red dye can be introduced into about 70 mol% or more of the hydroxyl groups.
[0018]
This second step is performed using tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethylsulfoxide, diethylsulfoxide, or the like as a reaction solvent.
The maleimide-norbornene copolymer of the present invention thus obtained has a weight average molecular weight of 7,000 to 15,000, a number average molecular weight of 5,000 to 10,000, and a polydispersity (Mw / Mn) of 1.25. -2.0, a reddish brown solid having a glass transition temperature of 195-200 [deg.] C. This compound is soluble in organic solvents such as methylene chloride, chloroform, and tetrahydrofuran and has a film-forming property. The optimum poling temperature of this is in the range of 130 to 160 ° C.
[0019]
【Example】
Next, the present invention will be described in more detail with reference to examples.
[0020]
Example 1
0.5 g (5.32 mmol) of 2-norbornene purified by distillation, 1.0 g (5.32 mmol) of hydroxyphenylmaleimide, 0.02 g (0.12 mmol) of 2,2'-azobisisobutyronitrile Was packed in a 5-ml ampoule with 3 ml of tetrahydrofuran purified by distillation, sealed after degassing, and then subjected to radical copolymerization at a temperature of 65 to 70 ° C. for 24 hours.
Next, the product was taken out and reprecipitated twice using ether to obtain 1.1 g (yield: 72%) of a pale yellow solid copolymer.
The molecular weight of this product was measured by gel permeation chromatography, and as a result, the number average molecular weight was 5,100, the weight average molecular weight was 7,700, and the polydispersity was 1.5. The glass transition temperature measured by DSC was 300 ° C.
FIG. 1 shows a ¹ H-NMR chart of this product.
[0021]
Next, 0.868 g (3.32 mmol) of triphenylphosphine was added to 0.563 g (1.2 mmol) of the copolymer obtained as described above, and R in the general formula (III) was a hydrogen atom. Then, 0.748 g (2.38 mmol) of a red dye DR-1 corresponding to a compound in which a nitro group is bonded to the azo group at the para position is dissolved in 20 ml of tetrahydrofuran purified by distillation, and dissolved in an argon atmosphere. Into this, 0.58 g (3.32 mmol) of diethyl azodicarboxylate was added dropwise. After reacting at room temperature for 48 hours, the product was recovered. The product is reprecipitated twice with methanol, purified, and dried under reduced pressure for 12 hours to give 2-norbornene and a compound of the formula

As a result, 1.1 g (yield 77%) of a copolymer (hereinafter abbreviated as PHND) with an N-substituted maleimide anhydride represented by the following formula was obtained as a red-brown solid.
This had a number average molecular weight of 6,700, a weight average molecular weight of 9,700, a polydispersity of 1.34, and a glass transition temperature of 197 ° C.
FIG. 2 shows the ¹ H-NMR chart of this product.
[0022]
Example 2
The copolymer PHND obtained in Example 1 was dissolved in tetrahydrofuran to prepare a 1% by weight solution, which was formed on a glass substrate by a spin coating method (700 rpm, 30 sec).
The film thus obtained was subjected to an orientation treatment using corona poling to produce a nonlinear optical material. That is, considering that the glass transition temperature of the copolymer is 197 ° C., 110 ° C., 140 ° C., 155 ° C., 170 ° C. and 200 ° C. are selected as the poling temperatures, and after the temperature is raised to these poling temperatures, In this state, an electric field of 5 kV / cm was applied for 20 minutes, and the temperature was lowered to room temperature.
The refractive index of the polymer was measured with an ellipsometer (measurement wavelength λ 632.8 nm, He-Ne laser, incident angle 70 °), and was 1.67.
Indicating the polling dependence of the thus d ₃₃ values measured in FIG.
As a result, the optimum poling temperature was found to be 140 ° C.
[0023]
Example 3
The copolymer PHND obtained in Example 1 was dissolved in tetrahydrofuran to prepare a 2% by weight solution, and this was used to form a film in the same manner as in Example 2 to prepare a film.
Optimum poling temperature for this film, i.e. polls at 140 ° C., placed in a thermostat at 80 ° C., removed it at predetermined time intervals, temporal stability of d ₃₃ value by measuring the second harmonic generation (SHG) The sex was examined.
The result is shown in FIG.
As can be seen from this figure, slight relaxation was observed at the beginning of the measurement, but was not observed after 30 hours, and 80% of the initial value (290 × 10 ⁻⁹ esu) was retained even after 250 hours. Have been.
[0024]
【The invention's effect】
The copolymer of the present invention is a novel compound having a second-order nonlinear optical property, and exhibits an excellent effect of suppressing the relaxation of the second-order nonlinear optical property at a high temperature for a long time.
[Brief description of the drawings]
FIG. 1 is an NMR chart of a copolymer of 2-norbornene and hydroxyphenylmaleimide.
FIG. 2 is an NMR chart of PHND.
3 is a graph illustrating the polling dependence of _{d 33} value of PHND.
Graph showing the temporal stability of the FIG. 4 _{d 33} value of PHND.

Claims (4)

(A) formula

And the formula (B)

(R in the formula is a hydrogen atom or a methyl group)
And a maleimide-norbornene copolymer having a weight average molecular weight of 5,000 to 15,000. The maleimide-norbornene copolymer according to claim 1, wherein the molar ratio of the structural unit (A) to the structural unit (B) is 5: 1 to 1: 2. N- (4-Hydroxyphenyl) maleimide and 2-norbornene are copolymerized in the presence of a radical polymerization initiator, and then the copolymer thus obtained has a general formula

(R in the formula is a hydrogen atom or a methyl group)
Wherein a red dye represented by the following formula is reacted:

And the formula (B)

(R in the formula is a hydrogen atom or a methyl group)
A method for producing a maleimide-norbornene copolymer having a weight average molecular weight of 5,000 to 15,000, comprising a structural unit represented by the following formula: (A) formula

And the formula (B)

(R in the formula is a hydrogen atom or a methyl group)
A second-order nonlinear optical material comprising a maleimide-norbornene copolymer having a weight average molecular weight of 5,000 to 15,000, comprising a structural unit represented by:

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