JPH0759635B2 - Thermotropic cholesteric liquid crystalline polypeptide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a polypeptide exhibiting thermotropic cholesteric liquid crystallinity. More specifically, glutamate γ
The present invention relates to a polypeptide having a thermotropic cholesteric liquid crystallinity, which is a copolymer of-(p-cyanobenzyl) ester and glutamic acid γ-alkylester.

<Prior Art and Problems to be Solved by the Invention> It is well known that there are three phases of solid, liquid and gas in general as a method of existence of a substance. A liquid crystal in a normal state is also known. Liquid crystals are classified into thermotropic liquid crystals that are thermally induced from the condition of forming a liquid crystal phase and lyotropic liquid crystals that become liquid crystals when mixed with water or another polar solvent. Further, the molecular arrangement state is classified into smectic, nematic, cholesteric and the like.

Conventionally, many liquid crystal compounds were low molecular weight compounds such as ammonium oleate, 4-cyano-4'-alkoxybiphenyl, and cholesteryl acetate, but in recent years, research on polymers exhibiting liquid crystallinity has become popular, and aromatic polyamide Aromatic polyester has been put to practical use as a high-strength fiber.

In the case of liquid crystalline polymers, the helical structure of cholesteric liquid crystals has been attracting attention due to its low optical functionality and low mechanical anisotropy in the mechanical strength of molded products. In using these liquid crystalline polymers, the issue is how to fix the liquid crystal state. For fixing the cholesteric liquid crystal structure, for example, (1) a solvent is gradually evaporated from a lyotropic state to form a solid film, (2) a thermotropic cholesteric liquid crystal is vitrified in a liquid crystal state,
(3) For example, lyotropic liquid crystal using a vinyl monomer as a solvent is photopolymerized to be immobilized.

Among these methods, (1) limits the solvent that dissolves the liquid crystalline polymer, and special attention must be paid to the evaporation of the solvent. (2) increases the crystallization speed of the liquid crystalline polymer and vitrification of the liquid crystal. Difficult, (3) has a drawback that it dissolves liquid crystal and has less photopolymerizable vinyl monomer as in (1). Further, none of these methods has been successful in controlling the cholesteric pitch (also simply referred to as pitch), which is a feature of the cholesteric liquid crystal, with good reproducibility.

On the other hand, from the standpoint of polymer moldability, thermotropic liquid crystalline polymers have been desired because they can be used by modifying the conventional thermoplastic resin molding method slightly.

As a polymer that solves these problems, a copolymer of glutamic acid-γ-benzyl ester and glutamic acid γ-alkyl ester can be mentioned (JP-A-62-116629).
issue). This thermotropic / cholesteric soluble crystallizable polypeptide copolymer has the following characteristics.

(1) The cholesteric pitch can be varied over a wide range depending on not only the temperature but also the type and composition of the copolymer.

(2) The cholesteric liquid crystal state can be fixed completely by quenching.

(3) After immobilization, it is extremely stable below the transition temperature to cholesteric liquid crystal.

(4) The phase transition temperature to liquid crystal is 100 ° C to 180 ° C, which facilitates molding.

(5) The α-helix structure of the polypeptide is stable.

(6) The temperature dependence of the pitch is remarkable, and the spectral width of the selective reflection wavelength light depending on the pitch is very narrow.

Therefore, in order to use a polymer as an optical material, it is necessary to control its birefringence. However, there is a problem that the birefringence of the above-mentioned thermotropic cholesteric liquid crystal polypeptide copolymer is too small for use as an optical material, and its value cannot be changed.

Therefore, from the viewpoint of expanding the range of application to optical materials, there has been a demand for a liquid crystal polymer capable of freely controlling birefringence.

<Means for Solving the Problems> As a result of the above, the inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, the liquid crystallizing temperature is low, and the cholesteric pitch is not limited to the temperature. A novel thermotropic polymer that can be controlled over a wide range depending on the type and composition of the polymer, can completely immobilize the liquid crystal structure, and can change birefringence freely according to the copolymerization composition ratio. The present invention has been accomplished by finding a cholesteric liquid crystalline polypeptide copolymer.

That is, the present invention relates to a γ-cyanobenzyl glutamate-γ-alkyl glutamate copolymer represented by the following general formula [I].

(In the formula, R represents an alkyl group having 10 to 30 carbon atoms, m and n are 30 ≦ m + n ≦ 2000, m / n = 80 to 10/20 to 90,
The p-cyanobenzyl ester unit and the alkyl ester unit are both L-forms or both D-forms. ) Hereinafter, the present invention will be described in detail.

The alkyl group used in the γ-cyanobenzyl glutamate-γ-alkyl glutamate copolymer represented by the general formula [I] of the present invention has 10 to 30 carbon atoms, preferably
It is an alkyl group of 13 to 25. When the number of carbon atoms is less than 10, it does not show thermotropic / cholesteric liquid crystallinity,
Further, when the number of carbon atoms is more than 30, it is difficult to synthesize the polymer, which is not preferable.

Specific examples of preferred alkyl groups include decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group,
Examples include pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, eicosyl group, heneicosyl group, docosyl group, tricosyl group, tetracosyl group, pentacosyl group, triancosyl group, etc. Alkyl groups having a structure can also be used. Among them, dodecyl group,
Tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, octadecyl group, eicosyl group, docosyl group, tetracosyl group and the like are particularly preferably used.

The cyanobenzyl group / alkyl group ratio (m / n in the formula [I]) in the copolymer of the present invention is 80 to 10/20 to 90, preferably 70.
~ 40/30 ~ 60. Outside this range, thermotropic / cholesteric liquid crystallinity does not appear clearly. In the cholesteric liquid crystal, when the selective reflection wavelength is λm, the cholesteric optical pitch is P, the refractive index is n, and the incident angle to the cholesteric surface is θ, the relationship of λm = nPsinθ is given between them. In the copolymer of the present invention, λm can be changed within a very wide range by changing the ratio of cyanobenzyl group / alkyl group within the above range. The degree of polymerization of the copolymer (m + n in the formula [I]) is 30 to 20.
00, preferably 100-1500. When the degree of polymerization is less than 30, the liquid crystal structure is difficult to develop, and when the degree of polymerization is too large, the moldability is deteriorated and the growth of the cholesteric structure is delayed, which is not practical.

Further, in order for the copolymer of the present invention to exhibit thermotropic / cholesteric liquid crystallinity, both the cyanobenzyl ester unit and the alkyl ester unit in the formula [I] are L.
It needs to be a body or both D bodies, otherwise it does not exhibit liquid crystallinity.

The birefringence of the copolymer of the present invention can be freely controlled in the range of 0.01 to 0.15 by changing the ratio of cyanobenzyl group / alkyl group. That is, it is possible to realize a large birefringence by increasing the content of the cyanobenzyl group.

The copolymer of the present invention can be obtained by various methods. For example, a monomer corresponding to each unit, a copolymerization of an optically active N-carboxyglutamic acid γ-cyanobenzyl anhydride and an N-carboxyglutamic acid γ-alkyl anhydride, or an optically active poly (γ-cyanobenzyl glutamate) is used. As a substance, there may be mentioned a method of carrying out a transesterification reaction with a corresponding alcohol. The reverse transesterification, that is, a method of transesterifying poly (γ-alkyl glutamate) with cyanobenzyl alcohol is also used.

As an example, the thermotropic cholesteric liquid crystalline polypeptide copolymer of the present invention is prepared by using poly (γ-alkyl-L-glutamate) as a starting polymer, p
-It is obtained by carrying out a transesterification reaction with cyanobenzyl alcohol. Poly (γ-alkyl-L-glutamate) can be easily obtained by ring-opening polymerization of N-carboxy L-glutamic acid γ-alkyl ester anhydride (NCA method). The NCA method also has the advantage that the molecular weight of the produced polypeptide can be adjusted arbitrarily.

The transesterification reaction is usually carried out in a solvent using an acid or a base as a catalyst.

The solvent used is dichloroethane, chloroform,
Those that dissolve polyglutamate such as dioxane are preferred. Also, hydrochloric acid, sulfuric acid, as an acid or base serving as a catalyst,
Examples thereof include toluene sulfonic acid, acidic ion exchange resins, alkali metal alkoxides, aluminum alkoxides, sodium hydroxide and amines.

The transesterification rate can be easily changed by the reaction temperature and the reaction time. The reaction temperature is room temperature to 150 ° C,
It is preferably 40 to 80 ° C. If the temperature is too low, transesterification will take too long, and if it is too high, the reaction will be difficult to control, which is not desirable.

The glutamic acid ester copolymer obtained by the method described above exhibits thermotropic / cholesteric liquid crystallinity and can be used for various purposes. That is, the thermotropic / cholesteric liquid crystalline polypeptide copolymer of the present invention is an optical filter (notch filter, bandpass filter, etc.), color display element, laser light optoelectronics element, memory element, temperature sensor, etc. Can be applied to.

<Examples> Examples will be shown below, but the present invention is not limited to these examples.

Various measuring methods used in the examples will be described below.

(1) Measurement of molecular weight GPC analysis was performed using chloroform as a solvent and GMH6 as a column. The calibration curve used was polystyrene.

(2) Composition of (Shianobenshiru group / alkyl group ratio) transesterification was dissolved poured and recovered polymer into methanol deuterated trifluoroacetic acid / deuterated chloroform (50/50 by volume) mixed solvent, ¹ The 1 H-NMR spectrum was measured and determined.

(3) Circular dichroism (CD spectrum) and degree of illuminance Using an optical dispersion recorder J-20 manufactured by JASCO Corporation,
The cholesteric optical pitch was measured in the wavelength range of 700 nm to 200 nm.

(4) Birefringence The copolymer was press-filmed and rapidly cooled before being cholesteric to fix the nematic structure. The thus obtained film was measured by changing its direction with an Abbe type refractometer to measure the refractive indexes no and ne for ordinary light and extraordinary light. ne-no becomes birefringence (Δn).

Example 1 (1) Poly (γ-alkyl-glutamate) (PAG)
Synthesis of N-carboxy-glutamic acid γ-alkyl ester anhydride obtained by a conventional method was added to 200 g of purified dioxane, and polymerization was carried out at 30 ° C. using triethylamine as a catalyst. After completion of the polymerization, the reaction mixture was poured into a large amount of methanol to collect the polymer. The degree of polymerization was adjusted by changing the monomer / catalyst ratio (molar ratio) to obtain poly (γ-alkyl-glutamate) as shown in Table 1.

(2) Synthesis of Thermotropic Cholesteric Liquid Crystalline Polypeptide (Transesterification Reaction) 1 g of PAG obtained in (1) above is mixed with 50 ml of 1,2-dichloroethane.
Dissolved in 10 g of p-cyanobenzyl alcohol and p
-Toluenesulfonic acid 1.0 g (catalyst) was added and the reaction was carried out at 70 ° C. The transesterification rate was adjusted by changing the reaction time. The results are shown in Table-2. The ¹ H-NMR spectrum and ¹³ C-NMR spectrum of the obtained copolymer are shown in FIGS.

(3) Measurement of Thermotropic / Cholesteric Liquid Crystal Characteristic The thermotropic / cholesteric liquid crystal characteristic of the γ-cyanobenzyl-glutamic acid γ-alkyl copolymer obtained in (2) above was measured. See Table 2 for polymer numbers in each figure.

DSC (Figs. 5 to 7) Using a film formed from a chloroform solution of polymer 4, the thermal behavior was investigated at a temperature rising rate of 10 ° C / mm and a temperature lowering rate of 10 ° C / mm.

As is clear from FIGS. 5 to 7, the copolymer of the present invention has a temperature of 60 ° C.
A phase transition temperature to liquid crystal was observed at ~ 145 ° C.

Relationship between temperature of cholesteric liquid crystal and selective reflection wavelength (λ (small letter of lambda) m) (Figs. 8 and 9) Samples of each polymer in Table 2 were sandwiched between two glass slides, and purple was developed from the melting point. Circular dichroism spectrum (CD spectrum) was measured by heating at temperature and spreading it thinly until equilibrium was reached. Next, the temperature was raised by 3 ° C. and the CD spectrum in the equilibrium state of the temperature was measured. The temperature was raised little by little by the same procedure, and the selective reflection wavelength corresponding to the temperature was measured. 8th
The temperature dependence of the selective reflection wavelength is shown in FIGS. That is, all of these polymers showed clear thermotropic cholesteric liquid crystallinity.

Relationship between polymer composition and birefringence index 0.2 g of each polymer in Table 2 was film-pressed at 120 ° C. and immediately quenched to immobilize the nematic structure. The polypeptide film was peeled off, the refractive index ne in the flow direction of the polymer and the refractive index no in the direction perpendicular thereto were measured with an Abbe type refractometer to determine the birefringence Δn. The results are shown in Table 3.

Sample numbers 1-, 1-, 1-, 2-, 2-
The relationship between the birefringence of 2-, 3-, 3-, 3- and the cyanobenzyl ester group content is shown in FIG.

From this, it is clear that the birefringence can be increased by increasing the cyanobenzyl ester group.

<Effects of the Invention> The γ-benzylglutamate-γ-alkylglutamate copolymer of the present invention exhibits thermotropic / cholesteric liquid crystallinity, and the kind of alkyl group, cyanobenzyl ester / alkyl ester ratio, temperature and the like can be changed. Thus, the cholesteric pitch can be freely changed, and the desired birefringence value can be realized by changing the cyanobenzyl ester / alkyl ester ratio.
Furthermore, since the cholesteric structure can be easily fixed, the cholesteric structure can be used in many applications such as optical parts and optoelectronic parts.

[Brief description of drawings]

1 to 4 are ¹ H-NMR spectrum and ¹³ C-NMR spectrum of the thermotropic cholesteric liquid crystalline polypeptide copolymer shown in Table 2. The strength of the static magnetic field was measured at 9.4 Tesla. The horizontal axis is the TMS-standard chemical shift value. 5 to 7 are examples of thermograms of the above copolymer. FIG. 8 and FIG. 9 are plots of the selective reflection wavelength of the cholesteric film produced from the above copolymer against the liquid crystal growth temperature. FIG. 10 shows the composition dependence of the birefringence (Δn) of the above copolymer.

Claims (1)

[Claims] 1. A γ- (p-cyanobenzyl) -glutamate-γ-alkyl glutamate copolymer represented by the following general formula [I]. (In the formula, R represents an alkyl group having 10 to 30 carbon atoms, m and n are 30 ≦ m + n ≦ 2000, m / n = 80 to 10/20 to 90,
The p-cyanobenzyl ester unit and the alkyl ester unit are both L-forms or both D-forms. )