CA1255653A

CA1255653A - Liquid crystalline materials useful to prepare polymeric films

Info

Publication number: CA1255653A
Application number: CA000431936A
Authority: CA
Inventors: Paul J. Shannon
Original assignee: Armstrong World Industries Inc
Current assignee: Armstrong World Industries Inc
Priority date: 1982-12-15
Filing date: 1983-07-06
Publication date: 1989-06-13
Also published as: GB8333323D0; GB8612237D0; JPS59110700A; LU85103A1; NL190525B; DE3340953C2; FR2537976A1; GB2174396B; BE897870A; JPH0116839B2; FR2537976B1; DE3340953A1; DE3347990C2; NL190525C; NL8304276A; GB2133406A; GB2133406B; GB2174396A

Abstract

LIQUID CRYSTALLINE MATERIALS USEFUL TO
PREPARE POLYMERIC FILMS

Abstract The present invention concerns novel cholesteric liquid crystalline monomers which are useful to form polymeric materials having unique optical properties.

Description

~2~6S;~

LIQUID CRYS~ALLINE MATERIALS USEFUL TO
PREPARE P~LYMERIC FILMS

The present invention relates to liquid crystals and more particularly to monomsric liquid crystals which are useful to prepare polymeric liquid crystalline materials.
Back rQund of the Invention The existance of liquid crystalline materials has been recognized since the late 1800~6. The terms "liquid crystal" or "mesogen" refer to a number of states of matter which lie between solid crystals and isotropic liquids, the latter being randomly ordered.
Liquid crystalline materials possess some structural charaateristics of crystals, yet they may be viscous or quite mobile liquids.
The varying degrees of order which are possessed by liquid crystals give rise to three distinct types of structures called mesophases. A liquid crystal, when in the crystalline state, has a three-dimensional uniform structure with orientational and positional order. As the crystal is heated, it may initially l OB e one dimension of its positional order.
This is raferred to as the smectic mesophase, a phase in which the liquid crystal retains the orientational order of the crystalline state, as well as two-directional positional order.
With further heating, the liquid crystal can convert to the nematic mesophase. In this phase, the , ~

~;~SS~;S3

-2- LFM-6892-7051 remaining positional order iB lo6t and the liquid crystalline material retains only the one-directional orientational order of the crystalline state. The molecular order of nematic mesophases is characterized by orientation of the molecules along an axis which coincides with the long axis of the molecules. The centers of gravity of the molecules are arranged randomly so that no positional long-range order exists.
In the cholesteric mesophase, the molecular order is characterized by orientation of the molecules along an axis which coincides with the long molecular axis as in a nematic phase; however, the axi~ changes direction in a continuous manner along a second axis perpendicular to the first. For this reason, cholesteric mesophases are often referred to as twisted nematic mesophases. Optical activity is necessary for a mesogenic material to form a cholesteric mesophase.
The term "cholesteric~ is primarily of historical significance because the first-discovered liquid crystalline material which exhibited a cholesteric mesophase was cholesteryl benzoate. It has long been recognized, however, that the presence of the cholesterol moiety is not required, and that non-cholesterol derivatives may also exhibit a cholesteric mesophase.
The Prior Art Substantial interest has been shown in liquid crystalline materials which exhibit cholesteric mesophases because these materials exhibit unique optical properties such as selective reflection of vi~ible light to produce iridescent colors, as well as circular dichroism. Thus, for example, U.S. Patent

3,720,623 discloses mixtures of cholesteric and nematic liquid crystals which are useful in temperature-sensitive visual displays; U.S. Patent 3,766,061 discloses dscorative films comprising solid materials which are proportioned such that the composition d monstrates cholesteric properties; U.S. Patsnt .~
. j S5~S3 3,923,6~5 discloses cholesteric materials which convert to the nematic state upon exposure to an electric field;
and U.S. Patent 3,931,041 discloses combinations of nematic and potentially cholesteric material which are useful in imaging and display devices.
Although the colored images produced using cholesteric material are quite useful, most such images are not permanent. Accordingly, there has been substantial interest in preparing cholesteric materials in which the color can be fixed. Thus, U.S. Patent 3,766,061, which was referred to above, discloses decorative films in which the color is fixed by cooling.
In addition, U.S.Patent 4,293,435 discloses a polymeric liquid crystal in which the color is fixed by lowering the temperature of the polymer below the glass transition temperature, thereby fixing the polymer in the solid state.
The use of temperature changes to fix the color i6 not always practical, however, and there has been interest in developing cholesteric materials whose color can be fixed by other means, such as by photopolymerization, whereby the resulting fixed color is temperature insensitive. Applicant is aware of only one such polymer. This was reported by a group of Japanese workers who disclosed the poly(gamma-butyl-L-glutamate) in triethylene glycol dimethacrylate could be photopolymerized to fix the color such that it was temperature insensitive.
Accor~ingly, one ob;ective of the present invention is to provide monomeric cholesteric liquid crystalline materials which are useful to prepare polymeric films having mixed, essentially temperature-insensitive colors.
Yet another objective of the present invention is to provide monomeric compounds which may be used in combination with other mesogenic materials to provide compositions which exhibit variable optical responses over a variety of temperature ranges.

~25S6~3

- 4 ~ 2 These an`d other objectives of the present invention will become apparent from the detailed description of preferred embodiments which follow.
; _ummary of th_ Invention 'rhe present invention concerns novel cholesteric liquid crystalline rnonomers which are useful to form polymeric materials having unique optical properties.
Deta_led Description of P_eferred Embodiments In one embodiment the present invention comprises photopolymerizable monomers which are useful to prepare polymeric films, said monomers having the structure y\/y I

CH2=C-C-O-R2-C-O
: Hy H
where Rl ~ H or CH3, R2 = an alkylene chain having from 3-14 methylene or lower alkyl-substituted methylene groups, and y = 0 or 1, provided that when Rl = CE~3, Y = 1.
In a second embodiment, the present invention : comprises photopolymerizable monomers which are useful to prepare polymeric films, said monomers having the structure .
r CH2-C-C-O--~ O
H
H

~SS~S3

- 5 ~ 'J ' where R1 = ~3 or CH`3, A = -R30- or -R40-, R3 = an alkylene chain having from 2-14 methylene or lower alkyl-substituted methylene groups, R4 = an alkylene or ! lower alkyl-substituted a]kylene ether, diether or triether having a total of rrom 3-14 carbon atoms in the alkylene linkages, provided that the terminal alkylene linkage adjacent the carbonate moiety comprises not less than two carbon atoms; and y = 0 or l.
In a third embodiment, the present invention comprises compounds which are useful as intermediates to ' prepare photopolymerizable monomers, said compounds L-having the structure ~/

`. R ~
Xl -R2 -C-~
y I
~ Y
where Xl ~ Br, I or a sulfonic acid ester, R2 = an alkylene chain having from 3-14 methylene or lower alkyl-substituted methylene groups, and y = 0 or l.
The cholesterol derivatives which may be used to practice the present invention are cholesterol (where y = 0) and 5,6-dihydrocholesterol (where y = l~.
In addition, a number of options are available in the three position side chain. Thus, the polymerizable moiety of the side chain can comprise an acrylate or methacrylate moiety which is bridged to an ester or carbonate linkage. Where an ester linkage is present, the bridge will comprise an alkyl chain comprising from 3-14 methylene or lower alkyl-substituted methylene groups. r.ower alkyl as used herein shall mean an alkyl group comprising from 1-4 carbon atoms. The methacry-late esters, where Rl = CH3 and n = 5, lO and 14, have been reported ;n the Russian literature; nowever, these esters were prepaL-ed for use in solution polymeri~ation reactions and there was no ~25S6~i3

- 6 - LFM-6892-7051 appreciation of their utility for preparing photo-polymerized films a~ disclosed herein.
On the other hand, where a carbonate linkage is present, the bridge may be more complex. Thus, it may comprise from 2-14 methylene or lower alkyl-substituted methylene groups, or an alkylene or lower alkyl-substituted alkylene ether, diether or triether having a ~otal of from 3-14 carbon atoms in the alkylene linkages, provided that the terminal alkylene linkage adjacent the carbonate moiety comprises not less than two carbon atoms. The reason for this restriction will be set forth in more detail below. Examples of ether moieties which may be utilized in practicing the present invention are those which are analogous to ethylene glycol, diethylene glycol, triethylene glycol, tetramethylene glycol, 3,3'-oxybis-1-propanol, 4,4'-oxybi~-1-butanol, 1,1'-oxybis-2~propanol, and the like.
When in the pure 6tate the compounds of the present invention are somewhat difficult to work with because they tend to crystallize at inopportune moments.
Furthermore, it is difficult to obtain colored polymers from the pure monomers because the majority of them will show either no colored cholesteric mesophase, or a very narrow colored cholesteric mesophase. Therefore, the pure compounds of the present invention are limited in their ability to produce polymeric films having desirable optical responses.
Surprisingly, it has been dissovered that these limitations may be overcome and that colored and uncolored films comprising compounds of the present invention can be prepared and photopolymerized in the presence of a suitable photoinitiator, thereby giving films having fixed optical characteristics. If the film is colored, the fixed color will preferably be sub~tantially the same as the color of the unpolymeri7.ed film; however, in certain instances, it may be desirable to obtain a polymerized film having a fixed color which ~ 5~3

- 7 - LFM-6892-7051 differs from that of the unpolymerized film. Details relating to these polymeric films and their preparation are set forth in Canadian Patent No. 1,214,592, issued November 25, 1986, said patent being entitled "Polymeric Liquid Crystals".
The cholesteryl ester derivatives of the present invention may be prepared in surprisingly good yield by reacting an w-substltuted-alkyl acid halide (I), which preferably is an w-bromoalkyl acid chloride, with the desired cholesterol derivative (II) to produce a cholesteryl w-substituted-alkyl ester (III). Reaction of this compound with an alkali metal acrylate or methacrylate (IV) in the presence of a radical inhibitor and an appropriate catalyst then yields the desired acrylate or methacrylate ester (V). This sequence may be visuali~ed by reference to the following general reaction:

y ~
Xl-R2- -X2 + H0 ~ ~ II

I H
Y y\/y X1-R2- ~ ~ I11 H~, ~' ,,~
. i .

12~56S3

- 8 - LFM-6892-7051 ~ 1 CH2=C-C-0-M + III

IV
I

C~12=1--C-O-R2- o~l v H

In the6e other reactions illustrated herein, R1 = H or CH3; R2 = an alkylene chain having from 3-14 methylene or lower alkyl substituted methylene groups; y = 0 or 1; X1 = Br, I or a sulfonic acid ester; X2 = Br or Cl; and M = Na or K. Examples of suitable sulfonic acid ester6 are CH3S03-; p-CH3C6H4S03-; C6HsS03-;
p-BrC6H4S03-; and the like. Preferably X1 will be Br and X2 will be Cl. Further, for intermediates of type III, R2 will preferably have from 4 to 14 carbon atoms in the alkylene chain.
The cholesteryl carbonate derivatives (IX) may be prepared in good yield by a somewhat different route.
In thi6 reaction 6equence, a haloalcohol ~VI) is reacted with an appropriate chole6teryl haloformate (VII) to yield an w-haloalkylcarbonate derivative (VIII). This compound is then reacted with an alkali metal acrylate or methacrylate (IV) as previously described to yield the carbonate monomer (IX). Alternatively, compounds of ; 35 type IX may be prepared by reacting a compound of type VII with a hydroxyalkyl acrylate or methacrylate (X). A
general reaction sequence illustrating these alternatives is illustrated below:

. , ~;~,.5S6~3 y\/y ~ ~ VII

Xl-A-H + X2-C-O~
H
VI H

y ~\ ~-Xl-A-C-0 ~ ~ VIII
` H
H
;

m IV + VIII--~CH2=C-C-0-A-C-0 ~ IX
Hy Y

CH2=C-C-0-A-H + VII

X

where Rl, Xl, X2 and y are as described above and A =
-R30- or -R40- where R3 - an alkylene chain having from 2-14 methylerle or lower alkyl-substituted methylene groups, and R4 = an alkylene or lower alkyl--substituted alkylene ether, diether or triether having a total of ~l~S5653 - 13 - !~ 5i from 3-14 carbon atoms in the alkylene linXages, provided that the terminal alkylene linkage adjacent the carbonate moiety comprises not less than two carbon atoms. Examples of suitable ether moieties were referred to above; however, the restrictions on the length of the one terminal linkage must be emphasized.
The terminal linkage in question is the alkylene group adjacent to the carbonate moiety in product IX. Neither synthetic route illustrated herein is amenable to the use of an ether having a single carbon atom adjacent this reaction site. Thus, compounds of type VI and type X
may not co~prise a -O-CH2-OH moiet~. Accordingly, the terminal alkylene linkage adjacent the carbonate moiety must comprise at least two carbon atoms.
~he advantages and attributes of the present invention will become more apparent from the following examples which are intended to illustrate but not to limit the scope of the preSent invention.
Example 1 The following example will illustrate- the preparation of the cholesteryl w-substituted-alkyl esters of type III. A 0.1 mol quantity of cholesterol or 5,6-dihydro-cholesterol, 0.12 mol of pyridine and 0.~2 mol of w--bromoalkanoyl chloride is dissolved in 25 200-300 ml of a suitable solvent such as ethanol-free chloroform or ether/dichloromethane. The mixture is stirred at 0C for 2 hours and at ambient temperature for 16 hours, and is then diluted with 300 ml of solvent. The organic phase is washed with two 200-ml portions of lN hydrochloric acid and then with water, after which it is aried over magnesium sulphate.` Upon concentrating the dried solution, the esters (III) are obtained and purified by recrystallization from a suitable solvent such as 1:1 ether-ethanol.
Representative compounds are illustrated in the following table:

~;2S~S3 ~ 2-7~51 y ~

Br-(C~ C-O ~ III
H
., Y
Compound n Y Yield(%) MP(C) IIIa 10 0 89 99-100 IIIb 5 0 86 120-121 IIIc 3 0 86 87-90 IIId 3 1 91 92-93 IIIe 10 1 87 65-67 Example 2 This example will illustrate the preparation of cholesteryl ester monomers of type V. A biphasic solution comprising 0.15 mol of potassium acrylate or methacrylate, 0.05 mol of ester III, 0.01 mol of N,N,N,N,-tet-ra-n-butylammonium bromide and 0.0034 mol of 2,6-di-t-butylcresol radical inhibitor is prepared in a mixture of water (30 ml) and chloroform (15 ml). The biphasic solution is heated and stirred magnetically for 40 hours in an oil bath maintained at 110-115 C. After cooling, the mixture is diluted with 500 ml of a 4:1 solution of ether and dichloromethane, and the organic phase is separated and washed twice with water. After being dried over magnesium sulphate, the organic phase is concentrated to yield the acrylate or methacrylate monomer (V) which is recrystalli~ed from a suitable solvent, such as ether-ethanol or acetone-ethanol.
Representative monomers are illustrated in the following table:

~SS653 - 12 - ~ 92-70~1 CH2=C-C--O-(CH2)r~-C~O 1~ ~' v H
H
Y

Melting or : Yield Mesophase ~ _o pound Rl n ~ ) Range (C) : Va H 10 0 83*54.5 - 71.5 ` 5 Vb CH3 10 0 88 ~58 - 64 Vc H 5 0 87*45.5 - 68.5 : Vd CH3 5 0 90 ~48 - 57.5 Ve H 3 0 83 68.5 - 70~5 (67.5) Vf CH3 3 0 75 73 - 74 (56.0) Vg~ H 3 1 58 41 - 43 (35.5) Vh CH3 3 1 71 43 - 45 (Below ~t) Vi H 10 1 70 62.5 - 64.5 (58.0) V~ CH3 10 1 56*33.7 - 49.0 :: :
: As used in this example and hereafter, the `~ 15 temperature ranges are melting ranges unless otherwise indicated by an asterisk (*) or by parentheses. `An asterisk signifies that the range is a mesophase range whereas parentheses indicate that the range is a ~;~ monotropic mesophase range, the latter being measured as the temperature is decreased. With materials that have ~: ~ ascertainable melting points, the monotropic mesophase ~:~ range is often below the melting range.

.

- ~2SS6S3 ~2-70,1 Example 3 _ _,, _ _ This example will illustrate the preparation of cholesteryl ester monomers of type V using a polar aprotic solvent system rather than phase transfer catalyzed conditions as set forth in Example 2. A
mixture comprising 0.05 mol of bromine-substituted ester III, 0.10 mol of potassium acrylate, and 0.0034 mol of 2,6-di-t-butylcresol radical inhibitor is prepared in dirnethylformamide (50ml). The mixture is heated with stirring for 3 hours in an oil bath maintained at 70-80 C. After cooling, the mixture is diluted with water (250 ml) and extracted with ether (4X 150 ml).
The organic phase is washed with brine, dried over maynesium sulfate, and concentrated to yield the acrylate monomer V which is recrystallited from ether-ethanol. Iodine-substituted esters of type III
will also give suitable results under these conditions.
Example 4 This example illustrates the preparation of cholesteryl w-haloalkyl carbonates of type VIII. To a solution of 6-bromohexanol (0.075 mol), and pyridine (0.055 mol) in dichloromethane (50 ml) is added a solution of commercially available cholesteryl chloroformate (0.05 mol) in 50 ml of dichloromethane.
The addition is achieved at room temperature and the resulting mixture is stirred for 18 hours, after which it is diluted with 200 ml of dichloromethane, washed twice with 75-ml portions of lN hydrochloric acid and then with water. The organic phase is dried over magnesium sulfate and concentrated to give a solid w-bromoalkyl carbonate of type VIII which is purified by recrystallization from ether-ethanol. The resulting compound (VIIIa), which is obtained in 78% yield, has a melting point of 87-88.5C.
Example 5 ... _ ., . .. ... . _ This example illustrates the preparation of cholesteryl acryloyl- or methacryloyloxyalkyl carbonates ffGm carbonates of type VI~I. A solution of 0.02 mol of ~56S3 - i4 ~ v,J2-7~1 the product of Example 4 (VIlIa) and 0.06 mol of potassium rnethacrylate is heated for 40 ho~rs as described in Example 2. Upon recrystallization of the solid prod~ct from a 1:1.5 solution of acetone-ethanol, a 68% yield of methacrylate monomer is obtained which melts at 58.5-60C.
Example 6 This example will illustrate the alternative method of preparing compounds of type IX by reacting a hydroxyalkyl acrylate or methacrylate of type X with the cholesteryl haloformate of type VII. To a solution of hydroxyalkyl acrylate or methacrylate (0.06 mol) and pyridine (0.044 mol) in 40 rnl of dichlororrlethane is ; added drop-wise a solution of cholesteryl haloformate (0.04 mol) dissolved in 40 ml of dichloromethane. The addition is achieved at 0C, after which the mixture is allowed to warm to ambient temperature and stirred for six hours. The resulting product mixt~re is diluted with 250 ml of dichloromethane, washed with 60 ml of lN
hydrochloric acid and then with water. The organic phase is dried over magnesi~m s~lfate and concentrated ; to give a solid which is recrystallized from a suitable solvent such as acetone-ethanol. Representative products are as follows:
;

CH2=C-C-O-A-C-O IX

H

~Z~5~S3 Meltir,s or Yield Mesophase Compound Rl _A y_ (%) Range (C) IXa CH3 (CH2)6 0 68 58.5 - 60 (51.0) IXb CH3 (CH2)2o o 82 80 - 81 (40.1) IXc H (CH2)2 81 85.5 - 87 (56.0) IXd H (CH2)6 48*~ *52 -- 62 **prepared by treating compound VIIIa as described in Example 2.
Example 7 This example will illustrate the preparation of alkylene ethers and diethers of type IX where A =
-(CH2CH2O)2- and -(cH2cH2o)3-. Starting compounds of type X were prepared by means described in the chemical literature and were reacted as described in Example 6 to give the following products:
Melting or Yield Mesophase Compound Rl A _y_ (%) ange (C) __ i 20 IXe CH3 (CH2cH2O)2 60 48.5 - 52.9 (33.1) IXf CH3 (CH2cH2o)3 0 62 no m. pt. (6.5) Example 8 This example sets forth the color ranges of various monomeric esters V of the present invention, measured with a Leitz optical microscope using transmitted light through cross-polars at 250X
magnification. A Mettler FP5 temperature regulator and a ~1ettler FP52 hot stage is used to control the temperature, cooling being obtained by passing a nitrogen stream through a dry-ice cooled copper coil - and, subsequently, the FP52 hot stage.

~LZ55653 - 16 - L.':-~892-/C'51 .
Co~lpo~nd ~ Color Range (C) Va 57.8 - 59.2 Vb (55.8 - 55.3) Vc (48.5 - 33.0) Vd t51.0 - 26.5) Ve No Color Vf No Color This invention is not restricted solely to the : descriptions and illUstratinS provided above, but 10 enc~asses all ~difications er~visaged by the follc~wing cla ms.

' .

I ~ ~
.

Claims

WHAT IS CLAIMED IS:

1. Compounds having the structure where R1 = H or CH3. R2 = an alkylene chain having from 3-14 methylene or lower alkyl-substituted methylene groups.

2. Compounds having the structure where R1 = H or CH3, A = -R3O-, and R3 = an alkylene chain having from 2-14 methylene or lower alkyl-substituted methylene groups.

3. Compounds having the structure where R1=H or CH3, A= -R4O-, R4= an alkylene ether, diether or triether having a total of from 3-14 carbon atoms in the alkylene moieties, provided that the terminal alkylene moiety adjacent the carbonate moiety comprises not less than two carbon atoms, and y=0 or 1.

4. The compounds as set forth in claim 3 hereof wherein the alkylene moieties of R4 are at least partially lower alkyl substituted.