Thermochromic polymerizable mesogenic composition

Details Thermochromic polymerizable mesogenic composition Thermochromic polymerizable mesogenic composition

2000-03-10

2001-11-13

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C428S001500, C252S299010, C252S299610, C252S299620, C252S585000, C522S170000, C549S464000

Reexamination Certificate

active

06316066

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a thermochromic polymerizable mesogenic composition comprising:
a) a component MA comprising at least one achiral polymerizable mesogenic compound comprising at least one polymerizable functional group,
b) a component MB comprising at least one chiral polymerizable mesogenic compound comprising at least one polymerizable functional group,
c) a photoinitiator, and
d) optionally a dye component.
The invention further relates to anisotropic polymers and polymer films with a chiral mesophase obtainable from said thermochromic polymerizable mesogenic composition and to the use of said thermochromic polymerizable mesogenic composition, of said anisotropic polymers and cholesteric polymer films for optical information storage, photomasks, decorative pigments, cosmetics, security applications, active and passive optical elements such as polarizers or optical retarders, color filters, scattering displays, adhesives or synthetic resins with anisotropic mechanical properties.
The term “mechanical properties” is used to distinguish from the electrooptical properties of these materials (like birefringence or dielectric anisotropy), and comprises, e.g., anisotropic material properties such as thermal expansion coefficient, shear modulus, response to external mechanical stress, etc.
Thermochromic compositions, i.e., compositions that show a change of color upon temperature variation, are known in prior art. Usually low molar mass liquid crystals exhibiting a chiral mesophase, like cholesteric liquid crystals (CLCs) are used in thermochromic compositions. These materials exhibit a helically twisted molecular structure and show selective reflection of a specific wavelength band of light, wherein the reflected wavelength maximum varies upon change of the temperature. Such thermochromic compositions are disclosed for example in WO 90/02161.
For many applications, such as the preparation of colored films that can be used as optical films, e.g., patterned color filters, photomasks or films for optical information storage, materials like CLCs are needed wherein the reflected wavelength band remains substantially constant over a wide temperature range.
A suitable material for these applications would be a polymerizable thermochromic composition, wherein the desired pitch length and thereby the waveband reflected from that composition could be easily selected by temperature variation and afterwards the molecular structure with the selected pitch be fixed by polymerization, so that the reflected wavelength remains stable over a wide temperature range.
The European Patent Application EP 0 661 287 A1discloses polymerizable liquid crystalline siloxanes that show thermochromic behavior and can be polymerized to give linear liquid crystalline polymers with mesogenic side chains.
However, linear polymers and in particular polymers comprising siloxane chains like those disclosed in EP 0 661 287 most often exhibit low glass transition temperatures and show only limited temperature stability. Upon heating of these polymers their optical properties often deteriorate.
Consequently, there has been a considerable demand for a thermochromic material that can be polymerized to give an anisotropic polymer or polymer film with a helical structure that exhibits a higher temperature stability and a reflection wavelength that remains substantially constant over a wide temperature range, and does not have the disadvantages of the materials of prior art as discussed above.
SUMMARY OF THE INVENTION
One of the aims of the present invention is to provide a thermochromic polymerizable mesogenic composition having these properties. Another aim of the invention is to provide an anisotropic polymer or polymer film that can be prepared by polymerization of such a composition. Yet another aim of the invention is a process of preparing a polymer film with a chiral mesophase from such a composition. Another aim of the present invention is to extend the pool of thermochromic polymerizable mesogenic materials available to the expert. Other aims of the present invention are immediately evident to the person skilled in the art from the following detailed description.
It has been found that the above-mentioned aims can be achieved by providing a thermochromic polymerizable mesogenic composition according to the present invention.
The terms polymerizable or reactive mesogen, polymerizable or reactive mesogenic compound or polymerizable or reactive liquid crystal (/line compound) as used in the foregoing and the following comprise compounds with a rodlike, boardlike or disklike mesogenic group. These mesogenic compounds do not necessarily have to exhibit mesophase behavior by themselves. In a preferred embodiment of the present invention they show mesophase behavior in mixtures with other compounds or after polymerization of the pure mesogenic compounds or of the mixtures comprising the mesogenic compounds.
The term “mesogenity supporting group” as used in the foregoing and the following indicates a rod-shaped, board-shaped or disk-shaped group, which does not necessarily have to show mesogenic behavior (i.e., the ability to induce mesophase behavior in a compound comprising such a group) alone. It is also possible that such a group shows mesogenic behavior if being combined in a compound with other groups, or if the compound comprising the mesogenity supporting group is polymerized or admixed with other compounds comprising the same or other mesogenic or mesogenity supporting groups.
Preferably, however, the polymerizable mesogenic compounds exhibit mesophase behavior on their own.
One object of the present invention is a thermochromic polymerizable mesogenic composition comprising:
a) a component MA comprising at least one achiral polymerizable mesogenic compound comprising at least one polymerizable functional group,
b) a component MB comprising at least one chiral polymerizable mesogenic compound comprising at least one polymerizable functional group,
c) a photoinitiator, and
d) optionally a dye component.
The components MA and MB comprise polymerizable mesogenic compounds with at least one polymerizable group. Preferably, these polymerizable mesogenic compounds have up to four, in particular up to three, very preferably one or two polymerizable groups.
The achiral polymerizable compounds of component MA are preferably selected from formula I
P—(Sp—X)
n
—MG—R  I
in which
P is CH
2
═CW—COO—, WCH═CH—O—,
 or CH
2
═CH-phenyl-(O)
k
— with W being H, CH
3
or Cl and k being 0 or 1,
Sp is a spacer group having 1 to 20 C atoms,
X is a group selected from —O—, —S—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S— or a single bond,
n is 0 or 1,
MG is a mesogenic or mesogenity supporting group preferably selected from formula II
—(A
1
—Z
1
)
m
—A
2
—  II
 wherein
Z
1
is in each case independently —COO—, —OCO—, —CH
2
CH
2
—, —OCH
2
—, —CH
2
O—, —CH═CH—, —CH═CH—COO—, —OCO—CH═CH—, —C≡C— or a single bond,
A
1
and A
2
are each independently 1,4-phenylene in which, in addition, one or more CH groups may be replaced by N, 1,4-cyclohexylene in which, in addition, one or two non-adjacent CH
2
groups may be replaced by O and/or S, 1,4-cyclohexenylene, or naphthalene-2,6-diyl, it being possible for all these groups to be unsubstituted, mono- or polysubstituted (e.g., up to 4 times) with halogen, cyano or nitro groups or alkyl, alkoxy or alkanoyl groups having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl (e.g., up to perfluoro or perchloro), and
m is 1, 2 or 3, and
R is an achiral alkyl radical with up to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen (up to perhalo) or CN (e.g., up to 4 times), it being also possible for one or more non-adjacent CH
2
groups to be replaced, in each case independently from one another, by —O—, —S—, —NH—, —N(CH
3
)—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —S—CO— or —C≡—O— in such a manner that oxygen atoms are not linked directly to one another, or a

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