Liquid-crystalline silicones having increased UV stability

Details Liquid-crystalline silicones having increased UV stability Liquid-crystalline silicones having increased UV stability

1999-12-06

2002-03-19

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

With bonding or intermediate layer of specified composition

C252S299010, C106S481000, C106S494000, C556S466000, C556S478000, C556S479000, C528S031000, C528S032000, C528S033000, C528S026000

Reexamination Certificate

active

06358574

ABSTRACT:

TECHNICAL FIELD
The invention relates to crosslinkable liquid-crystalline organosiloxanes (LC organosiloxanes) having increased UV resistance, to a process for their preparation, and to their use.
BACKGROUND ART
The preparation and use of crosslinkable LC organosiloxanes is known in principle, for example from U.S. Pat. No. 5,211,877 and U.S. Pat. No. 5,362,315. In addition to the mesogens which are the primary factors in determining the properties, these compounds also contain, in adjustable proportions, molecule constituents which firstly contribute to the mesogenic properties of the silicones, but secondly are capable, by means of polymerizable groups, of irreversibly fixing by three-dimensional crosslinking, certain physical and chemical properties which are characteristic of the crosslinked LC silicones thus prepared. Depending on the type and amount of further copolymerizable mesogens and/or chiral compounds and other constituents which participate in crosslinking, it is thus possible to prepare, for example, pigments whose color is based on the cholesteric phase of a copolymerized, optically active mesogen.
Although the LC pigments mentioned in U.S. Pat. No. 5,211,877 and U.S. Pat. No. 5,362,315 satisfy most requirements, they have the disadvantage of being inadequately resistant to UV light.
DISCLOSURE OF INVENTION
The object of the invention was therefore to provide crosslinkable building blocks which allow a more favorable construction of molecules suitable for preparation of UV stable LC organosiloxanes.
BEST MODE FOR CARRYING OUT THE INVENTION
The invention relates to crosslinkable LC organosiloxanes containing units of the general formula 1
[R
b
Mes
c
SiO
(4−b−c)/2
]  (1)
in which
R are C
1
-C
4
-alkyl radicals,
Mes is at least one group of the general formula 2 and, if desired, of the general formula 3,
b has the value 0, 1 or 2, and
c has the value 0, 1, 2, 3 or 4,
with the proviso that the sum of the values of b and c is a maximum of 4, where the Mes groups of the general formulae 2 and 3 exhibit the following structure:
—(CH
2
)
p
—(O)
q
—A—[B—A]
r
—E—F—VN  (2)
—(CH
2
)
m
—(O)
n
—(A)
t
—Q—X  (3)
in which
A is a divalent radical from the group consisting of a 1,4-cyclohexylene ring, a 4,4′-bicyclohexylene radical, a 1,4-phenylene ring, a 2,6-naphthylene radical, a 2,7-naphthylene radical, a 2,5-(1,3-dioxanylene) ring and a pyrimidinyl radical,
Q is a radical from the group consisting of —COO—, —OCO—, —O—, a chemical bond, and —O—(C═O)—O—,
X is a cholesteryl, dihydrocholesteryl, doristeryl, isosorbidyl, isomannidyl or cholic acid radical or an unsubstituted or substituted radical selected from the group consisting of 1,4-phenylene, 4,4′-biphenylyl, 1,4-cyclohexylene, 4,4′-bicyclohexylene, 4,4′-cyclo-hexylenephenylene, 2,5-(1,3-dioxanylene) and pyrimidinyl radicals, where the substituent can be a C
1
- to C
5
-alkoxy radical, a C
1
- to C
5
-alkyl radical, a cyano radical, a chlorine radical or a nitro radical,
B is a divalent radical from the group consisting of a chemical bond, —O—CH
2
—, —CH
2
—O—, —CH
2
—CH
2
—, —CH═CH—, —COO— and —OCO—,
E is a divalent radical from the group consisting of a chemical bond, —O—, —COO—, —OCO— and —CH
2
—O—,
F is a chain of from 0 to 11 CH
2
groups, in which individual, non-adjacent CH
2
groups may be replaced by oxygen,
VN is a —COO—CH═CH
2
, —COO—C(CH
3
)═CH
2
or —O—CH═CH
2
group, an oxiranyl group or a —(CH
2
)
u
—OCH═CH
2
group,
u is an integer from 2 to 8,
m and p are integers from 3 to 7,
n and q are 0 or 1,
t is an integer from 1 to 3, and
r is an integer from 1 to 3,
with the proviso that the combinations of rings A with binding groups B do not constitute phenyl ester derivatives of aliphatic, aromatic or heteroaromatic carboxylic acids.
The invention is based on the discovery that the lack of stability to UV light of the known crosslinkable LC organosiloxanes and crosslinked LC silicones is caused primarily by the use of phenyl carboxylates as mesogen components. Such mesogens are accessible inexpensively and in a technically uncomplicated way by normal esterification reactions. However, on exposure to UV light, phenol esters undergo a rearrangement of these moieties which is known from the literature as the “Fries photorearrangement”. Even daylight contains sufficient UV light to facilitate this rearrangement.
In this rearrangement, 4-substituted phenyl esters which are used to build up liquid-crystalline phases, or incorporated fragments of these esters in the mesogen, form a mixture of aromatic ketones and other compounds, which are usually relatively strongly colored and in which the substituents originally in the 4-position to the phenol oxygen are moved into other positions which hinder the formation of LC phases. The keto group formed from the carboxyl binding group likewise hinders the formation of LC phases.
The crosslinkable LC organosiloxanes containing units of the general formula 1 avoid mesogen components containing phenyl esters of carboxylic acids. This makes the LC organosiloxanes containing units of the general formula 1 more UV stable. Lateral phenyl substituents, such as, for example, fluorine radicals, in the ortho-positions to 1- and/or 4-substituents do not cause a lack of stability to UV light. The crosslinkable LC organosiloxanes preferably contain from 1 to 70 units of the general formula 1.
In order to achieve particular properties, the compounds according to the invention can be mixed together with isolated further components, for example crosslinking agents, as individual compounds or as mixtures thereof, and/or with further property-modifying, copolymerizable compounds. Examples include chiral compounds which are capable of hydrosilylation for establishing properties such as desired reflection wavelengths. The compounds according to the invention can also be mixed with non-copolymerizable compounds, and crosslinked in their presence.
The additional copolymerizable crosslinking agent components can be known compounds, preferably carrying a terminal and thus hydrosilylation-capable double or triple bond at one end of elongate molecules, and a crosslinkable group, such as the acryloyl radical or the methacryloyl radical, at the other end. These compounds conform, for example, to the general formula 4
CH
2
═CH—(CH
2
)
p−2
—(O)
q
—A—[B—A]
r
—E—F—VN  (4)
in which A, B, E, F, VN, p, q and r can adopt the meanings given for the general formulae 2 and 3, where, if necessary, proportions of additional crosslinking agent components which may also contain phenol ester groups can also occur here if the UV stability of the system as a whole is not thereby impaired, but other, desirable properties, such as, for example, a low glass transition temperature and/or a higher crosslinking density of crosslinked LC organosiloxanes prepared therewith can be achieved. An example of a compound of this type is 4-methacryloyloxyphenyl-4-allyloxybenzoate, known from WO 94/09086.
In addition, further mesogenic or non-mesogenic compounds containing at least one and optionally a plurality of polymerizable groups can be admixed with the organosiloxanes according to the invention and reacted together therewith to give a three-dimensionally crosslinked, insoluble LC substance, such as a pigment. Examples of such compounds are crosslinking agent components of the general formula 5
CH
2
═CH—(CH
2
)
p−2
—(O)
q
—A—[B—A]
r
—E—F—VN  (5)
in which A, B, E, F, VN, p, q and r have the meanings given for the general formula 2; bisacrylates or bismethacrylates of mesogenic compounds of the general formula 6
VN—(CH
2
)
r
—[M—A]
t
—M—(CH
2
)
r
—VN  (6)
in which
M is an oxygen atom, a carboxyl group or an oxycarbonyl group, and
VN, A, r and t can adopt the above meanings. These can be employed alone or as a mixture of various compounds of the general formulae 5 and 6 or as a mixture with non-mesogenic bisacrylates and/or bismethacrylates.

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