Preparation of acrylated liquid-crystalline compounds

Details Preparation of acrylated liquid-crystalline compounds Preparation of acrylated liquid-crystalline compounds

2000-04-18

2002-08-27

Wu, Shean C. (Department: 1756)

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

C252S299640, C252S299650, C560S086000, C560S089000, C560S108000, C560S109000

Reexamination Certificate

active

06440328

ABSTRACT:

TECHNICAL FIELD
The invention relates to a one-step process for the preparation of liquid-crystalline monomers containing acryloyl groups.
BACKGROUND ART
In general, the production of three-dimensional networks having a desired optically anisotropic property profile requires crosslinkable liquid-crystalline monomers in which the mesogenic units and the crosslinkable groups are separated front one another by spacer units. The incorporation of the spacers increases the mobility of the acrylic groups and is vital for achieving a sufficiently high degree of crosslinking. In addition, the liquid-crystalline phase of the monomers can be positively affected by the choice of suitable spacer lengths.
Owing to the necessity for a spacer, however, the desired monomers cannot be obtained by simple (meth)acrylation of the mesogenic alcohols, which are usually readily accessible. In some cases, significantly more complex synthetic routes must be followed here. It is in many cases favorable for the spacer to be bonded to the mesogenic unit via an ether bond. The corresponding compounds are particularly advantageous owing to their relatively good synthetic accessibility, their chemical stability, but in particular owing to their frequently very advantageous liquid-crystalline property profile.
The literature therefore describes numerous synthetic routes which in principle are suitable for the synthesis of crosslinkable mesogens containing corresponding spacers. However, these synthetic routes are without exception afflicted with specific disadvantages or limitations. Thus, for example, WO 96/24647 and WO 96/23036 describe processes in which a mesogenic diol is first reacted with an &ohgr;-haloalcohol. The resultant intermediate is subsequently esterified using (meth)acryloyl chloride to give the finished product. There are numerous problems associated with this process. First, the alcohols produced as intermediates generally have poor solubility properties, making not only their preparation, but also their isolation and purification, very complex. Second, the &ohgr;-haloalcohols required as starting materials are relatively expensive compounds which frequently cannot be produced on an industrial scale. This synthetic route is therefore disadvantageous for commercial production.
In another process, described, for example, in WO 98/47979 and EP 0 648 827, the starting materials are &ohgr;-halo(meth)acryloylalkanes, which can be reacted with a mesogenic monol or diol in a single step to give the desired end product. The labor-intensive isolation of a mesogenic intermediate containing hydroxylated spacer units is not necessary here. However, a disadvantage of this process is the preparation of the required &ohgr;-halo(meth)acryloylalkanes starting materials, since these compounds have a strong tendency toward undesired polymerization, and are therefore virtually impossible to handle without a stabilizer. The tendency toward polymerization is particularly pronounced in the case of the acryloyl compounds, and thus their synthesis and purification is only possible with difficulty in virtually all cases. In addition, scale-up of such reactions to an industrial scale requires complex safety precautions.
Finally, the literature also describes a number of preparation processes which follow a completely different strategy. However, it is common to all these that they can without exception only be achieved by multistep, and therefore very complex, synthetic routes.
DISCLOSURE OF INVENTION
The present invention has the object of overcoming the disadvantages of the known synthetic routes and of providing a process by means of which crosslinkable mesogens containing spacer-bonded acrylic groups can be prepared simply and in an acceptable manner with respect to the reaction and safety. This process can prepare the desired crosslinkable mesogens economically and in a single step.
BEST MODE FOR CARRYING OUT THE INVENTION
The invention relates to a one-step process for the preparation of acryloyl group-containing liquid-crystalline monomers of the general formula (1)
(Z—Y
1
—A
2
—Y
2
—)
m
M(—O—A
1
-acrylate)
n
  (1)
in which mesogenic alcohols of the general formula (2)
(Z—Y
1
—A
2
—Y
2
—)
m
M(OH)
n
  (2)
are reacted with esters of 3-chloropropionic acid of the general formula (3)
ClPr—A
1
—X  (3)
with elimination of HCl, where
acrylate is an acrylate radical,
ClPr is a 3-chloropropionate radical,
A
1
are identical or different alkyl chain spacers having 2-20 carbon atoms, in which the carbon chain may be interrupted by non-adjacent ether oxygen atoms, thioether sulfur atoms, or imino groups,
A
2
are radicals A
1
or single chemical bonds,
M is a mesogenic group,
X is a leaving group,
Z are alkyl radicals or crosslinkable groups,
Y
1
and Y
2
, independently of one another, are a single chemical bond, —O—, —S—, —O—CO—, —CO—O—, —O—CO—O, —CO—NR
1
—, —NR
1
—CO—, —O—CO—NR
1
—, —NR
1
—CO—O— or —NR
1
—CO—NR
1
—,
R
1
is hydrogen or a C
1
-C
4
-alkyl radical,
n has a value of 1, 2, 3 or 4, and
m has a value of 0, 1, 2 or 3.
The process according to the invention starts from a mesogen of the general formula (2) containing one or more free hydroxyl groups. The invention is based on the discovery that, in a single synthetic step, the ether bond between the mesogenic alcohol of the general formula (2) and the 3-chloropropionate of the general formula (3) can be formed with elimination of the leaving group X and simultaneously the acryloyl group can be liberated from the chloropropionate group by elimination of an HCl molecule.
The process according to the invention is highly suitable for the preparation of mesogens containing 1 to 4 spacer-bonded acrylic groups, where n has a value of from 1 to 4, in particular 2. The desired mesogen of the general formula (1) may be prepared in only a single synthetic step from readily accessible starting materials. Further, the process according to the invention allows a synthesis concept scheme in which the acrylic acid functionality of the 3-chloropropionate precursors of the general formula (2) are masked. The demasking is delayed until during the final reaction step of the entire mesogen synthesis, the described etherification of a mesogenic alcohol. Thus, unpolymerizable starting materials are exclusively employed in the synthesis sequence for the preparation of acrylated mesogens of the general formula (1), and in addition no polymerizable intermediates are formed. The performance of the individual synthetic steps, but in particular the handling of the intermediates, is thus significantly simplified.
A further advantage of the process according to the invention consists in the fact that the esters of the required 3-chloropropionic acid starting materials of the general formula (3) can easily be prepared by reaction of suitable alcohols or cyclic ethers with 3-chloropropionyl chloride, a chemical produced on a large industrial scale. Direct esterification of the free 3-chloropropionic acid, for example by azeotropic esterification using the targeted alcohol derivatives, is also possible. The reaction according to the invention is thus also extremely valuable for industrial applications.
The process according to the invention is suitable for the preparation of any desired liquid-crystalline compounds containing one or more spacer-bonded acrylic groups of the general formula (1). It is preferably employed for the preparation of liquid-crystalline bisacrylates of the general formula (1) in which m is 0 and n is 2 by reaction of a mesogenic diol of the general formula (2) in which m is 0 and n is 2, with 2 equivalents of a compound conforming to the general formula (3). Use of mixtures of a plurality of compounds conforming to the general formula (3) also allows the preparation of stoichiometric mixtures of symmetrical and asymmetrical bisacrylates. Preferably, only one compound of the general formula (3) is employed.
Furthermore, the process according to the invention can also be employed for the conversion of liquid-crystalline alcohols which already c

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