Homopolymers with high photoinduceable double refraction

Details Homopolymers with high photoinduceable double refraction Homopolymers with high photoinduceable double refraction

1999-11-08

2002-08-27

Henderson, Christopher (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S243000, C526S248000, C526S257000, C526S304000

Reexamination Certificate

active

06441113

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to polymers comprising photo-addressable side groups, in which a high level of birefringence can be induced by irradiation, so that they are suitable for the storage of information which is provided optically or are suitable as passive or optically switchable components.
BACKGROUND OF THE INVENTION
Various polymers comprising photochromic groups are known from the literature: the special peculiarity thereof is that their optical properties, such as absorption, emission, reflection, birefringence and scattering, can be induced by light and can be varied reversibly. Polymers of this type have a special branched structure: side groups which are capable of absorbing electromagnetic radiation are seated—via parts of molecules which act as spacers—on a linear backbone. The interest of experts in this field has recently been directed towards side group polymers such as these which comprise side groups of different types, one type of which is capable of absorbing electromagnetic radiation whilst the other type is a mesogenic group, the shape of which is anisotropic. Liquid crystalline side group polymers of this type are described in U.S. Pat. Nos. 4,631,328 and 4,943,617, for example. In their unoriented state, films of these polymers are turbid and scatter light; these films do not become clear and transparent until they are aligned.
Amorphous polymers which are suitable for storing optical information are known from DE-OS 38 10 722 and U.S. Pat. No. 5,173,381. These have the technical advantage that films made of these polymers exhibit usable optical properties immediately after they are produced.
Homopolymers are seldom mentioned in this connection. EP-A 617 110 describes azo-containing carbaminates which are rendered polymerisable by N-acylation with (meth)acrylic acid. In actuality, homopolymers are generally inferior to copolymers.
The only processes which have been described hitherto for the reversible storage of information are those where deletion of the information is effected by raising the temperature, and can be effected both by heat and by light. Moreover, deletion by light can exhibit the advantage that the process is limited to a defined location, which is why this variant is preferred. In general, it can be stated that on raising the temperature the property of retaining stored information is lost. The known compounds therefore have the disadvantage that the birefringence effects which are written in are not thermally stable. At elevated temperatures. particularly at temperatures approaching the glass transition temperature, birefringence becomes less pronounced and finally disappears completely. There is therefore a need for information storage media for which the stability of written information is as insensitive to temperature as possible.
SUMMARY OF THE INVENTION
Surprisingly, it has now been found that superior side chain polymers which are suitable for the production of photo-addressable information storage media can be produced if monomers are homopolymerised, which
contain groupings which are at least trinuclear, which are capable of absorbing the electromagnetic radiation of visible light, and which are structured so that in their thermodynamically stable state they are distended and strongly anisometric.
wherein the at least trinuclear groupings comprise at least one, preferably at least two, electron-attracting substituent(s) which give(s) rise to a dipole moment which forms an angle of at least 20°, preferably at least 30°, with the longitudinal axis of the at least trinuclear groupings.
DETAILED DESCRIPTION OF THE INVENTION
Thermally stable grey scales can be written into these new polymers under the effect of light.
In principle, at least two methods of influencing the dipole moment are possible, namely
substitution with lateral, electron-attracting substituents which are disposed unsymmetrically with respect to the longitudinal axis of the grouping, and
the use of nucleus-linking polar groups, the dipole moments of which do not point in the direction of their longitudinal axis.
Groups which are capable of forming hydrogen bonds with each other, such as —NH—CO— and —OC—NH— for example, are particularly preferred in this respect.
The expression “electromagnetic radiation of visible light” should be understood to mean light with a wavelength range from 350 to 750 nm.
The expression “thermodynamically stable state” should be understood in the sense of the present invention to mean the lowest energy configuration, such as that which occurs in the dark in a dissolved state in an organic solvent, for example. When cis/trans isomerism exists, such as that which occurs with stilbenes and azo compounds for example, the trans isomer is the isomer of lower energy in each case. The configuration which is present can be determined spectroscopically from the absorption bands.
“Distended” in the sense of the present invention is to be understood to mean a state in which the at least trinuclear groupings are situated within a cylinder with a length/diameter ratio of 2.5, preferably 3, wherein the length of the cylinder is identical to the length of the at least trinuclear grouping.
“Strictly anisometric” in the sense of the present invention means a structure in which none of the nuclei is directly or indirectly bonded (i.e. via a bonding group without a nucleus) to the next nucleus, i.e. it preferably (for trinuclear groupings) means a structure where the middle nucleus is a 6-membered ring which is directly or indirectly bonded via its 1- and 4-positions to the adjacent nuclei.
“Electron-attracting substituent” in the sense of the present invention is to be understood to mean substituents which reduce the basicity, i.e. the electron density, of the nucleus on which they are situated, due to induction and/or mesomeric effects. These substituents preferably comprise alkylcarbonyl, carboxyl, alkoxycarbonyl, carbamido, carboxylamino, cyano, nitro and ammonium, and—less preferably—comprise the halogens.
“Lateral” in the sense of the present invention can be explained by citing the example of an azobenzene group, and denotes that the substituent forms an angle with the longitudinal axis of the azobenzene and is therefore situated in the o- and/or m-position, whilst a substituent in the p-position is not considered as being “lateral” in the sense of the invention. If a phenyl radical of the azobenzene is replaced by a five-membered ring, for example, the substituents are “lateral” in all conceivable positions, because on a five-membered ring there is no position corresponding to the p-position on a 6-membered ring.
In principle, all groups which contain carboxyl groups are suitable as nucleus-linking polar groups, the dipole moment of which is at least 200. This can be well illustrated by using the amide group as an example:
The orientation of the dipole moment of the carboxyl group forms an angle &agr; with the longitudinal axis which is at least 20°.
The present invention also relates to homopolymers, formed from monomers which
contain groupings which are at least trinuclear, which are capable of absorbing the electromagnetic radiation of visible light, and which are structured so that in their thermodynamically stable state they are distended and strongly anisometric,
wherein the at least trinuclear groupings comprise at least one electron-attracting substituent which gives rise to a dipole moment which forms an angle of at least 20° with the longitudinal axis of the at least trinuclear groupings.
The preferred groupings which are at least trinuclear are those which contain at least two aromatic nuclei.
The preferred polymers according to the invention contain, on a main chain which acts as a backbone, covalently bonded side groups which branch therefrom, of formula
—S—T—Q—E  (1),
wherein
S denotes oxygen, sulphur or NR
1
.
R
1
denotes hydrogen or C
1
-C
4
alkyl.
T denotes a (CH
2
)
n
radical, which can optionally be interrupted by —O—, —NR
1
— or —OSiR
1
2
O— and/or which can optionally be substituted by methy

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