Liquid Crystal Polymers

This application is a 371 of PCT/GB93/01018 filed May 19, 1993.

This invention concerns novel liquid crystal polymer (LCP) materials and method for preparing same.

LCP's are known and are used in the electro-optical device industry, for example, in optical storage devices, in non-linear optical devices and in pyroelectric devices, see for example, GB 2146787 A and Makromol Chem, 186 2639-2647, 1985.

One known type of LCP consists of a polymeric backbone to which are attached pendant side chains which have a chemical structure than is mesogenic, ie. that induces liquid crystalline character, these being known as side chain liquid crystal polymers. Work in this field has identified a large number of side chain structures which are suitable, see for example GB 2146787 A. For some purposes it is desirable that the LCP shows a smectic C (Sc) or chiral smectic C (Sc*) liquid crystal phase, and a particularly preferred side chain for acheiving this is one which contains a laterally fluorinated biphenyl or terphenyl system.

Liquid crystal polyacrylates are known, Polymer Communications, 24, 364-365, 1988, having a polyacrylate backbone, eg. polymethacrylate, with pendent side chains, ie. of general structure: ##STR2## Where (CH.sub.2)m-X is the side chain and R is hydrogen or alkyl in the case of polyalkylacylates, being methyl in polymethacrylates.

According to the present invention there is provided a novel LCP material based on fumarate and maleate all-esters having improved liquid crystal properties over known LCP's, having a general formula I; ##STR3## R.sub.1 and R.sub.2 may or may not be the same but have the following general structure: ##STR4## p=2 to 14; q=0 or 1;

r=1 or 2;

s=1 or 2;

X=O, CO.sub.2, O.sub.2 C, CH.sub.2 ;

Y=C.sub.2 H.sub.4, O, CO.sub.2, O.sub.2 C;

Z=CN, halogen, R, CO.sub.2 R, OR, O.sub.2 CR, wherein R=chiral or achiral;

provided that when Z=alkoxy then q=0.

The general met,hod of preparation of LCP's of formula I is by polymerisation of a compound of general structure:

Wherein R.sub.1 and R.sub.2 have the general structure defined above.

4-hydroxy-4'cyanobiphenyl was stirred at room temperature with 11-bromo-1-undecanoic acid and trifluoroacetic acid in dichloromethane for 24 hours. The product was purified by recrystallisation from IMS.

Step 2

The product from step 1 was stirred at room temperature with fumaric acid and sodium hydride in hexamethyl phosphoramide for 18 hours, The solution was acidified and separated in ether/water, The product was purified by recrystallisation from IMS.

Step 3

The monomer was then stirred at 50.degree.-80.degree. C. in a little 1,2-dichloroethane with azoisobutyronitrile as the initiator for 24 hours. The polymer was separated by reprecipitation from DCM/IMS.

It will be appreciated that it is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art, being possible, without departing from scope thereof as defined in the appended claims.