Liquid crystal display element

In a liquid crystal display element comprising substrates having electrodes and liquid crystal orientation controlling films on the sides thereof facing a liquid crystal layer and one or more liquid crystal layers interposed between said substrates, the improvement wherein the liquid crystal orientation controlling film is made from a copolymer produced by reacting a dihydrazide of the formula:

• ##STR36## wherein Ar.sub.1 is a dihydrazide residue, a diamine of the formula:
• H.sub.2 N--Ar.sub.3 --NH.sub.2
• wherein Ar.sub.3 is a diamine residue, and a tetracarboxylic acid dianhydride of the formula:
• ##STR37## wherein Ar.sub.2 is a tetracarboxylic acid residue, in a solvent at a temperature of 50.degree. C. or less to form a polyhydrazide acid-amide acid having structural units of the formulae:
• ##STR38## wherein Ar.sub.1, Ar.sub.2 and Ar.sub.3 are as defined above;
• and values of m and n are those which can give a reduced viscosity (.eta..sub.sp/c) of 0.1 dl/g or more measured by using dimethyl sulfoxide as a solvent in a concentration of 0.1 g/l at 30.degree. C., said polyhydrazide acid-amide acid being subjected to ring closure with heating to give the copolymer having structural units of the formulae:
• ##STR39## wherein Ar.sub.1, Ar.sub.2 and Ar.sub.3 are as defined above.

In a liquid crystal display element comprising substrates having electrodes and liquid crystal orientation controlling films on the sides thereof facing a liquid crystal layer and one or more liquid crystal layers interposed between said substrates, the improvement wherein the liquid crystal orientation controlling film is produced by using a varnish comprising (a) a polyhydrazide acid-amide acid having structural units of the formulae:

• ##STR48## wherein Ar.sub.1 is a dihydrazide residue;
• Ar.sub.2 is a tetracarboxylic acid residue;
• Ar.sub.3 is a diamine residue;
• and values of m and n are those which can give a reduced viscosity (.eta..sub.sp/c) of 0.1 dl/g or more measured by using dimethyl sulfoxide as a solvent in a concentration of 0.1 g/l at 30.degree. C., and (b) a solvent, and heating said varnish for removing the solvent and conducting ring closure.