Optically anisotropic material, process for producing it, and retardation plate and liquid crystal display device using same

An optically anisotropic film comprising a polymer of a liquid crystal oligomer having positive refractive index anisotropy and showing nematic or smectic phase, said liquid crystal oligomer being selected from linear-chain or cyclic liquid crystal oligomers having the following recurring units (I) and (II):

• ##STR33## wherein A is a group represented by the following formula (III) or (IV):
• ##STR34## wherein, in the formula (III), --Si--O-- is a main chain of the recurring unit (I) or (II) and, in the formula (IV), --C--CH.sub.2 -- is linked to R.sub.1 -- and --(CH.sub.2).sub.k -- and is a main chain of the recurring unit (I) or to R.sub.2 -- and --(CH.sub.2).sub.k' -- and is a main chain of the recurring unit (II) and COO group is positioned as a side chain;
• when A in the formula (I) is the formula (III) and when A in the formula (II) is the formula (III), R.sub.1 and R.sub.2 are independently hydrogen, a C.sub.1-6 alkyl group or a phenyl group, and when A in the formula (I) is the formula (IV) and when A in the formula (II) is the formula (IV), R.sub.1 and R.sub.2 are independently hydrogen or a C.sub.1-6 alkyl group;
• k and k' are independently an integer of 2 to 10;
• m and m' are independently 0 or 1;
• Ar.sub.1, Ar.sub.2, Ar.sub.3 and Ar.sub.4 are independently a 1,4-phenylene group, a 1,4-cyclohexylene group, a pyridine-2,5-diyl group or a pyrimidine-2,5-diyl group;
• L and L' are independently CH.sub.2 --O--, --O--CH.sub.2 --, --COO--, --OCO--, --CH.sub.2 --CH.sub.2 --, --CH.dbd.N--, --N.dbd.CH-- or a divalent group represented by the formula:
• ##STR35## p and p' are independently 0 or 1;
• R is halogen, a cyano group, a C.sub.1-10 alkyl group or a C.sub.1-10 alkoxy group;
• and R' is hydrogen or a C.sub.1-5 alkyl group, wherein when the numbers of the recurring units (I) and (II) in one molecule of said oligomer are supposed to be n and n', respectively, n and n' are each an integer of 1 to 20 and satisfy the relation of 4.ltoreq.n+n'.ltoreq.21, and further characterized in that the terminal group of the recurring unit (II) is polymerized, and that the optical axis of said film is aligned in the direction of an angle from between 10.degree. and 80.degree. against the normal line of the film.