Negative birefringent rigid rod polymer films

A negative birefringent film prepared from a rigid rod polymer wherein the polymer is selected from the group consisting of polyamide, polyester, poly(amide-imide) and poly(ester-imide) for use in liquid crystal displays, the film having a negative birefringence of 0.001 to 0.2, wherein the negative birefringence of the film is determined by controlling the degree of in-plane orientation of the polymer by control of the backbone chain rigidity and linearity, the higher the rigidity and linearity of the polymer backbone, the larger the value of the negative birefringence of the polymer film, and wherein

• (A) when the polymer is selected from the group of polyamide and polyester, the polymer has a repeat unit of general formula (I):
• ##STR26## where each F is selected from the group consisting of a covalent bond, a C.sub.2 alkenyl group, a halogenated C.sub.2 alkenyl group, a CH.sub.2 group, a C(CX.sub.3).sub.2 group wherein X is a halogen or hydrogen, a CO group, an O atom, a S atom, a SO.sub.2 group, a Si(R).sub.2 group where R is a C.sub.1-3 alkyl group, a C.sub.1-3 halogenated alkyl, or a N(R) group wherein R is as previously defined and further wherein F is in a position either meta or para to the carbonyl functionality or to the Y group;
• B is selected from the group consisting of halogens, a C.sub.1-3 alkyl group, a C.sub.1-3 halogenated alkyl, phenyl, or substituted phenyl wherein the substituents on the phenyl ring are selected from the group consisting of halogens, C.sub.1-3 alkyls, C.sub.1-3 halogenated alkyls and combinations thereof;
• n is an integer from 0 to 4;
• z is an integer from 0 to 3;
• A is selected from the group consisting of hydrogen, halogen, C.sub.1-3 alkyls, C.sub.1-3 halogenated alkyls, nitro, cyano, thioalkyls of C.sub.1-3, alkoxy groups of OR wherein R is as previously defined, aryl, halogenated aryl, C.sub.1-9 alkyl esters, C.sub.1-12 aryl esters, and C.sub.1-12 aryl amides;
• p is an integer from 0 to 3;
• q is an integer from 1 to 3;
• r is an integer from 0 to 3;
• and
• Y is selected from the group consisting of O and NH;
• and
• (B) wherein when the polymer is selected from the group consisting of poly(amide-imide) and poly(ester-imide), a polyamide component of the poly(amide-imide) which is the reaction product of a diacid and a diamine and a polyester component of the poly(ester-imide) which is the reaction product of a diacid and a diol, the polyamide and polyester components have a repeat unit as shown in general formula (I), and wherein a polyimide component is selected from the group consisting of
• (1) the reaction product of a dianhydride and a diamine thereby forming the polyimide repeat unit shown in general formula (V) ##STR27## and further wherein G is selected from the group consisting of a covalent bond or linking bond, a CH.sub.2 group, a C(CX.sub.3).sub.2 group wherein X is as defined previously, a CO group, an O atom, a S atom, a SO.sub.2 group, a Si(R).sub.2 group and a N(R) group where R is as defined previously, and further wherein G is in a position either .gamma. or .delta. to a carbonyl functionality;
• and
• (2) the reaction product of a dianhydride and a diamine thereby forming the polyimide repeat unit shown in general formula (VI) ##STR28## wherein R.sup.1 is a substituent selected independently from the group consisting of H, phenyl, alkylated phenyl wherein the alkyl group is selected from C.sub.1-20, halogenated phenyl, alkyl and C.sub.1-20 halogenated alkyl.