Optically active monomer, liquid crystal polymer, and optical element

Abstract

To obtain a monomer having a large torsion force, to obtain a liquid crystal polymer which is excellent in a film-forming property, can easily control a helical pitch of a cholesteric phase, can form a grandjean orientation in a good monodomain state by an orientation treatment in a short time such as few minutes, and can stably fix it in a glass state, and to obtain an optical element having a circular dichroism, represented by the following formula (a), comprising a solidified product of the liquid crystal polymer, which is thin and light, is hard to change the oriented state such as pitch, etc., at a practical temperature, and has excellent durability and storage stability. An optically active monomer represented by (wherein R 1 represents a hydrogen atom or a methyl group, and A and B represent an organic group); a side chain type liquid crystal polymer having a structural unit comprising the optically active monomer; and an optical element showing a circular dichroism having a solidified layer of a grandjean oriented cholesteric liquid crystal phase comprising the liquid crystal polymer.

1 . An optically active monomer represented by following formula (a):  
                   wherein R 1  represents a hydrogen atom or a methyl group, and A and B represent an organic group:    
     
     
         2 . An optically active monomer of    claim 1   , wherein A in the formula (a) is represented by the formula (a1): COO(CH 2 ) m R 2 Z wherein m is an integer of 1 to 6; R 2  represents following chemical formula:  
                   and Z represents COO— or O—, and B represents following formula (a2):  
                 
   wherein Y represents OCO— or O—; 0≦n≦3; and R 3  represents —C d H 2d+1  when n is 0 and represents —OC d H 2 d+1, —H, —CN, or —Cl when 1≦n≦3 (wherein d is 1≦d≦3).    
     
     
         3 . A side chain type liquid crystal polymer having a structural unit comprising the optically active monomer as claimed in    claim 1   .  
     
     
         4 . A liquid crystal polymer showing a cholesteric liquid crystal phase, comprising a copolymer comprising the optically active monomer as claimed in    claim 2    and a monomer forming a polymer showing a nematic liquid crystal phase as components, said copolymer containing 1 to 40% by weight the above-described optically active monomer unit.  
     
     
         5 . A liquid crystal polymer showing a cholesteric liquid crystal phase, comprising a mixture of 1 to 40% by weight a polymer comprising the optically active monomer as claimed in    claim 2    as the whole monomer component and 99 to 60% by weight a polymer comprising a monomer forming a polymer showing a nematic liquid crystal phase as the whole monomer component.  
     
     
         6 . An optical element showing a circular dichroism, comprising a solid layer of a grandjean oriented cholesteric liquid crystal phase comprising the liquid crystal polymer as claimed in    claim 3   ,    4    or  5 .  
     
     
         7 . An optical element as claimed in    claim 6   , wherein the optical element shows a circular dichroism to a light of a visible light region.  
     
     
         8 . An optical element as claimed in    claim 6    or    7   , wherein the optical element comprises a laminate of the solid layers of the liquid crystal polymers each showing a circular dichroism to a light having a different wavelength.  
     
     
         9 . An optical element as claimed in    claim 6   ,    7    or  8 , wherein the optical element has a retardation layer of converting a circularly polarized light to a linearly polarized light.