Photoalignment layer and liquid crystal display

1. A photoalignment layer, comprising:

a polyimide; and

a capping terminal connected to a main chain terminal of the polyimide,

wherein the capping terminal is a stereo compound expressed as (Z—SiO 3/2 ) n , wherein n is an even number that is greater than 6, and a Z group of the stereo compound comprises at least one of a first compound expressed in Chemical Formula 1 and a second compound expressed in Chemical Formula 2:

wherein A1 and A2 are, independently, a C4 to C20 aromatic compound or a C4 to C20 aliphatic cyclic compound, and B1 and B2 are, independently, a flexible group comprising the alkylene group, —C m H 2m —, wherein m is a natural number from 2 to 21.

2. The photoalignment layer of claim 1 , wherein:

the flexible group of the second compound comprises a third compound expressed in Chemical Formula 3:

—X1-Y—X2-   (Chemical Formula 3), and

wherein X1 and X2 are, independently, a single bond, —O—, —S—, —COO—, —NHCO—, —NH—, —CH 2 CH 2 O—, —OCH 2 CH 2 —, a C6 to C30 aromatic compound, or a C4 to C20 aliphatic cyclic compound and Y is a single bond, —(CH 2 ) a1 —, wherein a1 is a natural number of 2 to 10, —(CH 2 OCH 2 ) a2— , wherein a2 is a natural number of 1 to 3, —(CH 2 CH 2 OCH 2 CH 2 ) a3 —, wherein a3 is 1 or 2, or —(OSi(OR) 2 ) a4 —, wherein R is C n H 2n+1 , n is a natural number of 1 to 10, and a4 is a natural number of 2 to 8.

3. The photoalignment layer of claim 2 , wherein:

the polyimide comprises a repeating unit of a fifth compound expressed in Chemical Formula 5:

 and

wherein R3 is a tetravalent organic group derived from an aliphatic cyclic acid dianhydride or an aromatic acid dianhydride and R4 is a divalent organic group derived from an aromatic diamine.

4. The photoalignment layer of claim 3 , wherein:

the Z group of the capping terminal connected to a main chain terminal of the polyimide is expressed in Structural Formula 2:

 and

wherein R3 is a tetravalent organic group derived from an aliphatic cyclic acid dianhydride or an aromatic acid dianhydride, R4 is a divalent organic group derived from an aromatic diamine, A2 is a C4 to C20 aromatic compound or a C4 to C20 aliphatic cyclic compound, and B2 is a flexible group comprising the alkylene group.

5. The photoalignment layer of claim 3 , wherein:

the polyimide is a copolymer of (a) at least one of cyclobutane dianhydride (CBDA) and a cyclobutane dianhydride (CBDA) derivative, and (b) a first diamine.

6. The photoalignment layer of claim 5 , wherein:

the first diamine includes a sixth compound expressed in Chemical Formula 6:

 and

wherein X is —(CH 2 ) h —, —S—(CH 2 ) h —S—, —O—(CH 2 ) h —O—,

 wherein h is a natural number of 1 to 10, and h1 and h2 are a combination of natural numbers selected so that the sum of the number of carbons of an alkylene group of X is 2 to 10.

7. The photoalignment layer of claim 6 , wherein:

the copolymer further comprises a polymer of (a) at least one of cyclobutane dianhydride (CBDA) and a cyclobutane dianhydride (CBDA) derivative, and (b) a second diamine expressed in Chemical Formula 7:

8. The photoalignment layer of claim 7 , wherein:

the copolymer comprises at least one of repeating units expressed in Chemical Formula 9 and repeating units express in Chemical Formula 10:

 and

wherein X is —(CH 2 ) h —, —S—(CH 2 ) h —S—, —O—(CH 2 ) h —O—,

 h is a natural number of 1 to 10, h1 and h2 are natural numbers selected so that the sum of the number of carbons of an alkylene group of X is 2 to 10, X1 to X8 are hydrogen, a halogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, and a substituted or unsubstituted heteroaryl group.

9. The photoalignment layer of claim 7 , wherein:

the copolymer comprises a compound expressed in Chemical Formula 11:

 and

wherein X is —(CH 2 ) h —, —S—(CH 2 ) h —S—, —O—(CH 2 ) h —O—,

 wherein h is a natural number of 1 to 10, h1 and h2 are natural numbers selected so that the sum of the number of carbons of an alkylene group of X is 2 to 10, a:b is 1:99 to 99:1, and X1 to X8 are, independently, hydrogen, a halogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, and a substituted or unsubstituted heteroaryl group.

10. A liquid crystal display, comprising:

a first substrate;

a thin film transistor disposed on the first substrate;

a first electrode connected to the thin film transistor; and

a first alignment layer disposed on the first electrode,

wherein the first alignment layer comprises a polyimide and a capping terminal connected to a main chain terminal of the polyimide, and

wherein the capping terminal is a stereo compound expressed as (Z—SiO 3/2 ) n , wherein n is an even number that is greater than 6, and a Z group of the stereo compound comprises at least one of a first compound expressed in Chemical Formula 1 and a second compound expressed in Chemical Formula 2:

 wherein A1 and A2 are, independently, a C4 to C20 aromatic compound or a C4 to C20 aliphatic cyclic compound, and B1 and B2 are, independently, a flexible group comprising the alkylene group, —C m H 2m —, wherein m is a natural number from 2 to 21.

11. The liquid crystal display of claim 10 , wherein:

the flexible group of at least one of the first compound and the second compound comprises a third compound expressed in Chemical Formula 3:

—X1-Y—X2-   (Chemical Formula 3), and

wherein X1 and X2 are, independently, a single bond, —O—, —S—, —COO—, —NHCO—, —NH—, —CH 2 CH 2 O—, —OCH 2 CH 2 —, a C6 to C30 aromatic compound, or a C4 to C20 aliphatic cyclic compound, and Y is a single bond, —(CH 2 ) a1 —, wherein a1 is a natural number of 2 to 10, —(CH 2 OCH 2 ) a2— , wherein a2 is a natural number of 1 to 3, —(CH 2 CH 2 OCH 2 CH 2 ) a3 —, wherein a3 is 1 or 2, or —(OSi(OR) 2 ) a4 —, R is C n H 2n+1 , wherein n is a natural number of 1 to 10, and a4 is a natural number of 2 to 8.

12. The liquid crystal display of claim 11 , wherein:

the polyimide comprises a repeating unit of a fifth compound expressed in Chemical Formula 5:

 and

wherein R3 is a tetravalent organic group derived from an aliphatic cyclic acid dianhydride or an aromatic acid dianhydride, and R4 is a divalent organic group derived from an aromatic diamine.

13. The liquid crystal display of claim 12 , wherein:

the Z group of the capping terminal connected to a main chain terminal of the polyimide is expressed in Structural Formula 2:

 and

wherein R3 is a tetravalent organic group derived from an aliphatic cyclic acid dianhydride or an aromatic acid dianhydride, R4 is a divalent organic group derived from aromatic diamine, A2 is a C4 to C20 aromatic compound or a C4 to C20 aliphatic cyclic compound, and B2 is a flexible group including] the alkylene group.

14. The liquid crystal display of claim 12 , wherein:

the polyimide is a copolymer of (a) at least one of cyclobutane dianhydride (CBDA) and a cyclobutane dianhydride (CBDA) derivative, and (b) a first diamine.

15. The liquid crystal display of claim 14 , wherein:

the first diamine comprises a compound expressed in Chemical Formula 6:

 and

wherein X is —(CH 2 ) h —, —S—(CH 2 ) h —S—, —O—(CH 2 ) h —O—,

 wherein h is a natural number of 1 to 10, and h1 and h2 are natural numbers selected so that the sum of number of carbons an alkylene group of X is 2 to 10.

16. The liquid crystal display of claim 15 , wherein:

the copolymer further comprises a polymer of (a) at least one of cyclobutane dianhydride (CBDA) and a cyclobutane dianhydride (CBDA) derivative, and (b) a second diamine expressed in Chemical Formula 7:

17. The liquid crystal display of claim 16 , wherein:

the copolymer includes at least one of a repeating unit expressed in Chemical Formula 9 and a repeating unit expressed in Chemical Formula 10:

 and

wherein X is

 wherein h is a natural number of 1 to 10, h1 and h2 are natural numbers selected so that the sum of the number of carbons of an alkylene group of X is 2 to 10, X1 to X8 are, independently, hydrogen, a halogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, and a substituted or unsubstituted heteroaryl group.

18. The liquid crystal display of claim 16 , wherein:

the copolymer comprises a compound expressed in Chemical Formula 11:

 and

wherein X is

 wherein h is a natural number of 1 to 10, h1 and h2 are natural numbers selected so that the sum of the number of carbons of an alkylene group of X is 2 to 10, a:b is 1:99 to 99:1, and X1 to X8 are hydrogen, a halogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, and a substituted or unsubstituted heteroaryl group.

19. The liquid crystal display of claim 10 , further comprising:

a second electrode disposed between the first substrate and an insulating layer.

20. The liquid crystal display of claim 19 , wherein:

the first electrode comprises a plurality of branch electrodes, and

the second electrode comprises a planar shape.

21. The liquid crystal display of claim 20 , wherein:

the branch electrodes overlap the second electrode.

22. The liquid crystal display of claim 21 , further comprising:

a passivation layer disposed between the thin film transistor and the second electrode, wherein the thin film transistor is connected to the first electrode through a contact hole penetrating through the passivation layer and the insulating layer.

23. The liquid crystal display of claim 22 , further comprising:

a second substrate facing the first substrate;

a second alignment layer disposed on the second substrate; and

a liquid crystal layer disposed between the first substrate and the second substrate, the liquid crystal layer comprising liquid crystal molecules,

wherein the second alignment layer is formed with a material that is substantially the same as the first alignment layer.