Polymer for liquid crystal alignment agent, liquid crystal alignment agent comprising the same, and liquid crystal alignment film and liquid crystal display device using the same

A polymer for a liquid crystal alignment agent comprising one or more repeating units selected from the group consisting of a repeating unit represented by Chemical Formula 1, a repeating unit represented by Chemical Formula 2 and a repeating unit represented by Chemical Formula 3:

• wherein, in Chemical Formulae 1 to 3,
• at least one of R1 and R2 is an alkyl group having 1 to 10 carbon atoms, and the other is hydrogen,
• X1 to X3 are each independently a tetravalent organic group, and
• Y1 to Y3 are each independently a divalent organic group represented by the following Chemical Formula 4:
• wherein, in Chemical Formula 4,
• A is a nitrogen, phosphorus, arsenic, antimony or bismuth,
• R3 is hydrogen or an alkyl group having 1 to 10 carbon atoms,
• a is an integer of 1 to 3, and
• at least one of Z1 to Z4 is nitrogen and the rest are carbon.