Method for making a treated polymer for a liquid crystal alignment agent, the treated polymer made thereby, and liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element containing the treated polymer

A treated-polymer for a liquid crystal alignment agent made by a process comprising the steps of:

• subjecting a tetracarboxylic dianhydride compound and a diamine compound to conduct a polymerization reaction to obtain an untreated polymer;
• preparing a co-precipitating solvent for the untreated polymer which includes a major amount of a poor solvent and a minor amount of a good solvent, the poor solvent being selected from the group consisting of a ketone, an ether, and a combination thereof;
• and
• subjecting the untreated polymer to a treatment with the co-precipitating solvent such that at least a significant amount of a polymer fraction having a molecular weight not larger than 3,000 is removed from the untreated polymer to obtain the treated polymer.

A liquid crystal alignment agent, comprising:

• a treated polymer made by a process comprising the steps of:
• subjecting a tetracarboxylic dianhydride compound and a diamine compound to conduct a polymerization reaction to obtain an untreated polymer;
• preparing a co-precipitating solvent for the untreated polymer which includes a major amount of a poor solvent and a minor amount of a good solvent, the poor solvent being selected from the group consisting of a ketone, an ether, and a combination thereof;
• and subjecting the untreated polymer to a treatment with the co-precipitating solvent such that at least a significant amount of a polymer fraction having a molecular weight not larger than 3,000 is removed from the untreated polymer to obtain the treated polymer;
• and
• an organic solvent for dissolving the treated polymer.

A liquid crystal alignment agent, comprising:

• a polymer obtained by subjecting a tetracarboxylic dianhydride compound and a diamine compound to conduct a polymerization reaction;
• and
• an organic solvent for dissolving the polymer,
• wherein the liquid crystal alignment agent has a value (T) ranging from 0 to 1.0%, which is determined by:
• mixing the liquid crystal alignment agent with methanol in a weight ratio of 1:6 to obtain a first mixture containing a first solid precipitate;
• filtering the first solid precipitate out of the first mixture using a filter of 0.2 μm;
• drying the first solid precipitate in an oven at a temperature of 60° C. for 12 hours to obtain a dried solid having a weight value (Ws);
• mixing the dried solid with N-methyl-2-pyrrolidone in a weight ratio of 1:15 to obtain a solution;
• mixing the solution with acetone in a weight ratio of 1:6 to obtain a second mixture containing a second solid precipitate;
• filtering the second solid precipitate out of the second mixture using a filter of 0.2 μm to obtain a filtrate;
• determining a weight value (WLS) of a solid content in the filtrate;
• and
• obtaining the value (T) by dividing the weight value (WLS) by the weight value (Ws).