Method for the fractionation of reactive terminated polymerizable oligomers

摘要

Acetylene or vinyl-terminated polymerizable oligomers of polyamic acid are fractionated to obtain an oligomer product having a molecular weight in the range of 2,000 to 4,000 which exhibits improved wetting and film forming properties. Fractionization is accomplished by dissolving the unfractionated polymerizable oligomer in a solvent in which the desired molecular weight fraction is soluble. The oligomer solution is passed through a filter which removes undissolved material having a molecular weight in excess of the desired molecular weight range. The filtrate is admixed with a hydrocarbon to precipitate the desired molecular weight fraction. Thereafter the collected solids can be redissolved in a ketonic solvent and the fractionation procedure repeated to further improve the molecular weight content of the fractionated oligomer.