| 摘要 |
The invention provides an economical and efficient process for preparing a dimeric cyclic ester of an alpha -hydroxycarboxylic acid by depolymerizing a corresponding alpha -hydroxycarboxylic acid oligomer, which comprises the steps of (1) heating a mixture containing the alpha -hydroxycarboxylic acid oligomer and at least one high-boiling polar organic solvent having a boiling point within a range of 230 DEG -450 DEG C. to a temperature, at which the depolymerization of the oligomer takes place, under atmospheric pressure or reduced pressure, (2) dissolving the oligomer in the solvent until a residual rate of a melt phase of the oligomer reaches 0.5 or lower, (3) further continuing the heating at the temperature, at which the depolymerization of the oligomer takes place, to depolymerize the oligomer, (4) distilling out the dimeric cyclic ester formed together with the high-boiling polar organic solvent, and (5) recovering the dimeric cyclic ester from the distillate. The invention also provides a process for purifying a crude dimeric cyclic ester of an alpha -hydroxycarboxylic acid.
|
