The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Nov. 03, 1998
Filed:
Jan. 23, 1997
Zenya Shiiki, Narashino, JP;
Yukichika Kawakami, Iwaki, JP;
Kureha Kagaku Kagyo KK, Tokyo, JP;
Abstract
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.degree.-450.degree. 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.