Process for the preparation of cyclic esters and method for purification of the same

A process for production of a cyclic ester by depolymerization of a high-molecular-weight aliphatic polyester with a weight-averaged molecular weight of 10,000 or more, which comprises:

• (i) a step of heating a mixture containing a high-molecular-weight aliphatic polyester (A), a polyalkylene glycol ether (B), which is represented by the following formula (1)
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• where R1 is a methylene group, or a straight-chain or branched-chain alkylene group with 2-8 carbons, X1 is a hydrocarbon group, Y is an alkyl or aryl group with 2-20 carbons, p is an integer not smaller than 1 and when p is 2 or greater, a plurality of R1 groups may be identical or different,
• and has a boiling point of 230-450° C. and a molecular weight of 150-450, and a solubilizing agent (C) of a monohydric alcohol or a polyhydric alcohol with at least two hydroxyl groups, each with a boiling point of 180° C. or higher, under normal or reduced pressure to a temperature at which depolymerization of the high-molecular-weight aliphatic polyester (A) takes place,
• (ii) a step of forming a substantially homogeneous solution phase consisting of the melt phase of the high-molecular-weight aliphatic polyester (A) and the liquid phase composed of the polyalkylene glycol ether (B) and the solubilizing agent (C),
• (iii) a step of continuing to heat the solution phase under reduced pressure to form the cyclic ester by depolymerization and distil out the cyclic ester together with the polyalkylene glycol ether (B), and
• (iv) a step of recovering the cyclic ester from the distillate.

A process for purification of a crude cyclic ester, which comprises the steps of heating a mixture containing the crude cyclic ester (A′) and a polyalkylene glycol ether (B), which is represented by the following formula (1)

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• where R1 is a methylene group, or a straight-chain or branched-chain alkylene group with 2-8 carbons, X1 is a hydrocarbon group, Y is an alkyl or aryl group with 2-20 carbons, p is an integer not smaller than 1 and when p is 2 or greater, a plural of R1 groups may be identical or different,
• and has a boiling point of 230-450° C. and a molecular weight of 150-450, under normal or reduced pressure in order to form a substantially homogeneous solution phase without phase separation of the components;
• continuing to heat the solution phase to distil out the cyclic ester (A) together with the polyalkylene glycol ether (B);
• and recovering the cyclic ester (A) from the distillate.