Process for preparing cyclic esters comprising unsaturated functional groups and polyesters prepared from same

1. A process for preparing a cyclic ester having the formula:

wherein each x is the same and is an integer ranging from 0 to 12;

wherein each R 1a and each R 1b , when present, is independently hydrogen, hydroxy, amino, thio, halogen, substituted or unsubstituted C 1 -C 6 alkyl, substituted or unsubstituted C 1 -C 6 alkoxy, substituted or unsubstituted C 1 -C 6 alkylthio, substituted or unsubstituted C 1 -C 6 alkylamino, or substituted or unsubstituted C 1 -C 6 hydroxyalkyl; provided that each R 1a is the same and each R 1b is the same;

wherein R 2 is hydrogen, hydroxy, amino, thio, halogen, substituted or unsubstituted C 1 -C 6 alkyl, substituted or unsubstituted C 1 -C 6 alkoxy, substituted or unsubstituted C 1 -C 6 alkylthio, substituted or unsubstituted C 1 -C 6 alkylamino, or substituted or unsubstituted C 1 -C 6 hydroxyalkyl; and wherein is an optional bond;

the process comprising heating a liquid reaction medium comprising an oligomeric α-hydroxyacid having the formula:

or a salt thereof, wherein n is an integer from 2 to 30, and wherein x, R 1a , R 1b , R 2 and are the same as defined above,

at a temperature of from about 150° C. to about 300° C. to form the cyclic ester, while removing from the liquid reaction medium a composition comprising the cyclic ester.

2. The process of claim 1 , wherein the liquid reaction medium does not comprise a solvent for dissolving the oligomeric α-hydroxyacid.

3. The process of claim 1 , wherein the liquid reaction medium further comprises a catalytically-effect amount of a transesterication catalyst.

4. The process of claim 1 , wherein the cyclic ester is distilled off from the liquid reaction medium at a pressure in the range of from about 0.02 torr to about 50 torr.

5. The process of claim 1 , wherein the oligomeric α-hydroxyacid is an oligomer of 2-hydroxy-4-pentynoic acid and the cyclic ester is 3,6-di(prop-2-yn-1-yl)-1,4-dioxane-2,5-dione.

6. The process of claim 1 , wherein the oligomeric α-hydroxyacid is an oligomer of 2-hydroxy-4-pentenoic acid and the cyclic ester is 3,6-diallyl-1,4-dioxane-2,5-dione.

7. The process of claim 1 , further comprising preparing the oligomeric α-hydroxyacid by polymerizing an α-hydroxyacid having the formula:

or a salt thereof, wherein x, R 1a , R 1b , R 2 and are the same as defined above;

by heating a liquid reaction medium comprising the α-hydroxyacid at a temperature of from about 100° C. to about 300° C. for a time ranging from about 0.5 hours to about 24 hours to form the oligomeric α-hydroxyacid in the liquid reaction medium.

8. The process of claim 7 , wherein the α-hydroxyacid is polymerized without the use of a solvent.

9. The process of claim 7 , wherein the process is carried out in a single reaction vessel.

10. The process of claim 7 , wherein the process is carried out in more than one reaction vessel.

11. The process of claim 7 , wherein the α-hydroxyacid is polymerized using a catalytically-effective amount of a polymerization catalyst.

12. The process of claim 7 , wherein the α-hydroxyacid is polymerized at a pressure less than about 760 torr.

13. The process of claim 7 , wherein the α-hydroxyacid is polymerized at a pressure in the range of from about 1 to about 50 torr.

14. The process of claim 7 , wherein the liquid reaction medium comprising the α-hydroxyacid further comprises a transesterification catalyst.

15. The process of claim 7 , wherein the α-hydroxyacid is 2-hydroxy-4-pentynoic acid, the oligomeric α-hydroxyacid is an oligomer of 2-hydroxy-4-pentynoic acid, and the cyclic ester is 3,6-di(prop-2-yn-1-yl)-1,4-dioxane-2,5-dione.

16. The process of claim 7 , wherein the α-hydroxyacid is 2-hydroxy-4-pentenoic acid, the oligomeric α-hydroxyacid is an oligomer of 2-hydroxy-4-pentenoic acid, and the cyclic ester is 3,6-diallyl-1,4-dioxane-2,5-dione.