Patent ID: 7169729

Claim:
In the (co)polymerization of cyclic esters, the improvement comprising using as catalyst zinc derivatives of the formula wherein L 1 is selected from the group consisting of —E 14 (R 14 )(R′ 14 )(R″ 14 ), —E 15 (R 15 )(R′ 15 ) and —E 16 (R 16 ); E is nitrogen or phosphorous; L 2 and L 3 are, independently, selected from the group consisting of —E 14 (R 14 )(R′ 14 )(R″ 14 ), —E 15 (R 15 )(R′ 15 ) and —E 16 (R 16 ), E 14 is carbon or silicon; E 15 is nitrogen or phosphorous; E 16 is oxygen or sulfur; R 14 , R′ 14 , R″ 14 , R 15 , R′ 15 and R 16 are, independently selected from the group consisting of hydrogen, alkyl, aryl and E′ —14 RR′R″; E′ 14 is carbon or silicon; R, R′ and R″ are, independently, hydrogen or alkyl.