Polymerization of macrocyclic polyester oligomers using N-heterocyclic carbene catalysts

A process for preparing a thermoplastic polyester comprising contacting at least one macrocyclic polyester oligomer with at least one N-heterocyclic carbene-containing catalyst described by the formula:

• wherein
• R5 is an adamantyl, alkaryl, or alkyl group;
• R6 and R7 are each independently hydrogen or a C1-12 alkyl group;
• n equals 1 or 2;
• and
• R8 equals R5 when n equals 1, and is an alkylene group when n equals 2.

A process for preparing a thermoplastic polyester comprising contacting at least one macrocyclic polyester oligomer with at least one N-heterocyclic carbene containing catalyst described by the formula:

• wherein:
• R9 and R11 are each independently an adamantyl, alkaryl, or alkyl group;
• and
• R10 is hydrogen or a C1-l2 alkyl group.

A process for preparing a thermoplastic polyester comprising contacting at least one macrocyclic polyester oligomer with at least one N-heterocyclic carbene precursor containing catalyst described by the formula:

• wherein:
• R12 is an adamantyl, alkaryl, or alkyl group;
• R13 and R14 are each independently hydrogen or a C1-12 alkyl group;
• n=1 or 2;
• R15 is the same as R12 when n=1, and is an alkylene group when n=2;
• and
• X is a halogen, BF4, or PF6.