Synthesis and Polymerization of Cyclic Polyester Oligomers

Cyclic oligomers of condensation polymers such as polycarbonates and polyesters have been known for quite some time. Early work by Carothers in the 1930s showed that preparation of aliphatic cyclic oligomers was possible via distillative depolymerization [1, 2], However, little interest in the all-aliphatics was generated, due to the low glass transition temperatures of these materials. Other small-ring, all-aliphatic cyclic ester systems, such as caprolactone, lactide 

Modem Polyesters Chemistry and Technology of Polyesters and Copolyesters. Edited by J. Scheirs and T. E. Long 2003 John Wiley Sons, Ltd ISBN 0-471-49856  

3 PREPARATION OF POLYESTER CYCLIC OLIGOMERS FROM ACID CHLORIDES 

It seems reasonable that polyester cyclics could be prepared by an extension of the /wendo-high-dilution [17] chemistry used for the preparation of cyclic carbonate oligomers [18, 19] however, such proved not to be the case. Brunelle et al. showed that the reaction of terephthaloyl chloride (TPC) with diols such as 1,4-butanediol did not occur quickly enough to prevent concentration of acid chlorides from building up during condensation [14]. Even slow addition of equimolar amounts of TPC and butanediol to an amine base (triethylamine, pyridine or dimethylaminopyridine) under anhydrous conditions did not form cyclic oligomers. (The products were identified by comparison to authentic materials isolated from commercial PBT by the method of Wick and Zeitler [9].) 

Further investigation of model reactions revealed that the reaction of aromatic acid chlorides with diols such as butanediol or ethylene glycol was too slow to be useful for kinetically controlled p.vcMdo-high-dilution reactions carried out 

PBT cyclics 40% with DABCO 85% with EtgN/DABCO 

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