TABLE OF CONTENTS Cyclic oligomers of condensation polymers such as polycarbonates and polyesters have been known for quite some time. The cyclics are found in commercial grades of polyester and polycarbonate at levels of 0.25 2.0%, being formed either under kinetic conditions (e.g. in phosgenation reactions), or in their equilibrium concentration from melt polymerization reactions. The cyclic oligomers have been separated from the polymers and characterized by several groups, and synthesis of many discrete cyclics has also been reported using classical high dilution techniques. Most of the early work was of academic interest, due to the fact that syntheses were inefficient and purification of products was always necessary.
Chemistry has recently been developed for the facile preparation of large quantities of mixtures of cyclic oligomeric polycarbonates and polyesters (dimer, trimer, tetramer, etc). Through use of specific pseudo-high dilution techniques in kinetically controlled reactions, cyclic oligomer mixtures can be prepared in yields as high as 90%, and with excellent selectivity over the formation of linear oligomers. High selectivity of cyclic over linear oligomers was necessary because the presence of linears would limit the ultimate molecular weights achievable upon ring-opening polymerization (ROP) of the cyclics. Furthermore, these reactions were designed specifically for high productivity synthesis, and have been scaled to hundreds of kilograms per batch. With the advent of this cyclic oligomer synthesis technology, use of ROP of the cyclic oligomers for preparation of high molecular weight polyesters and polycarbonates...
