Orthoesters bicyclic polymerization

Yokoyama, Y. and Hall, H. K. Ring-Opening Polymerization of Atom-Bridged and Bond-Bridged Bicyclic Ethers, Acetals and Orthoesters. Vol. 42, pp. 107—138. 

Monomers listed above polymerize by the cationic mechanism. For some groups of monomers (lactones, carbonates) anionic or coordinate mechanism also operates and, from a synthetic point of view, this is the preferred method of converting cyclic esters into linear polyesters. The cationic polymerization of lactones, glycolide and it substituted analog, lactide, as well as spiroorthoesters and bicyclic orthoesters has been studied in some detail. 

This is similar to polymerization of bicyclic orthoesters reported earlier where, depending on reaction conditions, polymers resulting from the opening of one or both rings could be prepared [210]. 

The review will be limited to atom- and bond-bridged bicyclic monomers. The important work of Bailey on the polymerization of spiro bicyclo orthoesters and spiro bicyclic orthocarbonates has been adequately described elsewhere 0 1 60 3. The outstanding and systematic body of work by Schu-erch2 3> and others on the ring opening polymerization of bicyclic acetals derived from carbohydrate precursors will also not be covered here. 

Many kinds of bicyclic ethers, acetals, and orthoesters have been cationically polymerized. Almost all bicyclic compounds have shown polymerizability. A few monomers give dimer or higher oligomers instead of polymers. The results are listed in Table 1. The polymerizability for unsubstituted bicyclic compounds is summarized in Table 2. 

Table 1. Polymerization of bicyclic ethers, acetals, and orthoesters...

Thermodynamical studies of the polymerization of bicyclic orthoesters has not yet been done. 

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