CATIONIC RING-OPENING POLYMERIZATION OF SPIROORTHOESTER - POLYMER STRUCTURE, POLYMERIZATION MECHANISM, AND VOLUME CHANGE ON POLYMERIZATION

The polymer structure and polymerization mechanism of cationic polymerization of a spiroorthoester were studied, and the relationship between volume change on polymerization and polymer structure was examined. Spiroorthoester, 1,4,6-trioxaspiro[4.6]undecane (1), was polymerized with SnCl4 (2 mol %) at various temperatures ranging from 0 to 120-degrees-C. The polymer structure was dependent on polymerization temperature. The polymer obtained at 0-degrees-C was entirely poly(cyclic orthoester), whereas the polymer obtained at 120-degrees-C consisted of 25% poly(cyclic orthoester) and 75% poly(ether-ester). The unit ratio of poly(ether-ester) increased with rising polymerization temperature. The polymerization mechanism is discussed in terms of the relation between the yield and the structure of the polymer synthesized at 80-degrees-C. It was suggested that the poly(ether-ester) unit was formed by acid-catalyzed intermolecular isomerization of the poly(cyclic orthoester) unit. Further, the volume change on polymerization was studied in relation to the polymer structure, and an increase of poly(ether-ester) units in the polymer suppressed shrinkage on polymerization.