The thermal effect of microwave energy on E-caprolactone (CL) monomer and polymerization reaction mixture of CL with stannous octoate [Sn(Oct)(2)] intimately depended on the power level of microwaves and the mass scale of materials. When 10 g of CL was heated by microwaves at a power of 680 W, its temperature increased rapidly from 20 to 355degreesC within 5 min after which it was self-regulated to keep constant at 360degreesC. Heat generation was observed when a polymerization reaction mixture of 10 g CL with 0.1% (mol/mol) Sn(Oct)(2) was irradiated at 680 W. The exothermic peak was recorded at 2-5 min and its temperature was over 300degreesC, with the maximum at 343degreesC. During this period the ring-opening polymerization of CL occurred quickly, resulting in poly(epsilon-caprolactone) with weight-average molecular weight (M-w) of 123,000 g/mol and yield of 95%. (C) 2003 Wiley Periodicals, Inc.