Dodecanidiol dimethacrylate (DDMA) was polymerized by a cyclization mechanism in low monomer concentration (0.075-0.5 mol/L) and high AIBN concentration (0.44-1.76 X 10(-2) mol/L). The linear soluble polymer was formed even if the conversion of DDMA was as high as 25.6%. The glass transition temperature of cyclized polyDDMA (PDDMA) is about 4.5 degrees C, which is 65 degrees C higher than its homolog-poly(dodecyl methacrylate). The structure of the polymer was established by infrared and H-1- and C-13-NMR spectroscopy. The head-to-tail contents in cyclized PDDMA, i.e., the formation of a 20-membered ring, is predominant compared with those of head-to-head contents of a 19-membered ring.