The polymerization of 1-methoxy -1-ethynylcyclohexane (MEC) was carried out by various transition metal catalysts. The catalysts MoC15, MoCli, and WCIC gave a relatively low yield of polymer (< 16%). The catalytic activity of Me-based chloride catalyst was greater than that of W-based chloride catalyst. However, catalyst tungsten carbene complex (I) gave a larger molar mass and higher yield in the presence of a Lewis acid such as AICIS than in the absence of a Lewis acid. The activity of the tungsten carbene complex was obviously affected by Lewis acidity. The catalyst PdC12was a very effective catalyst for the present polymerization and gave polymers in a high yield. The structure of the resulting poly (MEC) was identified by various instrumental methods as a conjugated polyene structure having an a-methoxycyclobexyl substituent. The poly (MEC)S were mostly lightbrown powders and completely soluble in various organic solvents such as tetrahydrofuran (THF), chloroform (CHC13), ethylacetate, n-butylacetate, dimethylformamide, benzene, xylene, dimethylacetamide, 1,4-dioxane, pyridine, and 1-methyl -2-pyrrolidinone. Thermogravimet ric analysis showed that the polymer started to lose mass at 125ยฐC and that maximum decomposition occurred at 418"C. The x-ray diffraction diagram shows that poly (MEC) has an amorphous Stmcture. ~1997 ,J~hnWilev & sons, Inc.