Interest in cyclic olefin polymers has been growing over the past decade owing to their thermal and chemical stability, high mechanical strength, and modulus, which originate from the restricted molecular motion of cyclic groups. In addition, some cyclic olefin polymers are recognized as promising optical materials because of their low birefringence and high transparency. Among the various cyclic unsaturated compounds, cyclic conjugated dienes are quite attractive monomer candidates because some of them can be derived from desirable raw materials. For instance, 1,3-cyclohexadiene (CHD) is readily prepared from cyclohexene, a known inexpensive byproduct from ε-caprolactam synthesis. Another example is cis-5,6-dihydroxy-1,3-cyclohexadiene, which is a microbial oxidization product of benzene utilizing Pseudomonas putida.1 If the cyclic diene compound is polymerized with controlled microstructure, the obtained polymer is expected to form a soluble precursor of an electron-conductive poly(p-phenylene) (PPP) (Scheme 18.1).1