p-Phenylenevinylene-2,5-diethyhexyloxy-p-phenylenevinylene and m-phenylenevinylene-2,5-diethylhexyloxy-p-phenylenevinylene homopolymers (3 and 4) have been prepared by the ring-opening metathesis polymerization (ROMP) of strained cyclophanedienes, initiated by the sceond generation Grubbs catalyst, The as-formed polymers have a backbone of alternating cis- and trans-vinylene linkages due to the opening of only one vinylene of the cyclophanediene. Irradiation with UV light results in an isomerization to an all-trans-vinylene microstrucure for all Polymers. The polymer chain ends remain active after complete consumption of the cyclophanediene. and block copolymers can be prepared by addition of further cyclophanediene. The optical and electronic properties of the homopolymers and block copolymers are reported.