Ring-opened polymers of (+)- and (+/-)-endo,exo-5,6-dimethylbicyclo[2.2.1]hept-2-ene(1) having cis double bond contents between 5 and 85% were prepared using Mo(CH-t-Bu)(NAr)(OR)2 (Ar = 2,6-C6H3-i-Pr2; OR = OCMe3, OCMe2(CF3), OCMe(CFS)2) complexes as initiators. The cis content of the polymers increased in proportion to the electron-withdrawing power of the alkoxide ligands. C-13 NMR spectra (125 MHz) of these polymers were interpreted in terms of the various possible diad structures. XX, XN (NX), and NN, where X and N refer to substituents derived from exo and endo methyl groups, m and r refer to the meso (isotactic) or racemic (syndiotactic) configuration of adjacent cyclopentane rings in the chain, and tt, tc (ct), and cc refer to the cis/trans double bond sequences. High-cis polymer made from 98% (+)-1 contained 78% m diads and had more than twice the optical rotatory power and a higher T, (85-degrees-C) than the high-trans polymer (48% m diads; T, = 55-degrees-C).