The physiochemical properties, comonomer sequencing, and regiospecificity of the linkages between monomeric units within homo/copolymers based on 5,6-di-substituted norbornene and 7-oxanorbornene type monomers by ring-opening metathesis polymerization are reported and correlated to their primary and secondary structural elements. In general, first-generation Grubbs-I1 ruthenium catalyst generates polymers with high trans content that exhibits an extended secondary structure with exo,exo substituents, whereas second-generation Grubbs-I2 catalyst produces polymers with high cis content that forms tight turns, resulting in a compact structure. Furthermore, I2-produced polymers exhibit a high level of alternating cis-trans double bonds along their polymeric backbone. In stark contrast, both first- and second-generation Grubbs catalysts display complete reversal in cis/trans selectivity when an oxygen atom is in position-7 of the norbornene-ring along with mono-endo-substitution in position-5 or 6, and hence highlighting the importance of stereoelectronic complexation by the catalyst with the next incoming monomer for cis/trans selectivity. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2477-2501