Embodiments in accordance with the present invention provide for forming essentially pure diastereomers of 5/6-substituted norbornene-type monomers. Further, embodiments in accordance with the present invention encompass polymerizing such diastereomers to form addition or ROMP polymers where a desired exo-/endo-ratio of the diastereomers is provided to the polymerization, such ratio designed to provide a desired ratio of endo-/exo-structured repeating units for a resulting polymer to have desired physical or chemical properties.