The ring-opening metathesis polymerization (ROMP) of dicydopentadiene and cyclooctene with norbornene lactone as a polar comonomer was studied. By incorporation of this rigid molecule the glass transition temperature was significantly increased. Thermal investigations showed a linear correlation between the amount of norbornene lactone in the copolymer and the observed glass transition. Thus, it was possible to vary the T-g within a broad temperature range.