Diesters of norbornene 2,3-dicarboxylic acid (NBE-(COOR) 2 ), in which R is an alkyl group, were synthesized from one-pot synthesis method with 5-norbornene-2,3-dicarboxylic acid and methanol and ethanol. The new monomers were, respectively, the dimethyl ester NBE-(COOCH 3 ) 2 and diethyl ester NBE-(COOCH 2 CH 3 ) 2 . Norbornene was mixed with these monomers at different proportions and copolymerized via ring-opening metathesis polymerization (ROMP) with 1 st generation Grubbs' catalyst. All experiments were conducted under air atmosphere to obtain the isolated polymer. Yield results show that elongation of the R group influenced the copolymerization process. At the same co-monomer proportion, the yield decreases as a function of the R group elongation. Thermogravimetric analysis (TGA) was performed and, in all cases, more than one thermal degradation process was observed. The first process was assigned to pendent group degradation, whereas the second process was assigned to main chain degradation. These thermal processes were also influenced by different elongation of the aliphatic group of the pendent chain.