Mono- or diesters of norbornene 2,3-dicarboxylic acid (NBE-(COOR)x), in which (COOR)x is the group R, were synthesized from one-pot synthesis method with 5-norbornene-2,3-dicarboxylic acid and methanol, ethanol or propanol. The new monomers were, respectively, the dimethyl ester NBE-(COOCH3)2, 1, diethyl ester NBE-(COOCH2CH3)2, 2, and monopropyl ester NBE-(COOH)(COOCH2CH2CH3), 3. Norbornene was mixtured with 1, 2 or 3 in different proportion and copolymerized via ROMP with 1st generation Grubb’s catalyst under air atmosphere. Yield results show that the elongation of the aliphatic group mono- or diesters influenced the copolymerization process. In the same proportion of co-monomers (0.5:0.5 and 1.0:1.0), the yield decreased as a function of the R group elongation, being from 41.5 to 22.9% and 32.2 to 22.4% for the respective proportions. TGA was performed and in all cases more than one thermal degradation processes was observed, in the same or different co-monomer proportion. The first degradation process was assigned to pendent group degradation and the second one to main chain degradation. Some thermal processes were also influenced by different elongation of the aliphatic group of pendent chain.