The reactions between benzylbromide or alpha,alpha'-dibromo-metes-xylene (DBMX) and sodium 1,2,3,4,5-pentamethylcycopenta-1,3-dienide (CpMe5circle minus, Na-circle plus) give only the expected pentamathylcyclopentadiene derivatives with a good yields. These products lead to endo isomer adducts via a Diels-Alder reaction with maleimide. New low molecular weight polypentamethylnadimides were obtained in this way from the Diels-Alder polymerization of bispenta-methylcyclopentadiene monomers and commercial or synthetic bismaleimides. The polyadducts were characterised by size exclusion chromatography (SEC), matrix assisted laser desorption ionization-time of flight (MALDI-TOF), nuclear magnetic resonance (NMR) and thermogravimetric analyses (TGA). The low molecular weight was attributed to methyl steric hindrance. For the lowest molecular weight products, two different endcapped oligomers were observed.