The present invention relates to polynorbornene (PNB) composition embodiments that are useful for forming microelectronic and/or optoelectronic devices and assemblies thereof, and more specifically to compositions encompassing PNBs having norbornene-type repeating units that are polyether functionalized and an additive package containing a phenolic antioxidant and a synergist, and the microelectronic and/or optoelectronic devices made therefrom are resistant to thermo-oxidative chain degradation of said polyether functionalization.