Characteristics and properties of polynorbornene can be regulated through side-chain engineering. In this contribution, a linear polynorbornene (PNI-TFVE) containing trifluorovinyl-ether (TFVE) side groups was synthesized via ring-opening metathesis polymerization. This linear polynorbornene was soluble in common organic solvents and showed good film-forming ability. Upon thermal post-polymerization, this linear PNI-TFVE can be easily transformed into crosslinked polynorbornene (PNI-PFCB) with perfluorocyclobutyl linkers. The resulted PNI-PFCB exhibited outstanding thermal stability with ultra-high glass transition temperature above 350 °C and a 5 % weight loss temperature of 479 °C. Due to the high crosslinking density and high fluorine content of PFCB, crosslinked PNI-PFCB also exhibited low thermal expansion of 73 ppm °C−1, as well as favourable storage modulus and hydrophobicity.