Side-chain symmetry and backbone structure as design parameters for transparent cyclic olefin polymer

Cyclic olefin polymers (COPs) are attractive for transparent coatings, yet balancing optical performance with processability remains challenging. We conducted a systematic structure–property study of oxanorbornene-based COPs with symmetric (OMM, OEE) and asymmetric (OME) ester substituents. Monomers were synthesized, polymerized via ring-opening metathesis polymerization, and hydrogenated to remove backbone unsaturation. NMR confirmed complete conversion and selective saturation without side-chain degradation. Thermal analyses revealed that symmetric, compact substituents increase glass-transition temperature (T_g) and thermal resistance, while asymmetric substitution decreases T_g but enhances chain mobility. Hydrogenation decreased T_g but increased decomposition temperatures (T_d) by ∼40 °C, improving stability. Optical analyses revealed that asymmetric P-OME achieves the highest transmittance (>97 %) and the most blue-shifted cutoff, whereas hydrogenated P-OMM gains transparency by eliminating residual double bonds. These findings establish side-chain symmetry and backbone saturation as key molecular design handles, offering guidelines for transparent, processable organic films for optoelectronic and protective applications.