Polymeric microstructures and dielectric properties of polynorbornenes with 3,5-Bis(trifluoromethyl)biphenyl side groups by ring-opening metathesis polymerization

Exo-Polynorbornenes containing bis(trifluoromethyl)biphenyl side groups were synthesized by ring-opening metathesis polymerization using different Grubbs' catalysts, the microstructures of the polymer chains were established using NMR and IR spectroscopy. The influence of monomer and catalyst structures on chain microstructure was revealed and the correlation of properties with microstructure was investigated in detail. The exo-poly(N-3,5- bis(trifluoromethyl)biphenyl-norbornene-pyrrolidine) (exo-PTNP) and exo-poly(N-3,5-bis(trifluoromethyl)biphenyl-norbornene-dicarboximide) (exo-PTNDI) formed using Ru-I show a trans double bond bias of 67% and 83%, respectively, whereas the corresponding polymers formed using Ru-III have lower contents of trans double bond, 30% and 50%, respectively. Compared to the highly trans endo-PTNP formed using Ru-I, which is isotactic and has a dielectric constant of about 20, the endo-PTNP formed using Ru-III, the exo-PTNDIs and the exo-PTNPs formed using Ru-I and Ru-III all have different proportions of trans and cis double bonds, they are atactic and display relatively low dielectric constants, in the range 6 to 9. DSC measurements indicate some dependence of T_g, varying 161 to 221°C, on tacticity and cis/trans ratios with higher trans contents tending towards higher T_g.