Synthesis of Vinyl-Addition Polynorbornene Copolymers Bearing Pendant n-Alkyl Chains and Systematic Investigation of Their Properties

The synthesis of vinyl-addition polynorbornene copolymers bearing pendant n-alkyl chains (octyl, decyl, and dodecyl groups) and systematic investigation of their properties are reported. Vinyl-addition polymerization using Pd2(dba)3/PCy3/Li[FABA] produces poly(norbornene-co-5-n-alkyl-2-norbornene)s, P(NB/NBCx) (x is the number of carbon atoms in the n-alkyl chain), with a high weight-average molecular weight (Mw) of 71.2–410.6 kDa, high yields of 68–87%, and a similar monomer content to the monomer feed ratio. The films of the resulting copolymers are successfully prepared by a solution-casting method. The glass transition temperature (Tg) of these films can be tuned from 91.7 to 192.4 °C depending on the length of the alkyl chain of NBCx and the NBCx content. The mechanical properties are controlled by these two parameters as well. The change from brittle to ductile properties is observed with the increasing NBCx content of P(NB/NBCx) films, where the increase in the length of the alkyl chain of NBCx increases the value of the strain at break, accompanied by a decrease in strength. The wide-angle X-ray scattering analysis provides information on nanostructure–property relationships in copolymers. All P(NB/NBCx) films display a high transmittance of more than 85% in the visible-light range.