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
(M
w) 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 (T
g) 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.
The control of gate dielectric properties of vinyl-addition polynorbornene copolymers bearing pendant vinyl groups for OFET applications is demonstrated through photoinitiated thiol–ene click chemistry.
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