Polyimide-tethered polyhedral oligomeric silsesquioxane, (R 7R′Si8O12) (POSS), nanocomposites with well-defined architectures are prepared by the copolymerization reaction of a new type of diamine monomer: POSS-diamine, 4,4′-oxydianiline (ODA), and pyromellitic dianhydride (PMDA). This type of polyimide-side-chain-tethered POSS nanocomposite presents self-assembly characteristics when the amount of POSS exceeds10 mol %, as evidenced by transmission electron microscopy studies. Furthermore, POSS/polyimide nanocomposites have both lower and tunable dielectric constants, with the lowest value of 2.3, and controllable mechanical properties, as compared to that of pure polyimide.
Low-dielectric-constant nanoporous films (dielectric constant, k = 2.4) with thermal
integrity and controllable mechanical strength have been prepared by covalently tethering
nanoporous polyhedral oligomeric silsesquioxane (POSS) molecules, 1-nm size, to the side
chains of polyimide. The tethered POSS molecules in the amorphous polyimide retain a
nanoporous crystal structure, but form an additional ordered architecture due to microphase
separation. With this approach, the dielectric constant of the film can be tuned by the amount
of POSS molecules introduced in the nanocomposite film; the polyimide molecules offer
additional advantages of maintaining certain thermal and mechanical strengths.
PHPIT, a new kind of intramolecular donor–acceptor side‐chain‐tethered hexylphenanthrenyl‐imidazole polythiophene is synthesized. The more‐balanced electron and hole mobilities and the enhanced visible‐ and internal‐light absorptions in the devices consisting of annealed PHPIT/PCBM blends both contribute to a much higher short‐circuit current density, which in turn led to a power conversion efficiency as high as 4.1%.
We have used Grignard metathesis polymerization to successfully synthesize a series of regioregular polythiophene copolymers that contain electron‐withdrawing and conjugated phenanthrenyl‐imidazole moieties as side chains. The introduction of the phenanthrenyl‐imidazole moieties onto the side chains of the regioregular polythiophenes increased their conjugation lengths and thermal stabilities and altered their bandgap structures. The bandgap energies, determined from the onset of optical absorption, could be tuned from 1.89 eV to 1.77 eV by controlling the number of phenanthrenyl‐imidazole moieties in the copolymers. Moreover, the observed quenching in the photoluminescence of these copolymers increases with the number of phenanthrenyl‐imidazole moieties in the copolymers, owing to the fast deactivation of the excited state by the electron‐transfer reaction. Both the lowered bandgap and fast charge transfer contribute to the much higher external quantum efficiency of the poly(3‐octylthiophene)‐side‐chain‐tethered phenanthrenyl‐imidazole than that of pure poly(3‐octylthiophene), leading to much higher short circuit current density. In particular, the short circuit current densities of the device containing the copolymer having 80 mol % phenanthrenyl‐imidazole, P82, improved to 14.2 mA cm–2 from 8.7 mA cm–2 for the device of pure poly(3‐octylthiophene), P00, an increase of 62 %. In addition, the maximum power conversion efficiency improves to 2.80 % for P82 from 1.22 % for P00 (pure P3OT). Therefore, these results indicate that our polymers are promising polymer photovoltaic materials.
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