We report a new method to synthesize rigid ladder polymers using efficient palladium catalyzed annulation reactions with low catalyst loading (1 mol %). Rigid ladder polymers with benzocyclobutene backbone linkages can be synthesized from copolymerization of readily accessible aryl dibromides and norbornadiene or polymerization of AB type monomers bearing norbornene and aryl bromide or triflate moieties. High molecular weight (10-40 kDa) rigid ladder polymers can be obtained with complete monomer conversions. Diverse monomers also gave different, fixed ladder polymer conformations. The ladder polymers exhibited excellent thermal stability, high carbonization yield, and large intrinsic porosity.
We
have previously reported a polymechanophore system, polyladderene,
which underwent dramatic bond rearrangement in response to mechanical
force to yield semiconducting polyacetylene. Herein, we report the
scalable synthesis of benzoladderenes as new mechanophore monomers.
Ring-opening metathesis polymerization of benzoladderenes yielded
homopolymers and block copolymers with controlled molecular weights
and low dispersity. The resulting nonconjugated poly(benzoladderene)
was mechanochemically transformed into conjugated poly(o-phenylene-hexatrienylene) by sonication, with degrees of transformation
up to 40–45%. These benzoladderenes and their resulting polymers
are easier to synthesize than the polyladderene system and allow mechanochemical
generation of conjugated polymers beyond polyacetylene.
The juxtaposition of fused cyclobutadienoid (CBD) with benzenoid creates intriguing alternating antiaromatic and aromatic conjugation. Synthetic accessibility of such molecules, however, has been challenging and limited in scope. We report a modular and streamlined synthetic strategy to access a large variety of polycyclic conjugated hydrocarbons with fused CBD. Synthesis was achieved through efficient palladium-catalyzed C-H activated annulation between abundant aryl bromides and oxanorbornenes, followed by aromatization under acidic conditions. The influence of four-membered ring was examined using spectroscopy, crystallography, and computation. This strategy will facilitate exploration on the chemical, structural, and electronic properties of such conjugated systems containing CBD.
We synthesized a series of rigid ladder-type diamines from readily available bromoanilines and norbornadiene in one step using facile catalytic arene-norbornene annulation (CANAL). Polycondensation of CANAL ladder diamines with 4,4'-(hexafluoroisopropylidene) diphthalic anhydride led to a series of microporous polyimides with different degrees of rotational freedom around the imide linkages. CANAL-PIs exhibited good solubility in a wide range of organic solvents, high thermal stability with decomposition temperature above 450 °C, high Brunauer-Emmett-Teller surface areas of ~ 200 -530 m 2 g -1 , and abundant micropore volume with variable pore size distributions. Mechanically robust membranes can be easily formed from CANAL-PIs and gave high gas permeabilities and moderate gas-pair selectivities. CANAL-PIs had higher permeability and similar permselectivity to analogous PIs synthesized from Tröger's base and carbocyclic Tröger's base diamines under identical test conditions. CANAL-PIs also exhibited relatively slow physical aging. These favorable properties and performance make microporous polymers based on CANAL ladder motifs promising membrane materials for gas separation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.