Regioisomeric Spirobifluorene CANAL Ladder Polymers and Their Gas Separation Performance

We synthesized and characterized two isomeric microporous hydrocarbon ladder polymers from catalytic arene norbornene annulation (CANAL) of regioisomeric bis-norbornene fused spirobifluorenes, where the ladder chains are connected either through the same fluorene unit or across two different fluorene units in spirobifluorene. This pair of isomeric polymers was used to investigate the effect of ladder macromolecular structures on the microporosity and transport properties. Both polymers form mechanically intact films with thermal stability up to 480 °C and relatively high BET surface areas. The polymer formed from 2,7-dibromospirobifluorene showed higher BET surface area and higher gas permeability than the polymer from 2,2'-dibromospirobifluorene despite similar intersegmental spacing as indicated by X-ray scattering. The aging behavior for both polymers followed the same trend as the previously reported CANAL-fluorene polymers, with dramatically increased permselectivities over time, resulting in gas separation performance above the 2008 upper bounds for H2/CH4 and O2/N2.

Norbornane-based covalent organic frameworks for gas separation

Covalent organic frameworks (COFs) have emerged as a new class of crystalline porous materials with distinct structural features, such as uniform pore distribution, tunable architecture, and modifiable skeletons. COFs hold significant promise for application in gas separation because of their high Brunauer-Emmett-Teller surface area and narrow pore-size distribution, which enable selective separation. The porosity and separation performance of COFs have been finely tuned by structurally modifying the starting materials. Along this direction, for the first time, we prepared W-shaped diamines by catalytic arene-norbornene annulation (CANAL) and then treated them with trialdehyde (Tp) to synthesize novel β-ketoenamine-linked norbornane-based COFs, i.e., ND-COF-1 and ND-COF-2, via a solvothermal Schiff-base condensation approach. The pore interior was decorated with methyl groups attached to the norbornane unit of the COF skeleton. Both COFs exhibited high chemical stability in different organic solvents and acidic media. Additionally, they showed high CO₂/N₂ selectivity compared with those of previously reported COFs. Moreover, their CH₄/N₂ separation efficiency was investigated, and the results revealed that ND-COF-1 is more selective than ND-COF-2, which could be attributed to the less hindered pathway offered to methane gas molecules by the framework pore.

High Performance Low Dielectric Polybenzocyclobutene Nanocomposites with Organic-Inorganic Hybrid Silicon Nanoparticles

In this study, benzocyclobutene-functionalized organic-inorganic hybrid spherical silicon nanoparticles (BCBNPs) with controllable size (200-600 nm) and good dispersion were synthesized by one-step sol-gel method in aqueous solution. The effect of...

Extraordinary electrochemical stability and extended polaron delocalization of ladder-type polyaniline-analogous polymers

Electrochemical stability and delocalization of states critically impact the functions and practical applications of electronically active polymers. Incorporation of a ladder-type constitution into these polymers represents a promising strategy to enhance the aforementioned properties from a fundamental structural perspective. A series of ladder-type polyaniline-analogous polymers are designed as models to test this hypothesis and are synthesized through a facile and scalable route. Chemical and electrochemical interconversions between the fully oxidized pernigraniline state and the fully reduced leucoemeraldine state are both achieved in a highly reversible and robust manner. The protonated pernigraniline form of the ladder polymer exhibits unprecedented electrochemical stability under highly acidic and oxidative conditions, enabling the access of a near-infrared light-absorbing material with extended polaron delocalization in the solid-state. An electrochromic device composed of this ladder polymer shows distinct switching between UV- and near-infrared-absorbing states with a remarkable cyclability, meanwhile tolerating a wide operating window of 4 volts. Taken together, these results demonstrate the principle of employing a ladder-type backbone constitution to impart superior electrochemical properties into electronically active polymers.

Facile Synthesis and Study of Microporous Catalytic Arene-Norbornene Annulation-Tröger's Base Ladder Polymers for Membrane Air Separation

We report the facile synthesis and study of two soluble microporous ladder polymers, CANAL-TBs, by combining catalytic arene-norbornene annulation (CANAL) and Tröger's base (TB) formation. The polymers were synthesized in two steps from commercially available chemicals in high yields. CANAL-TBs easily formed mechanically robust films, were thermally stable up to 440 °C, and exhibited very high Brunauer-Teller-Emmett surface areas of 900-1000 m² g^-1. The gas separation performance of the CANAL-TBs for the O₂/N₂ pair is located between the 2008 and 2015 permeability/selectivity upper bounds. After 300 days of aging, CANAL-TBs still exhibited O₂ permeability of 200-500 barrer with O₂/N₂ selectivity of about 5. The polymer with more methyl substituents exhibited higher permeability and slightly larger intersegmental spacing as revealed by WAXS, presumably due to more frustrated chain packing. The facile synthesis, excellent mechanical properties, and promising air separation performance of the CANAL-TB polymers make them attractive membrane materials for various air separation applications, such as aircraft on-board nitrogen generation and oxygen enrichment for combustion.

Polymer Networks: From Plastics and Gels to Porous Frameworks

Polymer networks, which are materials composed of many smaller components-referred to as "junctions" and "strands"-connected together via covalent or non-covalent/supramolecular interactions, are arguably the most versatile, widely studied, broadly used, and important materials known. From the first commercial polymers through the plastics revolution of the 20^th century to today, there are almost no aspects of modern life that are not impacted by polymer networks. Nevertheless, there are still many challenges that must be addressed to enable a complete understanding of these materials and facilitate their development for emerging applications ranging from sustainability and energy harvesting/storage to tissue engineering and additive manufacturing. Here, we provide a unifying overview of the fundamentals of polymer network synthesis, structure, and properties, tying together recent trends in the field that are not always associated with classical polymer networks, such as the advent of crystalline "framework" materials. We also highlight recent advances in using molecular design and control of topology to showcase how a deep understanding of structure-property relationships can lead to advanced networks with exceptional properties.

Flexible and low-k polymer featuring hard–soft-hybrid strategy

One of the main challenges for dielectric materials for advanced microelectronics is their high dielectric value and brittleness. In this study, we adopted a hard–soft-hybrid strategy and successfully introduced a hard, soft segment and covalent crosslinked structural unit into a hybridized skeleton via copolymerization of polydimethylsiloxane (PDMS), benzocyclobutene (BCB) and double-decker-shaped polyhedral silsesquioxanes (DDSQ) by a platinum-catalyzed hydrosilylation reaction, thus producing a random copolymer (PDBD) with a hybridized skeleton in the main chain. PDBD exhibited high molecular weight and thermal curing action without any catalyst. More importantly, the cured copolymer displayed high flexibility, high thermal stability and low dielectric constant, evidencing its potential applications in high-performance dielectric materials.

Hard–Soft-hybrid strategy is used to synthesize random copolymers with a hybridized main chain.

Arm-degradable star polymers with crosslinked ladder-motif cores as a route to soluble microporous nanoparticles

Star polymers were synthesized via cores crosslinking of (macro)molecular ladder motifs and converted to microporous polymer particles after arm degradation.

Palladium/Norbornene Cooperative Catalysis

Palladium/norbornene cooperative catalysis has emerged as a distinct approach to construct polyfunctionalized arenes from readily available starting materials. This Review provides a comprehensive overview of this field, including the early stoichiometric investigations, catalytic reaction developments, as well as the applications in the syntheses of bioactive compounds and polymers. The section of catalytic reactions is divided into two parts according to the reaction initiation mode: Pd(0)-initiated reactions and Pd(II)-initiated reactions.

Porous Organic Polymers via Ring Opening Metathesis Polymerization

Highly porous and solution processable organic polymers that can be structurally tailored for various applications are in great demand. Previously reported strategies to prepare porous polymers usually rely on a high level of cross-linking or structurally rigid polymer backbones. We now demonstrate that one-dimensional linear polymers with flexible backbones prepared through ring opening metathesis polymerization can be highly porous. This new strategy allows facile access to diversified porous organic polymers having tunable mechanical/chemical properties bearing different functionalities.

Functionalized Rigid Ladder Polymers from Catalytic Arene-Norbornene Annulation Polymerization

Rigid ladder polymers represent a unique polymer architecture but have limited synthetic accessibility and structural diversity. Using catalytic arene-norbornene annulation (CANAL) polymerization, we synthesized ladder polymers consisting of rigid and kinked norbornyl benzocyclobutene backbones and bearing various functional groups, such as alcohol, amine, ester, carbamate, amide, benzyl bromide, azide, and heterocycles. The incorporation of functional groups was achieved by either copolymerization of functionalized ladder-type dinorbornenes or postpolymerization functionalization. Functionalization of ladder polymers allows modification of their solubility, compatibility, and other properties, expanding their utilities. These ladder polymers remain microporous and highly glassy, which are desirable for separation and high-temperature applications.

Rigid-to-Flexible Conformational Transformation: An Efficient Route to Ring-Opening of a Tröger's Base-Containing Ladder Polymer

The synthesis of ladder polymers is still a big challenge in polymer chemistry, and in particular, there are few examples of conformationally flexible well-defined ladder polymers. Here we report an efficient and convenient route to conformationally flexible ladder polymers, which is based on a postpolymerization reaction of a rigid ladder polymer containing Tröger's base in its main chain. The postpolymerization reaction involves sequential N-methylation and hydrolysis for the Tröger's base unit, resulting in a diazacyclooctane skeleton that can exhibit a ring-flipping motion. Molecular dynamics simulations predicted that this motion provides conformational flexibility with the resultant ladder polymer, which was demonstrated by ¹H NMR spectroscopy in solution. The presence of the diazacyclooctane units in the flexible ladder polymer allowed further functionalization through reactions involving its secondary amine moiety. The present synthetic method may lead to the development of a new class of ladder polymers that exhibit both conformational and design flexibility.