Complex isomerism influencing the textural properties of organometallic [Cu(salen)] porous polymers: paramagnetic solid-state NMR characterization and heterogeneous catalysis.

Although organometallic porous polymer networks are recognized as promising heterogeneous catalysts, the relationship between ligand/monomer geometry and network parameters is usually not well understood due to the lack of atom-resolved characterization methods for the amorphous network matrix. In this work, a series of copper(II) salen-type metal complexes was synthesized, using trans- and cis-1,2-diaminocyclohexane segments, and thoroughly characterized by single-crystal X-ray diffraction and solution- and solid-state NMR spectroscopy. Terminal ethynyl groups of the complexes were then transformed into polyacetylene chains by coordination chain-growth homopolymerization, resulting in highly porous (458-655 m2 g-1) organometallic polymer networks with a copper(II) ion content of about 12 wt%. The presence of paramagnetic copper(II) moieties in these complexes and respective polymer networks required the application of tailored NMR techniques, which together with X-ray crystallography and DFT calculations of the paramagnetic NMR shifts made it possible to investigate the differences in the complex geometry in liquid, powder and crystalline form and compare it with the complex geometry in polymer networks. All prepared organometallic polymer networks were also tested as heterogeneous catalysts for styrene oxidation with uncommonly high substrate conversions and compared with their low-molecular-weight analogues. The high reusability of such heterogeneous polymer-based catalysts was also proven.

Combining Polymerization and Templating toward Hyper-Cross-Linked Poly(propargyl aldehyde)s and Poly(propargyl alcohol)s for Reversible H2O and CO2 Capture and Construction of Porous Chiral Networks.

Two series of hyper-cross-linked microporous polyacetylene networks containing either -[CH=C(CH=O)]- or -[CH=C(CH2OH)]- monomeric units are reported. Networks are prepared by chain-growth copolymerization of acetal-protected propargyl aldehyde and acetal-protected propargyl alcohol with a 1,3,5-triethynylbenzene cross-linker followed by hydrolytic deprotection/detemplating. Deprotection not only liberates reactive CH=O and CH2OH groups in the networks but also modifies the texture of the networks towards higher microporosity and higher specific surface area. The final networks with CH=O and CH2OH groups attached directly to the polyene main chains of the networks have a specific surface area from 400 to 800 m2/g and contain functional groups in a high amount, up to 9.6 mmol/g. The CH=O and CH2OH groups in the networks serve as active centres for the reversible capture of CO2 and water vapour. The water vapour capture capacities of the networks (up to 445 mg/g at 297 K) are among the highest values reported for porous polymers, making these materials promising for cyclic water harvesting from the air. Covalent modification of the networks with (R)-(+)-3-aminopyrrolidine and (S)-(+)-2-methylbutyric acid enables the preparation of porous chiral networks and shows networks with CH=O and CH2OH groups as reactive supports suitable for the anchoring of various functional molecules.

Microporous Hyper-Cross-Linked Polymers with High and Tuneable Content of Pyridine Units: Synthesis and Application for Reversible Sorption of Water and Carbon Dioxide.

New hyper-cross-linked porous organic polymers (POPs) with a high content of pyridine segments (7.86 mmol pyridine g-1 ), and a micro/mesoporous texture are reported. The networks are achieved by the chain-growth homopolymerization of 2,6- and 3,5-diethynylpyridines. The pyridine segments form links interconnecting the polyacetylene main chains in these networks. The content of pyridine segments in the networks can be tuned by copolymerizing diethynylpyridines with 1,3-diethynylbenzene. The pyridine rings in the networks serve as base and hydrophilic centers for the sorption of CO2 and water. The homopolymer pyridine networks are highly efficient in the low-pressure adsorption/desorption of CO2 . This sorption mode is promising for the postcombustion removal of CO2 from the fuel gas. The poly(3,5-diethynylpyridine) network exhibits high efficiency in capturing and releasing water vapor (determined capacity 376 mg g-1 at 298 K and relative humidity (RH) = 90% is one of the highest values reported for POPs) and is a promising material for the cyclic water harvesting from air. The reported networks are characterized by 13 C cross-polarization magic angle spinning NMR, thermogravimetric analysis, and N2 adsorption/desorption and their efficiency in CO2 and H2 O capturing is discussed in relation to the content and type of incorporated pyridine segments.

Conformation in Ultrathin Polymer Brush Coatings Resolved by Infrared Nanoscopy.

Polymer brush coatings are effective in preventing blood coagulation or bacterial attachment, but their chain conformation, while vital for this effect, was never characterized in high spatial resolution. Here, we report mid-infrared spectroscopic nanoscopy studies of few-nanometer-thin poly(ethylene oxide) (PEO) films which reveal marked spectral variations along the surface at a length scale smaller than 100 nm and originating only from the physical conformation of the chains. The conformation and average orientation of the polymer chains in the layer is extracted from the spectra with the aid of theoretic modeling, confirming the spontaneous formation of a crystalline phase. This result suggests spectroscopic nanoscopy as a powerful new tool to characterize polymer brush coatings.