Search Results (44)

The interest in macromolecular alkoxysilyl-functionalized hybrids (self-assembling or nanostructured), which could be used as precursors in biomimetic silica precipitation and for the synthesis of hollow spherical silica particles, is growing. Nevertheless, reports on all-organosilicon systems for bioinspired silica precipitation are scarce. Therefore, a new kind of polyalkoxysilane macromonomer–linear polysilsesquioxane (LPSQ) of ladder-like backbone, functionalized in side chains with trimethoxysilyl groups (LPSQ-R-Si(OMe)₃), was designed following this approach. It was obtained by photoinitiated thiol-ene addition of 3-mercaptopropyltrimethoxysilane to the vinyl-functionalized polysilsesquioxane precursor, carried out in situ in tetraethoxysilane (TEOS). The mixture of LPSQ-R-Si(OMe)₃ and TEOS (co-monomers) was used in a sol–gel process conducted under acidic conditions (0.5 M HCl/NaCl) in the presence of Pluronic^® F-127 triblock copolymer as a template. LPSQ-R-Si(OMe)₃ played a key role for the formation of microparticles of a spherical shape that were formed under the applied conditions, while their size (as low as 3–4 µm) was controlled by the stirring rate. The hybrid materials were hydrophobic and showed good thermal and oxidative stability. Introduction of zinc acetate (Zn(OAc)₂) as an additive in the sol–gel process influenced the pH of the reaction medium, which resulted in structural reinforcement of the hybrid microparticles owing to more effective condensation of silanol groups and a relative increase of the content of SiO₂. The proposed method shows directions in designing the properties of hybrid materials and can be translated to other silicon–organic polymers and oligomers that could be used to produce hollow silica particles. The established role of various factors (macromonomer structure, pH, and stirring rate) allows for the modulation of particle morphology. Full article

As part of a systematic study on the structures of the mixed halide isothiocyanates, Sn^IIHal(NCS), their single crystals were grown and structurally characterized. For Hal = F (1), the SnClF structure type was confirmed, while with Hal = Cl (2), Br (3), and I (4), there are three isostructural compounds of a new structure type, and for Hal = Cl (5), there is a second modification of a third structure type. These structure types have been described with respect to the composition and coordination geometry of the first, second, and van der Waals crust coordination spheres and their dependence on the halogen size and thiocyanate binding modes. With respect to the first coordination spheres, all three structure types constitute one-dimensional coordination polymers. In 1, “ladder”-type double chains result from μ₃-bridging fluorine atoms, and in 2–4, single-chains built up from μ₂-halogen atoms are pairwise “zipper”-like interconnected via κ²NS-bridging NCS ligands, which manage the halogen-linked chain assembly in the double chains of 5. Based on the octet rule, short atom distances are interpreted in terms of 2c-2e and various (symmetrical, quasi-symmetrical, and asymmetrical) kinds of 3c-4e bonds. Weak contacts, the topology of which suggests the extension of the latter bonding concept, are identified as electron-deficient, bifurcated tetrel bonds. Full article

Helical ladder polymers attract attention because of their well-defined, one-handed helical ladder structures and unique properties, which differ from precursor polymers that have random-coil conformations. However, the synthesis of helical ladder polymers is difficult and inhibits their functions and applications. In this study, we reported the synthesis of amphiphilic optically active 2,2′-tethered binaphthyl-embedded helical ladder polymers carrying hydrophilic oligo (ethylene glycol) (OEG) as side chains through quantitative and chemoselective acid-promoted intramolecular cyclization of random-coil precursor polymers. The obtained helical ladder polymers exhibited dramatic circular dichroism (CD) and circularly polarized luminescence (CPL) enhancement. Moreover, we further established a circularly polarized fluorescence-energy transfer (CPF-ET) strategy in which the helical ladder polymers work as a donor, emitting circularly polarized fluorescence to excite an achiral fluorophore (coumarin-6) as the acceptor, producing green CPL with luminescence dissymmetry factor (2.5 × 10⁻⁴). Full article

Microporous soluble polymers attract great attention as materials for membrane gas separation, gas storage and transportation, as sorbents, supports for catalysts, and matrices for mixed matrix membranes. The key problems in the development of this area of polymer chemistry include the search for methods of controlling the porous structure parameters and ensuring the stability of their properties over time. In this connection, a fruitful approach is to introduce bulky and rigid, often framework carbocyclic moieties into the polymer backbones and side chains. This review discusses the effect of carbocyclic moieties on gas transport properties, BET surface area, and FFV of glassy polymers, such as polyacetylenes, polynorbornenes, polyimides, and ladder and partially ladder polymers. In the majority of cases, the incorporation of carbocyclic moieties makes it possible to controllably increase these three parameters. Carbocyclic moieties can also improve CO₂/gas separation selectivity, which is displayed for ladder polymers and polynorbornenes. Full article

Three new coordination polymers, {[M(nbpdc)(DMF)(H₂O)₂]·H₂O}_∞ (M = Co and Ni) and [Zn(nbpdc)(DMF)(H₂O)]_∞, were synthesized from 2-nitrobiphenyl-4,4′-dicarboxylate (nbpdc²⁻). The isomorphous Co(II) and Ni(II) compounds exhibited a two-dimensional coordination network in which the chains with single-water bridges and the chains with single-nbpdc²⁻ bridges intersected each other by sharing the metal ions. The coordination networks were connected with uncoordinated water molecules through hydrogen bonds. The rarely identified single-water-bridged coordination chain was reinforced by water-based intrachain hydrogen bonds. The single-water bridges mediated modest antiferromagnetic superexchange in both Co(II) and Ni(II) compounds and afforded a spin-canting structure for the Co(II) compound at low temperatures. Water molecules played a distinct structural role in the Zn(II) compound, which was a one-dimensional coordination polymer with single-nbpdc²⁻ bridges. Instead of bridging metal ions, each water molecule was coordinated to one metal ion and hydrogen-bonded to the coordination spheres of other two metal ions, resulting to an infinite ladderlike hydrogen-bonding motif. The ladders interlinked the nbpdc-bridged chains into a three-dimensional supramolecular architecture featuring the 5-conneted {4⁴.6⁴} net. Full article

Nanocomposite materials composed of an organic matrix and an inorganic nanofiller have been the subject of intense research in recent years. Indeed, the synergy between these two phases confers improved properties thanks to an increased surface–volume ratio, which reinforces the interactions between the particles and the polymer matrix. These interactions depend on many factors such as the shape, size and dispersion of the nanoobjects. Polysilsesquioxanes (PSQs) are a silicon polymer family that offers different sizes, shapes and structures and possesses ceramics properties (i.e., high thermal and/or oxidative resistance and high chain rigidity), thanks to the siloxane backbone. In this article, we propose to incorporate polymer-grafted ladder polysilsesquioxanes (LPSQs) as nanofillers in thermoplastic matrices. Chloride-functionalized LPSQs were synthesized from two different precursors and thoroughly characterized by ¹H, ¹³C and ²⁹Si NMR, as well as by SEC and WAXS. The well-defined LPSQ was then converted into an azide analog. The resulting hybrid material was functionalized with poly(ethylene glycol) (PEG) chains and incorporated into poly(ethylene oxide) or poly(methyl methacrylate) matrices. We found that the viscoelastic properties of the nanocomposite materials were impacted by plasticizing or the reinforcement effect depending on the grafted PEG chain length. Full article

Poly-CPDTBT, as typical low-band gap copolymers, have potential applications in organic bulk heterojunction solar cells. To have a clear picture of its excited-state processes, the first task is to understand their excited states, in particular, electronic character and relevant optical absorption. Herein, the low-lying singlet excited states of Poly-CPDTBT oligomers were investigated via Algebraic Diagrammatic Construction Second Order (ADC(2)) and time-dependent density functional theory (TDDFT) method with several functionals. Six CPDTBT_N (N = 1–6) oligomers were taken as prototypes to study their excited states in detail. The results provide interesting clues to extrapolate the photophysical properties of such polymers with potential applications in photovoltaic materials. The result provided by ωB97XD functional gives good agreement with the experiment result. The vertical excitation energies of the four lowest excited states decrease almost linearly with increasing polymerization degree (N) for CPDTBT_N (N = 1–6). The transition density analysis indicates that the local excitations (LE) and the short-distance charge transfer (CT) excitations between two adjacent CPDT and BT units are dominant for low-lying excited states for short oligomers. For the long-chain oligomers (trimer to hexamer), the transition density shows a ladder (or zigzag) pattern along the diagonal blocks at the planar geometry. For long oligomers, the whole chain is involved in the transitions, and the CT excitations only exist between two adjacent CPDT and BT units. The present work provides a valuable basis for understanding the excited-state processes of Poly-CPDTBT and other conjugated polymers that conduct solar energy conversions, which has great significance for the development of new solar cells. Full article

Structure and reversibility of cross-link junctions play pivotal roles in determining the nature of thermoreversible gelation and dynamic mechanical properties of the produced polymer networks. We attempt to theoretically explore new types of sol–gel transitions with mechanical sharpness by allowing cross-links to grow without upper bound. We consider thermoreversible gelation of the primary molecules R{A${}_f$} carrying the number f of low molecular weight functional groups (gelators) A. Gelators A are assumed to form supramolecular assemblies. Some examples are: telechelic polymers ($f=2$) carrying $\pi$–$\pi$ stacking benzene derivatives at their both ends, and trifunctional star molecules ($f=3$) bearing multiple hydrogen-bonding gelators. The sol–gel transition of the primary molecules becomes sharper with the cooperativity parameter of the stepwise linear growth of the cross-links. There is a polymerization transition (crossover without singularity) of the junctions in the postgel region after the gel point is passed. If the gelator A tends to form supramolecular rings competitively with linear chains, there is another phase transition in the deep postgel region where the average molecular weight of the rings becomes infinite (Bose–Einstein condensation of rings). As a typical example of binary cross-links where gelators A and B form mixed junctions, we specifically consider metal-coordinated binding of ligands A by metal ions B. Two types of multi-nuclear supramolecular complexes are studied: (i) linear stacking (ladder) of the sandwich A${}_2$B units, and (ii) linear train of egg-box A${}_4$B units. To find the strategy towards experimental realization of supramolecular cross-links, the average molecular weight, the gel fraction, the average length of the cross-link junctions are numerically calculated for all of these models as functions of the functionality f, the concentration of the solute molecules, and the temperature. Potential candidates for the realization of these new types of thermoreversible gelation are discussed. Full article

Ladder-like poly(methacryloxypropyl)-silsesquioxanes (LPMASQ) are photocurable Si-based gels characterized by a double-stranded structure that ensures superior thermal stability and mechanical properties than common organic polymers. In this work, these attractive features were exploited to produce, in combination with alumina nanoparticles (NPs), both unmodified and functionalized with methacryloxypropyl-trimethoxysilane (MPTMS), LPMASQ/Al₂O₃ composites displaying remarkable thermal conductivity. Additionally, we combined LPMASQ with polybutadiene (PB) to produce hybrid nanocomposites with the addition of functionalized Al₂O₃ NPs. The materials underwent thermal stability, structural, and morphological evaluations via thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), Fourier transform infrared spectroscopy (FTIR), and solid-state nuclear magnetic resonance (NMR). Both blending PB with LPMASQ and surface functionalization of nanoparticles proved to be effective strategies for incorporating a higher ceramic filler amount in the matrices, resulting in significant increases in thermal conductivity. Specifically, a 113.6% increase in comparison to the bare matrix was achieved at relatively low filler content (11.2 vol%) in the presence of 40 wt% LPMASQ. Results highlight the potential of ladder-like silsesquioxanes in the field of thermally conductive polymers and their applications in heat dissipation for flexible electronic devices. Full article

Ladder polymers with poly(diketopyrrolopyrrole) (DPP) moieties have recently attracted enormous interest for a large variety of opto-electronic applications. Since the rigidity of the backbone increases with ladderization, a strong influence on the self-organization of thin films is expected. We study the molecular orientation of DPP-based ladder polymers in about 50 nm thin films using polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS). Exemplarily, for one polymer, the orientation in thicker films is qualitatively investigated by infrared spectroscopy in transmission. Further, this method allows us to rule out the effects of a possible azimuthal ordering, which would affect the analysis of the orientation by PM-IRRAS. For all polymers, the long axis of the polymer backbone is preferentially oriented parallel to the substrate surface, pointing to a high degree of ordering. It is suggested that the choice of the side chains might be a promising way to tune for face-on and edge-on orientations. The exemplarily performed investigation of interface properties on substrates with different work functions suggests that the choice of the side chains has a minor effect on the interfacial electronic interface structure. Full article

The synthesis of ladder-type 9,9′-bifluorenylidene-based conjugated polymer is reported. Unlike the typical synthetic strategy, the new designed ladder-type conjugated polymer is achieved via tandem Suzuki polymerization/Heck cyclization reaction in one-pot. In the preparation process, Suzuki polymerization reaction occurred first and then the intramolecular Heck cyclization followed smoothly under the same catalyst Pd(PPh₃)₄. The model reaction proved that the introduction of iodine (I) for this tandem reaction can effectively control the sequential bond-forming process and inhibit the additional competitive side reactions. Thus, small-molecule model compounds could be obtained in high yields. The successes of the synthesized small molecule and polymer compounds indicate that the Pd-catalyzed tandem reaction may be an effective strategy for improving extended π-conjugated materials. Full article

In order to expand the range of materials that can be used in outer space and in development of small spacecraft, ladder polyphenylsilsesquioxanes with different molar weights and the Nb-siloxane composites based on them were studied. The properties of the polymer films were studied, including tests in an oxygen plasma flow. Both initial and filled ladder polymers feature extremely low erosion coefficients in the region of 10^–26 cm³/atom O at a high fluence of atomic oxygen of 1.0 × 10²¹ atom O/cm². Ladder polyphenylsilsesquioxane films irradiated with atomic oxygen (AO) retain their integrity, do not crack, and exhibit good optical properties, in particular, a high transmittance. The latter slightly decreases during AO exposure. The Nb-siloxane filling retains the AO resistance and slight decrease in optical transmission due to diffuse scattering on the formed Nb-[(SiO)_x] nanoparticles. Ladder polyphenylsilsesquioxanes demonstrate their suitability for creating protective, optically transparent coatings for small spacecraft that are resistant to the erosive effects of incoming oxygen plasma. Full article

This paper presents the results of studies on the pervaporation properties (for benzene/hexane mixtures) and gas permeability (for He, H₂, N₂, O₂, CO₂, CH₄, C₂H₆, and C₄H₁₀) of ladder-like polyphenylsesquioxanes (L-PPSQ) with improved physical and chemical properties. These polymers were obtained by condensation of cis-tetraphenylcyclotetrasiloxanetetraol in ammonia medium. The structure of L-PPSQ was fully confirmed by a combination of physicochemical analysis methods: ¹H, ²⁹Si NMR, IR spectroscopy, HPLC, powder XRD, and viscometry in solution. For the first time, a high molecular weight of the polymer (Mn = 238 kDa, Mw = 540 kDa) was achieved, which determines its improved mechanical properties and high potential for use in membrane separation. Using TGA and mechanical analysis methods, it was found that this polymer has high thermal (T_d^5% = 537 °C) and thermal-oxidative stability (T_d^5% = 587 °C) and good mechanical properties (Young’s module (E) = 1700 MPa, ultimate tensile stress (σ) = 44 MPa, elongation at break (ε) = 6%), which is important for making membranes workable under various conditions. The polymer showed a high separation factor for a mixture of 10% wt. benzene in n-hexane (126) at a benzene flow of 33 g/(m²h). Full article

We suggest a new method for postsynthesis modification of silicones containing silanol groups. It was found that trimethylborate is an effective catalyst for dehydrative condensation of silanol groups with the formation of ladder-like blocks. The utility of this approach was demonstrated on postsynthesis modification of poly-(block poly(dimethylsiloxane)-block ladder-like poly(phenylsiloxane)) and poly-(block poly((3,3′,3″-trifluoropropyl-methyl)siloxane)-block ladder-like poly(phenylsiloxane) with a combination of linear and ladder-like blocks having silanol groups. The postsynthesis modification leads to a 75% increase in tensile strength and 116% elongation on break in comparison with the starting polymer. Full article

The new heterometallic compounds, [{Cu(pn)₂}₂Ni(NCS)₆]_n·2nH₂O (1), [{Cu^II(trien)}₂Ni(NCS)₆Cu^I(NCS)]_n (2) and [Cu(tren)(NCS)]₄[Ni(NCS)₆] (3) (pn = 1,2-diaminopropane, trien = triethylenetetramine and tren = tris(2-aminoethylo)amine), were obtained and characterized by X-ray analysis, IR spectra, XAS and magnetic measurements. Compounds 1, 2 and 3 show the structural diversity of 2D, 1D and 0D compounds, respectively. Depending on the polyamine used, different coordination polyhedron for Cu(II) was found, i.e., distorted octahedral (1), square pyramidal (2) and trigonal bipyramidal (3), whereas coordination polyhedron for nickel(II) was always octahedral. It provides an approach for tailoring magnetic properties by proper selection of auxiliary ligands determining the topology. In 1, thiocyanate ligands form bridges between the copper and nickel ions, creating 2D layers of sql topology with weak ferromagnetic interactions. Compound 2 is a mixed-valence copper coordination polymer and shows the rare ladder topology of 1D chains decorated with [Cu^II(tren)]²⁺ antennas as the side chains attached to nickel(II). The ladder rails are formed by alternately arranged Ni(II) and Cu(I) ions connected by N2 thiocyanate anions and rungs made by N3 thiocyanate. For the Cu(I) ions, the tetrahedral thiocyanate environment mixed N/S donor atoms was found, confirming significant coordination spheres rearrangement occurring at the copper precursor together with the reduction in some Cu(II) to Cu(I). Such topology enables significant simplification of the magnetic properties modeling by assuming magnetic coupling inside {Ni^IICu^II₂} trinuclear units separated by diamagnetic [Cu(NCS)(SCN)₃]³⁻ linkers. Compound 3 shows three discrete mononuclear units connected by N-H…N and N-H…S hydrogen bonds. Analysis of XAS proves that the average ligand character and the covalency of the unoccupied metal d-based orbitals for copper(II) and nickel(II) increase in the following order: 1 → 2 → 3. In 1 and 2, a weak ferromagnetic coupling between copper(II) and nickel(II) was found, but in 2, additional and stronger antiferromagnetic interaction between copper(II) ions prevailed. Compound 3, as an ionic pair, shows, as expected, a spin-only magnetic moment. Full article