We report novel nanoporous polyimides formed from jungle‐gym‐type rigid polyimide gels by supercritical CO2 drying. By virtue of supercritical CO2 drying to avoid the collapse of nanostructure, porosity above 90 vol.‐% was achieved. We found a rich variety of nanoporous structures in the range of 50–800 nm such as crisp fragments, minute network, and highly‐connected beads. These characteristic structures were formed by the competitive progress of liquid‐liquid phase separation and crystallization induced due to the two chemical reactions of end‐crosslinking and thermal imidization during gelation.
Summary: This paper presents the structural influence of the Si H functionality on the physicochemical properties of polysilanes. New low‐temperature restructuring processes were discovered using thermal analysis (TGA, DSC). Photoluminescent (FL) and X‐ray photoelectron spectroscopy (XPS) measurements revealed the optoelectronic properties‐chemical structure relationship of the synthesized polymers.
Highly reactive Si H groups lead to restructuring of the main polysilane chain. 相似文献
The preparation of associative networks containing multi‐walled carbon nanotubes (MWCNTs) with covalently attached cyclodextrin (CD) rings and poly[(isobutylene)‐co‐(maleic anhydride)‐co‐(maleic acid‐(4‐tert‐butylphenyl)amide)] in water is described in this study. The synthesis of CD containing MWCNTs is realized by an amidation reaction of oxidized MWCNTs with propargylamine followed by a 1,3‐dipolar cycloaddition with CD‐azide. Dispersion behavior indicated the high stability of these networks. An increase in viscosity compared to a solution of pure polymer as a cause of network formation is observed. The addition of a CD‐decomposing enzyme (taka‐diastase from Aspergillus oryzae) let the network collapse and results in sedimentation of the modified MWCNTs.
Summary: We describe an interesting approach to the fabrication of wettability gradients from hydrophobicity to superhydrophobicity in low‐density polyethylene (LDPE) films by first forming high porosity surfaces and placing the specimens onto linear temperature gradients. While the polymer chosen for the study is non‐polar, its microporous layer provides sufficient superhydrophobicity. Lateral gradient heating of the layer results in partial melting of the polymer and correspondingly decreases porosity thus decreasing hydrophobicity.
Fully‐atomistic molecular dynamics (MD) simulations have been carried out to model helium transport through four different glassy polyimides. While the polymer matrices had been pre‐validated, specific parameters and combination rules were used here in order to describe helium‐helium and helium‐polymer interactions. Gas permeabilities are in very good agreement with experimental evidence. Two ways to decrease chain cohesion and improve gas transport were considered – the replacement of an ODPA by a bulky BCDA dianhydride, and the substitution of a site on an ODA diamine by a CF3. The fluorinated polyimide appears to be the most promising material with more heterogeneity in the void‐space distribution, the highest model permeability and fewer constraints from an experimental point of view.
A novel poly‐L ‐arginine group microcapsule was produced to investigate its nutritional function and pharmacological efficacy. The molecular weight of poly‐L ‐arginine is an important parameter for its membrane strength, but does not obviously affect its release property. Thus, poly‐L ‐arginine can be used as a kind of new membrane material in microcapsules, and it is expected to be used as an therapeutic and biodegradable drug carrier.
Influence of the molecular weight of poly‐L ‐arginine on membrane thickness. 相似文献
A series of selenophene oligomers incorporating conjugated fluorinated phenylene units have been synthesised as potential semiconductor materials for organic field‐effect transistors (OFETs). X‐ray crystallography shows that the molecules are held in close proximity by several short intermolecular contacts, making them ideal candidates for OFET applications.
Bimodal fiber meshes with fiber diameters differing by one order of magnitude, are electrospun in a simple one‐step process, using a standard single syringe electrospin setup. The nano‐ and microfiber meshes combine the benefits of nanofibers (cell adhesion, proliferation) with those of microfibers (open structure, large pore size) and are therefore interesting as scaffolds for cellular infiltration.
A direct access to photochromic polymeric vesicles was demonstrated via polymerization‐induced self‐assembly and reorganization (PISR). The resulting vesicles displayed interesting photochromic behaviors different from that of their free polymer chains in DMF, and the vesicles exhibited stronger fluorescence and excellent photostability due to confinement of conformational flexibility of the polymer chains in aggregates.
Summary: Magnetic nanoparticles have been prepared by a co‐precipitation method and modified with methacryloxypropyltrimethoxysilane. Magnetic molecularly imprinted polymer particles have been prepared by suspension polymerization in silicone oil. The particles possess a high affinity to the template molecules and are rapidly separated under a magnetic field.
Summary: The evolution of the photoinduced birefringence in thin films of narrow polymer fractions is studied and compared with the behavior of the non‐fractionated polymer. The Δnind value decreases by increasing the degree of polymerization ( ) within the oligomeric range but becomes independent of molecular weight starting from a of ≈70. Thermal pretreatment of the films results in higher photoinduced birefringence. The films show good stability of the photorecording.
Birefringence induced after 10 min, Δnind(600) and its growth rate at the same moment versus molecular weight. 相似文献
A triblock amphiphilic macrocycle consisting of a macrocyclic aromatic segment, a hydrophilic oligo(ethylene oxide) branch, and a hydrophobic alkyl dendron is successfully synthesized and characterized. The resulting cyclic amphiphile is observed to self‐assemble into hollow double‐layered capsules in aqueous solution, as confirmed by dynamic light scattering and cryogenic transmission electron microscopy investigations. The capsules are able to encapsulate hydrophobic guest molecules through aromatic interactions with high stability.
A reactivity study of the most important elementary steps (propagation, intermolecular degradative transfer, and re‐initiation) in free‐radical polymerization of acrylfuranic systems, furfuryl acrylate (FA), and furfuryl methacrylate (FM), using the frontier molecular orbital theory is described. A qualitative explanation of reactivity trends of these steps for both systems is given based on absolute values of the SOMO/HOMO gap. The small difference between values of kp for FA and FM compared to that found for MA and MMA ( ) is justified semi‐quantitatively by applying a formulation for the change of energy in the transition state using second‐order perturbation theory.
The identification and control of a critical stage of polyaniline “nanotube” self‐assembly is presented, namely the granular agglomeration or growth onto nanorod templates. When the synthesis pH is held above 2.5, smooth insulating nanorods exhibiting hydrogen bonding and containing phenazine structures are produced, while below pH 2.5, small 15–30 nm granular polyaniline nanoparticles appear to agglomerate onto the available nanorod surface, apparently improving conductivity of the resulting structures by three orders of magnitude. This finding affects both fundamental theories of polyaniline nanostructure self‐assembly and their practical applications.
The Michael reaction of chitosan with acrylic acid was carried out successfully, even in water alone as the reaction medium. As a consequence of its good solubility in water, the reaction product, N‐carboxyethylchitosan, showed excellent biodegradable properties with standard activated sludge.
