We report syntheses of phenylene‐, biphenylene‐, and terphenylene‐layered polymers with a xanthene scaffold by the modified Suzuki‐Miyaura coupling reaction. Their optical properties were studied in detail. The polymer end‐capped by nitrobenzene units, which act as fluorescence quenchers, exhibited the photo‐excited energy transfer from the layered oligophenylenes to the terminal units.
Double helical microropes of polyvinylpyrrolidone (PVP) with diameters of less than 10 µm and lengths of up to 5 cm were fabricated using a new electrospinning technique. In contrast to the typical electrospinning set‐up, a negatively charged rotating collector tip was used in this work, so that the two jets from two positively charged spinnerets were induced to two bundles that met at the rotating collector tip, leading to the formation of microropes. The pitch of microropes could be monitored by simply adjusting the distance between the two spinnerets.
The Lewis acid B(C6F5)3 in combination with hydrosilanes exhibits remarkable activity in the oligomerization of sulfone‐ and phosphonate‐based monomers. This process opens new routes to high‐tech silicone‐based materials, i.e., thermoplastic elastomers and heat‐resistant polysiloxanes.
Well‐controlled radical polymerization of methyl methacrylate can be achieved by in situ photochemical generation of copper (I) complex from air‐stable copper (II) species without using any reducing agent at room temperature. The living character of this polymerization was confirmed by both the linear tendency of molecular weight evolution with conversion and a chain extension experiment.
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.
Communication: Phenoxycarbonyloxymethyl ethylene carbonate 4 was synthesized from glycerol carbonate and phenyl chloroformate. Polyurethanes with pendant hydroxyl groups were obtained from polycondensation reactions of this AA* monomer with diamines. These polymers contain primary as well as secondary hydroxyl groups. The obtained polyurethanes are amorphous materials. The glass transition temperature decreases with increasing number of methylene groups between the urethane groups.
As the number of methylene groups increases between the urethane groups, the glass transition temperature of the polymer decreases. 相似文献
Poly(dimethylsiloxane) copolymers were synthesized directly from AA/BB monomers employing a CuAAC reaction (click chemistry) in a polyaddition approach. Using organic dialkynes and oligo(siloxane)s end‐functionalized with azide moieties it was possible to obtain siloxane‐based copolymers with TPE properties by click chemistry for the first time. As seen from DSC experiments, properties were strongly dependent on the incorporated organic comonomer.
This communication reports a strategy for scale‐up of an in situ polymerization technique for polyolefin‐based nanocomposites preparation, taking layered silicate (clay) and multi‐walled carbon nanotubes (MWCNTs) as examples of nanofillers. The strategy is realized by transforming the nanofillers into granular “nanosupports” for Ziegler‐Natta catalysts. With a catalyst to polymer replication effect on particle morphology, the in situ prepared nanocomposites are of controlled granular particle morphology. With the polymer particle morphology controlled, the in situ polymerization technique becomes suitable for industrial olefin polymerization processes for mass production of polyolefin nanocomposites.
Summary: Amphiphilic graft polyphosphazenes (EtTrp/PNIPAm‐PPP) with different mole ratios of hydrophobic groups to hydrophilic segments were synthesized by ring‐opening polymerization and subsequent substitution reactions. The self‐assembly behavior of these graft copolymers was studied in detail by TEM, SEM, CLSM, and AFM. Depending on the copolymer composition and common organic solvent employed in dialysis process, supramolecular aggregates ranging from network, nanospheres, high‐genus particles to macrophage‐like aggregates were produced with graft copolymers.
Summary: We report a study of thermoreversible gelation of polybenzimidazole (PBI) in phosphoric acid (PA). The PBI gel in PA exhibits fibrillar network morphology and reversible first order phase transition. The gelation rate is measured by the tube tilting method and found to depend both upon gelation concentration and gelation temperature. The UV‐vis study demonstrates that the gelation process is a two‐step process: conformational transformation and aggregation which produces crystallites for gel formation. The WAXS study supports the presence of crystallites in the gel. The PA doping level of the membrane increases significantly because of gelation.
Thermoreversible gelation of polybenzimidazole in phosphoric acid and the membrane produced from the gel. 相似文献
Detection of the adduct radical by ESR spectroscopy and after‐effect ESR measurements of the adduct radical concentrations in the photosensitized polymerization of styrene (St) in the presence of dimers of α‐methylstyrene (MSD) and methyl methacrylate have revealed that the dominant mechanism of adduct radical loss changes from bimolecular termination to fragmentation as the temperature is increased beyond 90 °C for St/MSD.
