Summary: The synthesis, morphology, and photophysical properties of PF‐b‐PAA with different coil lengths in dilute solutions of dichloromethane/methanol are reported. A tape‐like lamellar morphology is observed at a short coil length of PF‐b‐PAA. As the coil length increases, a large compound micelle, sphere, or vesicle is observed with different methanol contents because of the enhancement of the PAA swelling with methanol and the interfacial tension between the PF core and the PAA corona. Upon further increase of the coil length, an inverted morphology of a sphere or rod with a PF corona and PAA core is first observed but the core/corona is then reversed at a high methanol content as a result of the enhanced solubility of PAA. The morphological transformation leads to a significant variation in optical absorption or fluorescence characteristics because of the possible H‐aggregate formation.
Some of the various morphologies observed upon varying the coil length and the selective solvent content. 相似文献
Ferrocenylmethyl methacrylate (FMMA) is one of the very few metallocene‐based monomers that are promising candidates for truly living anionic polymerization. Nevertheless, FMMA homopolymers with a narrow polydispersity, or block copolymerization studies that result in satisfying blocking efficiencies, are unknown so far. Here we describe a procedure that leads to highly regular FMMA‐based polymers for the first time, characterized by polydispersity indices (PDI) of less that 1.05 and very high blocking efficiencies (>95%) in sequential copolymerization with styrene. Some of the obtained poly[styrene‐block‐(ferrocenylmethyl methacrylate)]s show unusual microphase morphologies, presumably the consequence of high Tgs causing ‘frustrated’ non‐equilibrium states.
Novel luminescent electrospun (ES) fibers have been successfully prepared from a conjugated rod–coil block copolymer, poly[2,7‐(9,9‐dihexylfluorene)]‐block‐poly(methyl methacrylate) (PF‐b‐PMMA) using a single‐capillary spinneret. Experiment results indicate that PF‐b‐PMMA ES fibers prepared from THF, THF/DMF (50/50), and DMF contain PF block aggregated structures of dot‐like (5–10 nm), line‐like (10–20 nm), and ellipse‐like structure (25–50 nm), respectively. Such variation of aggregation size leads to a red‐shift of the absorption or luminescence spectra. In addition, the fiber diameters decrease upon enhancing the DMF content. The present study demonstrates that blue light‐emitting ES fibers are successfully prepared from conjugated rod–coil diblock copolymers and their aggregate morphology and photophysical properties could be tuned through use of selective solvent.
A series of well defined polyethylene-b-polystyrene diblock copolymers (ExSyz, where x and y represent the composition in weight % and z the molecular weight in Kg/mol) has been synthesized in a wide composition range by sequential anionic polymerization. The molecular weight of the PE block was kept constant. A fractionated crystallization behavior was observed for the PE block within E26S74105 (PE cylinders) and E11S89244 (PE spheres). When the PE blocks form a continuous or percolated phase (PE, E79S2141 and E53S4751), a “classic” self-nucleation behavior (where the usual three self-nucleation domains are obtained) was observed. When the PE block is located within isolated microphases (having dimensions on the nanometer scale) and a fractionated crystallization was detected (E26S74105 and E11S89244), the fraction of crystals formed at higher temperatures exhibits a “classic” self-nucleation behavior, while those crystals that crystallized at the largest supercooling (lower exotherms) can only be self-nucleated at lower temperatures where annealing of unmolten material has already started. An unusual fractionated crystallization behavior for isolated, spherical PE microphases (E11S89244) is reported. 相似文献
Summary: PE‐block‐PS and P(E‐co‐P)‐block‐PS block copolymers were synthesised via sequential monomer addition during homogeneous polymerisation on various phenoxyimine catalysts. One phenoxyimine catalyst was tailored to produce high molecular weight block copolymers containing both, polyolefin and polystyrene segments. According to chromatographic analysis and TEM morphology studies, blends of block copolymers and PE homopolymers [or P(E‐co‐P), respectively] were formed. The direct olefin/styrene block copolymer synthesis on phenoxyimine catalysts represents an attractive, new one‐pot route to styrenic block copolymers which are commercially prepared by anionic styrene/diene block copolymerisation followed by hydrogenation.
A PFS/PLA block copolymer was studied to probe the effect of strong surface interactions on pattern formation in PFS block copolymer thin films. Successful synthesis of PFS‐b‐PLA was demonstrated. Thin films of these polymers show phase separation to form PFS microdomains in a PLA matrix, and ultrathin films (<5 nm) formed SINPATs on silicon and mica. The SINPATs consisted of strongly surface‐adsorbed PLA blocks on top of which the PFS blocks dewetted into sphere‐like features. The lateral spacing between these features was regular, and was typically much larger than the length scale associated with regular block copolymer phase separation.
The morphology transitions in AB diblock and ABA triblock copolymers confined between flat and curved surfaces were investigated by MC simulations. Upon variation of the extent of frustration between thickness d and bulk lamellae period L0, parallel and vertical or distorted vertical lamellar structures appear in both flat and curved confinements. With increasing curvature, the compatibility of d and L0 becomes more perturbed so that perfectly parallel lamellae are formed with increasing difficulty. Owing to the smaller L0 of ABA as compared to AB, the transformation frequency of the incompatible region of d/L0(ABA) is more notable for ABA and the corresponding transformation period is larger than that of AB.
Summary: Amphiphilic triblock copolymers (PEOx‐b‐PDMSy‐b‐PEOx) with different block lengths were synthesized and multi‐morphological complex crew‐cut, star‐like, and short‐chain aggregates were prepared by self‐assembly of the given copolymers. The morphologies and dimensions of the aggregates can be well controlled by variation of the preparation conditions. TEM, SEM, FFR‐TEM, and LLS studies show the resulting morphologies range from LCMs, unilamellar or multilayer vesicles, LCVs, porous spheres to nanorods.
TEM images of the vesicles formed from PEO‐b‐PDMS‐b‐PEO. 相似文献
A rod‐coil block copolymer consisting of poly(3‐hexylthiophene) (P3HT) and poly(N‐vinylcarbazole) (PVK) ( P3HT‐ b ‐PVK ) in a single molecular architecture is prepared as the first example for WOLEDs. By obtaining the phase separated domains in thin film of the resulting block copolymer, it is possible to suppress energy transfer from PVK as wide bandgap units to P3HT as low bandgap blocks, yielding dual emissions for white electroluminescence with CIE coordination of (0.34, 0.33).
Summary: We report the multiple morphologies and their transformation of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) in low‐alkanol solvents. In order to improve the solubility of polystyrene block in alcohol solvents, the solution of block copolymer sample was treated at a higher temperature, and then the influence of rate of decreasing temperature on multiple morphologies (including spheres, rods, vesicles, porous vesicles, large compound vesicles, and large compound micelles) was observed. The transformation of spheres to rods, to tyre‐shaped large compound micelles, and to sphere‐shaped large compound micelles was also realized. The formation mechanisms of the multiple morphologies and their transformation are discussed briefly.
Aggregates of PS‐P4VP formed in butanol by quenching from 110 °C to room temperature. 相似文献
The effect of casting solvent on the morphology of sulfonated polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (SSEBS) was investigated using transmission electron microscopy and small‐angle X‐ray scattering. Proton conductivities and methanol permeabilities were measured and the related impact on morphological changes is discussed. SSEBS is transformed from a well‐ordered lamellar to a disordered structure as the concentration of MeOH in MeOH/THF mixtures increases. 相似文献
Poly(glycidyl methacrylate) (PGMA) was synthesized by the RAFT method in the presence of 2‐cyanoprop‐2‐yl dithiobenzoate (CPDB) chain transfer agent using different [GMA]/[CPDB] molar ratios. The living radical polymerization resulted in controlled molecular weights and narrow polydispersity indices (PDI) of ≈1.1. The polymerization of pentafluorostyrene (PFS) with PGMA as the macro‐RAFT agent yielded narrow PDIs of ≤1.2 at 60 °C and ≤1.5 at 80 °C. The epoxy groups of the PGMA block were hydrolyzed to obtain novel amphiphilic copolymer, poly(glyceryl methacrylate)‐block‐poly(pentafluorostyrene) [PGMA(OH)‐b‐PPFS]. The PGMA epoxy group hydrolysis was confirmed by 1H NMR and FTIR spectroscopy. DSC investigation revealed that the PGMA‐b‐PPFS polymer was amorphous while the PGMA(OH)‐b‐PPFS displayed a high degree of crystallinity.
The synthesis of poly(N‐vinylcarbazole)‐based block copolymers functionalized with rhenium diimine complexes or pendant terpyridine ligands is reported. The copolymers are synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization, and they exhibit interesting morphological properties as a result of the phase separation between different blocks. The rhenium complex polymer block may function as a photosensitizer, while the terpyridine‐containing polymer block can be used as the template for nanofabrication by selective deposition of zinc complexes.
Summary: In a low‐molecular‐weight polyethylene‐block‐poly(ethylene oxide) (PE‐b‐PEO) diblock copolymer, two pathway‐dependent melting processes were observed: Upon slow heating, the PE lamellar crystals melted at ≈97 °C into a disordered state. However, when the temperature rapidly jumped to above the melting point (e.g., 100 °C), the PE lamellar crystals transformed directly into an ordered lamellar melt, followed by an isothermal conversion into a disordered melt. This isothermal order‐to‐disorder transition was explained by superheating of the PE crystals using a G‐T diagram.
A schematic G‐T diagram explaining the pathway‐dependent double melting for a crystalline polyethylene‐block‐poly(ethylene oxide) copolymer. 相似文献
We report the synthesis of a series of block copolymers consisting of a rod‐like semiconducting poly(2,5‐di(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene) (DEH‐PPV) block and a flexible poly(lactic acid) (PLA) block that can be selectively degraded under mild conditions. Such selectively degradable block copolymers are designed as self‐assembling templates for bulk heterojunction donor–acceptor layers in organic solar cells. A lamellar microphase‐separated domain structure was identified for block copolymers with PLA volume fractions between 29 and 79% in bulk and thin films using SAXS, TEM, and AFM. Depending on the ratio of the two blocks we find either lamellae oriented parallel or perpendicular to the substrate in thin films.
Summary: Amphiphilic diblock copolymers consisting of a hydrophilic block, poly(acrylic acid), and a hydrophobic block, polystyrene, were synthesized by direct nitroxide‐mediated polymerization using the PS block as a macro‐initiator for the first time. Several techniques were used to characterize the amphiphilic block copolymers (size exclusion chromatography, NMR spectroscopy). The proposed method can lead to samples with a broad range of composition and molar mass. Preliminary studies of their self‐assembly in aqueous medium using fluorescence spectroscopy and small‐angle neutron scattering are presented.
Schematic of the formation of the PS‐b‐PAA block copolymers and their micellization in aqueous media. 相似文献
Summary: Tetraaniline‐block‐poly(L ‐lactide) diblock oligomers are synthesized via ring‐opening polymerization. The diblock oligomers cast from an L ‐lactide selective solvent (chloroform) show spherical aggregates for the leucoemeraldine state, and ring‐like structures that are composed of much smaller spherical aggregates for the emeraldine state. The formation mechanisms of the two different surface morphologies are discussed in detail.
Surface morphology changes induced by oxidation of the aniline segment of tetraaniline‐block‐poly(L ‐lactate) and drying effects. 相似文献
The step‐wise solution self‐assembly of double crystalline organometallic poly(ferrocenyldimethylsilane)‐block‐poly(2‐iso‐propyl‐2‐oxazoline) (PFDMS‐b‐PiPrOx) diblock copolymers is demonstrated. Two block copolymers are obtained by copper‐catalyzed azide‐alkyne cycloaddition (CuAAC), featuring PFDMS/PiPrOx weight fractions of 46/54 (PFDMS30‐b‐PiPrOx75) and 30/70 (PFDMS30‐b‐PiPrOx155). Nonsolvent induced crystallization of PFDMS in acetone leads in both cases to cylindrical micelles with a PFDMS core. Afterward, the structures are transferred into water for sequential temperature‐induced crystallization of the PiPrOx corona, leading to hierarchical double crystalline superstructures, which are investigated using scanning electron microscopy, wide angle X‐ray scattering, and differential scanning calorimetry.
