Summary: Starting in the 1960s, several kinds of photodeformable polymers have been developed, such as monolayers, polymer gels, solid films and liquid‐crystalline elastomers with different photodeformation mechanisms. This field evolved slowly until recently when significant achievements have been made. Most recently, Lendlein and co‐workers have put forward another new concept – using photo‐crosslinking to prepare deformable polymers with various pre‐determined shapes (Nature 2005 , 434, 879). This highlight gives a general introduction into photodeformable polymers and brings forth future challenges.
A polymer film doped with SCAA molecules where (a) is the permanent shape, (b) is the temporary shape and (c) is the recovered shape. 相似文献
Core‐shell type microspheres with fluorescent dansyl groups at random sites in crosslinked poly(N‐isopropylacrylamide) (PNIPAM) shell chains and core‐hair type microspheres with dansyl groups at terminal sites of PNIPAM hair chains graft‐polymerized with living‐radical mechanism were prepared. Fluorescent spectra indicating the microenvironments of dansyl groups attached to the microspheres and their dependences on temperature and solvent compositions were compared to those of dansyl groups in PNIPAM bulk gels and in free solutions. Fluorescence peak wavelength of dansyl groups in the core‐shell type microspheres showed an extraordinary blue shift in water, suggesting that dansyl groups are incorporated in the semi‐interpenetrating polymer network (SIPN) region of the core‐shell boundary. This is supported by a confocal laser‐scanning fluorescence microscope (CLFM) image of a single particle for the core‐shell type microsphere. Dansyl groups at the chain ends of PNIPAN hairs of the core‐hair type microspheres in water are also located on the surface of hydrophobic cores.
The orientation developed in biaxially stretched sPS (BoSPS) films before and after crystallization is studied using XRD and FT‐IR. On BoSPS films, thermal treatment induces crystallization into the trans‐planar α‐crystalline phase and a “planar” crystalline phase orientation is observed. In contrast, solvent treatments on BoSPS films induce crystallization into the helical δ‐crystalline phase, representing the first example of a polymeric framework that is able to absorb low‐molecular‐mass guest molecules from water and air at low activities and that is promising for applications in chemical separation or water purification applications; in this case a high degree of a//c// “uniplanar” crystalline phase orientation is observed.
The selective localization of carbon nanotubes (CNTs) in an immiscible polymer blend has attracted much attention. If the two component polymers could react with each other, do selectively located CNTs affect those reactions? Here, an immiscible polyester blend based on polycarbonate/poly(trimethylene terephthalate) (PC/PTT) is studied. CNTs introduced during melt mixing are selectively located in the PTT phase and on the phase interface during the middle stage of melt mixing. The interface‐located CNTs can act as additional substrate to catalyze or even participate in the transesterification themselves, homogenizing the phase morphology of the matrix blend. The degree of randomness of the composite systems is increased, accompanied by a reduced number‐average length of the copolymer sequences.
Summary: Biaxial side‐on cholesteric copolysiloxanes with laterally attached mesogenic groups were investigated in mixtures with a low molar mass liquid crystal. While mixtures with a low concentration of the polymer exhibit the conventional fingerprint texture, for concentrations above about 60 mol‐% characteristic irregularities appear in the cholesteric structure that are obviously due to phase biaxiality. Besides the absence of pseudo‐isotropic lines, irregular patterns perpendicular to the helix axis emerge and the periodic distance of regions with similar optical properties along the helix axis is strongly disturbed. This suggests that the photonic band gap width of a uniaxial cholesteric phase becomes strongly affected when a phase transformation into a biaxial cholesteric phase occurs.
Cholesteric fingerprint texture of a mixture of uniaxial nematic monomer and biaxial cholesteric polymer. 相似文献
A hyperbranched polyethylene (HBPE) is employed herein for noncovalent nonspecific functionalization and solubilization of multi‐walled carbon nanotubes (MWCNTs) in organic solvents. Though constructed solely from ethylene without any specific functionality, this unique hyperbranched polymer has been found to effectively solubilize MWCNTs at surprisingly high concentrations (up to 1 235 mg · L?1) in organic solvents such as chloroform and THF. These solubilities are comparable to and even better than the reported best values obtained through noncovalent specific functionalization with conjugated polymers capable of forming specific π‐π interaction with nanotubes in organic solvents. TEM and XRD results confirm that the nanotubes are completely exfoliated and debundled/de‐entangled upon functionalization with HBPE.
Summary: Copolymerization of 1‐hexene with a symmetrical diene, namely 2,5‐norbornadiene was studied using four different metallocene catalysts. Copolymerization was found to occur exclusively through one of the two equally reactive endocyclic double bonds with all the four catalysts. Copolymerization results in low molecular weight oligomers with the number average molecular weight ( ) varying from 1 000–3 000. End group analysis of the co‐oligomers revealed that the β‐hydrogen transfer after 2,1 insertion also occurs in the presence of highly regiospecific catalysts. The regio errors were also found to depend on various reaction parameters such as polymerization time, Al/Zr mol ratio, metallocene concentration and polymerization temperature.
Plots of variation in end groups and NBD incorporation with time. 相似文献
Thermosensitive hollow capsules were successfully fabricated by the layer‐by‐layer deposition onto colloid particles of oppositely charged diblock copolymers each containing a poly(N‐isoproprylacrylamide) (PNIPAM) block and by the subsequent decomposition of the core. The multilayer growth was characterized by electrophoresis and single particle light scattering. By combining confocal microscopy observation and FRAP measurements, we showed that the morphology and the permeability of the capsules change upon heating in aqueous solution. The decrease of size accompanied by a decrease of the permeability with increasing temperature was attributed to structural rearrangements in the shell. However, this process is only partially reversible upon cooling, limiting the thermoresponsive behavior of the capsules.
CLSM images of hollow capsules in presence of 6‐carboxyfluorescein (left) and fluorescein‐labeled dextran (right). 相似文献
A synthetic route that allows modification of 1‐vinyl‐2‐pyrrolidone with an alcohol or thiol group in its 3‐position in a one‐pot reaction without using protecting groups is described. The strategy used to achieve this goal is the reaction of the carboxamide anion of 1‐vinyl‐2‐pyrrolidone with cyclic precursors of these functionalities. It is furthermore shown that VP‐monomers functionalized with OH groups are suitable for the preparation of the corresponding copolymers with pure VP. As a second application of the new compounds, we also describe the synthesis of the first asymmetric crosslinker based on VP.
This paper reports the preparation of inclusion complexes of amylose with synthetic polymers by means of enzymatic polymerization of α‐D ‐glucose 1‐phosphate monomer (Glc‐1‐P). The synthetic polymers, employed as the guests, are poly(ε‐caprolactone), poly(δ‐valerolactone), and poly(ester‐ether), containing ester groups in the main chains. The formation of the inclusion complexes was carried out by the enzymatic polymerization of Glc‐1‐P catalyzed by phosphorylase in the presence of the guest polymers.
Novel polyureas are synthesized from lysinyl residues. The polyurea thus prepared yields a durable self‐standing membrane that can be converted into a molecular recognition material by using Z‐D ‐Glu or Z‐L ‐Glu as a print molecule. The Z‐D ‐Glu molecularly imprinted membrane adsorbes the D ‐isomer of Glu in preference to the corresponding L ‐Glu and vice versa. Even though the polyurea consists of L ‐lysinyl residues, both Z‐D ‐Glu and Z‐L ‐Glu work as print molecules to construct molecular (chiral) recognition sites in the membrane. Those molecularly imprinted membranes show chiral separation abilities when a concentration gradient or an applied potential difference is applied as a driving force for membrane transport.
Summary: “Swiss‐cheese” polyelectrolyte gels, i.e., gels containing isolated voids filled with water were synthesized and studied. The gels were obtained by three‐dimensional copolymerization of neutral and charged monomers in the presence of oil/water emulsion stabilized by ionic surfactant. After removal of the surfactant and droplets of oil from the gel, the latter contains voids surrounded with charged swollen polymer network. Experiments were performed with slightly cross‐linked gels of copolymers of sodium‐2‐acrylamide‐2‐methyl‐1‐propanesulfonate with acrylamide. The gel containing voids absorbs much more anionic dyes than the control gel with the same chemical composition of the network obtained in homogeneous solution. This effect is due to strongly inhomogeneous distribution of the low molecular weight anions between the voids and the anionic matrix of the gel. The study of diffusion of the dyes in the gels with and without voids and of the kinetics of their swelling and collapse shows that the voids in the gel are isolated.
Optical micrograph of polyelectrolyte gel with embedded emulsion droplets. 相似文献
Alternating copolymers of maleimides containing pyrenyl and alkynylpyrenyl moieties with isobutene (IB) were synthesized as a new class of heat‐resistant and fluorescent polymers. N‐(1‐Pyrenyl)maleimide (1) and N‐[4‐(1‐pyrenylethynyl)phenyl]maleimide (2) were copolymerized with IB in the presence and absence of N‐methylmaleimide (3) . The obtained maleimide/IB copolymers showed excellent thermal stability and high glass transition temperatures, and were soluble in common organic solvents. The copolymers including the alkynylpyrenyl fluorophore emitted strong fluorescence with a high quantum efficiency (Φ = 0.83) even in the presence of air and upon heating. Solid‐state fluorescence in transparent films was also investigated.
Summary: Gas‐phase assisted surface polymerization (GASP) of methyl methacrylate (MMA) and styrene (St) was investigated with Fe‐based radical initiating systems, FeCl2/2,2′‐bipyridine (Bpy)/methyl α‐bromophenylacetate (MBPA), etc. GASP with these initiating systems proceeded to produce corresponding polymers on substrate surfaces. The resulting PMMA had very high PDI values, suggesting an uncontrolled reaction. In an attempt to control the GASP, polymerization with a simple initiating system, Fe(0)/MBPA, was examined on Fe(0)‐metal surfaces, resulting in significant polymerization activity to produce high‐molecular‐weight PMMA. The results of time‐course tests on GASP of MMA and St suggested that a change had taken place to produce physically controlled propagation sites on the Fe(0) powder surfaces.
GASP schemes with a simple initiating system Fe(0)/MBPA. 相似文献
Novel reactive polymers with condensed benzopinacol moieties in the main chain were synthesized and their acid‐catalyzed pinacol rearrangement in the polymer backbone proceeded to afford poly(benzopinacolone)s quantitatively. Since the pinacol rearrangement shows an intramolecular mechanism, no crossover between the polymer chains was observed through the rearrangement. Although the number‐averaged molecular weights and their distributions were not changed, the optical and thermal properties of the poly(benzopinacolone)s were completely different from the parent poly(benzopinacolone)s.
Summary: Cylindrical brushes with poly(L ‐lysine) and poly(L ‐glutamate) side chains were prepared by “grafting through” and “grafting from” techniques. Grafting from is shown to be more successful for the synthesis of cylindrical brushes with high molar mass main and side chains.
AFM height image of polypeptide brushes with protected polylysine side chains spin‐cast from HFIP solution. 相似文献
As part of a strategy to explore highly functionalized macromolecular semiconductors, a series of highly substituted twelve‐armed macromolecules F1CzTr‐F3CzTr consisting of truxene, 9‐phenylcarbazole and oligofluorene units were synthesized. To accomplish the synthesis of twelve‐armed targets, a high yield microwave enhanced synthesis method for direct twelve‐fold Suzuki couplings was developed. The resulting materials exhibited high purity and good monodispersity (PDI 1.01–1.03). The molecular weight of the compound F3CzTr achieved 14 266 g · mol?1, representing one of the largest well‐defined starburst conjugated molecules. The thermal, photophysical and electrochemical properties were investigated.
Summary: Polymer blend nanocomposites containing linear low density polyethylene (LLDPE), nylon 6 and organoclays were prepared by melt mixing, and their morphologies and structures were examined with a field emission scanning electron microscope (FE‐SEM) and an X‐ray diffractometer (XRD). The size of phase‐separated domains decreased considerably with increasing content of organoclay. The d‐spacing of organoclay in the nanocomposites was increased from about 18.6 to over 28 Å. This effect was highly dependent on nylon 6 contents because nylon 6 is more polar and shows higher affinity to the organoclays compared to LLDPE.
Summary: Stable free‐radical copolymerizations (SFRP) of styrene with N‐acryloyl morpholine (AMo), 2‐ethoxyethyl acrylate (EOEA) and isobornyl acrylate (iBoA), respectively, were carried out under control of the stable nitroxide radical 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl (OH‐TEMPO). The polymerizations were initiated by a polystyrene macroinitiator (PS‐MI). No accelerating agents were used. In contrast to the experiences made with methacrylates there was no decrease in the polymerization rates up to 50 mol‐% of AMo or EOEA in the monomer mixture. This behavior was ascribed to a compensation of the lack of thermal initiation by the high propagation rate constants of the acrylates. The produced AB diblock polymers were successfully employed in block extension reactions in styrene yielding ABA triblock polymers. Copolymerization reactivity ratios (r‐values) and glass transition temperatures have been estimated.
