We have investigated the shape‐memory effects of uniaxially‐deformed, chiral, smectic C (SmC*) elastomers for two different types of crosslinker, namely, a hydroquinone‐type crosslinker and a rod‐like crosslinker. Mesogens tilt with decreasing temperature from the SmA phase to the SmC* phase in SmC* elastomers synthesized with the hydroquinone‐type crosslinker. As for SmC* elastomers with the rod‐like crosslinker, however, not mesogens but smectic layers are tilted in the smectic phases, because the crosslinker is sufficiently rigid to hinder mesogens from tilting. Because the shape change of such elastomers is coupled to the transformation of molecular alignment, SmC* elastomers synthesized with the hydroquinone‐type crosslinker elongate with increasing temperature in SmC* because of the decrease in molecular‐tilt angle, whereas those with the rod‐like crosslinker have an almost constant sample length in the temperature range of the SmC* phase, despite the rearrangement of the layer structure. Both types of elastomer exhibit a reversible shape change that corresponds to the reversible change in molecular alignment during a heating and cooling process, within successive phase transitions between the isotropic phase and the smectic C* phase.
Polymers with narrow molecular weight distributions and controlled architectures were generated by living ring‐opening metathesis polymerization of exo‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboximide. The dicarboximide units have been previously shown to exhibit biological activity, can selectively bind to the nucleic acid base adenine by hydrogen‐bonding, and are readily functionalizable. Block copolymers containing these moieties were generated, and underwent self‐assembly into nanoscale spherical aggregates, with surface localized molecular recognition motifs.
Summary: Stabilized nanoparticles functionalized with carboxy groups were synthesized directly from dextran and acrylic acid (AA), without using any organic solvent and surfactant. The composition and morphology of these dextran‐based nanoparticles, as well as the mechanism of this one‐pot synthesis, were also investigated in this paper. This approach is anticipated to be applicable to various water‐soluble polysaccharides to fabricate nanoparticles facilely.
Facile synthesis of stabilized nanoparticles functionalized with carboxy groups from dextran and AA. 相似文献
A novel synthetic method for the preparation of high‐molecular‐weight conjugated polymers is presented. It consists of the oxidation copolymerization of different arenes with triphenylamine. The structure of the copolymers was characterized by 1H and 13C NMR spectra. The copolymers have good solubility in common organic solvents and are thermally stable. Photoluminescence (PL) spectra (see Figure) showed that the color of emission depends on the type of arene units in the copolymer chain. Cyclic voltammetry (CV) measurements revealed electrochemical activity of the copolymers.
Time‐resolved synchrotron X‐ray and DSC experiments were applied to investigate the phase behaviour of poly(diethylene glycol p,p′‐bibenzoate), PDEB. The DSC results are indicative of the formation of a smectic mesophase, previously identified as a SmCA type, which can be easily quenched down to room temperature. However, the synchrotron results show that the SmCA phase undergoes some kind of ordering or transformation at temperatures below 110 °C. Moreover, the annealing of PDEB at temperatures above Tg for sufficiently long times leads to the formation of a highly ordered structure, although very thin crystals and low crystallinities are obtained.
Scattering profiles corresponding to sample PDEB85 in a melting experiment. 相似文献
Fluorene‐based single‐chain copolymers with a white light emitter consisting of a blue and an orange chromophore have been synthesized and their photophysical and electroluminescent properties are investigated. The experimental results suggest that only a relatively small fraction of the orange‐emitting units incorporated into the fluorene is needed to achieve efficient white light emission by controlled incomplete energy transfer. A device from a copolymer with 0.02% DDQ content showed the highest external quantum efficiency of 2.64% with a luminance efficiency of 4.06 cd · A?1 with CIE coordinates (0.28, 0.24). The EL emissions are extremely stable over a wide range of current densities.
The mesophase formation process of a main‐chain BB‐5(1‐Me) polyester in the supercooled isotropic‐liquid state has been studied using DSC, WAXD, and optical microscopy. The supercooled isotropic liquid follows two different SmCA formation processes. Above 85 °C, it forms the expected SmCA phase. Below, it yields a metastable SmA phase that displays a layer spacing almost twice the one of the SmCA phase. The SmA phase develops from a homogeneous nucleation followed by 3D growth and thereafter transforms to the SmCA phase. This two‐step SmCA formation involves a change in polymer chain configuration: first, the chains are folded in each two units to form the SmA phase and then they stretch to achieve the characteristic zigzag arrangement of the mesogens in the SmCA phase.
Summary: The synthesis and thermal behaviour of two new polyoxetanes with side chains having a dimer structure mesogen‐spacer‐mesogen and a long terminal alkyl group are reported. The two polymers differ in the chemical structure of the central spacer. The polyoxetanes have been obtained by cationic ring‐opening polymerisation of an appropriately substituted oxetane ring. Both polyoxetanes studied exhibit liquid crystalline properties showing a similar sequence of phases. DSC and synchrotron experiments indicate that a highly ordered phase with a probable orthorhombic packing is observed at low temperature. On heating, this phase melts into a mesophase with hexagonal order within the smectic layers, which, on further heating, is transformed into a disordered smectic mesophase.
Synchrotron X‐ray diffraction patterns of one of the poyoxetanes in a heating experiment. 相似文献
Time‐resolved wide‐angle X‐ray scattering (WAXS), as well as differential scanning calorimetry (DSC) and polarisation microscopy studies, were applied to investigate the structure and phase transitions of poly(heptamethylene p,p′‐bibenzoate). Temperature dependencies of several structural parameters were determined. Complete transformation from an isotropic melt to a smectic phase was suggested whereas the transition from a smectic to crystalline phase is only partial (around 30%), although it takes place from the ordered SCA phase. Crystals are formed within the SCA domains with nearly the same coherent length. On the basis of the analysis of the position and the profile of the diffuse wide‐angle X‐ray scattering and mesogenic layer spacing, it was assumed that either crystallisation modifies the smectic structure, or mesophase losses its positional order because of the lack of mobility of the spacers at low temperatures.
WAXS scattering profiles corresponding to P7MB: a) cooling from the isotropic melt at 2 °C · min?1; b) subsequent melting at 12 °C · min?1. 相似文献
Two terthiophenes bearing core fluorinated thienyl units have been synthesised as potential semiconductor materials for organic field‐effect transistors. Polymerisation of these compounds has been achieved using conventional iron(III) chloride oxidative coupling methods and by electrochemical oxidation. Characterisation of the fluorinated materials has been achieved by absorption spectroscopy and cyclic voltammetry. A soluble hexyl‐functionalised polymer (poly 8b ) was used in an OFET device; hole mobilities were measured up to 3 × 10?3 cm2 · V?1 · s?1, and the device had an on/off ratio of 105 and a turn‐on voltage of +4 V.
Summary: We investigated the formation of thermoresponsive gold nanoparticle/poly(N‐isopropylacrylamide) (AuNP/PNIPAAm) core/shell hybrid structures by surface‐initiated, atom transfer radical polymerization (SI‐ATRP) in aqueous media and the effect of cross‐linking on the thermoresponsiveness of the AuNP/PNIPAAm hybrids. The disulfide containing an ATRP initiator was attached onto AuNPs and the monomer, NIPAAm, was polymerized from the surface of AuNPs in the absence or presence of a cross‐linker, ethylene diacrylate, in aqueous media at room temperature. The resulting brush‐type and cross‐linked AuNP/PNIPAAm hybrids were characterized by Fourier‐transform infrared spectroscopy, transmission electron microscopy, and variable temperature dynamic light scattering.
Homopolypeptides of linear and star‐like architectures were prepared by polymerizing benzylic‐protected L ‐glutamic acid and L ‐aspartic acid N‐carboxyanhydrides (Glu NCA, Asp NCA) in DMF. The polymerization rate of the Glu NCA is faster than that of Asp NCA. Using a simple monoamino initiator, its hydrochloride, di‐, tri‐, and tetraamino functional initiators, homopolypeptides with well‐defined structures and molar masses were obtained. The molar‐mass averages of the poly(γ‐benzyl‐L ‐glutamate)s lie very close to calculated values, according to the initial [M]:[I] ratios, while those of the linear poly(β‐benzyl‐L ‐aspartate)s were lower than the predicted ones. PBAs had somewhat broader molar‐mass distributions than PBGs.
In this article, we present the results of a study of the preparation of a cyclohexene oxide (CHO) mid‐chain functional macromonomer via ATRP of styrene (St) and epoxidation on work‐up with 3‐chloroperoxybenzoic acid. The ATRP initiator, Br? CH? Br, was synthesized by the condensation of 3‐cyclohexene‐1,1‐dimethanol with 2‐bromopropanoyl bromide. The ATRP of St with Br? CH? Br and Cu(I)/bpy yielded well‐defined polystyrene with a cyclohexene mid‐chain group (PSt? CH? PSt). Epoxidation of the PSt? CH? PSt was performed using 3‐chloroperoxybenzoic acid. GPC, IR and 1H NMR analyses revealed that a low polydispersity macromonomer of polystyrene with CHO functionality at the mid‐chain (PSt? CHO? PSt) was obtained. The photoinduced cationic polymerization of PSt? CHO? PSt yielded comb‐shaped and graft copolymers.
Summary: A novel glyco‐peptide dendrimer‐type AIDS vaccine model with a well‐defined structure was synthesized. A low‐substituted, monodispersed, glyco‐peptide dendrimer was prepared by binding maltose to a proline‐poly(lysine) dendrimer with monofunctional prolyl amino groups on the periphery. To the hemispherical maltose‐proline‐poly(lysine) dendrimer, succinic anhydride was reacted to provide succinylated dendrimer with an average of 13 succinyl carboxyl groups per dendrimer. The reactivity of succinyl‐maltose‐proline‐poly(lysine) dendrimer was investigated by coupling a tripeptide to the carboxyl group in water using 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide hydrochloride (EDC) as a condensing agent. By binding two kinds of peptide sequences included in the envelope glycoprotein of HIV to the dendrimer, AIDS vaccine models with glyco‐peptide dendrimer scaffold were synthesized. The structure of the vaccine models was determined by NMR and MALDI‐TOF mass analyses.
The synthesis and phase behaviour of PB32 is reported. The results indicate that PB32 develops a low‐ordered smectic mesophase of the type SmCalt. The slow formation of such a mesophase allows the quenching of the isotropic melt into an amorphous state so that both amorphous glass and smectic glass can be obtained, which exhibit different glass‐transition temperatures. Mechanical tests indicate that the macromolecular chains in the mesophase of PB32 can be oriented either parallel or perpendicularly in relation to the streching direction, depending on the deformation conditions. Solid‐state 13C NMR spectroscopy results show that the mobility of the chains is rather similar in both phases.
A well‐controlled two‐step process, the polymerisation of isoprene or isoprene/hex‐1‐ene copolymerisation followed by ε‐caprolactone polymerisation, affords trans‐polyisoprene or (trans‐polyisoprene/hex‐1‐ene copolymer)–poly(ε‐caprolactone) diblocks of various lengths. The single component initiator is an allylsamarocene compound. An atomic force microscopy study shows that these copolymers are efficient compatibilisers for poly(ε‐caprolactone) and polyisoprene blends.
Poly(ε‐caprolactone) chain growth from Sm–polyisoprene chain. 相似文献
Summary: The photopolymerization of two reactive mesogens with photopolymerizable acrylate endgroups, the methyl substituted 1,4‐phenylene‐bis{4‐[6‐(acryloyloxy)hexyloxy]benzoate} 1 and acrylic acid 6‐{4‐[6‐(6‐acryloyloxyhexyloxy)naphthalen‐2‐yl]‐phenoxy}hexyl ester 2 has been investigated using Photo‐DSC measurements. Photocrosslinking of 1 in the nematic phase at 100 °C leads to a final conversion of 87% of the acrylate groups. It is possible to perform photopolymerization with very small amounts of photoinitiator. Even with 0.001% (10 ppm) of photoinitiator, 47% of the acrylate groups polymerize within 15 min. The polymerization of the reactive mesogen 2 proceeds faster in the smectic A phase at 100 °C compared to the isotropic phase at 120 °C and leads to a higher conversion of 75%. This can be explained by an increased local concentration of the acrylate groups between the layers of the smectic cores.
Three novel photochromic azobenzene‐containing comb‐shaped polyacrylates are synthesized and their phase behavior and photo‐optical properties are studied. The influence of the side photochromic group structure, thermal treatment, and light irradiation on aggregation of azobenzene chromophores in thin spin‐coated films of the polymers is investigated in detail. Special attention is paid to studying the photo‐orientation processes in polymers films induced by polarized blue light (473 nm). The relationship between the photochromic group architecture, phase behavior, thermal treatment of films, and kinetics of chromophore photo‐orientation is established and discussed. It is found that the position of the N?N bond in chromophores plays an important role in the kinetics of the process, but does not affect the maximum value of dichroism.
The synthesis of a polymeric, photoresponsive drug‐delivery system on the basis of 4‐methylcoumarin‐side‐chain‐functionalized methacrylic copolymers with different degrees of functionalization is reported. Drug‐release experiments in solution indicated a maximum release of 22 µg of 5‐fluorouracil per 1 mg of polymer. Polymer analogous photochemical drug immobilization does not lead to observable intermolecular cross‐linking. Miscibility experiments with PMMA suggest that the bulk polymerization of homogeneous, transparent polymer sheets for intraocular lens fabrication, using MMA as the matrix monomer and incorporating the polymer‐drug conjugates as a functional component, is possible.
Novel water dispersible poly(benzimidazobenzophenanthroline) polymers functionalized with poly(ethylene oxide) (BBL:PEO) have been investigated by cyclic voltammetry, in situ UV‐vis spectroscopy and atomic force microscopy. The cyclic voltammograms recorded during n‐doping indicate that the drop coated BBL:PEO films retain their properties despite functionalization. A small influence of the PEO side chains on redox properties of the investigated polymers was found, diminishing however after annealing. During spectroscopic experiments structural changes connected with polymer charging were observed (in accordance with a two electron transfer process). The functionalization of BBL with PEO side chains provided an easy processing method to obtain smooth and reproducible polymer films.
