Photo‐crosslinkable side‐chain liquid‐crystalline polymers (LCPs) containing photoreactive benzophenone cores are synthesized in order to obtain their corresponding side‐chain liquid‐crystalline elastomers (LCEs). This strategic synthesis allows thin elastomeric films and their integration into microsystems for actuators and micromachines to be obtained. As an example of this principle, a gripper was developed. The position of its arms can be changed by applying voltages from 1.5 to 3.5 V at different rates. Small changes in the liquid‐crystalline elastomer film cause strains of up to 150% in the microdevice and the capacity to move up to 400 times its own mass due to the nematic‐to‐isotropic transformation.
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
D‐A‐D‐type polymers are of high interest in the field of photovoltaics and electrochromism. In this study we report the synthesis and electrochemical properties of PPyBT along with its photophysical properties and photovoltaic performance. PPyBT is soluble in common organic solvents and both n‐ and p‐type dopable, which is a desired property for conjugated polymers. During electrochemistry studies, the onset potentials of the polymer were determined as +0.2 V for oxidation and ?1.4 V for reduction. Using these values, HOMO and LUMO energy levels were calculated. The photovoltaic properties of PPyBT were also studied. PL studies showed that there is a charge transfer between PPyBT (donor) and PCBM (acceptor).
A series of anthracene‐based conjugated copolymers containing 9,10‐bis(6‐bromonaphthalen‐2‐yl)‐2‐tert‐butylanthracene (BNA) and 2,7‐diphenyl substituted fluorene (DPPF) moieties are prepared via a palladium‐catalyzed Suzuki polymerization. All of the synthesized polymers emit blue light at around 450 nm and show good thermal and color stability. Their electroluminescence spectra remain unchanged at high driving voltage. The double‐layer polymer light‐emitting diode (PLED) fabricated with ITO/PEDOT:PSS/DPPFBNA3/CsF/Al, produces a maximum brightness of 1 650 cd · m?2 and has a luminance efficiency of 0.39 cd · A?1. The ITO/PEDOT:PSS/TFB/DPPFBNA3/CsF/Al multilayer PLED, incorporating a TFB layer to facilitate hole transportation, produces a maximum brightness of 5 371 cd · m?2 and a luminance efficiency of 1.18 cd · A?1.
Summary: The synthetic routes to three series of liquid crystal conducting polymers (based on pyrrole, thiophene, and aniline monomers) are reported and the optimum conditions for polymer preparation are described. These polymers show increased conductivity when laser‐aligned, the greatest effect being shown by the N‐substituted pyrrole‐based system. Information on their liquid crystal and spectroscopic properties and other characteristics are also included.
New polyurethanes containing Y‐shaped chromophores, symmetrical derivatives of 4‐(dicyanomethylene)‐2‐methyl‐6‐[p‐(dimethylamino)styryl]‐4H‐pyran, have been prepared. The polymers show high glass transition temperatures (Tg) and a good thermal stability. SHG measurements on poled polymer films of the synthesized polymers have been carried out and a maximum d33 of 15 pm · V?1 has been found at 1 368 nm fundamental wavelength. Time stability measurements on the most active polymer have shown that after the initial fast relaxation, the d33 value remains constant at 80 °C for 60 d.
Three new cyanobiphenyl polysiloxanes presenting long thioether spacers have been carried out. This type of spacer leads to very stable liquid‐crystalline polymers at room temperature and remove the crystallinity phenomenon. Dielectric analysis results show that the thioether spacer brings much more molecular flexibility to the system.
Example of an “interdigitated” structure observed by X‐ray analysis. 相似文献
CROP has been used to synthesize well‐defined POXZ with a monofunctional (iodomethane) or a bifunctional (1,3‐diiodopropane) initiator. POXZ has been functionalized with an azido group at one (α‐azido‐POXZ, = 3.58 × 103 g · mol?1) or both ends (α,ω‐azido‐POXZ, = 6.21 × 103 g · mol?1) of the macromolecular chain. The Huisgen 1,3‐dipolar cycloaddition has been investigated between azido‐POXZ and a terminal alkyne on a small or larger molecule (PEG). In each case, the click reaction has been successful and quantitative. In this way, different telechelic polymers (polymers bearing different functions such as acrylate, epoxide, or carboxylic acid) and block copolymers of POXZ and PEG have been prepared. The polymers have been characterized by means of FTIR, 1H NMR, and SEC.
SCLCPs are synthesized using “click chemistry”. The resulting polymers, P1 and P2, have good solubilities and molecular‐weight distributions. Their and polydispersities are in the ranges of 26.7–8.4 × 103 g · mol?1 and 1.99–1.29, respectively. DSC and POM studies reveal that both polymers exhibit liquid‐crystalline behavior. P1 and P2 are found to display blue emission. DSSCs are fabricated using P1 and P2 as matrices for electrolytes. The maximum PCE of the P1‐ and P2‐based polymer electrolytes is 4.11% (at 1 sun). This synthesis route has again proven to be a useful synthetic methodology for fabricating SCLCPs that are promising materials for device applications.
An efficient synthetic procedure for the phosphonation of aromatic polymers was developed and is here exemplified for polyphenylsulfone. This procedure involved the bromination of the polymer and the subsequent bromine‐phosphorus exchange by means of a Pd(0)‐catalyzed P? C coupling reaction. In the resulting product, the phosphonate ester pendant groups were attached to aromatic rings of the polymer chain without alkylene spacer units. A substitution degree of almost one phosphonate moiety per repeating unit of the polymer was achieved in the presence of Pd2(dba)3 · CHCl3 as catalyst at 120 °C. Polymers with free phosphonic acid groups were prepared by ester hydrolysis.
π‐Conjugated polymers composed of dialkoxybenzo[1,2‐b:4,5‐b′]dithiophene and thiophenes bearing cyano‐alkoxycarbonylethenyl [? CH?C(CO2R)CN] and bis(alkoxycarbonyl)ethenyl groups [? CH?C(CO2R)2] were prepared. The optical properties of the obtained polymers were investigated by UV‐vis and photoluminescence spectroscopy to demonstrate that the absorption maxima of the polymers were tunable by varying the substituent of thiophene unit. The photoluminescence wavelengths and intensities of the polymer in solution were significantly dependent on the polymer side chain. The HOMO energy level of the polymer was lowered by up to ?5.51 eV by introducing electron‐deficient cyano groups. Polymer solar cells based on the new polymers were fabricated to achieve a PCE of 1.90%.
Summary: A stereospecific polymerization of a novel aromatic acetylene containing an alkyl sulfide group, i.e., (p‐methylthiophenyl)acetylene (pMeSPA) was successfully performed to selectively give the corresponding polymer bearing a cis‐transoid structure as a main geometrical form and a very high molecular weight, = 1.7–5.8 × 106 in high yields. This was accomplished when a Rh complex catalyst, [Rh(norbornadiene)Cl]2, was used in the presence of triethylamine (TEA) solvent as a cocatalyst and its mixed solvents with TEA, together with a detailed characterization of the resulting polymers before and after compression at room temperature. Based on the data obtained before and after compression, it was concluded that compression of the PpMeSPA polymers induced a cis‐to‐trans isomerization at room temperature under vacuum even in the solid state (the Figure shows the radical generated by compression).
Summary : New carbazole‐based ladder‐polymers have been prepared utilising a 3,6‐diacyl‐2,7‐dibromocarbazole building block 4 . Suzuki polycondensation of 4 with carbazole‐2,7‐diboronic acid followed by addition of methyl lithium and ring closure with boron trifluoride gave ladder‐polymers 9 with all methine bridges, analogous to ladder‐type poly(para‐phenylene). In very dilute solution, these polymers show blue‐green fluorescence similar to that from the corresponding LPPP. At higher concentrations, a broader red‐shifted emission is seen which suggests that the chains are aggregating in solution. Homopolymerisation of 4 followed by condensation of the carbonyls with boron sulfide produced a novel ladder‐type structure 13 with alternating five‐ and six‐membered rings. This ladder‐polymer displays bright yellow‐green fluorescence. Cyclic voltammetry indicated that these materials have HOMO energy levels comparable to the work function of ITO, making them good candidates for use as hole accepting emissive materials for LEDs.
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.
Summary: This paper describes the use of trialkylsilanes for photoinduced patterning of electroluminescent polymers as a new field of application for this type of organosilicon compounds. Under UV irradiation, trialkylsilanes selectively saturate the vinylene groups in poly(p‐phenylenevinylene) (PPV)‐type polymers, while leaving aromatic units virtually unaffected (selective photobleaching). Spin cast films of polymer blends consisting of two or three different conjugated polymers were UV irradiated in the presence of gaseous trialkylsilane reagents (trimethylsilane and ethyldimethylsilane) to achieve multicolor patterning. Exploiting the host‐guest concept with polyfluorene (PF) derivatives as totally aromatic host matrix and PPV derivatives as guest polymers, dual‐color displays and, with constraints, three‐color LED displays were realized. Compared to previously reported reagents such as hydrazine and thiols, trialkylsilanes enable photochemical patterning under non‐toxic and odorless conditions. Possible mechanisms for the photoreaction with trialkylsilanes as well as perspectives for applications are discussed.
Electroluminescence spectra of LEDs based on the host‐guest system. 相似文献
Summary: The appropriate choice of comonomers can be used to create a wide range of polymer properties, leading to considerable improvement of product performance. Experimental runs were performed to evaluate the effect of 1‐butene on the crystallinity, the melt temperature and the molecular weight distribution (MWD) of the final propylene/1‐butene copolymer resins. According to the results obtained, the melt temperature of the copolymer material can be reduced significantly compared to that of the polypropylene homopolymer. The incorporation of 1‐butene into the copolymer chain leads to a decrease of the sealing initiation temperatures of propylene polymer resins. GPC analyses of copolymer samples showed that 1‐butene concentration does not seem to significantly influence either the shape of the MWD or the polydispersity indexes for a given set of reaction conditions. Therefore, a family of propylene/1‐butene random copolymers grades can be successfully developed for gas phase processes for packaging and film applications.
Novel polymer cladding materials were synthesized and their potential for use in optical waveguide devices was investigated. 9‐[2‐(2,3,5,6‐Tetrafluoro‐4‐vinylphenoxy)ethyl]‐9H‐carbazole and 1‐pentafluorophenylpyrrole‐2,5‐dione were used as comonomers for preparing the acrylic cladding copolymers. These showed a low resistivity (≈2 × 1013 Ω · cm) at room temperature and a low optical loss (?0.6 dB · cm?1) at a wavelength of 1.55 µm. The refractive indexes and the glass transition temperatures of the polymer cladding materials can be controlled by the composition of the copolymers. The resulting polymers are good candidates for cladding materials for practical applications in devices.
1,2,4‐triazole‐functional PGMA polymers have been synthesized and their anhydrous proton‐conducting properties were investigated after doping with phosphoric acid and triflic acid. PGMA was prepared by solution polymerization and then modified with 1H‐1,2,4‐triazole (Tri) and 3‐amino‐1,2,4‐triazole (ATri). FT‐IR, 13C NMR and elemental analysis verify the high immobilization of the triazoles in the polymer chain. Phosphoric‐acid‐doped polymers showed lower Tg and higher proton conductivities. PGMA‐Tri 4 H3PO4 showed a maximum water‐free proton conductivity of approximately 10?2 S · cm?1 while that of PGMA‐ATri 2 H3PO4 was 10?3 S · cm?1. The structure and dynamics of the polymers were explored by 1H MAS and 13C CP‐MAS solid‐state NMR.
The atom transfer radical polymerization (ATRP) technique has been successfully applied to synthesize a series of nonlinear optically (NLO) active homopolymers, 4‐(4‐nitrophenyl‐diazenyl) phenyl acrylate ( P ‐ NPAPA ) and 4‐(4‐methoxyphenyl‐diazenyl) phenyl acrylate ( P ‐ MPAPA ), containing azobenzene groups on the side chain. The third‐order NLO properties of the polymer films were measured by the degenerated four‐wave mixing (DFWM) technique. A dependence of the χ(3) values and response times of polymers on their number‐average molecular weight and the electronic effect of the substituent (nitro‐ or methoxy‐) on the azobenzene group have been evidenced. The increasing χ(3) value of the polymer films at the magnitude of about 10?10 was displayed with increasing molecular weight and the presence of the push‐pull electronic system contributes much in enhancing the third‐order NLO susceptibility of polymers.
