We have synthesized polyethoxysiloxanes starting from the AB3‐type monomers triethoxysilanol and acetoxytriethoxysilane. The polymers are liquid and soluble in organic solvents. 29Si NMR spectroscopy and MALDI‐ToF mass spectrometry analyses show that the polymers have a hyperbranched structure with additional internal cyclization. 29Si NMR spectroscopy indicates that the polymer synthesized from acetoxytriethoxysilane is less branched than the polymer synthesized from triethoxysilanol. Analysis of the molar mass and mass distribution of the polymers via size exclusion chromatography (calibrated via MALDI‐ToF MS and viscosimetry) yields a molar mass of Mn ≈ 2 kg · mol?1 and Mw ≈ 8 kg · mol?1 for polymers synthesized from triethoxysilanol. The molar mass of the polymers synthesized from acetoxytriethoxysilane can be controlled by variation of the polymerization time in the range of Mn ≈ 1.8–12 kg · mol?1 and Mw ≈ 2.1–2 200 kg · mol?1.
Photograph of a vial containing polyethoxysiloxane obtained from triethoxysilanol and a schematic drawing of the proposed molecular structure of the polymer. 相似文献
A copolymer of 2,3,5,6‐tetrafluoro‐1,4‐phenylenevinylene and 2,5‐dioctyloxy‐1,4‐phenylenevinylene [co(TFPV‐DOPV)], containing more than 60% of tetrafluorophenylenevinylene monomeric units, was synthesized by the Stille cross‐coupling reaction. Its linear and nonlinear optical properties were investigated. Linear absorption and photoluminescence measurements performed on thin films and solution indicate interchain migration upon excitation. The Z‐scan technique was used to evaluate the third‐order nonlinear susceptibility at λ = 1064 nm. A very high refractive nonlinearity (n2 = (?10 ± 2) × 10?12 cm2 · W?1) was measured with a value one order of magnitude larger than that of the corresponding dialkoxy‐substituted homopolymer.
The properties of an oligomeric cyanate ester polymer were modified by the addition of 0.01–3 wt.‐% multi‐walled carbon nanotube (MWNT) containing particles. The dynamic mechanical behavior and thermal properties of the cyanate ester/MWNT nanocomposites were evaluated. The storage modulus, G′, of the nanocomposite with 1 wt.‐% MWNT particles was nearly 60 and 600% higher than the neat polymer at 100 and 200 °C, respectively. The glass transition temperature of the nanocomposite was also raised by 30 °C and its thermal stability in air and nitrogen was increased by 58 and 25 °C, respectively. The property improvements are attributed to reinforcement of the cyanate ester as a result of good nanotube dispersion and effective polymer‐MWNT interaction.
The control of the radical polymerization of styrene by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl is reported here in bulk at 90 °C, 120 °C and in miniemulsion. Similarly, the control by its sodium complex is reported in bulk at 90 °C.
Summary: Here we report about the synthesis of colloidal particles of nematic and smectic liquid‐crystalline polymers. For this purpose mesogen‐containing acrylate monomers were synthesized and polymerized in a special modification of a precipitation polymerization called dispersion polymerization. By variation of the polymerization conditions colloidal particles of different size and polydispersity could be obtained including very narrowly distributed samples in optimized batches. On azobenzene‐containing colloidal particles switching experiments with polarized light were performed. It could be observed that the nematic director of the mesogens within the colloidal particles can be rotated due to the photochemical trans‐cis‐isomerization of the azobenzene chromophores.
A procedure for synthesis aromatic‐aliphatic PAK, completely functionalized with p‐fluorophenyl terminal groups, is presented. This synthesis uses the nucleophilic aromatic substitution of DFB with various secondary aliphatic diamines [CH3? NH? (CH2)m? NH? CH3] (m = 3, 6, and 8) and cesium fluoride as the base catalyst in the melt. The linearity and the complete functionalization of the PAK compounds with p‐fluorophenyl terminal groups are demonstrated with the aid of MALDI TOF mass spectrometry. PAK compounds are semi‐crystalline as shown by WAXS and DSC measurements. The degree of crystallinity ranges between 2 and 25%. Nucleophilic aromatic substitution reactions in the fluorine end groups are demonstrated by reaction of PAK (m = 6) with the strong S‐nucleophile mercaptoacetic acid.
A series of ethylene and acrylonitrile composite elastomers were prepared using (1,4‐bis(2,6diisopropylphenyl)‐acenaphtenediimine‐nickel(II))‐dichloride/ethylaluminum sesquichloride (EASC). The xylene‐soluble polymer fraction showed nitrile bands in infrared spectroscopy at 2 245 and 2 214 cm?1 and polyacrylonitrile‐enriched structures were detected in the xylene‐insoluble fraction by1H and 13C NMR. In addition, TEM detected nanosized polyacrylonitrile domains dispersed in the polyethylene matrix. Differential scanning calorimetry scans conducted from ?70 to 350 °C measured exothermic bands corresponding to the cyclization and aromatization of the nitrile groups dispersed in the polyethylene matrix.
A new type of ‘intelligent’ hydrogels has been developed in the form of organic/inorganic hybrid materials by making use of the sol‐gel technology. Poly(N‐vinylcaprolactam) (PVCL) has been incorporated in these materials for its thermo‐responsive properties. The synthesis of the hybrid hydrogels was achieved by the in situ formation of an inorganic silica phase in the presence of an aqueous solution of high molecular weight PVCL. This methodology results in the preparation of micro‐heterogeneous systems in which silica particles of nanometer dimensions act as physical cross‐links for the PVCL molecules. Hydrogen bonds between the remaining non‐condensed silanol groups and the PVCL carbonyl functions, together with physical entanglements, are responsible for the strong interactions between the organic and inorganic phases. Stress‐strain tests on highly swollen materials demonstrated that the unique structure of these thermo‐responsive hybrid hydrogels improves the mechanical stability to a great extent as compared to conventional hydrogels. Transmission measurements demonstrate that the presence of the inorganic phase does not influence the cloud point temperatures of PVCL significantly. On the other hand, the response of the reinforced hybrid hydrogels to temperature becomes less pronounced for increasing silica fractions. The reversibility of the swelling/deswelling process has been demonstrated by swelling experiments as a function of temperature.
Ordered nanostructures are observed in the melt and solid state for a series of three peptide/PEG conjugates containing fragments of amyloid β‐peptides. These are conjugated to PEG with = 3 300 g · mol?1 and a melting temperature Tm = 45–50 °C. The morphology at room temperature is examined by AFM and POM. This shows spherulite formation for the weakly fibrillizing KLVFF‐PEG sample but fibril formation for FFKLVFF‐PEG. The fibrillization tendency of the latter is enhanced by multiple phenylalanine residues. Simultaneous SAXS and WAXS was used to investigate the morphology as a function of temperature. The secondary structure is probed by FTIR.
Polymer solar cells based on poly(phenylenevinylene‐alt‐4,7‐diphenyl‐2,1,3‐benzothiadiazole) (PP‐DBT):[6,6]‐phenyl C71 butyric acid methyl‐ester (PC71BM) blend films are optimized. The results show that the solar cell has a better performance at a 1:4 blend ratio than at 1:1, 1:2, 1:3, and 1:5 blend ratios, due to the higher hole mobility of active layer and the optimized morphology. The device prepared from chlorobenzene (CB) has a higher power conversion efficiency (PCE) than the devices prepared from chloroform and o‐dichlorobenzene, because the former has a much higher short‐circuit current density (Jsc) resulting from the morphology with proper phase separation. The solar cell modified with two layers of ZnO nanocrystals achieves the best performance with an open‐circuit voltage of 0.9 V, a Jsc of 7.46 mW cm?2, fill factor (FF) of 0.50, and PCE of 3.36%.
This paper reports the assignment of the 13C NMR resonances of the Sββ and Sαγ methylenes observed in the spectra of copolymers of propylene with trace amounts of enriched ethylene‐1‐13C. The assignment is achieved by comparing the chemical shifts calculated by an empirical method (at the CH2 stereochemical pseudohexad level), with the experimental spectra of regioregular copolymers with different stereochemical structure. The implications of the observed Sββ and Sαγ resonances on the stereochemical polymerization mechanisms are also discussed.
A series of π‐conjugated alternating copolymers consisting of Th‐ITN‐Th and p‐C6H2(OR)2 units were synthesized. XRD indicated that the copolymers assume an interdigitation packing mode, and UV‐Vis spectra revealed a strong tendency for self‐assembly. Upon molecular assembly of the copolymer, the UV‐Vis absorption shifted by about 100 nm to a longer wavelength from that of the single molecule. The copolymers underwent electrochemical oxidation (or p‐doping) and reduction (or n‐doping) at 0.2 and ?2.0 V versus Ag+/Ag, respectively. A p‐doped copolymer film showed an electrical conductivity of 182 S · cm?1, and the temperature dependence of electrical conductivity was measured. The copolymer showed piezochromism and served as a p‐channel material for a field‐effect transistor.
Summary: Ethylene and butadiene were copolymerized with a silylene‐bridged bis(fluorenyl) complex {[Me2Si(C13H8)2]NdCl} ( 1 ) in combination with various alkylating agents (BuLi/AlH(iBu)2, (Bu)MgCl, Mg(Bu)(Oct)). Copolymers have a unique microstructure since they contain 1,2‐cyclohexane rings and unsaturations along the polymer chain. An intramolecular mechanism was proposed for the formation of six‐membered rings. The influence of these cyclic structures on thermal properties of the copolymers has been investigated.
Proposed mechanism for formation of 1,2‐cyclohexane rings. 相似文献
The microphase structure of polyisoprene‐block‐poly(methyl methacrylate) diblock copolymers was studied using solid‐state NMR techniques. Wideline separation spectroscopy reveals a narrow interphase between the two polymers. The domain sizes of a lamellar sample and a sample with hexagonally ordered cylinders were determined using 1H spin diffusion. The lamellar sample shows a domain size of 16 ± 2 nm for the minor polyisoprene phase and a long period of 33 ± 4 nm. The cylindrical structure has a long period of 38 ± 7 nm, the diameter of the PMMA cylinders is 21 ± 4 nm. These results are about 20% below the estimates obtained from theoretical calculations according to Helfand and Wasserman.
Morphologies of an a) lamellar, and b) hexagonally ordered cylindrical sample (schematic). The triangle in (b) indicates the symmetry that can be used to calculate the dL. 相似文献
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
In order to incorporate iridium(III) complexes covalently into an oxetane‐bearing hole‐transporting matrix, a new oxetane‐equipped acetoacetate derivative was introduced as an ancillary ligand. Model complexes with an analogical nonpolymerizable ligand were also prepared in order to perform comparative investigations. Therefore, a series of bis‐cyclometalated Ir(III) complexes, showing orange (C?N‐ligand, coumarin 6) and green (C?N‐ligand, phenylpyridine) emission were synthesized and fully characterized. The emission maxima are 569 nm for the orange and 518 nm for the green‐emitting Ir(III) complexes. Entirely solution processed devices, based on crosslinkable hole‐conductors, partially doped with the described orange and green Ir(III) emitters, respectively, were fabricated and tested.
The interaction energy densities of poly(2‐vinylpyridine) (P2VPy)/4,4′‐(1,4‐phenylenediisopropylidene)bisphenol (PDIPBP) blend and poly(N‐vinyl‐2‐pyrrolidone) (PVP)/PDIPBP blend were determined using melting point depression method. The interaction between PVP and PDIPBP is stronger than that between P2VPy and PDIPBP. Wide‐angle X‐ray diffraction study revealed that PDIPBP crystallizes out from the polymer/PDIPBP blends at high PDIPBP contents. The phase equilibrium calculation supports that the single‐Tg behavior is a result of miscibilization rather than an overlap of two close Tg's of two separated phases. The critical miscibilization content of PDIPBP obtained from spinodal phase boundary calculation is lower than the saturation content, and therefore, there is enough PDIPBP in the amorphous phase to miscibilize P2VPy and PVP. Scanning electron microscopy showed a drastic reduction in domain size in single‐Tg blends.
Semitelechelic (ω‐), telechelic (α,ω‐), as well as 3‐ and 12‐arm star polyisoprenes (PI), end‐functionalized with the same dimethylamino group, were synthesized by anionic polymerization high vacuum techniques, using 3‐dimethylaminopropyllithium as initiator and chlorosilanes as linking agents. The dimethylamino groups were transformed to phosphatidylcholine analogues through reaction with 2‐ethoxy‐2‐oxo‐1,3,2‐dioxaphospholane. The association behavior of the phosphoro‐zwitterionic PI (PZw‐PI) was studied in cyclohexane by low angle laser light scattering, viscometry, and dynamic light scattering. The linear PZw‐PIs present relatively low weight‐average degree of association (Nw: 2–6), as compared with the corresponding sulfo‐zwitterionic PI (Nw: 10–45). The Nw values decrease with increasing molecular weight of the PI. In the case of the star PZw‐PI, the multiple intermolecular associations lead to the formation of gels, which break down by addition of a small amount of 1‐heptanol. In very dilute solutions and for high arm molecular weight stars, intramolecular dominates over intermolecular association.
The unprecedented ability of neodymium‐based metal organic frameworks (MOFs) as polymerisation pre‐catalysts towards isoprene is reported. Combined with methylaluminoxane (MAO) or modified MAO (MMAO), they afford mainly cis‐selective polyisoprene, up to 90.7%. Both the activity and the selectivity are tentatively ascribed to the intrinsic microstructure of the starting materials. Compared to conventional carboxylates, MOFs associated to an Al co‐catalyst are less active but the selectivity is found to be higher, and it may be modified by controlling the access to the pores, which would be favored at higher temperatures. Some residual crystalline MOF remains disseminated within the polymer matrix, as shown by X‐ray diffraction and X‐ray absorption spectroscopy studies.
