Hydrolysis of 3-methyl-2-cyclohexenylidene laurylamine (I) in the presence and absence of laurylsuccinoylpoly(ethylenimine) has been studied. Water attack on the conjugate acid of I in the polymer environment is about 102 times faster than in bulk medium. To achieve the same rate in bulk media by general base catalysis, about 70 M acetate or cacodylate would be needed. This indicates that the reactivity of the carboxylate attached to the polymer is substantially enhanced by the polymer environment. 相似文献
The interaction of the [Ni(PPh3)3]BF4 complex with styrene and the products of styrene conversion in the polymerization reaction were studied by EPR and 13C NMR spectroscopy. The structure of the σ-carbocationic complex of Ni(I) formed by the interaction of styrene with the [Ni(PPh3)3]BF4 cationic phosphine complex of Ni(I) was characterized in detail. It was found that the reaction of styrene polymerization occurred with the participation of the coordination center of the σ-carbocationic complex (coordination catalysis), whereas the reaction of telomerization occurred with the participation of the cationic center of this complex (ionic catalysis). The resulting polymer contained active terminal double bonds; it is a promising macromonomer for the synthesis of grafted copolymers. The discovered capacity of alcohols to undergo nucleophilic addition to a growing polymer chain offers strong possibilities for preparing functional polymers and block copolymers. 相似文献
The kinetics of the formation of polyacrolein microspheres by ionizing radiation (polymer I) were investigated. Their structure and reactivity were compared with polyacrolein microspheres prepared by base catalysis (polymer II). The study of Fourier infrared (IR) spectra of polymers I and II showed structural differences. The reaction of polyacrolein spheres with m-aminophenol indicated the presence of conjugated groups. The reaction of antibodies with polyacrolein spheres was investigated as a function of pH and the number of reactive aldehyde groups was determined by nitrogen analysis of polyacrolein-hydroxylamine adducts. Intensely fluorescent polyacrolein microspheres obtained by Co-γ-irradiation in sizes of 100 Å–4 μm have already found applications as immunoreagents for cell labeling and separation. 相似文献
A bifunctional polymer is formed when low-molecular-weight poly(2,6-dimethyl-1,4-phenylene oxide) (I) reacts with 3,3′,5,5′-tetramethyl-4,4′-diphenoquinone (II). Infrared (IR), nuclear magnetic resonance (NMR), and gel permeation chromotography (GPC) measurements indicate that the quinone is bound covalently to the polymer chain as a biphenyl moiety which can be located at a terminal position (III, a = 0) or an internal position (III, a > 0): Acetylation of III produces a diacetate ester characterized by field desorption mass spectrometry to confirm the bifunctional nature of III. The reaction of I with II proceeds at 25°C but is faster at elevated temperatures or with amine catalysis. Oxidation of III with oxygen and a copper/amine catalyst of the type used initially to prepare I regenerates II from the biphenyl moiety in III in high yield and converts the remaining oxyphenylene units to high-molecular-weight polymer. 相似文献
Flow-through catalysis utilising (2-methylthiomethylpyridine)palladium(II) chloride species covalently attached to a macroporous continuous organic polymer monolith synthesised within fused silica capillaries of internal diameter 250 μm is described, together with related studies of ground bulk monolith compared with supported catalysis on Merrifield and Wang beads and homogeneous catalysis under identical conditions to bulk supported catalysis. The monolith substrate, poly(chloromethylstyrene-co-divinylbenzene), has a backbone directly related to Merrifield and Wang resins. The homogeneous precatalyst PdCl2(L2) (L2=4-(4-benzyloxyphenyl)-2-methylthiomethylpyridine) contains the benzyloxyphenyl group on its periphery as a model for the spacer between the ‘PdCl2(N∼S)’ centre and the polymer substituent of the resins and monolith. Suzuki-Miyaura and Mizoroki-Heck catalysis exhibit anticipated trends in reactivity with variation of aryl halide reagents for each system, and show that supported catalysis on beads and monolith gives higher yields than for homogeneous catalysis. The synthesis of 2-methylthiomethylpyridines is presented, together with crystal structures of 4-bromo-2-bromomethylpyridine hydrobromide, 4-(4-hydroxyphenyl)-2-methylthiomethylpyridine (L1), PdCl2(L1) and PdCl2(L2). Hydrogen bonding occurs in 4-bromo-2-bromomethylpyridine hydrobromide as N-H?Br interactions, in 4-(4-hydroxyphenyl)-2-methylthiomethylpyridine as O-H?N to form chains, and in PdCl2(L1) as O-H?Cl interactions leading to adjacent π-stacked chains oriented in an antiparallel fashion. 相似文献
Polyphenylenes supported N-heterocyclic carbene Pd-complexes were synthesized for catalysis of cross-coupling Suzuki-Miyaura reactions. Starting polyphenylenes were prepared by cyclocondensation reaction of diacetylaromatic with monoacetylaromatic compounds. N-metylimidazole has been involved to the polymer through the mono-functional acetyl monomer, in which in p-position to acetyl group the group of haloalkyl was situated, and haloalkyl group interacted with N-methylimidazole. N-heterocyclic carbene complexes of Pd were synthesized usually by the reaction of imidazolium salts with the salts of transition metals in the presence of a base, obtaining the complex (N-heterocyclic carbene)2PdX2. The catalysis reaction was carried out between arylhalides (iodo- or bromobenzene) and phenylboronic acid with the presence of 1 mol% of Pd. The yields of biphenyl are from 70 to 95%, which is comparable with homogeneous catalysis. 相似文献
Ion-exchange resins have been often used as catalysts especially those based on styrene-divinylbenzene copolymers with sulfonic acid groups in the aromatic rings of polymer chains. That is due to the advantages of heterogenous catalysis over the homogeneous acid catalysis. Moreover, resin catalysts can often lead to high selectivity in organic reactions due to the matrix effects. Therefore, the study of copolymers synthesis conditions to determine the type of polymer structure produced as well as the characterization of sulfonic resins obtained thereof are of great interest. The current paper describes the synthesis, characterization and evaluation as catalysts of sulfonic resins derived from polymer supports synthesized by aqueous suspension polymerization of styrene and divinylbenzene. The reaction conditions were varied and polymer supports with different physical properties and morphological characteristics were obtained. The polymer supports were chemically modified by sulfonation. The resultant sulfonic resins had their catalyst activity evaluated in the esterification of acetic acid with n-butanol. 相似文献
Thermoimidization kinetics of polypyromellitamic acids prepared from 2,5-bis(p-aminophenyl)pyrimidine and 4,4-diaminoterphenyl have been investigated by IR spectroscopy. It has been shown that the activation energy for the pyrimidine-containing polymer is nearly twice as low as that for the aromatic analog. This is explained by base catalysis of cyclization of the amidoacid fragments by pyrimidine rings in polymer chains. Base catalysis facilitates the process of imidization and favors the formation of polyimidic macromolecules with a lower incidence of defects. Also, the pyrimidine rings obviously catalyze the resynthesis of amidoacid fragments from the anhydride rings and amino groups formed on the destruction of the polymer chain during thermoimidization, and ensure almost complete recovery of the macromolecules with the previous bonds.For part 3, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 429–432, March, 1994.The authors are grateful to T. K. Meleshko for consultations about chemical imidization. 相似文献
The first chiral helicene-NHC gold(I) complexes efficient in enantioselective catalysis were prepared. The L-shaped chiral ligand is composed of an imidazo[1,5-a]pyridin-3-ylidene (IPy) scaffold laterally substituted by a configurationally stable [5]-helicenoid unit. The chiral information was introduced in a key post-functionalization step of a NHC-gold(I) complex bearing a symmetrical anionic fluoreno[5]helicene substituent, leading to a racemic mixture of complexes featuring three correlated elements of chirality, namely central, axial and helical chirality. After HPLC enantiomeric resolution, X-ray crystallography and theoretical calculations enabled structural and stereochemical characterization of these configurationally stable NHC-gold(I) complexes. The high potential in asymmetric catalysis is demonstrated in the benchmark cycloisomerization of N-tethered 1,6-enynes with up to 95 : 5 er. 相似文献
A new member of the polyporphine series—cobalt polyporphine of type I (pCoP-I)—was prepared from the starting magnesium polyporphine of type I (pMgP-I) by ion exchange, i.e. by sequential processing of the pMgP-I polymer film on the electrode surface with solutions of trifluoroacetic acid (forming metalfree polyporphine of type I, pH2P-I) and cobalt(II) acetate in organic solvents. The completeness of each stage of ion exchange can be judged from the change in the electrochemical and spectral characteristics of the obtained polymer films of unsubstituted porphine (?H2P-I) and cobalt porphine (pCoP-I) of type I. Oxidative transformation of this polyporphine pCoP-I was performed, which led to the formation of additional bonds between the neighboring porphine units in the polymer film (transition of polymer of type I into polymer of type II, pCoP-II). The behavior of the polymer films of cobalt polyporphine of types I and II in oxygen electroreduction was studied. The films showed catalytic activity in this process. 相似文献
Method that could regulate the ion transport in nanochannel in an efficient and rapid manner is still a challenge. Here, we introduced enzyme‐catalysis‐induced polymer growth in nanochannels to develop a new method to regulate the ion transport and evaluate the enzyme catalysis kinetics in nano‐space. As a model enzyme, Horseradish peroxidase (HRP) was immobilized in the nanochannels through a volume‐controlled‐drying method. In the presence of H2O2, HRP catalyzed o‐phenylenediamine (o‐PD) to trigger its polymer growth, in turn blocked the ion transport and led to the decrease of the ion current. Taking advantages of the high efficiency of enzyme catalysis and the nano‐confinement of nanochannels, the system readily achieved blocking ratios of ion current even reaching 99.6 % of the initial. Based on above concept, we developed a new method to evaluate the enzyme catalysis kinetics in nano‐confined space. By comparing with those in free state in solution and absorbed on planar surface, HRP confined in nanochannels presented similar apparent Michaelis constant (Km) values for the substrate H2O2 but much higher Km values for the substrate o‐PD, due to the steric hindrance and diffusion suppression. The enzyme‐catalysis‐induced polymerization in nanochannels might lead to new concept for the nano‐blocking/switching and provide a new platform for single molecule analysis and detection. 相似文献
Interfacial assemblies capable of determining glutamate by redox catalysis are prepared by electrostatic assembly of alternating layers of ferrocene poly(allylamine) polymer and glutamate oxidase on a gold electrode. Deposition of the polymer was confirmed in cyclic voltammetry measurements by the presence of a surface wave corresponding to the oxidation of the ferrocene group. In the presence of glutamate in the adjacent electrolyte solution, the current increases and approaches a pseudosteady state, consistent with redox catalysis. Electrodes modified with glutamate oxidase had a linear response to glutamate up to 0.0045 M with sensitivity of 20 μA/cm2 and a limit of detection of 31.4 μM glutamate. An apparent Michaelis–Menten constant of 0.40(±0.13) mM for the confined glutamate oxidase was determined for this assembly. When used in flow‐injection experiments, glucose oxidase modified electrodes responded to transient zones of glucose; however, the detection limits of the assemblies to the flowing stream were substantially higher than found for measurements on static solutions. 相似文献
A quaternary ammonium salt readily immobilized on a soluble poly(ethylene glycol) polymer support efficiently catalyzes different reactions carried out under phase-transfer catalysis conditions; the catalyst, easily recovered by precipitation and filtration, shows no appreciable loss of activity when recycled three times. 相似文献