The carbenium ion - oxonium ion exchange processes related to vinyl and ring-opening polymerization

It has previously been proposed (Ref. 1) that in the cationic vinyl polymerizations, proceeding with termination due to the collapse of ion pairs, addition of bases increases “livingness”, because of the fast convertion of the otherwise dead (within the time of polymerization) covalent species into the onium ions; these, in turn, fast convert into carbenium ions, the actually propagating species. Equilibria between carbenium ions (CH₃OCH₂⁺A⁻ has been used as a model) and their onium counterparts ((CH₃)₂O taken as a model base) as well as between covalent species (CH₃OCH₂OSO₂CF₃) and the corresponding oxonium ion (with a (CH₃)₂O ligand) have been studied by dynamic ¹H and ¹⁹F NMR. Total ionization of methoxymethyl triflate (CH₃OCH₂OSO₂CF₃) has been shown to increase indeed from 10⁴ (-10°C) to 10⁶ (-70°C) times when 1,0 mol·L⁻¹ of (CH₃)₂O is added. Although this model system better describes polymerization of cyclic acetals than that of vinyl ethers, it shows at least qualitatively the importance of bases in ionization of covalent species, which may be responsible for reinitiation in the cationic polymerization of vinyl ethers.     

Synthesis of block copolymers by sequential carbenium ion polymerization

The sequential carbenium ion block copolymerization of ethyl vinyl ether (EVE) and isobutyl vinyl ether (IBVE) with N-vinylcarbazole (NVC) is described. Requisite conditions for the successful application of the sequential synthesis technique to these systems were established: (1) the use of stable carbocation initiator salts (e.g., Ph₃CSbCl₆) which lead to essentially terminationless polymerizations; (2) low solvent-to-monomer ratios in order to suppress any possible chain transfer to methylene dichloride molecules; (3) high ratios of initiator to monomer which create a pseudo-“living” system. The block products (PEVE-b-PNVC and PIBVE-b-PNVC) were isolated by precipitation and extraction. The intrinsic viscosities of these products displayed minima at 30°C.     

First example of memory of chirality in carbenium ion chemistry

The non-Kolbe reaction of N-benzoyloxazolidine derivatives 6 derived from L-serine gave optically active N,O-acetals 7 when graphite was used as an anode material. This reaction represents the first example of "memory of chirality" in carbenium ion chemistry. The material used for the anode was critical for the memory of chirality. The substitution of carboxyl group with methoxyl group was found to proceed with an inversion mechanism.     

Acid-base chemistry of a carbenium ion in a zeolite under equilibrium conditions: verification of a theoretical explanation of carbenium ion stability

The 1,3-dimethylcyclopentenyl carbenium ion (C7H11(+)) was reproducibly prepared on zeolite HZSM-5 using a pulse-quench reactor, and then each of a number of bases was coadsorbed into the catalyst channels to either compete with the cation for protonation or to possibly react with it as a nucleophile. For seven bases with proton affinities (PA) between 142 and 212.1 kcal/mol, there was no reaction with C7H11(+). Coadsorption of smaller amounts of dimethylacetamide (PA = 217 kcal/mol) also produced no reaction, but with a higher loading, a proton was transferred from the carbenium ion to the base to leave 1,3-dimethylcyclopenta-1,3-diene in the zeolite as a neutral olefin. Deprotonation was the primary reaction with coadsorption of either pyridine (PA = 222 kcal/mol) or trimethylphosphine (PA = 229.2 kcal/mol). The estimated experimental deprotonation enthalpy for C7H11(+), approximately 217 kcal/mol in the zeolite, is in excellent agreement with MP4/6-311G gas-phase value of 215.6 kcal/mol. Coadsorption of either NH3 (PA = 204.0 kcal/mol) or PH3 (PA = 188 kcal/mol) does not deprotonate the carbenium ion, but these species do react as nucleophiles to form onium ion derivatives of C7H11(+). Analogous onium complexes with pyridine or trimethylphosphine formed in lower yields due to steric constraints in the zeolite channels. The essential experimental observations were all predicted and explained by density functional calculations (B3LYP/6-311G) and extensions of our recently developed theory of carbenium ion stability in zeolites. In addition, we report theoretical geometries for several complexes which contain unusual C-H- - -X hydrogen bonds.     

Preparation of pH-sensitive polymer by thermal initiation polymerization and its application in fluorescence immunoassay

A fluorescence immunoassay for human IgG (Ag) was developed using a pH-sensitive polymer prepared by thermal initiation or redox initiation polymerization as a carrier. In the competitive immunoassay, appropriate quantity of Ag was immobilized on the polymer and the standard Ag (or sample) solution, and a constant amount of fluorescein isothiocyanate labeled goat anti-human IgG antibody (Ab-FITC) was added. Immobilized Ag and the standard (or sample) Ag competed for binding to the Ab-FITC in 37 °C in homogeneous format. After changing the pH to separate the polymer-immune complex precipitate, it was re-dissolved and determined by fluorescence method. The results showed that the immobilization efficiency, immunological reaction activities of immobilized Ag and phase transition pH range were improved as Ag was immobilized by thermal initiation instead of redox initiation polymerization. Under optimum conditions, the calibration graphs for the Ag in both methods, thermal initiation and redox initiation, were linear over the concentration range of 0.0-1000 ng mL⁻¹, with detection limits 8 (thermal initiation) and 12 ng mL⁻¹ (redox initiation), respectively. Moreover, some pH-sensitive polymer prepared only in organic solvent or under high temperature could also be used as an immunoreaction carrier by thermal initiation polymerization. Thermal initiation polymerization was a better immobilization mode.     

The initiation process in the polymerization of tetrahydrofuran with carbonium ion salts

The initiation process for the polymerization of tetrahydrofuran with (C₆H₅)₃C⁺SbCl₆^? has been studied. Two mechanisms have been considered: a cation-addition process, and a process in which tetrahydrofuran donates a hydride ion to the cation of the initiator to form triphenylmethane. The biscarbonium salt [(C₆H₅)₂C⁺C₆H₄CH₂]₂(SbCl₆^?)₂ has been synthesized and used to initiate the polymerization of tetrahydrofuran. The results are consistent with the hydride-ion mechanism but may be inconclusive because of chain transfer. NMR experiments with 0.05–0.2M solutions of initiator in tetrahydrofuran show that triphenylmethane is rapidly produced in an amount equal to the molar amount of initiator originally present. Some NMR evidence for the presence of an acetal end group in the polymer has been obtained. It is concluded that the initiation process in this system definitely involves the formation of triphenylmethane, although a detailed, unique mechanism cannot be selected at this time.     

Batch process monitoring and its application to polymerization systems

Slight changes in raw material properties or operating conditions during critical periods of operation of batch and semi-batch polymerization reactors may have a strong influence on reaction mechanism and impact final product quality. Online process monitoring, fault detection, fault diagnosis, and product quality prediction in real-time ensure safe reactor operation and warn operators about excursions from normal operation that may lead to deterioration in product properties. Multivariate statistical process monitoring and quality prediction using multiway principal components analysis and multiway partial least squares have been successful in detecting abnormalities in process operation and product quality. When abnormal process operation is detected, fault diagnosis tools are used to determine the source cause of the deviation. Illustrative case studies are presented via simulated polyvinyl acetate polymerization.     

Study of the ceric ion behavior on the initiation of butyl acrylate polymerization onto amylose

A study of the Ce(IV) ion consumption during graft polymerization of butyl acrylate with amylose was carried out. The Ce(IV) consumed was ca. 80% and the ratio of Ce(IV) to anhydroglucose units was 1/15. Poly(butyl acrylate) (PBA) chains were isolated from the grafted copolymer by the perchloric acid hydrolysis method. The molecular distribution was obtained by gel permeation chromatography (GPC). The number-average molecular weight (M_n) of the grafted chains was 276,000 and the weight-average molecular weight (M_w) was 1,320,000. The total number of grafted chains (mmol) ranged from 0.4410^?3 to 8.710^?3 (amylose from 0.08 g to 1.23 g). Frequency of grafting ranged from 1042 to 704.     

Homo-DNA templated chemistry and its application to nucleic acid sensing

We have investigated the homo-DNA templated Staudinger reduction of the profluorophore rhodamine azide and have applied this reaction to the detection of natural DNA with a hybrid homo-DNA/DNA molecular beacon. In this system the sensing and the reporting unit are bioorthogonal to each other which facilitates sequence design and increases fidelity.     

103Rh NMR spectroscopy and its application to rhodium chemistry

Rhodium is used for a number of large processes that rely on homogeneous rhodium-catalyzed reactions, for instance rhodium-catalyzed hydroformylation of alkenes, carbonylation of methanol to acetic acid and hydrodesulfurization of thiophene derivatives (in crude oil). Many laboratory applications in organometallic chemistry and catalysis involve organorhodium chemistry and a wealth of rhodium coordination compounds is known. For these and other areas, 103Rh NMR spectroscopy appears to be a very useful analytical tool. In this review, most of the literature concerning 103Rh NMR spectroscopy published from 1989 up to and including 2003 has been covered. After an introduction to several experimental methods for the detection of the insensitive 103Rh nucleus, a discussion of factors affecting the transition metal chemical shift is given. Computational aspects and calculations of chemical shifts are also briefly addressed. Next, the application of 103Rh NMR in coordination and organometallic chemistry is elaborated in more detail by highlighting recent developments in measurement and interpretation of 103Rh NMR data, in relation to rhodium-assisted reactions and homogeneous catalysis. The dependence of the 103Rh chemical shift on the ligands at rhodium in the first coordination sphere, on the complex geometry, oxidation state, temperature, solvent and concentration is treated. Several classes of compounds and special cases such as chiral rhodium compounds are reviewed. Finally, a section on scalar coupling to rhodium is provided.     

Multiple gamma-ray detection method and its application to nuclear chemistry

A new radionuclide quantification method is proposed on the basis of multiple gamma-ray detection, which is two or higher fold gamma-ray coincidence method. The coincidence method has so far been used for nuclear structure study. We apply this method for quantification of radioactive nuclei. The advantage of this method consists of high energy resolution and high sensitivity. It is successfully applied to nuclear waste analysis, neutron activation analysis and prompt gamma-ray analysis. The principle of the multiple gamma-ray detection method and future perspectives for an innovative pulsed neutron source and a new detector system will be presented.     

Macromonomers from vinyl and cyclic monomers prepared by initiation with stable carbenium salts

The initiation of polymerization of α-methylstyrene and p-methoxystyrene with 9-anthranylmethyl salts proceeds by hydride transfer from the monomer to the initiator. As a result, macromonomers with a double bond as head group are formed. These products polymerize and copolymerize by radical and ionic mechanism leading to graft and block copolymers. Styrene and α-caprolactone polymerize with the same initiator by cationation of the monomer. In this case each macromonomer contains one photoreactive anthranylmethyl group which may photodimerize. As a result copolymers of the type A? A or A? B are produced.     

ESR study on radical polymerization and its application to microemulsion systems

Well-resolved electron spin resonance (ESR) spectra of propagating radicals of vinyl and diene compounds were observed in a single scan by a conventional CW-ESR spectrometry without the aid of computer accumulation and the specially designed cavity and cells. Although solvents which could be used for ESR measurements were restricted to nonpolar solvents, such as benzene, toluene, and hexane, new information on dynamic behavior and reactivity of the propagating radicals in the radical polymerization of vinyl and diene compounds were obtained. Thus, values of propagation rate constants (k_p) for vinyl and diene compounds were determined by an ESR method. Some of the k_p values were in a fair agreement with those obtained by a pulsed laser polymerization (PLP) method. Furthermore, polymer chain effect on apparent k_p was clearly observed in the radical polymerization of macromonomers and in the microemulsion polymerization. In ESR measurement on inclusion polymerization system, important information on the origin of the 9-line spectrum observed in the radical polymerization of methacrylate propagating radicals was obtained.     

头孢克洛降解产物的电化学行为和测定

研究了在0.5mol/LNaOH溶液中,头孢克洛碱性降解产物在汞膜电极上的电化学为,并依此建立了头孢克洛的微分脉冲伏安测定法。头孢克洛碱性降解产物于～-0.85V(vs.Ag/AgCl)处出一灵敏的阴极还原峰,用循环伏安法、线性扫描极谱法、微分脉冲伏安法等手段研究了其电化学行为和机理。实验表明:头孢克洛降解产物在汞膜电极上具有明显的吸附性,电化学反应的电子转移数为2。伏安峰高与头孢克洛的浓度在1.0×10-8～5.0×10-6mol/L范围内有良好的线性关系。方法的检出限为5.0×10-9mol/L,方法可用于药品欣可诺颗粒剂中头孢克洛的测定。     

Radical/cation transformation polymerization and its application to the preparation of block copolymers

p-Methoxystyrene (MOS), butyl vinyl ether (BVE), and N-vinylcarbazole (VCZ) were polymerized in high yield by azoinitiators such as 2, 2'-azodiisobutyronitrile (AIBN) in the presence of electron acceptors such as Ph₂I⁺PF₆⁻. An electron paramagnetic resonance (ESR) study of the model radicals of the propagating radical showed the transformation of the radical to the corresponding cation in the presence of the electron acceptors. In the case of BVE, the polymer formation was caused by cationic species produced by the transformation of the initiating radical. The polymerizations of MOS and VCZ were ascribed to the transformation of the growing radical to the corresponding cation during the propagation step which was classified as the radical/cation transformation polymerization. Block copolymers of MOS/cyclohexene oxide (1, 2-epoxycyclohexane) (CHO) and VCZ/CHO were effectively prepared by the radical/cation transformation polymerization of the appropriate monomers in the presence of AIBN, electron acceptor and CHO. The formation of block copolymers was characterized by turbidimetry, thin-layer chromatography, and solubility tests.     

Preparation of PDMS-ormosil and its application in miniemulsion polymerization

With the assistance of ultrasound, octamethylcyclotetrasiloxane (D4) and slight silane coupling agent γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560) were sufficiently mixed with silica sol, and the in situ ring-opening polymerization of D4 on the surface of silica nanoparticles, catalyzed by dodecylbenzene sulfonic acid (DBSA), was enhanced as well. Thus, polydimethylsiloxane (PDMS)-modified silica (PDMS-ormosil) mixture was obtained. A slight addition of silane coupling agent γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560) could significantly enhance the modified efficiency. The PDMS-ormosil mixtures were directly dispersed in the mixed monomer methyl methacrylate and butyl methacrylate. Then, miniemulsion polymerizations of acrylate monomers containing PDMS-ormosils were carried out, with free PDMS as hydrophobe and neutralized DBSA as emulsifier, both preexisted in the PDMS-ormosil mixture. Thus, the troubles of separation, purification, and redispersion in the traditional techniques can be omitted. Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscope, scanning electron microscope, and water contact angle tests were utilized to demonstrate that nanocomposite particles with a core–shell structure were synthesized; when the silica content was 3 wt% of the monomers, the average particle size was 97 nm, and the generated PDMS improved the hydrophobicity of the nanocomposite latex.     

Sensing cyanide ion via fluorescent change and its application to the microfluidic system

We introduce a cyanide selective microfluidic platform, in which fluorescent chemodosimeter 1 displayed a selective green fluorescence upon the addition of cyanide. Our system was examined in aqueous solution, and the ‘OFF-ON’ type emission change can be monitored over 500 nm. In addition, colorimetric change was also observed upon the addition of cyanide. The practical use of the probe was demonstrated by its application to the detection of cyanide in the living cells.     

The spatial effect of near-infrared spectroscopy and its application to the study of supramolecular chemistry

An unlooked-for experimental observation that in near-infrared spectroscopy (NIR) the absorption peak of the second overtone of aniline adsorbed by 13X molecular sieve nearly disappeared led us investigate a fundamental question: the behavior of NIR when the outside space surrounding a molecule is too small to allow the molecule to vibrate freely. Through NIR of various organic compounds adsorbed by different porous inorganic materials like 13X molecular sieve, silica gel and active aluminium oxide, and NIR of supramolecular cyanuric acid-melamine, we can reasonably confirm a theoretical inference that in the micro-environment above, all intensities of NIR absorbance decrease, and the second overtone decreases more than the first overtone does. Furthermore, one distinct feature of NIR, higher sensitivity to the size of micro-environmental space as compared with mid-infrared (MIR), and its potential application to the study of supramolecular structure are outlined by our experiments.