Recently, a research/development program has been initiated to investigate the kinetics of synthesis, characterization and applications of polyelectrolyte networks. The research on crosslinking involves both theoretical development and experimentation. Herein, is provided a summary of this work. In the experimental polymerization done to date, acrylic acid (AA)/N.N'-methylenebisacrylamide (BAM) was studied in considerable detail. The polymerization conditions were: temperature, 50°C; initial monomer concentration, 5 wt%, of which 1.0 mol% is BAM; K2S2O8(KPS) as the initiator, 10−3 mol/L; pH range, 1 − 13; sodium chloride concentrations up to 3.1 mol/L. Measurements included: monomer conversion, polymer composition, sol/gel fraction, swelling ratio, and the densities of primary cyclization, secondary cyclization and crosslinking. It was found that the effect of polymerization parameters on the resulting polymer network microstructure was dramatic, and in particular, the pH and ionic strength of the reaction medium were important parameters. In the theoretical studies, the Tobita-Hamielec kinetic gelation model was extended to incorporate the concept of ion pair interaction and the divinyl loop formation. The system was treated as a multi-component polymerization of acrylic acid, acrylate ion, acrylate ion pair and bisacrylamide. The model permits one to investigate the development of the crosslinking density distribution among primary polymer chains during the course of polymerization as a function of pH and ionic strength. 相似文献
Free-radical acrylic polymerizations of n-butyl methacrylate and n-butyl acrylate at temperatures above 120°C show significant departure from classic free-radical kinetics. An extended model of depropagation, where the equilibrium monomer concentration varies with temperature and polymer content, is postulated and shown to adequately explain the data for n-butyl methacrylate. Intramolecular chain transfer and scission is postulated to explain the apparent reduction in molecular weight and rate of polymerization seen in n-butyl acrylate polymerization, with supporting experimental evidence found via electrospray-ionization mass spectrometry. 相似文献
The kinetics of high-energy radiation initiated polymerization of acrylate and methacrylate monomers were studied in dilute cyclohexane solutions. The absorption spectra of the intermediates were obtained by pulse radiolysis with optical detection. In solutions of acrylates at longer times after the pulse the presence of oligomer radicals was observed. In solutions of methacrylates the beginning of the oligomerization reaction was detected at higher monomer concentrations. From the kinetic curves the rate coefficients of termination were calculated. 相似文献
Real time ultraviolet (RTUV) spectroscopy was used to study the photolysis kinetics of a radical-type morpholino initiator, during the polymerization of a multiacrylate monomer exposed to UV radiation in bulk, in solution, in a polyurethane-acrylate resin, and in a poly(methyl methacrylate) matrix. The photolysis rate constant k was determined from the exponential loss profile recorded; it was found to vary between 0.1 and 3s?1, depending on the light intensity and on the monomer concentration. The quenching of the photoinitiator excited states by the acrylate monomer was shown to be an important deactivation pathway which substantially reduces the rate of initiation. The observed influence of the film thickness and photoinitiator concentration on the k value were accounted for by the internal filter effect. Conversion versus time curves were recorded by real time infrared (RTIR) spectroscopy for the various systems examined, thus allowing a direct comparison of both the actual polymerization rate and the residual unsaturation content of the cured polymer. Various factors were shown to be responsible for the early stop of the polymerization, such as depletion of the photoinitiator, O2 inhibition, or vitrification of the polymer. The photoinitiated cationic ring-opening polymerization of a cycloaliphatic diepoxy monomer was also studied in real time by RTUV and RTIR spectroscopy. Despite a very fast photolysis of the triarylsulphonium initiator, the polymerization of the epoxy monomer developed less rapidly than for the acrylic monomer, with shorter kinetic chain lengths. A linear relationship was found to exist between the decay rate constant and the light intensity, for both the radical and the cationic photoinitiators, as expected for a direct photolysis process. 相似文献
The colloidal chemical properties of triple block copolymers of polypropylene oxide and polyethylene oxide (pluronics of various structures) were studied in comparison. All of them are shown to be surfactants but differ in interfacial tension, surface activity, surface area occupied in the adsorption layer, and adsorption layer thickness. The kinetic regularities of polymerization of styrene and methyl methacrylate were studied. The particle diameters and their size distribution were determined. Distinctions in the kinetic regularities of polymerization are shown: the shape of the conversion—time curves (for the duration of the initial and stationary stages of polymerization) and the dependences of the diameter on the surfactant concentration and monomer to water volume ratio. In the presence of the water-insoluble pluronics, the mechanism of formation of polymer—monomer particles and interfacial layer on the surface differs from that when using water-soluble surfactants, which makes it possible to distinguish these processes into an independent type of heterophase polymerization.
A kinetic investigation of the alternating copolymerization of butadiene and methyl methacrylate with the use of a system of ethylaluminum dichloride and vanadyl chloride as a catalyst was undertaken. The relation between the polymer yield and the molar fraction of methyl methacrylate in the feed was examined by continuous variation of butadiene and methyl methacrylate, the concentrations of total monomer, ethylaluminum dichloride, and vanadyl chloride being kept constant. This continuous variation method revealed that the polymer yield attains its maximum value with a monomer feed containing less than the 0.5 molar fraction of methyl methacrylate. This value of the molar fraction of methyl methacrylate affording the maximum polymer yield decreased on increasing the total monomer concentration but was not changed on varying the concentration of ethylaluminum dichloride. The number of active species estimated from the relation between yield and molecular weight of the polymer was almost constant, regardless of the molar fraction of methyl methacrylate in the feed. Consequently, it can be said that the maximum polymer yield depends mainly on the propagation reaction, not on the initiation reaction or the termination reaction. Three types of the mechanism have been discussed for this alternating copolymerization: polymerization via alternating addition of butadiene and methyl methacrylate complexed with ethylaluminum dichloride by the Lewis-Mayo scheme; polymerization via the ternary intermediate of butadiene, methyl methacrylate, and ethylaluminum dichloride; polymerization via the complex formation of butadiene and methyl methacrylate complexed with ethylaluminum dichloride occurring only at the growing polymer radical. From the kinetic results obtained, it was shown that the first and third schemes are excluded, and polymerization by way of the ternary intermediate is compatible with the data. 相似文献
Copolymerization studies of methacrylate-terminated polystyrene macromonomers (M1) with several comonomers (M2) verified the modified kinetic scheme and permitted prediction of graft polymer compositions and structures. Instantaneous and cumulative copolymer compositions, average graft distributions, and grafts per molecule are predicted from FORTRAN IV or BASIC programs. The r2 relative reactivity ratios determined from styrene copolymerization (0.61) or from low conversion acrylic monomer in aqueous suspension (~0.4) had good agreement with literature values (about 0.6 and 0.4, respectively). Decreased macromonomer reactivity determined at high acrylic monomer conversions was attributed to phase separation phenomena. The Macromers also exhibited lower reactivity than predicted when copolymerized with acrylic monomers in DMSO/benzene solutions (r2 ~ 0.8). 相似文献
The effect of the chain length of oligomer acrylic acid obtained in the presence of a low-molecularmass trithiocarbonate and the position of trithiocarbonate fragment (within the chain or at the chain end) on the process of emulsion polymerization of n-butyl acrylate and characteristics of the resulting dispersions has been studied for the first time. It has been found that, when using an oligomer with trithiocarbonate group located within the chain in the emulsion polymerization of n-butyl acrylate in a wide range of monomer–water phase compositions, triblock copolymers self-organizing in aqueous medium to give stable particles with the core–shell structure are formed. Oligomers with Mn ~ (5–10) × 103 are optimal for synthesis of stable dispersions. In this case, block copolymers with the controlled length of hydrophobic block and a rather narrow MWD may be obtained. Thin films formed from these copolymers retain the structure of the initial dispersions on solvent removal. If the trithiocarbonate group in the oligomer is located at the chain end, the main polymerization product is a diblock copolymer. In this case, the formation of polymer–monomer particles occurs during a longer period of time, the control of MWD is weakened, and the dispersions of particles lose the aggregative stability after thin film formation. 相似文献
The thermal polymerization of acrylic acid in bulk is faster than that of styrene. The conversion curves exhibit auto-acceleration and the product contains a significant fraction of syndiotactic polymer. The overall activation energy is 14 kcal/mol. The rate of the thermal polymerization decreases sharply when the monomer is diluted with toluene. In 50% monomer solutions, the conversion curves are linear and the overall activation energy is 29.8 kcal/mol. With 75 and 90% monomer solutions, the Arrhenius diagrams showed breaks caused by a change in the type of auto-association of the monomer. A comparison of these results with earlier findings obtained in the radiation polymerization of acrylic acid makes it possible to estimate the activation energies of the thermal initiation. It is found that Ei is 14.1 kcal/mol in systems where the monomer forms linear oligomeric association complexes and 34.4 kcal/mol if only cyclic dimers are present in the system. 相似文献
The results on radical polymerization and copolymerization of alkyl bromide salts of 2-dimethylaminoethyl methacrylate having a different alkyl chain length in various solvents giving micellar and isotropic solutions are summarized to obtain an insight into micellar polymerization. The monomer micellization of the cationic surface-active monomers at concentrations far above their critical micelle concentration (cmc) leads to great increases in the rate of polymerization and the molecular weight of the resulting polymers for both aqueous and inverse micellar systems and the tendency toward alternation of the copolymerization for aqueous micellar systems, whereas it has little influence on the tacticity of the resulting polymers. Applications of the polimerization and the copolymerization of the surface-active monomer to the polymer encapsulation of silica particles are also reported. 相似文献
Summary: This work demonstrates that acrylic acid (AA), glycidyl acrylate (GA) and several other acrylic monomers can be photopolymerized and photografted onto high‐density polyethylene (HDPE) by self‐initiation. The self‐initiation mechanism of these acrylic monomers is possibly by an excitation of the monomer to a triplet state (T3) with enough energy to abstract hydrogen from the polymer substrate and initiate the grafting.
Grafting conversion of acrylic acid (AA), methacrylic acid (MAA), 2‐hydroxyethyl acrylate (HEA), glycidyl acrylate (GA), 2‐hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) methacrylate (PEGMA) as a function of irradiation time. 相似文献