Frontal Polymerization is a process that converts monomers into polymers by means of a propagating spatially localized reaction
front. Such fronts exist with free-radical polymerization, where in the simplest case, a mixture of monomers and initiator
is placed into a test tube and upon initiation of the reaction at one end of the tube, a self-sustained wave develops and
propagates through the tube. Isothermal Frontal Polymerization (IFP), often referred to as interfacial gel polymerization,
occurs due to the coupling of mass diffusion of the species and the gel effect. Utilizing the free volume theory of Vrentas
and Duda for describing the self-diffusive behavior of the gel effect, we mathematically model and study this IFP process.
We determine, both numerically and analytically, characteristics of the process including the propagation velocity of the
reaction zone, the structure of the wave, and the distance traveled by the front before it breaks down due to reactions ahead
of the front 相似文献
Frontal polymerization (FP) is a process in which a front propagates in a localized reaction zone, converting monomer into polymer through the coupling of thermal diffusion with the Arrhenius kinetics of an exothermic reaction. Fillers are added to control the rheological properties of the formulation and to enhance the mechanical properties of the product. However, the thermal and chemical effects of these fillers on the front propagation have not been thoroughly explored. Herein we report the thermal and chemical effects of fillers on free-radical frontal polymerization. It was found that fillers with high thermal diffusivities, such as milled carbon fiber and boron nitride increased the front velocity. Despite their high thermal diffusivities, fillers such as aluminum and alumina decreased the front velocity. This is likely due to the radical-scavenging ability of aluminum oxide, which was explored with clay minerals. It was found that the presence of water within clay fillers can also decrease the front velocity. To probe the chemical effects, acid-activated clay minerals were utilized. The results demonstrate that some fillers can increase front velocity through their high thermal diffusivities while others decrease it by acting as radical scavengers. 相似文献
Frontal polymerization is a process in which a localized reaction zone propagates from the coupling of thermal transport and the Arrhenius rate dependence of an exothermic polymerization; monomer is converted into polymer as the front passes through an unstirred medium. Herein we report the first study of charge transfer complexes (CTCs) as photo/thermal initiators for free-radical frontal polymerization. Front velocity was studied as a function of mole ratio between an aromatic amine, such as dimethyl-p-toluidine or dimethylaniline, and an iodonium salt. It was found that the front velocity reached a maximum at a certain mole ratio of amine to iodonium salt. The velocity remained constant upon increasing the ratio of amine to iodonium salt past this critical ratio. Fronts were also studied using N-phenyl glycine as an electron donor, but its utility was limited by low solubility. Lastly, the steric and electronic effects of the iodonium salt and counter anion were explored. It was found that CTCs using iodonium salts with less nucleophilic anions gave higher front velocities. In terms of intrinsic reactivity, the CTC composed of N,N-dimethyl-p-toluidine and bis[4-(tert-butyl)phenyl]iodonium tetra(nonafluoro-tert-butoxy)aluminate gave the highest front velocity per molal of iodonium salt. 相似文献
Frontal copolymerization is a process in which a spatially localized reaction zone propagates into a mixture of two monomers, converting them into a copolymer. In the simplest case of free‐radical copolymerization, a mixture of monomers and initiator is placed into a test tube. Reaction is initiated at one end of the tube, and a self‐sustained thermal wave, in which chemical conversion occurs, develops and propagates through the tube. We develop a mathematical model of the frontal copolymerization process and analytically determine the structure of the polymerization wave, the propagation velocity, maximum temperature, and degree of conversion of the monomers. Specifically, we examine their dependence on reactivity ratios as well as other kinetic parameters, monomer feed composition, and exothermicity of the reactions. Our analytic results are in good quantitative agreement with both direct numerical simulations of the model and experimental data, which are also presented in the paper.
Dependence of front velocity on monomer feed composition for different heat release parameters. 相似文献
Frontal polymerization (FP) is a mode of converting a monomer into a polymer via a localized reaction zone that propagates through the monomer. In this study, segmented polyurethane was successfully prepared by FP. The reactants, poly (propylene oxide) glycol, 2, 4-toluene diisocyanate and 1,4-butanediol and the catalyst stannous caprylate, were mixed together at an initial temperature in the presence of dimethylbenzene (as the solvent). The reactions were thermally ignited at one end of the tubular reactor, and the resultant hot fronts propagated throughout the reaction reactor. No further energy was required for polymerization to occur. The effect factors of front velocity, stannous caprylate concentration and temperature on the FP, along with comparison of FP with bulk polymerization, were thoroughly investigated. Fourier transform infrared and differential scanning calorimetry were employed to characterize polyurethane (PU). The polymer materials obtained by FP displayed features similar to those obtained by batch polymerization. The reaction time of FP for preparing PU was lower than that of BP. 相似文献
Frontal polymerization of cobalt nitrate containing metal-complex monomers with acryl-amide, compared to the frontal polymerization of liquid monomers, has several peculiarities with intricate (three- and two-stepped) structure of heat polymerization waves. Also, density increase elevates monotonically the upper-limit temperature of heat waves, broadens the gradient of temperature profiles, as well as changes the rate of the front propagation non-monotonically.Presumably, the surface tension energy and wetting power of crystalline monomers play an important role in the dynamics of propagation of heat waves as it was shown by the specially designed experiments.Experimentally, three ranges of thermal regimes were determined: (i) the range where stationary (steady-state) heat waves exist; (ii) non-steady-state range; and (iii) the range where no wave regimes are possible to exist.In the form of spin and other non-linear structures, one-, two-, three- and multi-set regimes were ascertained in non-steady-state range. 相似文献
In this study, poly(N-methylolacrylamide)/polymethylacrylamide (PNMA/PMAA) hybrids were produced successfully by frontal free-radical polymerization
at ambient pressure. In a typical run, the appropriate amounts of reactants (N-methylolacrylamide, NMA; methylacrylamide, MAA) and initiator (ammonium persulfate) were dissolved in dimethyl sulfoxide
at ambient temperature. Frontal polymerization (FP) was initiated by heating the wall of the tube with a soldering iron, and
the resultant hot fronts were allowed to self-propagate throughout the reaction vessel. Once initiated, no further energy
was required for polymerization to occur. The dependences of the front velocity and front temperature on the initiator concentration,
reactant dilution, and NMA/MAA components were thoroughly investigated. The front temperatures were between 69 and 116 °C,
depending on the persulfate concentration. We have also investigated the FP of PNMA/PMAA hybrids with N-methyl-2-pyrrolidone as solvent. Results show that FP can be exploited as a means for the preparation of PNMA/PMAA hybrids
with the potential advantage of higher throughput compared to the traditional mode. 相似文献
Stimuli-responsive polymers are macromolecular materials that undergo changes in response to small external stimuli in the environmental conditions. Among stimuli-responsive hydrogels are several polyacrylamides. Frontal polymerization is a fast, easy and inexpensive polymerization technique used for the synthesis of macromolecules.Aim of this work was the evaluation of the Frontal polymerization technique as new method for the preparation of controlled release dosage forms in which drug loading and polymer preparation occur together, as well as the possibility of obtaining more dosage units by a unique preparation. Hydrogels based on polyacrylamide containing diclofenac sodium salt were prepared using the Frontal polymerization and compared with similar systems obtained by the classic batch method. Polymers characterized by three different degree of cross-linking were prepared. The stability of the drug during the sample preparation was evaluated by IR analysis. The obtained samples were characterized in terms of drug content, morphology, in vitro drug release and swelling properties. Samples were studied also divided into disks. The results show that hydrogels based on polyacrylamide can be prepared by Frontal polymerization; these samples show similar properties to those obtained by batch polymerization. The drug is stable in the polymerization reaction conditions. Samples characterized by the lowest degree of cross-linking show drug loading values always higher than samples with the highest one regardless of the preparation method employed. The swelling ratio decreases as the degree of cross-linking increases. Loaded samples swell more than drug free ones. From a single preparation of hydrogel, three disks showing same drug content and in vitro release behaviour can be obtained and thus they can be used as three single dosage units. 相似文献
Frontal polymerization (FP) is a process in which a spatially localized reaction zone propagates into a monomer converting it into a polymer. Two types of FP processes have been observed experimentally. One is exothermic FP, which occurs due to diffusion of heat released in the polymerization reactions and which we have previously studied. The other is an isothermal FP process, also referred to as interfacial gel polymerization, which is due to mass diffusion of the species coupled with the gel effect. In a previous work we proposed and studied analytically a model of interfacial gel polymerization. That work discussed the case of an excessive amount of initiator in the initial mixture. In addition, it was assumed that the parameters of the problem were such that the steady‐state assumption (SSA) concerning the total concentration of radicals holds not only in the bulk region, which is typically the case, but also in the gel region, which may limit the applicability of the results. In this work we seek to resolve the limitations associated with these two main assumptions. We relax the SSA in the gel region, analyze the various situations of initiator consumption for a weak gel effect, and study the case of a strong gel effect. We obtain analytical results, including the time‐dependent propagation velocity of the reaction zone and the distance traveled by the front before it breaks down due to reactions ahead of the front, which are in good agreement with our numerical simulations. 相似文献