In this chapter, the causes of the stability violation of self-propagating heat waves in the process of frontal polymerization (FP) are studied. FP is an autowave process of the propagation of polymerization heat waves. One of the major factors for the practical implementation of FP is the necessity to establish the causes and boundaries of the stability violation of propagating heat waves in the process of FP. The paper clarifies one of the causes of stability violation during FP of complexes of acrylamide (AAm) with transition metals. Taking into account that, for the specified monomers, the cause of stability violation and appearance of spin modes is shrinkage of polymer, we have investigated nanoparticle additions to the polymerizing media. It is shown that it is possible to regulate the stability violation during FP of the monomers depending on the amount of nanoparticle additions.

Abstract Taking into account the fact that since the 1970s frontal polymerization (FP) reactors in flow have been the subject of our study, the work gives a brief chronology of the development of FP reactors for the synthesis of high molecular polymers, polymeric hydrogels with cross-linked structure, their advantages and drawbacks. The reasons for the impossibility of the practical implementation of tubular FP reactors in flow for the synthesis of polymers are established. The possibility of implementation of tubular FP reactors for the synthesis of polyacrylamide hydrogels (PAH) capable of absorbing and releasing large amount of water is presented. The paper also presents some data on the methods for the synthesis of PAHs with prescribed properties in tubular continuous FP reactors by way of using nano-additives and regulating the kinetics of the synthesis process. As a result, the synthesis process of PAHs with the required properties both in the absorption and release of water, and in the physical-mechanical properties was carried out in frontal tubular-type reactors in flow, and the water absorption kinetic curves and physical-mechanical properties of the obtained hydrogels are presented.

The purpose of this work was to study the causes of the formation of nonlinear and spin modes in the process of frontal polymerization (FP). The latter is an autowave process of the propagation of polymerization heat waves, and is a nontraditional method for the synthesis of various polymers and polymeric composites. Monomers of metal-complexes of acrylamide with and without additions of inert and nano-fillers were chosen as objects of study. Research data on dilatometric analysis, as well as on kinetics and macrokinetics of the polymerization processes of the monomers in frontal mode are presented. On the basis of the results obtained, a conclusion was drawn on the stability loss and transition boundary from a stationary mode to nonstationary one during FP. It was shown that, during the polymerization processes, shrinkage of the resulting polymer composites occurs, commensurate with the phase of the heat wave oscillations, which disturbs the propagating heat waves from layer to layer and violates the stationarity of the process. This, in turn, results in the formation of spin-like rings and a nonstationary mode of FP.

This paper discusses the results of theoretical and experimental studies on the implementation of frontal polymerization in continuous-flow reactors of various geometric designs. The stationarity and stability of propagation of the front wave are shown to depend on macrokinetic and kinetic parameters. The effects of the feed rate, reactor dimensions, and concentration of the mixtures of initiators and polymer additives on the conversion rate and molecular-weight characteristics of the formed polymer are studied. The causes of frontal stationarity disturbance, which are manifested by the formation of nonlinear phenomena in the form of various oscillation modes, are revealed. Brief characteristics of tubular reactors, as found theoretically and experimentally, and their shortcomings are presented. A cylindrical reactor for the frontal polymerization of methyl methacrylate is presented, which was developed at the Experimental Plant in Chernogolovka (Moscow oblast) and introduced into industrial production in Dzerzhinsk. A tubular reactor that was built in to a flow for the synthesis of hydrogels under the conditions of frontal polymerization is also presented.

The method of frontal polymerization (FP) has been presented repeatedly in different publications but, taking into account the aim of this review, we intend to focus detailed and oriented attention on the process specificity that causes its unexpected advantages. This work has disclosed the ways to detect, reveal, and investigate the foundations of the frontal polymerization method and their use in different areas of science and technology. As researchers gain closer insight into this nontypical method of polymerization, they reveal new advantages and possibilities for its use to solve many problems both in the synthesis of polymer nanocomposites with retention of nanoscale dimensions, uniform distribution, and the optimal number of nanoparticles and in the synthesis of intercalated polymeric high-temperature superconductors, multifunctional gradient materials, hydrogels with prescribed properties, and other materials. It has been shown that the models and revealed features for the transition of linear autowaves into nonlinear ones are of interest and can be used similarly to the autowave processes that occur by the Belousov–Zhabotinsky mechanism in biology and human organism. With allowance for that noted above, this paper also describes the kinetic features of frontal polymerization that cause us to reconsider certain approaches and principles of formal kinetics. The ways and methods to pass from formal (isothermal) kinetics to nonisothermal kinetics (by the example of adiabatic polymerization) with finding the new principles of kinetic computations under nonisothermal conditions in application to frontal polymerization are given.

The effect of different nanoparticles (bentonite, SiO2) and finely disperse fillers (chalk, diatomite) on peculiarities of acrylamide frontal free-radical polymerization initiated by azo-iso-butyronitrile and benzoyl peroxide was studied. It was determined that the increase in an order with respect to initiator is conditioned by influence of nano and micro additives not only on the mechanism of initiator decomposition but also on the reaction of chains bimolecular termination.

With the use of yttrium and bismuth ceramics' powders (Y 1 Ba 2 Cu 3 O 6.97 andBi 2 aSr 2 Ca 2 Cu 2 O 8), on the basis of super-high molecular polyethylene binder, current-carrying polymer-ceramic nanocomposites are obtained. It is shown that the implementation of the proximity effect between the ceramics' grains leads to obtaining superconducting polymer-ceramic nanocomposites with a transport current. Additives of silver and aluminum nano-scale powders cause significant increase of current density, and the application of acoustic fields during the formation of samples allows to further increase the density to ∼ 4 - 103 A cm - 2 $ \sim 4 - 103{\text{A}}\,{\text{cm}}^{ - 2} $ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315365985/93067212-2742-4adb-9a79-69b21685310d/content/inline-math2.tif"/> . Physical and mechanical properties of current-carrying polymer-ceramic nanocomposites have been investigated and it is shown that nano-sized aluminum additives increase the breaking strength and the elasticity modulus of the samples. The morphological features of currentcarrying polymer-ceramic nano-composites' interphase layer on the basis of various binders (polymethylmethacrylate, polystyrene, super-high molecular polyethylene and isotactic polypropylene) have been studied.

On the examples of frontal polymerization, tumor growth, and propagation of the nerve impulse, we examined nonlinear phenomena in chemistry and biology. The results of theoretical and experimental studies on the loss of stability of thermal waves of frontal polymerization were presented. The stationarity loss limits for the reactions of epoxide resin curing, polymerization of metal-containing acrylamide complexes, and copolymerization of methyl methacrylate and styrene in the presence of single-walled nanotubes were experimentally studied and theoretically calculated. It was shown that stability of the frontal process waves depends on the heat balance of the exothermic polymerization reaction. Nonlinear phenomena at variation of the polymerization kinetic parameters were studied. The limits of the transition from stationary to nonstationary mode were determined on the basis of experimental data and theoretical calculations. Theoretical study of a diffusion-kinetic model of tumor growth was discussed; the wave nature of the propagation of tumors was shown. The FitzHugh–Nagumo model was studied in view of the diffusion equation; the possibility of formation of the oscillatory modes during the nerve impulse propagation was demonstrated.

Characteristics of the frontal copolymerization of acrylamide with methyl methacrylate in the presence of single-wall carbon nanotubes in different amounts are studied. It is shown that adding of bentonite, which represents the natural lamellar nanomaterial with nanodimensional layers, results in the formation of polyacrylamide-bentonite hydrogels. It is shown that the filling by nanotubes by more than 20% (of the initial weight of comonomers) causes the loss of stability of copolymerization thermal waves with occurrence of periodical, spin and chaotic modes. The mechanism of periodical modes formation is offered. Physical and mechanical, dynamic and mechanical and thermochemical properties of obtained polymer nanocomposites are studied. On the basis of analysis of the data on the influence of amounts of single-wall nanotubes on the properties of copolymer nanocomposites the conclusion is drawn relative to the intercalation of copolymer macromolecules into the inner surface of nanotubes.

State Engineering University of Armenia, 105 Teryana Str., Yerevan, 375009, Armenia, E-mail: atonoyan@mail.ruAbstract ................................................................................................. 220 20.1 Introduction ................................................................................ 220 20.2 Experimental Part ....................................................................... 221 20.3 Influence of Amounts of SWCNT on the Characteristicsof Frontal Copolymerization ...................................................... 222 20.4 Physical and Mechanical, Dynamic and Mechanicaland Thermochemical Properties of Nanocomposites................. 227 Keywords .............................................................................................. 230 References ............................................................................................. 230ABSTRACTCharacteristics of the frontal copolymerization of acrylamide with methyl-methacrylate in the presence of single-wall carbon nanotubes in different amounts are studied. It is shown that adding of bentonite which represents the natural lamellar nanomaterial with nanodimensional layers results in the formation of polyacrylamide-bentonite hydrogels. It is shown that the filling by nanotubes by more than 20% (of the initial weight of comonomers) causes the loss of stability of copolymerization thermal waves with occurrence of periodical, spin and chaotic modes. The mechanism of periodical modes formation is offered. Physical and mechanical, dynamic and mechanical and thermochemical properties of obtained polymer nanocomposites are studied.

In the presented chapter the advantages of frontal polymerization, which promotes the deagglomeration of nanoparticles, as well as the uniform distribution and preservation of the nanoparticle sizes in the obtained nanocomposites are shown. The data on the synthesis of various nanocomposites by frontal polymerization, the results of investigations on the influence of nano additives on the polymerization kinetics and the properties of obtained nanocomposites are presented.

The influence of added nano-particles (SiO2, TiO2) on the process of frontal copolymerization (acrylamide + methylmetacrylate, acrylamide + styrene) is investigated, and the thermo-physical properties of the obtained nano-composites are studied. Having data of the influence of the amount of nano-particles on the limiting temperature of thermal waves, on the front velocity, and on the law of additive changes concerning the relative thermal capacities of the obtained nano-composites, conclusions can be drawn regarding the positive influence of thermal waves on the process of nano-particle deagglomeration. It is shown, that the dependence of this relative thermal capacity on the amount of nano-particles is non-additive. An analysis of these results shows, that the characteristic sizes of the rigid amorphous fraction formed on the nano-particle surface are characterized not only by the nature and size of the nano-particles, but also by polymeric binding. The thickness of the rigid amorphous fraction is independent of the quantity of nano-additives. (C) 2014 Published by Elsevier Ltd.

A one-dimensional and two-dimensional model of the frontal reaction of epoxy compounds by aromatic amines in tubular flux reactors is investigated. The influence of relevant kinetic factors (velocity, activation energy, and others) on the velocity of the traveling front, the heat regimes of the reactor, and the geometric dimensions of the reactor is studied. An optimal steady-state condition of the tubular reactor under continuous action is determined. Profiled armored carbon and glass plastics forming laboratory installation are constructed, as derived from the obtained theoretical results. It is shown that the theoretical and practical results are in satisfactory agreement. Several physico-mechanical properties (e.g., bending strength, longitudinal modulus of elasticity), as based on the reactor wall temperature, angle of armoring, and tension are determined.

This chapter reviews the preparation and study of high-temperature superconducting (SC) nanocomposites based on SC ceramics and various polymeric binders. Regardless of the size of the ceramic grains, any increase in their quantity results in an increase of resistance to rupture and modulus and a decrease in limiting deformation, whilst a similar increase in the average ceramic grain size worsens resistance properties. Investigation of the SC, thermo-chemical, mechanical and dynamic-mechanical properties of the samples are discussed. Superconducting properties of the polymer–ceramic nanocomposites are explained by intercalation of macromolecule fragments into the interstitial layer of the ceramic grains, a phenomenon that leads to a change in the morphological structure of SC nanocomposites.

This paper analyzes available data on the synthesis and properties of polymer nanocomposites prepared by various techniques (sol-gel processing and microemulsion and frontal polymerizations) and containing polymethyl methacrylate, polydimethylsiloxane, natural rubber, and other polymers as binders, and various amounts of nano- and microadditives: SiO 2 , TiO 2 , FeO, clay, and Y 1 Ba 2 Cu 3 O 7 − x . We consider the physicomechanical, dynamic mechanical, superconducting, thermophysical, thermochemical, and other properties of the polymer nanocomposites. Also examined are data on the activated anionic polymerization of ɛ-caprolactam in the presence of various amounts of SiO 2 nanoparticles. Results on crystallization kinetics and electron microscopy data lead us to conclude that SiO 2 nanoparticles act as heterogeneous nucleation centers for the crystallization of the forming poly(ɛ-caprolactam). Analysis of our results and data reported by other groups demonstrates that the intercalation of polymer macromolecules and their fragments into the interlayer spaces of ceramic grains increases the superconducting transition temperature of the ceramic by 1–3°C.

1 State Engineering University of Armenia, 105 Teryan Street, 375009 Yerevan, Armenia 2 Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 Kosygin Street, Moscow 119991, Russia 3 Institute of New Materials Chemistry, National Academy of Sciences of Belarus, 36 Fr. Skorini, 220141 Minsk, Belarus 4 Ivane Javakhishvili Tbilisi State University, Ilia Chavchavadze Avenue, 0179 Tbilisi, Georgia

Physical causes of the absence of steady-state heat regimes of frontal radical polymerization of vinyl monomers at a nonzero rate of chemical transformations of initial reaction media are discussed. The effect of the dimensionless "cutting" temperature of a heat-generation source on the relative velocity of poly-merization front propagation is studied. There is an interval of "cutting" temperatures of the source where the velocity of polymerization front propagation is independent of the "cutting" temperature of the source. As for combustion processes, the front velocity depends on dimensionless parameters that are intrinsic for the heat regime of the process.

The main stages of the development of frontal polymerization are presented. The processes taking place at cryogenic temperatures, under high (up to 5 kbar) pressures and usual conditions, when the polymerization is performed in glass ampoules without excessive pressure, are discussed. Depending on the Semenov parameter, the conditions of polymerization in low-temperature quasi-isothermal and high-temperature adiabatic or frontal thermal modes are considered. Theoretical and experimental data for the dependence of the front velocity on the various parameters. The influence of the nature of initiator, monomer, and dispersed inorganic on the reaction order with respect to the initiator is analyzed. Monomers polymerizing in the reaction front propagation are classified regarding their polymerization rates and boiling temperatures. The articles of various authors devoted to the synthesis of polymer materials and polymer-based composites difficult to obtain under conventional conditions are considered. The reactors of frontal polymerization in turbulent and laminar flows, widely applied in practice, are studied. Certain conclusions are made on the further development of frontal polymerization processes on the basis of data available in the literature.

Quasi-stationary concentration principle (QSC) was used to study radical polymerization of vinyl monomers during reaction traveling front. Based on the experimental results and numerical calculation of the one-dimensional front, it was shown that the zone could be both narrow and wide. Full and quasi stationary problems were solved for different sets of kinetic and thermo-physical parameters typical for vinyl monomers' radical polymerization.Anion activated copolymerization of epsilon-caprolactam with co-dodecalactam has been investigated during heat wave propagation. It was shown that separation of polymerization and crystallization auto waves takes place at 130 degrees C (initial temperature of the reaction mixture). The observed limiting heating temperature oscillation leads to disruption of the crystallization auto waves. It was assumed that the reasons for these unstable regimes are the multiple sequential melting and crystallization processes. A thermometric method of determination of the composition of co-polymers is proposed.A one-dimensional and two-dimensional model of frontal solidification of epoxy compounds by the aromatic amines in tubular flux reactors is investigated. The influence of some kinetic factors on the velocity of traveling of the front, on the reactor heat regimes and on the geometric dimensions of the reactor is studied. Profiled armored carbon and glass plastics forming laboratory installation is constructed based on the obtained theoretical results. It was shown that the theoretical and practical results correspond satisfactorily. Several physical-mechanical properties (bending strength, longitudinal modulus of elasticity) as based on the reactor wall temperature, angle of armoring and tension is determined.Front dynamics and stability boundaries of stable frontal regimes in the frontal polycondensation of epoxy oligomers in the presence of the m-phenylene diamine (m-PDA) and the frontal polymerization of the nitrate containing metal-complex monomers were investigated. Three mechanisms of instabilities have been observed.We show that the increase of heat loss from the reacting zone to the environment can cause the onset of periodic modes of propagation and loss of stability of the steady fronts. It was found that a nonstationary pulsation in frontal processes of epoxy oligomers solidification leads to deterioration of the physico-mechanical properties polymer samples obtained. An analysis of experimental data concerning the structure and the coordinate of a propagation thermal wave allow an estimation of the front stability.Similar results were found in the study of the frontal polymerization of cobalt nitrate containing metal-complex monomers with acrylamide.

Anion activated adiabatic polymerization of epsilon-caprolactam was investigated in the presence of various quantities of nano-SiO2. The parallel processes of crystallization and polymerization are separated first. Based on the crystallization kinetics and electron microscopic investigations it was shown that nano-SiO2 particles are heterogeneous nuclei for the crystallization of poly-epsilon-caprolactam. Further the time dependence of mean length of amorphous polymer macromolecules is determined experimentally.