Heterophase systems, mechanisms

Rubber-resin heterophase systems are classified as (1) resin as the disperse phase, (2) rubber as the disperse phase, (3) grafted rubber latex particles as the disperse phase, and (4) filled graft rubber as the disperse phase. Adhesion mechanisms related to these systems are discussed. Special emphasis is made on the last two systems which involve grafting. The graft rubber isolated from the fourth system is characterized. The graft rubber is shown to function as a compatibilizer and as an adhesive or a coupling agent for the rubber-resin interface. 

The proper characterization and description of the interfaces between the phases is a key technical challenge to simulating the mechanical properties of heterophasic systems under large deformations. This challenge will be discussed now in the context of the conceptual framework of cohesive (bulk) and adhesive (interfacial) failure which was introduced in Section 7.C. 

The important factor in heterophase systems is the intensity of mixing of the ingredients [106]. Time and intensity of mixing were not varied in these investigations. The sterns investigated were mixed using a mechanical mixer for 3 min at 600 rev/min. 

The description of motions in heterophase systems, by continuous medium mechanics methods based on the Euler approach, correlates with the introduction of the multispeed continuum concept and determination of the interpenetrating motion of the dispersion system components. A multispeed continuum is the sum total of N continuums with each representing its own specific mixture component (phase or component) and fills the same space. For each of the continuums, the density p is trivially determined, as well as the motion rate and other parameters. Thus, any point of the area filled by a mixture, is determined by N densities, N rates, and so on. These values can be used for the determination of parameters characterising a whole mixture of components, which are density and the average weight of the mixture flow rate. 

The formation mechanism of structure of the crosslinked copolymer in the presence of solvents described on the basis of the Flory-Huggins theory of polymer solutions has been considered by Dusek [1,2]. In accordance with the proposed thermodynamic model [3], the main factors affecting phase separation in the course of heterophase crosslinking polymerization are the thermodynamic quality of the solvent determined by Huggins constant x for the polymer-solvent system and the quantity of the crosslinking agent introduced (polyvinyl comonomers). The theory makes it possible to determine the critical degree of copolymerization at which phase separation takes place. The study of this phenomenon is complex also because the comonomers act as diluents. 

In more recent years, Herman Mark has, as we all know, concentrated more on the effects of heterophase morphology of polymers on their mechanical properties. This has enabled him to set up a useful classification system of the various types of heterogeneities which can occur in polymers, e.g., crystallinity, incompatibility, particulate and fibrous inclusions, etc. and to discuss these in the context of their effect on the mechanical properties. Such an "overview" has again kept Mark in great demand as a speaker. 

Detailed analysis of the isothermal dynamic mechanical data obtained as a function of frequency on the Rheometrics apparatus lends strong support to the tentative conclusions outlined above. It is important to note that heterophase (21) polymer systems are now known to be thermo-rheologically complex (22,23,24,25), resulting in the inapplicability of traditional time-temperature superposition (26) to isothermal sets of viscoelastic data limitations on the time or frequency range of the data may lead to the appearance of successful superposition in some ranges of temperature (25), but the approximate shift factors (26) thus obtained show clearly the transfer viscoelastic response... 

New kinetic regularities at polymerization of vinyl monomers in homophase and heterophase conditions in the presence of additives of transition metal salts, azonitriles, peroxides, stable nitroxyl radicals and radical anions (and their complexes), aromatic amines and their derivatives, emulsifiers and solvents of various nature were revealed. The mechanisms of the studied processes have been estabhshed in the whole and as elementary stages, their basic kinetic characteristics have been determined. Equations to describe the behavior of the studied chemical systems in polymerization reactions proceeding in various physicochemical conditions have been derived. Scientific principles of regulating polymer synthesis processes have been elaborated, which allows optimization of some industrial technologies and solving most important problems of environment protection. 

Aqueous heterophase polymerization is not only an industrially important radical polymerization technique but also scientifically challenging as well as offering unique possibilities for basic scientific studies. All advantages as well as all kinetic peculiarities of heterophase polymerizations are grounded on the heterogeneous nature of the reaction system creating at least two, extremely different reaction loci. The potential ability to produce amphiphilic block copolymers via a simple radical polymerization mechanism under such circumstances was recognized already 1952.[y... 

Heterophase polymerization systems can be defined as two-phase systems in which the resulting polymer and/or starting monomer are in the form of a fine dispersion in an immiscible liquid medium defined as the polymerization medium , continuous phase , or outer phase . Even if oil-in-water (o/w) systems are greatly preferred on an industrial scale, water-in-oil (w/o) systems may also be envisaged for specific purposes. Heterogeneous polymerization processes can be classified as suspension, dispersion, precipitation, emulsion, or miniemulsion techniques according to interdependent criteria which are the initial state of the polymerization mixture, the kinetics of polymerization, the mechanism of particle formation and the size and shape of the final polymer particles (Fig. 4.2) [18]. 

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