Polymers formation mechanisms

Thus, powder formation can be viewed as a polymer deposition process occurring by the same polymer formation mechanism that applies to the formation of films. In other words, no special monomer, reactive intermediate, or a different agent of polymer formation is needed for powder formation. The infrared spectra of films and powders are virtually identical [11], as shown in Figure 8.19 and Table 8.3. 

Such phenomena give rise to the assumption of the following polymer formation mechanism ... 

In Fig. 13, a kinetic curve conversion degree — reaction duration Q, is shown schematically, on which the technique of estimation of the characteristic times t, and tj, corresponding to termination of initial section and autoacceleration section of curve Q, are indicated. The calculated according to the Eq. (4) of Chapter 1 D value, which is equal to 1.65, defines unequivocally polymer formation mechanism as diffusion-limited aggregation cluster-cluster. However, as it was indicated above, in polymerization process beginning at t = 0 monomers (particles) solution was the initial reactive mixture, where macromolecular coils were absent. Let us remind that for such coil formation a macromolecule should consist of, as a minimum, 20 monomer links [35], Therefore, it is obvious, that on the first stage of polymerization mechanism particle-clrrster should be realized and this mechanism will act until in solution macromolecirlar coils (clusters) sufficient number is not formed for mechanism cluster-clrrster realization [36], Hence it follows that... 

In addition to graft copolymer attached to the mbber particle surface, the formation of styrene—acrylonitrile copolymer occluded within the mbber particle may occur. The mechanism and extent of occluded polymer formation depends on the manufacturing process. The factors affecting occlusion formation in bulk (77) and emulsion processes (78) have been described. The use of block copolymers of styrene and butadiene in bulk systems can control particle size and give rise to unusual particle morphologies (eg, coil, rod, capsule, cellular) (77). 

An expression for the number of particles formed during Stage I was developed, assuming micellar entry as the formation mechanism (13), where k is a constant varying from 0.37 to 0.53 depending on the relative rates of radical adsorption in micelles and polymer particles, r is the rate of radical generation, m is the rate of particle growth, is the surface area covered by one surfactant molecule, and S is the total concentration of soap molecules. 

The olefins that undergo metathesis include most simple and substituted olefins cycHc olefins give linear high molecular-weight polymers. The mechanism of the reaction is beheved to involve formation of carbene complexes that react via cycHc intermediates, ie, metaHacycles. Industrial olefin metathesis processes are carried out with soHd catalysts (30). 

Due to the unique HETP characteristics, it is important to consult the manufacturer on the specific system involved and operating conditions. Care must be exercised in selecting these or any other type of packing since plugging with suspended solids, polymer formation on surfaces, and similar mechanical problems can influence performance and life of the packing system. 

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. 

Quantum chemical calculations, 172 Quantum chemical method, calculations of the adsorption of water by, 172 Quantum mechanical calculations for the metal-solution interface (Kripsonsov), 174 and water adsorption, 76 Quartz crystal micro-balance, used for electronically conducting polymer formation, 578... 

On the basis of the above described studies, we propose a model for the structure formation mechanism during the induction period when a polymer is crystallized from the unstable state. Figure 24 shows a schematic diagram of... 

The symposium was planned as a state-of-the-art meeting, focusing on the basic science. Program areas included high heat polymers, fire performance of polymers, hazard modeling, mechanism of flammability and fire retardation, char formation, effects of surfaces on flammability, smoke assessment and formation mechanisms, and combustion product toxicity. 

An NMR investigation of water exchange at [Pt(H20)2(oxalate)2] is relevant to the mechanism of formation of one-dimensional mixed valence oxalatoplatinum polymers. In fact the rate constant for this presumably dissociative (AS = + 42 JK mol-1) reaction is considerably too low for water loss to be, as recently proposed, the first step in formation of these polymers. The mechanism of trans to cis isomerization for this oxalate complex, and for its (2 -methyl)malonate analogues, is intramolecular (Bailar or Ray-Dutt twist), since there is no concurrent incorporation of labeled solvent (177). 

Thanks to its versatility, the general approach described hereabove gives a good grip of the synthesis of many different families of block polymers. However, in several cases where the formation mechanisms of the two types of chains are not amenable to this quantitative active end-group conversion technique, a still more general answer is needed. 

Scheme 1 Classical formation mechanism of conducting polymers [7].

The work function of the rubbing surfaces and the electron affinity of additives are interconnected on the molecular level. This mechanism has been discussed in terms of tribopolymerization models as a general approach to boundary lubrication (Kajdas 1994, 2001). To evaluate the validity of the anion-radical mechanism, two metal systems were investigated, a hard steel ball on a softer steel plate and a hard ball on an aluminum plate. Both metal plates emit electrons under friction, but aluminum produced more exoelectrons than steel. With aluminum, the addition of 1% styrene to the hexadecane lubricating fluid reduced the wear volume of the plate by over 65%. This effect considerably predominates that of steel on steel. Friction initiates polymerization of styrene, and this polymer formation was proven. It was also found that lauryl methacrylate, diallyl phthalate, and vinyl acetate reduced wear in an aluminum pin-on-disc test by 60-80% (Kajdas 1994). 

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