Polymerisation system microheterogeneity

From this point of view, the difference between microheterogeneous model and DCR approach consists only in the way that they consider or do not consider the microheterogeneity of polymerising system as an essential and important factor determining the main features of polymerisation process to the high degrees of conversions. 

Generally, the kinetic model of block 3-dimensional polymerisation of multifunctional monomers based upon microheterogeneity of polymerising system theory and especially the role of the interface layer of the boundary liquid monomer - solid polymer has been... 

Equations (4.24) and (4.34) (taking into account that dt = dx) represent by themselves the kinetic model of polymerisation in microheterogeneous system in the integral-differential form. The integrated form of kinetic model will be obtained, if we rewrite ... 

Thus, the integral kinetic model of polymerisation in microheterogeneous system can be notified in accordance with Equation (4.37) and Equation (4.40) as follows ... 

The microheterogeneity of the polymerisation system in a case of three-dimensional polymerisation is observed at very low conversions and is not an experimentally proven fact. Theoretically, this fact can be explained both thermodynamically (as a poor coexistence of the network polymer with monomer) and kinetically (by small viscosity of the monomer block, the solubility of polymer in which is small). 

In a case of a microheterogeneous system, polymerisation proceeds in the three reaction zones in saturated monomer-polymeric solution, at the interphase layer of the boundary of MPPh and micrograins of PMPh, and in the solid polymermonomeric solution. 

It follows from this, that the rate contribution (dP/dt) = %/ [MJ of the polymerisation process into PMPh in microheterogeneous system can be determined by expression ... 

The general kinetic equation of polymerisation in a microheterogeneous system at P > P° can be calculated as follows ... 

Characterisation of the Peculiarities of the Linear Polymerisation of the Microheterogeneous System... 

The experimental data represented as a conversion dependence upon time does not permit selection of the separate components of the linear polymerisation process, to estimate their share into the rate of the process and to underline its characterised features. The kinetic model gives this possibility. Let us consider the most interesting stage of the polymerisation in the microheterogeneous system, i.e., from the moment of the polymer -monomer phase extraction. 

Figure 4.4 Calculated dependence via Equations (4.62) and (4.63) and also the summary polymerisation rate, dP/dt in the microheterogeneous system curve 3) and it components, namely (dP/dt) is polymerisation rate in volume of PMPh curve 1), is polymerisation rate in volume of MPPh and interphase layer on the boundary of a MPPh and PMPh curve 2). Variants a), b) and c) correspond to variants presented in the Table in Figure 4.2.

The study of the influence of turbulent mixing on the modification of microheterogeneous Ziegler-Natta systems has been carried out in an experimental pulse-mode device (Figure 3.11), with a varied method of catalyst preparation. Isoprene polymerisation conversion curves have been obtained by gravimetric method. 

A similar dependency of catalyst dispersity can be observed in another microheterogeneous catalytic system based on the VOCl3-Al(i-C4H9)3 compound, which is widely used in isoprene and butadiene polymerisation processes. A substantial change of particle size in a two-component (V-Al) catalytic system, and the hydrodynamic impact on a catalytic system in a turbulent mode, is not observed with traditional process technology. A substantial decrease of catalyst particle size is observed after modification of the V-Al catalyst using piperylene additives. The hydrodynamic impact on the modified catalytic system results in an additional reduction of catalyst particle size. In addition, the particle size distribution for the Ti-Al catalyst narrows as it does for the V-Al catalyst. 

The change of reaction rate is well known to change with the intensity of mixing, indicating that elementary stages of the process are diffusion controlled. Preliminary turbulent mode mixing of a reaction mixture, for isoprene and butadiene polymerisation with a microheterogeneous titanium catalytic system, decreases the diffusion limitations when the surface structure of the catalyst is formed. 

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