Polymeric grain propagation

The identification of polymeric grains as microreactors, in which the polymerization process is localized from the moment of grain formation and until the moment of their contact and propagation into a microheterogeneous polymeric body, has been carried out by sol-gel analysis [122] and thermometrical methods [1231 in studies of oligoesteracrylates polymerization kinetics. 

As result of investigation the composition of reactive system as a function of the polymerization depth T, for oligoesteracrylates with 2-6 functional groups the following dependence has been determined  

At this time, / j is not changed by the polymerization and is equal to the maximum value at the respective temperature  

We can conclude from equations (3.28)-(3.30) that and the sol-fraction consists of the starting monomer [124-126]. Correspondly, the reactive system of the polymerizing process proceeding consists of only two components, namely the non-soluble densely-cross-linked polymer (so-called gel) with maximum conversion depth and the starting monomer. 

A correlation between the sol-fraction yield and 3-D polymerization depth obtained using equation (3.28) allows us to propose the following chemical mechanism of grain 

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Kinetic reasons cause the formation of a micro-gel particle formation in which a local gel-effect proceeds. Further polymerization is carried out at the expense of growing new outlying layers on the surface of polymeric grains that arc micro-reactors in which the polymerization process is localized. At the state of the transformation when the volumetric part of the propagating discrete particles is sufficient for their interaction, these particles are joined. The growth into a uniform structure in the monolytization state proceeds at the expense of polymerization transformations in the joint zones. 

Propagation of the polymeric grains into the monolith in the late states of polymerization... 

A monolytization state should be characterized by a sharp change of the properties of formed polymer. Grain propagation in the polymerization system proceeds via at least two states. The first state is reached when the size of grains is sufficiently small. In this... 

The indicated characteristic of the 3-D polymerization is a direct proof of the microheterogeneity of a process, of an active role of the liquid monomer-solid polymer interface layer and also proof of the fluctuative mechanism of polymeric grain formation and propagation. This is reflected, first of all, in the kinetic constant the numerical value of which depends on the ratio of fractal characteristics of the surface and volume of the clusters of the solid polymeric phase into the liquid monomeric phase and liquid monomer into the solid polymeric matrix. Exactly that is why the calculations of IVo according to stationary kinetic equation (4.46) cannot take into account the individual character of the postpolymerization curves. 

Starting from the polymerization depth the formation of new polymeric chains will stop, since each new chain in its propagation will be attached compulsory to at least one link of the former formed macromolecule with the formation of the joint with its particle. It can be assumed that each primary chain is a nucleus of the isolated particle in the solution of an oligomer. The maximum quantity of the isolated grains that can be accumulated in the system until the moment is reached is equal to... 

The formation of densely-cross-linked polymeric particles with their following propagation at the expense of polymerization transformation of the starting monomer leads to a range of consequences. Of these consequences the most important is the existence of a state of polymerization propagation of discrete grains into monolith. 

A fractal approach [11] instead of a geometric one [8] has been used by us for functional determination of the volumetric part (p of the interface layer. In accordance with this fractal approach we suppose that propagating grains or clusters of solid polymeric phase are characterized by their fractal structure, the dimensionality of which generally does not coincide with the dimensionality of the Euclidean space. For example, the volume... 

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