Epoxy polymers description

The description of the variety of chemistries that are used to produce thermosetting polymers can be the subject of a whole book and is beyond the scope of this chapter. A description of chemistries involved in the synthesis of several families of thermosets can be found elsewhere [2]. In this section, we focus on some aspects of the chemistry of epoxy polymers because it provides examples of both step-growth and chain-growth polymerizations employed in the synthesis of polymer networks. 

The purpose of the present review is the application of the previously mentioned models for the description of a specific type of polymerisation - formation of crosslinked networks of epoxy polymers. It will be made using as example two series of halogen containing epoxy polymers [28]. 

Hence, formation of the structure and properties of epoxy polymers during curing is determined by fundamental physical principles. This is accompanied by the change in the characteristic ratio C (molecular characteristics), although the structure of the macromolecule remains invariant. The use of the above physical principles even in the simplest version provides a correct description of the structure and properties of network polymers. 

The authors of Ref [9] conducted cross-linked polymers microhardness description within the frameworks of the fractal (structural) models and the indicated parameter intercommunication with structure and mechanical characteristics clarification. The epoxy polymers structure description is given within the frameworks of the cluster model of polymers amorphous state structure [10], which allows to consider polymer as natural nanocomposites, in which nanoclusters play nanofiller role (this question will be considered in detail in chapter fifteen). 

As it has been noted above, at present it is generally acknowledged [2], that macromolecular formations and polymer systems are always natural nanostructural systems in virtue of their structure features. In this connection the question of using this feature for polymeric materials properties and operating characteristics improvement arises. It is obvious enough that for structure-properties relationships receiving the quantitative nanostructural model of the indicated materials is necessary. It is also obvious that if the dependence of specific property on material structure state is unequivocal, then there will be quite sufficient modes to achieve this state. The cluster model of such state [3-5] is the most suitable for polymers amorphous state structure description. It has been shown, that this model basic structural element (cluster) is nanoparticles (nanocluster) (see Section 15.1). The cluster model was used successfully for cross-linked polymers structure and properties description [61]. Therefore, the authors of Ref [62] fulfilled nanostmetures regulation modes and of the latter influence on rarely cross-linked epoxy polymer properties study within the frameworks of the indicated model. 

Hence, the results stated above have shown accuracy in the scaling approach to the description of the curing reaction of the haloid-containing epoxy polymer. Application of the indicated concept allows elucidation of the physical aspects of this process and the main distinctions of real chemical reactions from those obtained by computer simulation. Up to the gel formation point spatial disorder, defined by the different intensities of diffusion of reagents at various curing temperatures, completely controls the curing reaction course. After the gel formation point, tightening cluster formation levels these distinctions [51]. 

Using Equations 5.12 and 5.13 for local order domains (clusters) the description of the growth of epoxy polymers and nucleation is based on the fact that clusters by their physical essence are analogous to crystallites with stretched chains (CSC) [5, 6]. The cluster characteristic size is accepted to be equal to the statistical segment length which is calculated according to Equation 1.8. 

Let us consider further the application of irreversible aggregation models for the description of epoxy polymer structure. This was partly carried out above (for... 

In the present chapter the description of the main properties of crosslinked epoxy-polymers within the frameworks of structural notions, stated in Chapters 1, 2 and 5, will be given. 

The authors of paper [76] showed the distinction of micro- and macroexpansion in amorphous polymers and explained it by a certain degree of ordering of chain macromolecules. In other words, the authors [76] found interconnection of thermal expansion and supramolecular structure for a number of amorphous polymers. However, the quantitative structural model for absence of the amorphous state does not allow similar interconnection details to be more precise. Therefore the authors [77] carried out the study of interconnection for amorphous epoxy polymers EP-1 and EP-2 of thermal expansion and structure, for the description of which the cluster model [8, 9] was used. 

However, the mentioned model does not explain the causes of extreme reduction of the melt viscosity of HDPE/EP nanocomposites. Therefore for explanation of this effect the authors [11] used another treatment. As it is known [13], the extreme change of properties of blends in the case of their interaction (both chemical and physical) is realised at equimolar (stoichiometric) component contents. Since for the considered nanocomposites the extremum is reached at 2.0-3.0 mass percentage EP, then this means that the polymer matrix interacts not with the entire epoxy polymer, but only a part of it consisting of 4-6 mass percentage HOPE. In this case for estimation of rig (further designated as Tjo) the relationship applied for description of the chemical reaction kinetics of two components can be used [14] ... 

The authors of paper [60] gave the description of the microhardness of crosslinked epoxy polymers within the frameworks of fractal (structural) models and elucidated the indicated parameter interconnection with structure and mechanical characteristics. Description of the structure of the epoxy polymers is given within the frameworks of the cluster model of the amorphous state structure of polymers [5-7], which allows polymers to be considered as natural nanocomposites in which nanoclusters play the role of nanofiller. 

Despite the approximate character of Equation 9.42, it can be used for the description of the theoretical temperature dependence of a p, to calcnlate the value of according to Relationship 6.15. Figure 9.34 shows the dependence a p T) for epoxy polymer... 

Latexes are usually copolymer systems of two or more monomers, and their total solids content, including polymers, emulsifiers, stabilizers etc. is 40-50% by mass. Most commercially available polymer latexes are based on elastomeric and thermoplastic polymers which form continuous polymer films when dried [88]. The major types of latexes include styrene-butadiene rubber (SBR), ethylene vinyl acetate (EVA), polyacrylic ester (PAE) and epoxy resin (EP) which are available both as emulsions and redispersible powders. They are widely used for bridge deck overlays and patching, as adhesives, and integral waterproofers. A brief description of the main types in current use is as follows [87]. 

Figure 3. Effect of EME 58 (58 wt% mercaptoester units co-polymer) coupling agent concentration on the peel strength of flexible epoxy (amine-cured)/AD = acetone-degreased steel test panels following (a) I day and (b) 3 day exposure to 57°C condensing humidity. See Appendix 4 for epoxy resin and cure description.

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