Epoxy polymers, characteristics

The measured G(x) value of representative epoxy polymers is approximately 10, but this value depends strongly on the structure of the polymer, its glass transition temperature and other characteristics. Since the crosslinking reaction that characterizes the COP resist functionality is a chain reaction, in theory, a single, electron-initiated event could result in the insolublization of an entire film of the resist material. Fortunately, because of the existence of chain terminating reactions, this does not occur and high resolution imaging of the resist material can be accomplished. 

The most common advanced composites are made of thermosetting resins, such as epoxy polymers (the most popular singlematrix material), polyesters, vinyl esters, polyurethanes, polyimids, cianamids, bismaleimides, silicones, and melamine. Some of the most widely used thermoplastic polymers are polyvinyl chloride (PVC), PPE (poly[phenylene ether]), polypropylene, PEEK (poly [etheretherketone]), and ABS (acrylonitrile-butadiene-styrene). The precise matrix selected for any given product depends primarily on the physical properties desired for that product. Each type of resin has its own characteristic thermal properties (such as melting point... 

Oligophenylethoxysiloxanes are used as modifiers for various polymers to improve their weather resistance and other technical characteristics, as well as to increase the heat resistance of coatings. E.g., PES-50 is used to modify polyethers, aciylic and epoxy polymers PES-80 is used to modify alkyd and urea-formaldehyde resins. Besides, PES-80 is used as an additive in paints and enamels (to improve their flow properties, gloss and colour), as well as in concrete mixes (to improve the water resistance and durability of concrete works). 

Reiser reports that in order not to terminate the reaction and hence inhibit propagation, the counter anion must have very low nucleophilicity, since strong nucleophiles or bases will terminate the reaction immediately. Nevertheless, the polymerization can tolerate a small amount of water (1-2%), which is important for the practical usefulness of the system. Oxygen, which acts as a biradical, shows no effect on cationic polymerization—quite an important practical advantage. Characteristically, the epoxy polymers that are the result of the curing process tend to have excellent mechanical properties, including thermal and dimensional stability, nontoxicity, and chemical inertness. 

The use of fractal analysis makes it possible to relate molecular parameters to characteristics of supermolecular structure of polymers. Figure 11.12 illustrates the linear correlation between D and df [dj was estimated from Equation (11.27)] for epoxy polymers. When the molecular mobility is suppressed (D = 1), the structure of the polymer has the fractal dimension df = 2.5, which corresponds to p. = 0.25. The given value of the Poisson coefficient corresponds to the boundary of ideally brittle structure at p< 0.25, the polymer is collapsed without viscoelastic or plastic dissipation of energy [3]. This is fnlly consistent with the Kansch conclnsion [117] stating that any increase in the molecular mobility enhances dissipation of the mechanical energy supplied from the outside and, as a conseqnence, increases plasticity of the polymer. When D = 2 the df value is equal to 3, which corresponds to p = 0.5, typical of the rubbery state. 

Structure parameters and characteristics of properties of epoxy polymers are not random values either. Thus the length of statistical segment 4, obeys the automodelling relationship ... 

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. 

As noted above, a change in the density of chemical crosslinking vf) in epoxy polymers results in an extremal variation of the characteristic ratio (C ) with the minimum K 1.0 [118]. If the section of a macromolecule between chemical crosslinks is modelled by a freely jointed chain, the use of known and values results in a typical fractal dependence [122] ... 

Table 11.6 Calculated molecular characteristics of epoxy polymers [8] ...

Wilson, Second-order nonlinear optical properties and relaxation characteristics of poled linear epoxy polymers with tolane chromophores, J. Appl. Phys. 69 8011... 

Modification of epoxy polymers by rubbers results in decrease of the residual stresses Cdresid cured in. Thus, for the polymers based on UP-637 and cured by UP-0639, Cdfesid monotonically from 5.5 to 2.0MPa as the SKD-KTRA rubber content increases from 0% to 30%. For the compoimds based on the diane oligomer, the stresses decrease under the same conditions from 10.2 to 5.5 MPa because of the increase of the deformation characteristics and of the acceleration of relaxation. 

Thus, the formation of the two-phase system by the method with PER ensures optimal values of some of the physical-mechanical characteristics. These conclusions are confirmed by the results of electron-microscopic studies. With chemical bonds between the epoxy polymers and the rubber particles, the developing crack does not pass round the rubber particle but penetrates it, which causes delocalization of stresses at the tip of the crack and results in improvement of the physical and mechanical properties of the ERC. 

From the above, one can conclude that for ERC with SKN-3KTR the conditions are met for maximal adhesion interaction between the epoxy polymer and the rubber due to the components compatibility. The maximal values of K c are determined for ERC obtained by the method with PER (Fig. 3.20). It should also be noted that these conditions ensure the higher adhesion strength of ERC (Fig- 3.21). Small additions of surfactant to ERC obtained by the method with PER allow additional improvement of their adhesion characteristics. 

Donnet JB, Ehrburger P, Carbon fibre in polymer reinforcement. Carbon, 15, 143-152, 1977. Dauksys RJ, Graphite fiber treatments which affect fiber surface morphology and epoxy bonding characteristics, J Adhesion, 5, 211-244, 1973. 

The number of epoxide reactions possible is practically infinite and has resulted in a huge variety of epoxy polymers. Paint formulators have taken advantage of this variability to provide epoxy paints with a wide range of physical, chemical, and mechanical characteristics. The term epoxy encompasses an extremely wide range of coatings, from very-low-viscosity epoxy sealers (for penetration of crevices) to exceptionally thick epoxy mastic coatings. 

Polymer mechanical properties are one from the most important ones, since even for polymers of different special-purpose function a definite level of these properties always requires [20]. Besides, in Ref [48] it has been shown, that in epoxy polymers curing process formation of chemical network with its nodes different density results to final polymer molecular characteristics change, namely, characteristic ratio C, which is a polymer chain statistical flexibility indicator [23]. If such effect actually exists, then it should be reflected in the value of cross-linked epoxy polymers deformation-strength characteristics. Therefore, the authors of Ref [49] offered limiting properties (properties at fracture) prediction techniques, based on a methods of fractal analysis and cluster model of polymers amorphous state structure in reference to series of sulfur-containing epoxy polymers [50]. 

The values (p j and can be determined according to the Eqs. (4.66) and (2.16), respectively. The theoretical dependence of (where - 1) on the ratio curing agent - oligomer AT, obtained by the indicated mode, is adduced in Fig. 7.9 (the shaded line). Its comparison with the experimental data shows the Eq. (7.15) inadequacy for epoxy polymers considered series (. estimation. Since the same equation describes well the data for a linear pol5uners number [51], then the comparison of the data of Fig. 7.9 and the results of Ref [51] assumes adequate usage of this method in the case of pol5uner molecular characteristics invariability only. 

In Fig. 7.9, the comparison of values 6p calculated according to the Eq. (7.11) and obtained experimentally, is adduced. Now the good coirformity of theory and experiment is observed, both quantitative and qualitative. This confirms postulate that molecular characteristics change in epoxy polymers curing process actually occurs and, if this factor is not taken into account, the Ejprediction can give incorrect results. 

TABLE 9.2 The Adaptability Critical Characteristics of Structure of Epoxy Polymers with Different Curing Agents Before and After Yielding [20]... 

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). 

Let us consider the intercommunication between microhardness // and other mechanical characteristics, in particular yield stress <5 for the studied epoxy polymers. Tabor [12] foimd for metals, which were considered as perfectly plastic solid bodies, the following relationship between // and Oy-... 

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. 

Barton SJ, Pritchard G (1994) The moisture absorption characteristics of crosslinked vinyl terminated polyethers compared with epoxies. Polym Adv Technol 5(5) 245-252 Blikstad M, Sjoblonl OW, Johannesson TR (1988) Long-term moisture absorption in graphite/ epoxy angle-ply laminatesin. Environmental effects of composite materials. Technomic Lancaster, PA, pp 107-121... 

It is known that the introduction of adamantane fragments in epoxy polymers exercises an essential influence on their characteristics. In papers [19,20] the effect of such network structures is examined in the example of EP modified by adamantane acids. The interpretation of the results obtained in [19, 20] within the frameworks of the cluster model of the amorphous state structure of polymers [5, 6] allows to suppose availability of two types of clusters in the studied EP stable ones, formed by main chain segments, and unstable ones, formed at the expense of the interaction of adamantane fragments. The authors of papers [21-23] studied the problem of how much the indicated notions corresponded to the real structure of the studied EP. This can be carried out with the aid of the methods of [3], based on the study of wide angle X-ray halos. 

In turn, the macromolecule effective diameter dj can be determined from Bragg s interval value d according to Equation 4.10. Simulating the crosslinked epoxy polymer macromolecule as a cylinder and using experimental values and d, the important molecular characteristics 5 and can be estimated [23]. 

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