ANALYSIS OF EPOXY RESINS

Analytically, epoxy groups are determined by the reaction with hydrogen halide and back titration with a standard base. Other functional groups present may cause interference problems and result in poor end points. Pyridinium chloride-pyridine is a recommended reagent for the analysis of bisphenol-diglycidyl ether resins [22,23], 

More recently, Eggers and Humphrey [28] have reported on the application of gel permeation chromatography to monitor epoxy resin molecular distributions and curing. The preparation given describes an infrared spectrophotometric method to follow curing. 

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FIGURE 5.2 Analysis of epoxy resin, three columns AMGEL 10 A, AMGEL Iff A, AMGEL SOOA 300 X 7.8 mm, eluant THF, flow rate I ml/min, temperature 30°C, detector (DRI). 

The first moment of the distribution is Pt0T the total, cumulative molar concentration of polymeric material. As the molecular weight of polymeric species increases, branching and crosslinking reactions yield a thermoset resin. Chromatography analysis of epoxy resin extracts confirms the expected population density distribution described by Equation 4, as is shown in Figure 2. Formulations and cure cycles appear in Table II. 

Size Exclusion Chromatography Analysis of Epoxy Resin Cure Kinetics... 

The analysis of epoxy resins has been a particular challenge for the polymer chemist because of the complexity of the repeating units. The multitude of comonomers, the number and type of initiators, the variety of possible polymerization reactions, the insoluble nature of the product and the susceptibility of the network to hydrolysis and other types of chemical attack. Consequently there has been little knowledge of the structural basis of the physical, chemical and ultimate mechanical properties of the epoxy resins. However, it is essential that knowledge of the structures and curing processes be obtained in order to optimize the performance of the epoxy resins. 

Fig. 25 a and b. Analysis of epoxy resin prepregs. a = SEC with UV detection at 280 nm, comparison of sample SP 250 with formulation standard, b = Gradient elution of these samples on a RP 18 column with water/THF gradient program 40 to 80% B in 50 min, non-linear. (From Ref. e9) with permission)... 

Figure 8 shows the temperature dependencies of e" at four frequencies for Epikote 1001 (M w=1396) in comparison with that of a/E0 calculated from the data by the DC conduction measurements [10]. A broad peak is observed for each of the four frequencies at low temperatures on the plot of e", which is due to the rotational diffusion of the dipole moments. A good agreement is observed between e" (plots) and o/E0 (a solid curve) at higher temperatures and at lower frequencies in Fig. 8. The dielectric loss e" can be used as an indicator of the ionic conduction in the DGEBA oligomer at a fixed frequency at the temperatures where the dipole component is negligible. The ionic conduction from the dielectric loss can be measured in a short period of time and is widely used for the cure analysis of epoxy resin systems [62,79-82].

This loading plot shows features similar to the sigmoidal curve generated by the integrated heat flow during a DSC run for the analysis of epoxy-resin cure (Figure 3.5, Section 3.2.2) that measures the extent of reaction as a function of cure time. 

Pasch, H., Unvericht, R., and Resch, M., Analysis of Epoxy Resins by Matrix-... 

Hagenauer GL, Setton I, Compositional analysis of epoxy resin formulations, J Liq Chromatogr,... 

The difference between taffy-processed and fusion advancement solid resin can be noted in HPLC chromatograms. In the advancement process, the even-membered oligomers predominate, whereas taffy-produced resins exhibit both even- and odd-numbered ohgomers. Compounds that contribute to hydrolyzable chloride and a-glycol content can be quantified by HPLC. The presence of branched chain components is detectable in studies using an improved reversed-phase gradient HPLC method (92,93). Excellent reviews of applications of chromatographic techniques to the analysis of epoxy resins are available (94). 

Figure 13.3 Thermomechanical analysis of epoxy resins. Measurements of glass transition temperature. Source Author s own files)...

Scheme 4. Scheme for group analysis of epoxy resin-hardenets by TLC on silica gel layers... 

The TFG-analysis of epoxy resins depends on the defined thermal breakdown of the polyadducts to low molecular, mostly phenolic conqrounds, under eolations of thermolysis (T ax < 500 °C). The medianisms of degradation which r ly here have been extensively studied and accord with our aiuil3rtical results According to this, the thermal breakdown of epoxy resins b ins with dehydration or dehydrogenation of the secondary alcohol function. This is followed by homol3rtic and/or... 

BUlaud, C., R. Legras, and V. Carher, Quantitative Analysis of Epoxy Resin Cure Reaction A Study by Near-Infrared Spectroscopy. A/ / /. Spectrosc., 2002. 56 1413-1421. 

The application of liquid chromatography coupled to mass spectrometry for the analysis of epoxy resins was shown in two examples. Electrospray (ESI) and atmospheric pressure chemical ionisation (APCI) were compared with respect to the ionisation of diglycidyl ether of bisphenol A (DGEBA)-based epoxy resins. Byproducts in a typical modified solid DGEBA-based... 

In a way similar to that described for polyethylene fere-phthalate (Sect. 4.2), some antiplasticiser small molecules with a specific chemical structure are able to affect the ft transition and the yield stress of epoxy resins, but they do not have any effect on the y transition. In the case of HMDA networks, an efficient antiplasticiser, EPPHAA, whose chemical structure is shown in Table 8, has been reported [69]. The investigation of such antiplasticised epoxy networks by dynamic mechanical analysis as well as solid-state NMR experiments [70] can lead to a deeper understanding of the molecular processes involved in the ft transition and of their cooperativity. 

The fact that a viscosity increase after phase segregation (for t > tp) is connected with such mechanism is evidenced by the results of gel chromatographic (GPC) analysis of solfi action in the network formation process of low-molecular siloxane rubbers (Fig. 15). As the reaction proceeds the molecular mass of the sol fraction decreases and so does its viscosity. However, network formation of a number of epoxy resins cured with amines or other curing agents conform the homogeneous model without microgel formation [88 a]. 

Figure 10.16 Examining the curing status of epoxy resins. The first scan reveals the curing process and the second scan shows a completion of curing. (Reproduced with kind permission of Springer Science and Business Media from M. Brown, Introduction to Thermal Analysis, Kluwer Academic Publishers, Dordrecht. 2001 Springer Science.)...

Analyses have been carried out assuming a cavitated particle, that is, the particle is replaced by a void (see the section Cavitation of the Rubber Particles ). The analysis is applied to an annulus of epoxy resin. The volume fraction of the void is 20%. The elastic material properties used for the epoxy matrix are shown in Table I. The elastic-plastic material properties used are shown in Figure 4. Nonlinear geometric effects were included to take account of large deformations. Final failure of the cell was defined (23) to be the applied strain required for the maximum linear tensile strain in the resin to attain the value of 20%. 

The reaction mechanism of liquid dimer polyamides and fatty amido amines with epoxy resins has been studied by Peerman et al. (27). who employed infrared spectroscopic analysis to determine reaction rates. They showed that the terminal epoxy content of a blend of amino-containing polyamide and epoxy resin disappeared more rapidly at 150 °C than does the epoxy content of blends of epoxy resin with triethylenetetramine or tris[(dimethylamino)-raethy1Jphenol. Both of these compounds are well-known for their fast cure at ambient temperatures. Correspondingly, the liquid polyamide or fatty amido amines-epoxy combinations cure slower than the other two systems at ambient conditions. 

The kinetics of copolymerization or curing of epoxy resins with cyclic anhydrides initiated by tertiary amines was investigated by chemical analysis 52,65,73,74,90) differential scanning calorimetry isothermal methods electric methods , dynamic differential thermal analysis , IR spectroscopy dilatometry or viscometry Results of kinetic measurements and their interpretation differ most authors agree, however, that the copolymerization is of first order with respect to the tertiary amine. 

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