Epoxy oligomers indicators

In connection with the facts that the peak at 213 K corresponds exactly to the glass transtion of the SKD-KTRA rubber and that system softening at 328 K coincides with the glass transition of the epoxy matrix, one can affirm the incompatibility of the rubber and epoxy components of the above EEC. Electron-microscopic data also indicate the existence of the EEC two-phase structure only in the case of SKD-KTEA as a modifier, which is thermodynamically incompatible at the stage of blending with the epoxy oligomer. 

Thus, the phase separation that runs in parallel with the reaction of formation of the three-dimensional epoxy polymer network in ERG, obtained by the PER method with apphcation of SKN-3KTR rubber that is thermodynamically compatible with the epoxy oligomer, does not occur, indicating the conservation of the phase structure of the compound formed at the blending stage and in the cured state. This supports the possibility of using the thermodynamic approach for describing the physical-mechanical properties of ERG obtained by the PER method. 

The comparison of these data with the series of the catalytic activity of the metal acetylacetonates in the reaction of the epoxy oligomers with the phenolformaldehyde resins [Eq. (2)] as well as with the series of the thermal stability of these diketonates [Eq. (3)] indicates that the catalytic effect of these complexes depends on the stability of the chelate molecules. This stability is defined by the strength of the chelate rings whoch depends on the ligand structure (e.g., compare the decreased activity of Mn in [Eq. (4)] with its increased catalytic effect in [Eq. (2)]. 

As will be discussed, incorporation of siloxane oligomers modified the elastic moduli and the fracture properties of the crosslinked epoxy network. Previous work 15) indicated that the surface of these materials was rich in siloxane, which is believed to foster a low energy surface. These characteristic properties have led to our interest in the friction and wear of siloxane-modified epoxies. 

Siloxane-modified networks were prepared for testing via two steps. A linear precursor was generated by reacting the epoxy resin with the siloxane oligomer for one hour under vacuum at 65 °C. PACM-20 was then added, and the mixture was stirred for five minutes under vacuum at 50 °C. Previous studies indicated 151 that reaction between the AEP-terminated siloxane oligomers and the curing agent is not possible, as one would expect. 

In Table 2 are tabulated the Tg values for resins modified with the siloxane copolymers described in Table 1. Transition temperatures for samples modified with oligomers containing primarily dimethyl siloxane units give little indication of intimate mixing beween epoxy and rubber. Evidence for partial miscibility with increasing... 

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].

As seen from Pig. 3.22, the concentration dependence of the thermodynamic interaction parameter X2,3 of the above mixtures is nonmonotonic and is bimodal in character (the maxima are observed at 20% and 70% of Laproxide 703M). The existence of two maxima indicates that these systems have two regions of composition with least-stable thermodynamic equilibrium, which is a function of temperature. It follows from the temperature dependence of X2,3 that the thermodynamic compatibiliiy of these mixtures of polymers declines as the temperature drops—there is the top mixture critical temperature. Whereas at the blending stage there is thermodynamic compatibility of the ED-20 oligomers and Laproxide 703M for modifier contents up to 40% at 298 K, the parameter X2,3 of the mixture of the two epoxy... 

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. 

Tertiary amines like benzyldimethylamine, pyridine, and imidazole have been widely used as a base to initiate the anionic polymerization of PGE and its derivatives as well as for the synthesis of epoxy resins of diglycidyl ether of bisphenol A (DGEBA). Even if initiation occurs with amine alone, the introduction of an alcohol is a common procedure to suppress the observed induction period and increase the polymerization rate. Two initiation mechanisms have been proposed (Scheme 18) (1) direct nucleophilic attack of the amine onto the cyclic monomer to yield the zwitterion (a) and (2) formation of alkoxide (b) via proton transfer in the presence of alcohol. Fast exchange between dormant alcohol and active alkoxide allows chain growth from both initial amine (a) and alcohol (b). Poly(PGE) oligomers whose degree of polymerization does not exceed 5 are obtained. The presence of terminal double bonds indicates significant transfer to the monomer via... 

High temperature epoxies. Polybenzimidazole oligomers. Polyimide oligomers. Specimens bonded in vacuum bags (625 mm Hg) placed in autociave at the indicated pressure. Polyamic acid. Polyphenylquinoxaline. Poly(ether-imide). Thermoplastic polyimide. Epoxy-BMI. 

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