Epoxy resin systems Tetrafunctional

The tetrafunctional epoxy resin systems cured with BAPPO showed enhanced dynamic mechanical properties due to increased crosshnking density and rigidity. 

Fig. 9a and b. TBA spectra for a series of isothermal cures showing changes in (a) the relative rigidity and (b) the logarithmic decrement vs. time. Gelation and vitrification are evident in the 80, 125 and 150 °C scans, but only vitrification is observed in the 200 and 250 °C scans. The system studied was a trifunctional epoxy resin, XD7342 [triglycidyl ether of tris(hydroxyphenyl)-methane, Dow Chemical Co.], cured with a tetrafunctional aromatic amine, DDS (diamin iphenyl sulfone, Aldrich Chemical Co.)... 

Such TTT diagrams have also been useful in describing the cure of polyimide systems, as shown in Palmese (1987), which shows the TTT diagram of a polyamicacid/polyimide system. The TTT diagram of a polycyanurate system is developed by Simon (1993) on the basis of FT-IR, DSC and torsional braid measurements. Kim et al (1993) developed a TTT diagram for a thermoset-thermoplastic blend, specifically a tetrafunctional epoxy-resin/poly(ether sulfone)/dicyandiamide thermoset-thermoplastic blend (Figure 2.9). 

A linear-chained epoxy resin was formulated from phenyl glycidyl ether and nadic methyl anhydride, catalysed by benzyldimethylamine (248). An IR fibre-optic probe was used to follow the conversion of a thermosetting tetrafunctional epoxy resin in which the hardener was an aromatic diamine and a carboxylic dianhydride. A polymerisation system consisting of a cycloaliphatic diepoxide, epoxidised natural rubber (ENR), glycidyl methacrylate (GMA) and a cationic photoinitiator, triphenylsulfonium hexafluoro-antimonate, was studied (75). Multifunctional epoxy/ amine formulations (Epon 825 plus 4,4 -methylene-... 

The very high crosslinking density of the cured tetrafunctional epoxy add to the possibility that the inclusion of low concentrations of PES is not sufficient to produce formation of shear bands. The Young s modulus of the modified system was found to be slightly lower than the values for the neat epoxy resin, possibly due to a reduction in crosslinking density as a result of the dilution effect of the uncrosslinked PES chain. 

Diamant and Moulton [ 184] have also investigated the toughening of a tetrafunctional epoxy resin using various ductile thermoplastic polymers possessing a high glass transition temperature. They observed that a mixture of epoxy resin and PES did not possess a two-phase structure, and that the fracture toughness of the modified system was not markedly different from the values measured for the unmodified epoxy. 

The Tg and storage modulus of tetrafunctional epoxy resins cured by BAPPOO were higher than that of the resins cured with DDM as it is clear from Table 3.5. For example, Tg of TGDDM/DDM system was 200°C and its storage... 

The flcune retardcuicy of all epoxy systems was enhcuiced by the incorporcition of POSS nano reinforcements (Table 3.8). This might possibly be due to the formation of oxidatively stable, nonpermeable surface char and a multilayered carbonaceous sflicate structure that acted as an insulator. Besides this, the better exfohation of POSS within the polymer matrices may also have accomited for an enhanced flame retardancy to epoxy resins. The effect of POSS towards flame retardmcy wcis more in the case of phosphorous- and siloxane-modified tetrafunctional epoxy systems them the sulphone and need epoxies, thereby supporting the results obtained from mechanical, thermo-mechanical and thermal studies as discussed earher. 

The resin cured with excess DICY (assuming DICY is tetrafunctional) is a single phase system while the resins cured with DICY with epoxy groups in excess are two-phase systems which exhibit two maxima in tan 8. Since the IR analysis shows that all NH and epoxy groups disappear, the main reaction is assumed to be the addition reaction of the epoxy groups to the NH groups. 

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