Epoxy anhydrides

Measured against this second heating reference line, the temperatures at half of the heat capacity difference, Ti Cp, equal -37 ( go), 104 and 131°C, respectively. 

Comparison of the evolutions of Cp and Tg with reaction temperature clearly shows that the three transitions in heat capacity, characterised by 

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Typical epoxy—anhydride systems are described in Table 7. 

Table 7. Epoxy—Anhydride System Handling and Performance...

Epoxy (Anhydride-Cured) Epoxy resins may be crosslinked with various anhydrides by using a tertiary amine accelerator and heat. These cured polymers generally have good chemical resistance especially to acids. 

Epoxy—amino resin weight ratios, 10 445 Epoxy—anhydride systems, properties of, 10 403-404... 

R Musto, M. Abbate, G. Ragosta and G. Scarinzi, A smdy by Raman, near-infrared and dynamic-mechanical spectroscopies on the curing behaviour, molecular structure and viscoelastic properties of epoxy/anhydride networks, Polymer, 48, 3703-3716 (2007). 

Testing of these cases, in the laboratory and in gun firings, showed that these cartridges were fairly stable in storage and their ballistic properties were not seriously affected by elevated temps. Compressive strength results at ambient temp were inconclusive, but at extreme temps (160°F -65°F) and after temp and humidity cycling the epoxy--anhydride binder was least affected... 

The solution of the precursors of the thermosetting polymer (mixture of monomers or oligomers with or without initiators, catalysts and different additives) is usually a liquid at room temperature e.g., unsaturated polyester styrene, some epoxy anhydride and epoxy amine formulations, cya-nate esters, one-stage phenolics, etc. Cooling any of these solutions below room temperature leads to a glass. The temperature at which the glass-liquid transition of the initial formulation takes place is denoted as Tg0. Some other particular formulations, such as two-stage phenolics (novo-lac-hexa mixtures), some epoxy-amine systems, etc., exhibit a Tg0 above room temperature. 

Figure 4.6 DSC thermograms of an epoxy-anhydride system cured at 80°C (a) and 130°C (b), for different times, tc (h). (Montserrat, 1992 - Copyright 2001 - Reprinted by permission of John Wiley Sons, Inc.)...

In an isothermal cure process, vitrification will be always observed if Tc is selected in the range between Tgo and Tgco. So, vitrification was not observed when the epoxy-anhydride formulation was cured at Tc= 130°C(> Tgoo). 

A simplified model of this system is based on the assumption that an almost simultaneous addition of an epoxy/anhydride couple to the growing chain takes place. Therefore, the propagation step may be described by a single rate constant. 

A survey of the extensive literature of kinetic results reported for epoxy-anhydride-tertiary amine systems is surprising. Both nth order and autocatalytic expressions have been reported for the same system. As an example, we analyze the results reported for the copolymerization of a diepoxide based on diglycidyl ether of bisphenol A (DGEBA) with methyl-tetrahydrophthalic anhydride (MTHPA), initiated by benzyldimethylamine (BDMA). 

Other authors observed the same inconsistent results for other epoxy-anhydride-tertiary amine systems. For example, Peyser and Bascom (1977) observed first-order kinetics under isothermal and dynamic conditions however, the activation energy for dynamic runs was E = 104.2 kJ mol-1, much larger than the value for isothermal runs, E = 58.6 kJ mol-1. 

Therefore, the mechanistic kinetic model gives a consistent explanation of the different rate equations reported in the literature for epoxy-anhydride-tertiary amine systems. 

Metal complexes have been used as spectroscopic probes in several thermosetting resins, including various epoxy/anhydride mixtures. The systems investigated (3) have consisted of the cycloaliphatic resin, (3,4-epoxycyclohexyl)methyl-3,4-... 

Ph2-phen) in the cycloaliphatic epoxy (ERL-4221)/anhydride resin at 293 K. The electronic absorption spectrum ( ) of the uncured epoxy/anhydride resin without the incorporation of the organometallic complex is also shown. The excitation spectrum was recorded with emission monitored at 610 nm. (From Ref. 80.)... 

Figure 9 illustrates the dynamic moduli and complex viscosity results for the cycloaliphatic epoxy/anhydride resin. The tgei value denotes the time to gelation based on the dynamic moduli crossover (G = G") and is estimated at... 

Accelerators are often used to increase the reactivity of epoxy-anhydride systems. The proper amount of cure accelerator is empirically determined and varies according to the material being used as the accelerator, the anhydride and epoxy resin used, and the desired cure speed and end properties. 

The reactivity of the epoxy-anhydride reaction is slow therefore, an accelerator is often used at 0.5 to 3 percent to speed the gel time and cure. Most often the accelerator is a tertiary amine, and the optimum concentration is dependent on the anhydride, the resin used, and the cure conditions. The accelerator concentration, like the anhydride concentration, is usually determined experimentally based on a specific set of end properties. 

Environment Epoxy + polyamine Epoxy + anhydride Epoxy + polyamide Epoxy- phenolic Epoxy- polysulfide Epoxy-nylon Phenoxy (thermoplastic)... 

Room temperature cured paste (epoxy-polyamide, epoxy-anhydride)... 

Epoxy- anhydride High molecular weight epoxy resins cross-linked with anhydride hardeners Good Very good Internal white for three piece cans... 

Shortly thereafter, Aiken and coworkers also reported that quinine (4) could be used as a catalyst (50mol%) to promote the methanolytic desymmetrization of the meso-epoxy anhydride 8a to give the lactone 9a in 57% yield and 76% ee (Scheme 11.6) [4]. Lowering the reaction temperature to 0 or —30 °C did not result in any increase in selectivity. meso-Aziridine anhydride 8b was also tested under similar reaction conditions, but a lower enantioselectivity (40% ee) was obtained (Scheme 11.6). 

Most of the evaluation studies were made using a 1 1 stoichiometric bisphenol A epoxy-anhydride formulation. The various quaternary phosphonium compounds were added at a 0.01 to 0.25Z level (based on the combined anhydride and epoxy resin weights). With the exception of MTPP-DMP, which showed partial insolubility in the resin formulation, excellent solubilities at ambient temperature were found. 

The data shown in Tables II and III indicate the effectiveness of two of the phosphonium compounds as accelerators for epoxy-anhydride resins. From the data in Table II, it is noted... 

Phosphonium Latent Accelerators in Epoxy-Anhydride Resins... 

Table III. Viscosity (Storage) Data for Quaternary Phosphonixun Latent Accelerators in Epoxy-Anhydride Resins...

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