Anhydride-cured resin

Fig. la-c. Schematic structure of fully cured epoxy resin, a amine cured resin b anhydride cured resin c catalyst cured resin... 

Recently, the dynamic mechanical properties of the resins cured with a series of linear poly anhydrides having the structures shown in Table 5 were studied by Ramon41 . The dynamic mechanical properties are very similar to those of the resins cured with diamine hardeners as shown in Fig. 10. The relationships between the number of CH2 groups n and Tg Eire shown in Fig. 8. Tg drops rapidly below that of an alkyldiamine-cured resin as n increases. This is considered reasonable because, compared with the hardener.unit in an amine-cured resin, the acid anhydride segment existing in the main chain of the anhydride-cured resin is twice as long. 

However, the validity of Eq. (21) for the systems montioned in chapter 3 cannot be proved. As shown in Fig. 17, hydrazide-cured resins having a maximum in 82 also exhibit a maximum E. Besides, the solubility parameter (82) computed from the values reported by Hoy 55) is 9.9 for the anhydride-cured resins and 10.6 for the DETA-cured resins, while E of the anhydride-cured resins is higher than that of the DETA-cured resin. These results have been derived from the ten-second shear modulus [3G(10)] and flexural modulus (Table 7) 40,46). in the resins obtained according to Eqs. (4) to (7) (e.g., anhydride-cured resins), the network formation is not perfect and there exist many dangling chains. 

As shown in Table III, all of the anhydride-cured resins were essentially hydrophobic. The amount of water uptake showed little or no trend with size or branching of the alkyl substituents. Water uptake was reversible, also. 

Anhydride-cured resins generally have better thermal stability. Pyromellitic dianhydride with higher functionality produces tightly cross-linked products of high heat-distortion temperatures. Heat-distortion temperatures as high as 290°C have been quoted. Table 4.28 summarizes the characteristics of some of the anhydride hardeners. 

The main differences that were observed between amine-cured and anhydride-cured resins are [511] ... 

The aliphatic segments of the amine cross-linked resins yield more acetaldehyde than acetone. The reverse is true of the anhydride-cured resins. This is thought to be due to preferential rupture of carbon-nitrogen bonds [511] ... 

The prime function of the saturated acid is to space out the double bonds and thus reduce the density of cross-linking. Phthalic anhydride is most commonly used for this purpose because it provides an inflexible link and maintains the rigidity in the cured resin. It has been used in increasing proportions during the past decade since its low price enables cheaper resins to be made. The most detrimental effect of this is to reduce the heat resistance of the laminates but this is frequently unimportant. It is usually produced by catalytic oxidation of o-xylene but sometimes naphthalene and is a crystalline solid melting at 131°C. 

Anhydride hardener Parts used phr Typical cure schedule Physical form Max. HDT of cured resin °C Use... 

As a very general rule it may be said that the amines are fast curing and give good chemical resistance but most are skin sensitive. The organic anhydrides are less toxic and in some cases give cured resins with very high heat distortion temperatures. They do not cross-link the resins at room temperature. 

The epoxidised polybutadiene resins available to date are more viscous than the diglycidyl ethers except where volatile diluents are employed. They are less reactive with amines but have a similar reactivity with acid anhydride hardeners. Cured resins have heat distortion temperatures substantially higher than the conventional amine-cured diglycidyl ether resins. A casting made from an epoxidised polybutadiene hardened with maleic anhydride and cured for two hours at 50°C plus three hours at 155°C plus 24 hours at 200°C gave a heat... 

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. 

The resin system selected to initiate these studies is a step-growth anhydride cured epoxy. The approach to the kinetic analysis is that which is prevalent in the chemical engineering literature on reactor design and analysis. Numerical simulations of oligomeric population density distributions approximate experimental data during the early stages of the cure. Future research will... 

The phthalic anhydride based resins were the first developed useful unsaturated resins. Using phthalic anhydride offers resin producers the flexibility to substitute, mole-for-mole , maleic anhydride out of the formulation and therefore reduce the active double-bond sites. Consequently, the product becomes less brittle. Furthermore, aromatic acid components in the polymer backbone provided much better strength for the cured products. Phthalic anhydride is not a costly material and historically it is similarly priced to maleic anhydride. By... 

This paper rerports an investigation of the yield behavior of several amine and anhydride cured DGEBA resin systems. The Argon theory is used to assess the controlling molecular parameters from the experimental results. Such parameters are then compared with the known chemical structures of the resins. The mechanisms of plastic flow in thermoset polymers such as epoxies is demonstrated. 

The plastic deformation in several amine and anhydride cured epoxy resins has been studied. The experimental results have been reasonably interpreted by the Argon theory. The molecular parameters determined from the data based on the theory reflect the different molecular structures of the resins studied. However, these parameters are in similar enough range to also show the structural similarity in these DGEBA based systems. In general, the mechanisms of plastic deformation in epoxy resins below T are essentially identical to those in amorphouE thermoplastics. The yield stress level being related to the modulus that controls the intermolecular energy due to molecular deformation will, however, be affected by the crosslinks in the thermosets. 

For polyamine-cured resin, recycle of presoaked epoxy also increased both impact strength and heat deflection temperature. For polyamide-cured resin, recycle also increased volume resistivity. Pre-soaked recycle dramatically increased adhesion to aluminum, especially in the anhydride system. 

Tertiary amines are used to accelerate both amine and anhydride cures of epoxy resins (B-67MI11501). Certain heterocyclic amines have been used for this purpose, including pyridine and piperidine. In the case of anhydride cures, the use of an amine catalyst not only accelerates the cure, but also improves the thermal stability of the cured resin. 

The catalytic effect has been explained in terms of the activation of the anhydride by interaction with the amine to give a zwitterionic intermediate (47 Scheme 10) (B-68MI11501). Imidazoles have also been suggested as accelerators for anhydride cures (68USP3394105). A review of the patent literature (B-77MI11502) shows that several heterocyclic compounds are of interest as curatives for epoxy resins. 

The results of DSC studies on the anhydride cure of epoxy resins are summarised in Table 2. These studies have confirmed that the cure mechanism is complex. The early stages show autocatalytic features while the later stages are complicated by the effects of diffusion control. Intermediate stages of cure can show an approximation to overall kinetic orders of 1 or 2. In general the isothermal DSC data are easier to... 

Reference to Table 14 will show the effect of increasing levels of APES on the compressive properties of an anhydride cured epoxide/silica microballoon foam, the APES being added on the resin content. The notation w/r (wt% resin) has been used in the tables. Both the yield stress and strain to failure increased steadily with increased silane content, with a corresponding increase in compressive modulus. At the 5 wt% level there was no real increase in yield stress but a marked increase in strain to failure, resulting in a lower modulus. However, at the 4% level the compressive strength was more than double that of the nonsilane control. 

Tetrakis(acetylacetonato)zirconium, which has a square antiprism structure, shows marked smoke-retarding properties in poly(vinyl chloride)5 and it is effective as an accelerator in anhydride-cured epoxy resins.26... 

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