Methylene dianiline -cured

Effect of HTTHG treatment on bond durability (57°C) of methylene dianiline cured adhesive joints (0) HTTHG, ( ) control. 

Section 19.S.1.2), and reported increases in toughness comparable to those achieved with CTBN. A further, but inconclusive, study compared pre-formed poly(n-butyl aciylate)-based particles made by emulsion and by suspension polymerization [97]. Dispersion polymerization in an epoxy resin has been used to give directly dispersions of acrylic rubber particles in the epoxy for subsequent use in toughening epoxy resins [98]. Core-shell toughening particles comprising 70 wt% of CFOSslinked polybutadiene cores, with a grafted functionalized shell have been claimed [99] to improve the fracture toughness of a methylene dianiline cured epoxy resin by a factor of 10. 

Diamine curatives were the first cross-linking agents for fluorocarbon mbbers. They are corrosive to mild steel molds and have been replaced in many appHcations by the bisphenol or other more recent cure systems. Nevertheless, some diamines are stiU used for food-contact appHcations of fluorocarbon mbbers and in zinc-free cures of halobutyl mbbers for pharmaceutical stoppers. Methylene dianiline and triethylene tetramine are cross-linking agents for ethylene—acryflc elastomers. 

Methylene dianiline is normally a very reactive diamine in the presence of diisocyanates. However, a sodium chloride complex that is relatively unreactive at room temperature is commercially available. When the complex is heated to 21°C, it activates to quickly cure the urethane [76]. 

In this work, bis-phthalonitrile networks (1, 2) were examined by dynamic mechanical and dielectric methods, supplemented with infrared measurements of state of cure, DSC, vapor pressure osmometry, and solvent extraction. For resins cured with 4,4 -methylene dianiline as co-reactant, a simple network model rationalizes the data. 

Materials Description. Three CIBA-GEIGY epoxy/hardener systems were studied Araldite 6010/906, Araldite 6010/HY 917 and Araldite 6010/972 with stoichiometries 100/80, 100/80 and 100/27, respectively. Araldite 6010 was a DGEBA epoxy resin. The hardeners 906, HY 917 and 972 were, respectively, methyl nadic anhydride (MNA), methyltetrahydro phthalic anhydride (MTPHA) and methylene dianiline (MDA). These systems were investigated previously for the matrix controlled fracture in composites (6-8). The curing cycles used can be found in (6). The ideal chemical structures of the systems are shown in Table I. Neat resins were thoroughly degassed and cast into 1.27 cm thick plates for preparation of test specimens. 

With the diglycidyl derivative of bisphenol A, aromatic amines such as 4,4 -methylene dianiline or diaminodiphenyl sulfone provide good thermal stability for the final cured resin. Although aliphatic primary amines react more rapidly (triethylenetetramine cures the above epoxy resin based on bisphenol A in 30 min at room temperature and causes it to exotherm up to 200°C), they are more difficult to handle and offer poor thermal stability. 

Figure 8. Shear strength durability in a 57°C water immersion of epoxy/steel torsional joints with and without EME 90 (90 wt% mercaptoester unit co-polymer) coupling agent pretreatment. From ref. 6. Adhesive diglycidyl ether of bisphenol A (Epon 828) cured with a stoichiometric amount of methylene dianiline for I h at 120°C followed by 2 h at 150°C.

Examples of these formulations are systems based on a difunctional LC epoxy monomer (diglycidyl ether of 4-4 -dihydroxy-Q -methylstilbene), cured with methylene dianiline (Ortiz et al., 1997). The generation of liquid-crystalline microdomains (smectic or nematic) in the final material required their phase-separation before polymerization or at low conversions. This could be controlled through the initial cure temperature. Values of GIc, (kJm-2) were 0.68 (isotropic), 0.75 (nematic), and 1.62 (smectic). The large improvement produced by the smectic microdomains was attributed to an extensive plastic deformation. 

The cure of PMR-15 and its model compound 4,4 -methylene dianiline bi-snadimide (MDA, BNI) has been studied by simultaneous reaction monitoring and evolved gas analysis (SIRMEGA) using a FTIR with a mercury-cadmium telluride detector. The system allows the observation of the variation in IR spectra correlated to the gas evolution during the curing. The data show that the cy-clopentadiene evolution involves only minor modifications in the spectrum [39]. 

Shih et al. [60] studied the modification of a novolac-type epoxy resin with PDMS to overcome brittleness and poor impact resistance. This kind of resin is typically cured via their epoxy functions. The authors also introduced isocyanate monofunctionalized PDMS. Hence, the common treatment with MDA (4,4 -methylene dianiline) not only cured the resin on the one hand, but also made it possible to form the branched copolymer. Mechanical and thermal analyses showed that an optimum in isocyanate-terminated PDMS content was required to reach good thermal and physical properties and low moisture absorption. 

Methylene dianiline (MDA) is also a solid diaromatic amine. Similarly to MPDA, MDA is not often used in adhesive formulations because of the difficulty in compounding and curing practical epoxy formulations and the resulting brittleness of cured structures. MDA also has relatively low polarity so its adhesion properties would be suspect. 

Temperature-resistant two-part, elevated-temperature curing epoxy adhesives can be formulated with aromatic amines, such as metaphenylenediamine (MPDA), methylene dianiline (MDA), or a eutectic blend of the two. These adhesives will provide relatively high temperature strength, but they are generally brittle. When mixed with epoxy resin at concentrations of about 15 pph for MPDA and 26 pph for MDA, they provide complete cure in about 30 min at 175°C. The aromatic amines also provide a working life of several hours at room temperature. Starting formulations for aromatic amine cured epoxy adhesives are shown in Table 12.4. 

Metaphenylenediamine (MPDA) is the best known of these aromatic amines. Methylene dianiline (MDA) requires somewhat longer cures and has a higher processing viscosity. Both products are solids and generally must be melted before being blended with resin. The difficulty in handling these materials as hot melts has led to the development of aromatic amine eutectics, which are liquid at room temperature. 

The effects of impurities, or synthesis byproducts, and stoichiometry on the cure kinetics of N,N -tetraglycldyl methylene dianiline (TGMDA) resins formulated with dlaminodiphenyl sulfone (DDS) are evaluated using gel permeation chromatography and differential scanning calorimetry. 

Liquid crystalline thermoset system 1. Liquid crystalline thermoset prepolymer dihydroxy methylstilbene epoxy (Mn, 3600) 2. Curing agent 4,4 -methylene dianiline ... 

The materials used were Epon 828 epoxy resin and methylene dianiline (Tonox), both from the Shell Chemical Co. The resin and curing agent were melted together, mixed, degassed, and cast between glass plates. The cure cycle was as follows 45 min at 60 C, 30 min at 80 C, and 2.5 hr at 150 C then slow cooling to room temperature. The amine to epoxy ratio (A/E) was varied from 0.7 to 2.0 (in terms of equivalents). Compositions are given in Table I. 

Resin II contains tetraglycidyl methylene dianiline (TGMDA) as the principal epoxide with small amounts of a cresol novolac and DGEBA. DICY as curing agent is present in an amount such that the amine epoxy ratio is 0.25. Diuron is the accelerator. The supplier s recommended standard cure is the same as for SP250. However, in this system approximately 20 percent of the epoxide remains unreacted following the cure cycle (1 ). Selected resin plates were subjected to additional cure at 170°C and 220°C. The samples post cured at 220 C for forty minutes showed no residual epoxide absorbance in the IR spectrum. 

The effect of water immersion (57°C) on the torsional shear strength of methylene dianiline (O) and DMP-30 ( ) high temperature cured adhesive joints. 

Aromatic primary amines. These ofier improved heat and chemical resistance and longer pot life with reduced exotherm, but poor color stability and sluggish cure. They are generally solids and require some formulating to produce easily handleable products. Reactions proceed best at elevated temperatures, where their irritancy can be a problem. For room-temperature cures they should be used with catalysts, of which phenols, BF3 complexes, and anhydrides are the best. m-Phenylene diamine (MPDA) and methylene dianiline (MDA) are the best examples. 

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