Various methods of preparation of epoxy resin/clay mixtures, before the addition of the crosslinking agent and curing to form epoxy-based polymer layered silicate (PLS) nanocomposites, have been investigated to determine their effect on the nanostructure. Organically modified montmorillonite clay was used, and the mixtures were prepared by both simple mixing and solvent-based methods. X-ray diffraction shows that intercalation of the resin into the clay galleries occurs for all clay loadings up to 25 wt % and for both preparation methods, but the dispersion of the clay in the resin, observed by optical microscopy, is significantly better for the solvent preparation method. Differential scanning calorimetry (DSC) shows that the intercalated resin has the same molecular mobility as the extra-gallery resin, but suggests that the intercalated resin does not penetrate completely into the galleries. Prolonged storage of the resin/clay mixtures at room temperature leads to changes in the DSC response, as well as in the response to thermogravimetry, which are interpreted as resulting from homopolymerization of the epoxy resin, catalyzed by the onium ion in the modified clay. This confirms and explains the earlier observation of Benson Tolle and Anderson (J Appl Polym Sci 2004, 91, 89) that ''conditioning'' of the resin/clay mixtures at ambient temperature has a significant effect when the crosslinking agent is subsequently added, and indicates that the preparation method has important consequences for the nanostructure development in the PLS nanocomposites.

SYNOPSISThe effect of a reactive diluent (RD) on the kinetics of the curing of an epoxy resin, based on diglycidyl ether of bisphenol A (DGEBA), with a carboxylic anhydride derived from methyl-tetrahydrophthalic anhydride (MTHPA) catalyzed by a tertiary arnine has been studied. The reactive diluent was a low-viscosity aliphatic diglycidyl ether, and the compositions per 100 parts by weight (pbw) of DGEBA were 10, 30, and 50 pbw of RD with the stoichiometric quantity of MTHPA and 1 pbw of catalyst. The curing kinetics was monitored by differential scanning calorimetry (DSC), and the kinetic parameters were determined from the nonisothermal DSC curves by the method described by MBlek. The kinetic analysis suggests that the two-parameter autocatalytic model is the more appropriate to describe the kinetics of the curing reaction of this epoxy-anhydride system. The kinetic parameters thus derived satisfactorily simulate both the nonisothermal DSC curves and the isothermal conversion-time plots. Increasing the RD content leads to a small increase in both the nonisothermal and the isothermal heats of curing and has a slight effect on the kinetic parameters E, In A , m, and n and, consequently, on the overall reactivity of the system. On the other hand, the increase of the RD content significantly affects the structure of the crosslinked epoxy. It is confirmed that the introduction of aliphatic chains in the structure of the epoxy increases the mobility of the segmental chains in the glass transition region. The consequence of this chemical modification is a decrease of the glass transition temperature, Tg. 0 1996 John Wiley & Sons, Inc INTRODUCTIONReactive diluents (RDs) are used as additives in epoxy resin formulations in order to reduce the viscosity of the initial mixture and to aid the "processability" of the resin. With this additive, the properties of both the system during curing and the crosslinked epoxy can be modified.' The addition of a n RD in a n epoxy-anhydride system improves the casting and impregnation properties of the resin when it is used in electrical or electronic components. There are two main types of RD, the epoxybased diluents and chemical compounds with a re-* To whom correspondence should be addressed.Journal of Applied Polymer Science, Vol. 61, 1663-1674 (1996) C Z 1996 J n h n Wiley & Sons, Inc.CCC OOZl-S995/96/101663-I2 active group other than an epoxide. The presence of epoxide groups allows the crosslinking reaction of the diluent a t the same time that the epoxy resin is cured by the hardener. In the case of a monoepoxy diluent, the curing reaction leads to a decrease of the crosslink density of the resin, but in the case of "polyfunctionality," the behavior of the diluent is considered to be similar to that of the basic epoxy component and the crosslink density seems not to be affected. ' The curing reaction of the catalyzed epoxy-anhydride system has been described by various author~,'-~ but there is less information when an RD is used in the formulation of the r e~i n .~.~ The o...

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