Differential scanning calorimetry in dynamic and isothermal modes was used to study the cure kinetics of the commercial epoxy system Narmco 5208, whose main components are bis[4-(diglycidylamino)phenyljmethane and bis(4-aminophenyl) sulfone. The data were analyzed in terms of a new mechanistic approach described in the preceding paper. The treatment explicitly takes into account both the epoxideamine reactions and the subsequent etherification reaction. The kinetics can be completely described in terms of three rate constants, which obey the Arrhenius relationship. Excellent agreement with the experimental data is obtained if the etherification reaction is assumed to be first order with respect to the concentrations of epoxide groups, hydroxyl groups, and the tertiary amine groups formed in the epoxide-amine reaction. This model applies over the whole range of conversion up to the point where the resin vitrifies and the reaction becomes diffusion-controlled. The effect of the diffusion control is described very well by an approach based on simple equations proposed in the literature. Altogether, the model allows accurate prediction of the degree of conversion over the whole range of cure and over the temperature range 160-200°C , which covers the usual curing conditions. Although the rate constants derived are specific to Narmco 5208, the model itself is generally applicable to other epoxy amine systems.

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Differential hybridization and screening with cloned inserts was used to identify two families of cytochrome P-450 cDNA clones in libraries prepared from total liver poly(A)+RNA of individual Aroclor-treated rats. One family has cDNA inserts for the major phenobarbital-inducible P-450s, P-450b and P-450e. Two types of P-450e inserts were identified. In addition, irregular inserts were characterized from two clones (PB23 and PB24) of this group. The other family has cDNA inserts for the major 3-methylcholanthrene-inducible species, P-450c and P-450d. No coding sequence restriction site variants were detected among 26 P-450d and P-450c inserts analyzed. The restriction map of the irregular 2.2-kb PB23 insert has a P-450b-like portion, followed by a 3' extension that hybridizes to RNAs of 2.7 and 4.8 kb, which are also detectable with a classical P-450b probe. The PB23 insert and the 2.7- and 4.8-kb RNAs presumably represent 3' extensions of P-450b/P-450e mRNAs, polyadenylated at downstream sites. The 858-bp sequence of the PB24 insert encodes the carboxy-terminal portion of a P-450b/P-450e-like protein. There is approximately 20% divergence at the polypeptide level between the PB24 and P-450b/P-450e sequences; nevertheless, they share many essential features. A PB24-specific probe hybridizes to a 1.9-kb RNA species which is present in the liver of untreated rats and which is not appreciably induced by phenobarbital or Aroclor. The PB24 cDNA most likely represents a constitutive cytochrome P-450, related to phenobarbital-inducible forms.

Samples of Narmco Rigidite 5208/WC3000 carbon-epoxy prepreg were exposed to ambient temperature (22°C) and 50% relative humidity for different periods up to 66 days. They were analyzed in depth using various techniques to determine the extent of the chemical changes occurring. The physicochemical techniques used were Fourier transform infrared spectroscopy (transmission, attenuated total reflection, diffuse reflection), liquid chromatography (reverse-phase, highspeed reverse-phase, and high-performance size-exclusion), thermal analysis (differential scanning calorimetry and thermogravimetric analysis), and pyrolysis-gas chromatography. All showed evidence of significant changes, the most sensitive being Fourier transform infrared spectroscopy (FT-IR) and reversephase liquid chromatography (RPLC). FT-IR showed that the number of unreacted epoxy groups decreases steadily at a rate of 0.34% per day, based on the initial amount. At the same time, the number of free amine-hardener molecules, as monitored by RPLC, drops at a rate of 1.05% per day. RPLC also showed that the amount of initial epoxy-amine reaction product increases significantly over the first 30 days, but then declines as it undergoes further reaction to give highermolecular-weight products. The heat of polymerization of the resin, measured by thermal analysis, decreased by 0.26% per day from its initial value of 561 J/g.