Epoxide conversion profiles

Part cures were characterized by exothermic reaction wave propagation. Figures 6a-9b show the development of the reaction waves. The waves propagate from the walls of the part towards the center. A comparison of the temperature and epoxide conversion profiles revealed that the highest temperature corresponded to the highest conversion. As the part initially heats the resin/glass matrix nearest the walls heats fastest however, as the part exotherms the temperatures in the interior of the part exceeded the wall temperatures. The center temperature does not become the hottest temperature until the waves intersect. It must be noted that the hottest temperature does not always occur at the center of the part. The wave velocities are proportional to the wall temperatures. In Figures 6a to 9b the mold temperature was 90 C and the press temperature was elevated to 115 C. Since the press does not heat the part until after it is wound, the press temperature was elevated to accelerate the reaction wave from the press so that the waves would intersect in the center of the part. 

In a comparative study [130] with p-chlorostyrene as model substrate, the influence of the oxygen source in CPO-catalyzed epoxidation was investigated. The time profile for the substrate conversion and product formation are shown in Fig. 7 for fBuOOH (a) and H2O2 (b). Both oxygen donors exhibit the same selectivities (ee 66-67%) but with fBuOOH the epoxide was obtained in 35% yield and H2O2 afforded only 11 % of the product. 

For this comparative study, the catalytic epoxidation of cyclooctene was used as a representative transformation, since it allows for accurate determinations of conversion and yield because cyclooctene is not prone to allylic oxidation and its corresponding epoxide is not prone to hydrolysis. Conversion-time profiles for each catalyst system were measured under identical conditions, that is, a catalyst loading corresponding to 0.1 mol% W, 1.5 mol equiv 50% H2O2, and toluene as solvent at 60 °C. The results are shown in Fig. 16.2. 

Figure 7 (150) contains profiles of the polymerization rate and conversion as function of time for cationic photopolymerization of an epoxide monomer obtained using a photo-DSC. As shown in the figure, the reaction rate profile has a general shape that is characteristic of cationic photopoljunerizations. Immediately... 

IR spectroscopy is highly appropriate for the direct recording of curing rates -that is, the degree of conversion as a function of time [97,98]. Typical polymerization profiles obtained upon UV exposure of an urethane-acrylate resin and an acrylate/epoxide blend (diacryl derivative of bis-phenol A/bicycloaliphatic diepoxide) are shown in Figure 2.30. While the radical polymerization of the acrylate monomer occurred faster than the cationic polymerization of the epoxide... 

---