Epoxy resin is a material commonly used for the encapsulation of light-emitting diodes (LED). Three epoxy resins were chosen in this study: D.E.R.-331 was a bisphenol A type epoxy resin, Eporite-5630 was a bisphenol A type epoxy resin modified with a UV stabilizer, and ERL-4221 was a cyclo-aliphatic epoxy resin. The curing agent was methyl hexahydrophthalic anhydride (MHHPA), and the catalyst was tetra-butyl ammonium bromide (TBAB). Thermal, environmental, and optical properties of the cured epoxy resins were studied. It was found that cured ERL-4221 had better UV resistance, but other properties of ERL-4221 were lower because of the internal stress generated during the curing process. D.E.R.-331 showed better thermal stability, but the aromatic groups in the main chains caused sensitivity to photodegradation. Eporite-5630 had the advantages of D.E.R.-331 and better UV resistance than D.E.R.-331 because of the addition of UV stabilizer. Among the three materials, Eporite-5630 was the best choice of the balance properties for LED applications. This finding may assist in the selection of epoxy resins used in LED technology. C

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The inverse gas chromatography method was extended to study the concentration dependent FloryHuggins interaction parameter between poly(vinyl chloride) (PVC) and plasticizers using literature data. For both PVC/ polyadipate and PVC/epoxidized soybean oil (ESO) systems, the miscibility was better at the high PVC end. The specific interaction between PVC and plasticizers was estimated from the difference between the experimental results and the enthalpies of mixing predicted by the solubility parameter model. The interaction was negative and skewed toward the high PVC end, and rendered the overall interaction parameter negative at high PVC compositions. Chemical potential was used to determine the phase composition of PVC/plasticizer mixtures.

ABSTRACT:The three-dimensional solubility parameter model was applied to analyze solution thermodynamic data of 27 solutes in poly(-caprolactone) (PCL) between 70 and 110°C. A linear regression method was compared with a nonlinear least square regression method, which searches solubility parameter components by minimization of the sum of error squares. The parameters of polymers were the same by both methods. When compared with the error in predicting RT/V, the data showed a different slope from the simple three-dimensional model. These deviations were reduced by a different model using a smaller weight on the polar and hydrogen bonding components. In the new model, the solubility parameter components were closer to the value of a structure analogue of PCL. The confidence intervals for the parameters were estimated from a linearized equation based on the sum of error squares. The solubility parameter components obtained were different from the average values of the five solutes with the smallest . The inclusion of solutes with high hydrogen bonding components contributed to the increase of the component in the nonlinear regression method.

he presence of traces of impurities in commercial isoprene obtained from petroleum has a profound influence on the qualities of the isoprene for polymerization purposes.Of these impurities the paraffins, cycloparaffins, and simple acetylenes have little or no effect. The monoolefins, for the most part, have a slight retarding influence on polymerization rate in emulsion. Certain olefins, however. having the structural unit ^/C=CCII<^, have a substantially larger retarding effect than the others. This includes such compounds as 3-methyl-l-butene, isoprene