CONTROLLING THE REFRACTIVE INDEX OF EPOXY ADHESIVES
John M. Messinger, & Peter T. Lansbury
A SARGENT-WELSH PYE UNICAM SP8-150 ultraviolet-visible wavelength spectrophotometer was used for absorbance measurements. A Bausch and Lomb 33-45-52 Abbe type refractometer was used for measuring the refractive index of cast epoxy blocks. Cargille immersion liquids were used in conjunction with the Becke line test for determining the refractive index of glass pieces. Halogenated compounds were prepared by standard methods of synthetic organic chemistry.
Physical Data of Compounds:
Typical preparation of epoxy samples: 12.00 g of Ablebond¯ resin, 0.67 g of 1,2-epoxy-3-[2,4,6-tribromophenoxy]propane (2), and 1.33 g of 1,2-epoxy-3-[2,4,6-triiodophenoxy]propane (3) were placed in a 10 ml beaker. The mixture was gently warmed over a microburner to dissolve the halogenated compounds in the resin. The mixture was kept warm either on a hotplate or in front of a heat lamp until ready for use and was used to prepare all 6:1 resin-to-halogenated compound samples. This mixture was divided into four portions. To the first was added enough hardener to prepare a 100:20 parts-by-weight mixture of resin:hardener. This material was cast into ca. 3 mm × 12 mm × 20 mm blocks in warmed molds made of silicon molding material. The mixed adhesive was cured at 50°C in an oven or at about 40°C in front of a heat lamp. Resin-to-hardener ratios of 100:25, 100:30, and 100:35 were prepared in like fashion. After curing for 24 to 48 hours the blocks were removed from the molds, and their six faces were ground and polished with 1 micron alumina.