Optical adhesives based on blends of methylmethacrylate-co-glycidylmethacrylate copolymer and bisphenol-A diglycidyl ether

In pursuit of nonbirefringent optical adhesives, various copolymers of methylmethacrylate and glycidylmethacrylate (MMA-co-GMA) were synthesized and subsequently blended with bisphenol-A diglycidyl ether (EPON-828) epoxy prepolymer using acetone as a common solvent. Miscibility and optical properties of these adhesive blends were investigated by means of differential scanning calorimetry (DSC), dielectric thermal analysis (DETA), and refractive index measurements. The increasing trend of the single glass transition temperatures of the copolymers as well as of their refractive indices with increasing MMA content suggests that these copolymers are probably of a random type. The adhesive blends, after curing with trimellitic anhydride (TMA), remained transparent, suggestive of a single-phase character. The complete miscibility of the adhesive blends made the refractive indices to be adjustable by simply varying the ratio of MMA-co-GMA copolymer in the blends. In addition, the positive and negative dielectric anisotropies (intrinsic birefringence) of the constituent molecules can be compensated fully in their cured states, thereby yielding significant reduction in the net birefringence in the blends of 50–80 wt % copolymer and a zero-birefringent optical adhesive at 60 wt %. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1911–1917, 1997