Vinyl Ketones Containing Fluorene Skeletons for Acrylic Resins with High Refractive Index and Negative Birefringence

Abstract

The radical (co)polymerization of 2-acryloylfluorene (1a) and 2-acryloyl-9,9-dimethylflureoene (1b) with methyl methacrylate and the thermal and optical properties of the resulting (co)polymers are investigated. Because the two methyl groups at the 9-position prevent the interaction of aromatic rings, the solubility is drastically improved for the homopolymer of 1b. The incorporation of 1b-units increases both the glass transition temperature (118°C–170°C) and 5% weight-loss temperature (289°C–354°C). In addition, the refractive index of the polymers at 589 nm increases from 1.49 to 1.65 with higher mole fractions of 1b-units, whereas the negative birefringence significantly increases. These features are attributed to the restricted bond rotation of the rigid aromatic pendant groups bound to the backbone via an sp² carbon atom (carbonyl group).