Polynorbornenes Bearing Cyclic Fluoroalkyl Side Groups for Achieving High Glass Transition Temperature and Low Refractive Index

Abstract

Partially fluorinated polymers exhibit various properties owing to their fluoroalkyl groups: thus, understanding the types of fluoroalkyl groups incorporated into a polymer chain is crucial for controlling the physical properties and is of significant academic interest. Although polymer backbone structures frequently incorporate short linear fluoroalkyl groups, cyclic fluoroalkyl groups are comparatively rare. To achieve both a high glass transition temperature (T_g) and low refractive index (n), polynorbornenes with several types of cyclic fluoroalkyl side groups are synthesized by ring-opening metathesis polymerization. Most of the synthesized polymers could form thin films via spin coating from nonfluorinated organic solutions. The films were transparent to the ultraviolet and near-infrared wavelengths region. The T_g and n of partially fluorinated polynorbornenes depend on the steric bulk of the side groups. Furthermore, the effect of substituting oxygen atoms for methylene groups within the polymer backbone and side groups on T_g and n is investigated. The incorporation of cyclic fluoroalkyl side groups is promising for the molecular design of amorphous optical materials with high thermal stability.