Rheological, thermal and processing studies of Perfluorocyclobutyl (PFCB) polymers

Polymeric materials are of interest to the fiber optics industry as glass-silica fibers are prone to fracture. However, the thermal resistance properties of current polymeric materials have limited their use in some optical applications including high performance lasers and high speed telecommunication systems. Therefore, it is of interest to develop new polymer materials and systems with enhanced thermal properties and processability for application in optics. This work focuses on the novel Perfluorocyclobutyl (PFCB) polymer systems. PFCB polymers possess characteristics that make them suitable for optics applications including: a low refractive index, high thermal stability and high chemical resistance. However, little is known about the thermal and rheological properties and the processability of PFCB polymers. In this study, two PFCB polymeric materials are investigated: 4,4'-Bis(4-trifluorovinyloxy) biphenyl (hereafter referred to as BPVE) and 2,2-Bis(4-trifluorovinyloxyphenyl)-1,1,1,3,3,3-hexafluoropropane (hereafter referred to as 6F). BPVE and 6F of different molecular weights were employed. Both the pure materials and blends of BPVE and 6F were studied. A systematic approach was undertaken to study the thermal and flow properties of PFCB polymers and blends in which both molecular weight and the concentration in a blend could be manipulated. Films were also produced employing a lab scale twin-screw microcompounder with film casting attachment. The experiments employed demonstrated the different effects of molecular weight on the thermal and viscoelastic properties of PFCB polymers (pure and blends). For the PFCB blends, the concentration of 6F (varying from 20% to 80%) has a significant impact on the rheological and thermal behavior of the materials. For the melt processing of PFCB materials, BPVE polymers with low molecular weight and blends of BPVE/6F were successfully extruded under specific conditions. This study suggests that the molecular weight of PFCB polymers strongly affects the melt processing, as a large increase in molecular weight (Mw) is observed after films are successfully extruded. For specific blends however, containing relatively high molecular weights, films can be processed as it is demonstrated that 6F reduces the viscoelastic properties in the BPVE/6F blends.