This work is an investigation of the influence of bulky fluoroalkoxy side groups on the properties of polyphosphazenes. A new series of mixed-substituent high polymeric (fluoroalkoxyphosphazenes) containing trifluoroethoxy and branched fluoroalkoxy side groups was synthesized and characterized by NMR and GPC methods. These polymers contained 19-29 mol % of dibranched hexafluoropropoxy groups or 4 mol % of tribranched tert-perfluorobutoxy groups which serve as regio-irregularities to reduce the Macromolecular microcrystallinity. The structure property correlations of the polymers were then analyzed and interpreted by several techniques: specifically by the thermal behavior by DSC and TGA methods, the crystallinity by wide-angle X-ray diffraction, and the surface hydrophobicity/oleophobicity by contact angle measurements. Ultraviolet cross-linkable elastomers were prepared from the new polymers through the incorporation of 3 mol % of 2-allylphenoxy and photoirradiation. The mechanical properties and the elastomeric deformation recovery behavior were then monitored by varying the time of ultraviolet irradiation. Side reactions detected during the synthesis of the high polymers, such as side group exchange reactions and a-carbon attack, were analyzed via use of a cyclic trimer model system. The new polyphosphazenes with branched fluorinated side groups expand the scope of phosphazene-related materials and provide an understanding of the effect of different side group geometries on the overall properties of the fluoroelastomers.