Elastomeric Polyphosphazenes with Phenoxy–Cyclotriphosphazene Side Groups

New polymers with a phosphazene backbone and both 2,2,2-trifluoroethoxy- and phenoxy-functionalized cyclotriphosphazene substituents exist in three phases depending on the side group ratios. At low concentrations of the bulky substituents (up to ∼7 mol %), the polymers are semicrystalline thermoplastics, with properties that are minor variations of poly­[bis­(2,2,2-trifluoroethoxy)­phosphazene]. However, after the incorporation of between ∼7 mol % and ∼20 mol % of the bulky cyclic trimeric side groups, the polymers lose their semicrystalline properties and become amorphous elastomers. At still higher trimer loadings (>20 mol %) the materials develop gum-like behavior. The elastomeric phase appears to be generated by interdigitation or agglomeration of the bulky aryloxy-cyclotriphosphazene side groups, which act as quasi-physical cross-links between the polymer chains. The presence of these interactions allows the materials to experience high strain values before rupture (up to 1000%), and elastic recovery of more than 85% of the original dimensions when stressed up to 60% of the break elongation over four cycles. In addition, the chemical and physical nature of the substituents on the cyclic trimeric side groups alters the physical characteristics of the polymer in a way that provides a facile method to tune the properties.