Polyphosphazenes with Cyclotetraphosphazene Side Groups: Synthesis and Elastomeric Properties

Abstract: Trifluoroethoxy cyclotetraphosphazene units, [N₄P₄(OPhO–)(OCH₂CF₃)₇], have been linked to the main chain of fluoroalkoxy polyphosphazenes through –OPhO– spacer groups. The thermal and mechanical properties of these inorganic backbone polymers have been investigated to examine the influence of the bulky cosubstituent groups. Five polymers with OCH₂CF₃ as the major substituents (90–99 %) and [N₄P₄(OPhO–)(OCH₂CF₃)₇] units as the minor side groups (1–10 %) have been synthesized and characterized. The glass transition temperatures and microcrystallinity are influenced dramatically by the incorporation of the cyclotetraphosphazene side groups. Specifically, the polymers range from leathery to elastomeric materials as the percentage of the cyclotetraphosphazene side groups increases from 1 to 10 %. Tensile stress vs strain tests were carried out for the polymers with 4.0 and 8.3 % cyclotetraphosphazene side groups respectively. Break elongations of 838 and 1485 % for polymers with 4 and 8.3 mol% of the bulky side groups respectively were recorded, with both polymers showing reversible elongation with some deformation. The special elastomeric properties are attributed partially to non-covalent cross-links from interdigitation of the bulky cyclotatraphosphazene units. Graphical Abstract: [Figure not available: see fulltext.]