Initiator‐Free Synthesis of Semi‐Interpenetrating Polymer Networks via Bergman Cyclization

Semi‐interpenetrating polymer networks (semi‐IPNs), composed of two or more polymers, forming intertwined network‐architectures, represent a significant type of polymer combination in modern industry, especially in automotive and medical devices. Diverse synthesis techniques and plentiful raw materials highlight semi‐IPNs in providing facile modifications of properties to meet specific needs. An initiator‐free synthesis of semi‐interpenetrating polymer networks via Bergman cyclization (BC) is reported here, acting as a trigger to embed a second polymer via its reactive enediyne (EDY) moiety, then embedded into the first network. (Z)‐oct‐4‐ene‐2,6‐diyne‐1,8‐diol (diol‐EDY) is targeted as the precursor of the second polymer, swollen into the first polyurethane network (PU), followed by a radical polymerization induced by the radicals formed by the BC. The formation of the semi‐IPN is monitored via electron paramagnetic resonance (EPR) spectroscopy, infrared‐spectroscopy (FT‐IR), and thermal methods (DSC), proving the activation of the EDY‐moiety and its subsequent polymerization to form the second polymer. Stress−strain characterization and cyclic stress−strain investigations, together with TGA and DTG analysis, illustrate improved mechanical properties and thermal stability of the formed semi‐IPN compared to the initial PU‐network. The method presented here is a novel and broadly applicable approach to generate semi‐IPNs, triggered by the EDY‐activation via Bergman cyclization. An initiator‐free synthesis of semi‐interpenetrating polymer networks (semi‐IPN) via a Bergman cyclization (BC) is reported. Ene‐diyne‐precursors of the second polymer are swollen into the first polyurethane network (PU), followed by radical polymerization. The resulting semi‐IPNs is then composed of both, flexible and rigid phases with highly tunable mechanical properties.