Softening the rigid chain of high-topology polyetherketoneketone toward fully-condensed and super-strong fiber

Controlling the condensed structures is crucial during polymer processing, while chain structure significantly influences the condensation process. In thermoplastic polymers, the high rigidity and unique topology of polyetherketoneketone lead to interchain locking, severely hindering segmental motion and close packing, limiting its performance. Here, we report a chain softening strategy to reduce the disentanglement barriers and promote segment movement, achieving full and dense condensation of chains. The softener 1,2-dichloroethane reduces the torsional energy barrier and gyration radius of polyetherketoneketone chains by inducing electron density shifts via intermolecular interactions. The solution exhibits a broad relaxation time distribution and rapid stress relaxation. After chain softening, the porosity of polyetherketoneketone condensates significantly decreases, and the fiber density is comparable to that of the hot-pressed sheet. Upon removing 1,2-dichloroethane, the chains in the fiber re-interlock due to the recovery of rigidity and topologicity, thereby giving it excellent performance. This method of controlling condensed structure by changing molecular physical properties has positive implications for polymer processing.