Single Crystals of Ultrahigh Molecular Weight Poly(ethylene-alt-CO)s for Solvent-Free Processing and Enhanced Thermal Stability

Aliphatic polyketone poly(ethylene-alt-CO) (PK-E) is a remarkable material known for its exceptional thermal and mechanical properties, potential photodegradability, and overall carbon neutrality. Here, we elaborate the making of high-strength uniaxially oriented polyketone tapes through a sustainable solid-state processing route, from nascent single crystalline ultrahigh molecular weight poly(ethylene-alt-CO) (UHMWPK-E). Using a cationic palladium catalyst coordinated with a sterically protected bis(diarylphosphino)methanamine-type ligand and carefully selected polymerization conditions, we achieved the synthesis of single crystals of nascent UHMWPK-Es with molecular weights (M_w) reaching up to 5.50 × 10⁶ g mol^-1. All synthesized crystalline UHMWPK-Es were characterized using NMR, ATR-FTIR, Raman spectroscopy, TGA, DSC, GPC, WAXD, SAXS, TEM, and SEM. These nascent UHMWPK-Es exhibited enhanced thermal stability and interesting surface morphologies. The highly crystalline UHMWPK-E was uniaxially drawn in the solid state at least 35 °C below the peak melting temperature. This resulted in an impressive tensile strength of 1.12 GPa and an initial tensile modulus of 32 GPa for a draw ratio of 10, exceeding that reported for solution spun fibers.