Understanding Enhanced Melt Memory in Poly(Octamethylene Carbonate)-Based Random Copolycarbonates with Mixed Isodimorphic/Isomorphic Crystallization

Poly-(hexamethylene carbonate-ran-octamethylene carbonate) (PC6/PC8), poly-(heptamethylene carbonate-ran-octamethylene carbonate) (PC7/PC8), and poly-(dodecamethylene-ran-octamethylene carbonate) (PC12/PC8) are the first random copolymers known to crystallize with a mixed isodimorphic and isomorphic mode. Here, we investigate for the first time how this dual crystallization mode affects melt memory. Self-nucleation experiments, combined with synchrotron X-ray scattering, polarized light microscopy, and dielectric spectroscopy, show that crystallization in the isodimorphic mode decreases melt memory as the comonomer content increases, as expected. Conversely, compositions that crystallize in the isomorphic mode, where a new crystalline phase forms that is different from the parent components or their polymorphs, display increased melt memory, with Domain IIa widthsdirectly related to melt memoryreaching up to 30 °C, significantly surpassing those in homopolymers. This heightened melt memory is due to stronger intermolecular interactions within the new phase, as shown by higher dielectric constants. These results establish the crucial role of intermolecular interactions within the crystal lattice in determining enhanced melt memory in copolymers showing both isodimorphic and isomorphic crystallization, highlighting the critical role of comonomer incorporation in tuning crystallization behavior and melt memory.