Extensive Reorganization of Crystals in Nanopore-Confined Isotactic Polypropylene

Polymers confined within nanopores typically exhibit strongly depressed crystallization temperatures ( T c ) while their melting temperatures ( T m ) remain nearly unchanged, resulting in an apparent deviation from the classical Hoffman–Weeks relationship. Using isotactic polypropylene (iPP) confined within anodic aluminum oxide (AAO) nanopores as a model system, we demonstrate that the endothermic peak during heating measured by conventional differential scanning calorimetry (DSC) does not reflect the melting of the imperfect crystals initially formed during cooling. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses further reveal continuous structural and morphological evolution during heating, indicating extensive crystal reorganization over a broad temperature range (∼60–140 °C). As a result, the observed melting behavior predominantly reflects the reorganized crystals formed during subsequent heating and is nearly independent of the preceding cooling conditions. By kinetically suppressing recrystallization through ultrafast heating using fast scanning calorimetry (FSC), the intrinsic T c – T m relationship is recovered, consistent with the classical Hoffman–Weeks framework. These results reveal the critical role of crystal reorganization in determining the apparent melting behavior of nanoconfined polymers and provide a physically consistent interpretation of melting in confined polymer systems.