Remote Regulator of Polybutene-1 Polymorphic Transformation by a Precrystallized Polypropylene Framework

Structural confinement is a decisive yet poorly quantified regulator of polymorphic pathways in crystalline/crystalline polymer blends. Here, we show that the precrystallized polypropylene (PP) framework acts as a remote structural regulator that governs the solid-solid transformation of polybutene-1 (PB) from metastable form II to stable form I in PB/PP (80/20) blends. By stepwise isothermal crystallization, PP spherulite size (dav,PP) is tuned to modulate the PP framework geometry and the associated PB-rich interstitial environment. Small PP spherulites (dav,PP ≤ 60 μm) primarily promote PB form II nucleation, whereas large PP spherulites (dav,PP ≥ 138 μm) correspond to a more restrictive PP framework environment that suppresses PB chain diffusion and lamellar growth, leading to reduced PB-II crystallinity and less efficient supramolecular packing. Strikingly, such a regulator-induced frustrated state markedly accelerates the form II-I transformation, decreasing the transformation half-time from 5.8 h (neat PB) to 3.1 h (PB/PP blend with dav,PP = 138 μm). The acceleration is attributed to two synergistic effects, including amplified internal-stress accumulation within constrained PB form II lamellae and mitigated interfacial crowding that accommodates the densification-associated lateral shrinkage during transformation. These findings establish a direct mechanism link between high-melting-temperature component morphology and low-melting-temperature component polymorphic kinetics, offering a general strategy to direct phase transformation using pre-existing rigid crystalline frameworks in multicomponent polymer systems.