Pressure-induced crystallization and polymorphic transitions of polybutene-1: High-pressure PVT study

Isotactic poly(1-butene) exhibits pressure-sensitive polymorphism, yet quantitative, phase-resolved volumetric evidence across processing-relevant pressures remains limited. High-pressure PVT dilatometry was employed to monitor specific-volume changes during controlled melt crystallization and remelting between 10 and 200 MPa at a fixed cooling rate. The resulting dilatometric fingerprints enable phase attribution after crystallization under each pressure condition. At low pressures ( ≤ 60 MPa) crystallization proceeds predominantly to form II; in an intermediate window (approximately 75–100 MPa) hydrostatic pressure markedly accelerates the solid–solid II → I transformation during or shortly after crystallization, yielding form-I–dominated structures. At higher pressures ( ≳ 110 MPa) signatures of form I ′ emerge and intensify, and beyond ∼ 175 MPa the melting response is consistent with predominantly form I ′ . Across the series, specific volume of the solid phase follows the expected order ( V I ≲ V I ′ < V II ), providing a consistent volumetric basis for phase assignment. Phase-resolved V ( T , P ) maps for the melt and for forms I, II, and I ′ are assembled from these data, offering practical inputs for shrinkage prediction and process design. The findings delineate pressure protocols that suppress persistence of metastable form II and enable direct access to targeted polymorphs, mitigating delayed post-crystallization dimensional change in polybutene components.