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 (VI≲VIjavax.xml.bind.JAXBElement@2330adc3