Macromolecular Architecture‐Dependent Polymorphous Crystallization Behavior of PVDF in the PVDF/γ‐BL System via Thermally Induced Phase Separation

Abstract

This study investigates the effect of the macromolecular architecture of poly(vinylidene fluoride) (PVDF) on its thermally induced phase separation (TIPS) behavior and polymorphic crystallization in the PVDF/γ‐butyrolactone (PVDF/γ‐BL) system. Preparative PVDF fractions with specific macromolecular architecture and phase constitution are generated. The results show that PVDF's macromolecular architecture, particularly the degree of branching and regio‐defects, plays a significant role in its temperature‐dependent crystallization and resulting polymorphic phases. While regio‐defects dominate crystallization in the temperature range between 30 and 25 °C, the degree of branching becomes decisive in the 25–20 °C interval. The developed fractions of PVDF are further analyzed in terms of their molecular weight distribution, revealing that the PVDF fractions crystallized out of solution have similar molecular weight distributions with lower dispersity compared with the feed polymer. These findings are crucial for macromolecular separation and adjustment of PVDF polymorphic properties and hence for the development of tailor‐made PVDF matrix materials for composites and membranes. The findings suggest the possibility of polymorphous phase tailoring of PVDF based on macromolecular architecture due to temperature‐controlled crystallization out of solution and strongly motivate further research to reveal deeper knowledge of regio‐defect and branching influence of PVDF solution crystallization.

Poly(vinylidene fluoride) Aerogels with α, β, and γ Crystalline Forms: Correlating Physicochemical Properties with Polymorphic Structures

“…Fischlschweiger and co-workers reported the formation of the γ form of PVDF using γ-butyrolactone and demonstrated that the crystallization temperature of the PVDF solution determines the fractions of the α and γ forms. In the present work, the PVDF gel in γ-butyrolactone shows the predominant γ form . However, unlike the PVDF/cyclohexanone gel, the PVDF/γ-butyrolactone gel shows a crystal–crystal transition upon the solvent exchange process, and the disordered γ form is transformed to the β form, 2θ = 20.7° (110/200) (Figure b, middle panel). , To enhance our understanding of this crystal–crystal transition, we measured WAXD patterns upon systematic exchange at different time intervals (Figure S1).…”

“…It was reported that the PVDF crystalline forms are affected sensitively by the nature of the solvent used and also by the crystallization conditions (temperature and crystallization rate). 62,63 As detailed in the Experimental Section, the gelation solvent was exchanged with ethanol and water before freeze-drying to obtain the respective aerogels.…”

“…The thermal and mechanical properties of PVDF gels were not discussed in this work, as these properties are sensitive not only to the crystalline forms but also to the concentration of the polymer and the polarity of the gel solvent. It was reported that the PVDF crystalline forms are affected sensitively by the nature of the solvent used and also by the crystallization conditions (temperature and crystallization rate). , As detailed in the Experimental Section, the gelation solvent was exchanged with ethanol and water before freeze-drying to obtain the respective aerogels.…”

“…In the present work, the PVDF gel in γ-butyrolactone shows the predominant γ form. 63 However, unlike the PVDF/cyclohexanone gel, the PVDF/γ-butyrolactone gel shows a crystal− crystal transition upon the solvent exchange process, and the disordered γ form is transformed to the β form, 2θ = 20.7°( 110/200) (Figure 2b, middle panel). 40,43 To enhance our understanding of this crystal−crystal transition, we measured WAXD patterns upon systematic exchange at different time intervals (Figure S1).…”