Miscibility, Hierarchical Structures, and Enhanced Mechanical Properties of Acrylic Rubber by the Formation of a Chemically and Physically Crosslinked Partially Miscible Interpenetrating Polymer Network with Poly(vinylidene fluoride)

Herein, a partially miscible interpenetrating polymer network comprising rubber (acrylic rubber, ACM) and a semicrystalline polymer [poly(vinylidene fluoride), PVDF] with chemical and intercrystalline crosslinks was prepared at a low PVDF content. Further, its miscibility, hierarchical structure, and thermal and mechanical properties were investigated. The appearance of a lower critical solution temperature (LCST)-type phase separation above the melting point of PVDF (Tm) indicated that the blend rubber was miscible in the melt state below the LCST-type phase separation temperature. In addition, although atomic force microscopy images showed that some ACM formed phase-separated domains within the spherulite due to exclusion coupled with a liquid/liquid phase separation below the Tm, a combination of dynamic mechanical analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, and various scattering measurements revealed that the other ACM was trapped in the interlamellar amorphous region of PVDF with partial miscibility. The blend rubber was simultaneously stiffened, strengthened, and toughened by blending with PVDF and further via crosslinking. The in situ wide-angle X-ray scattering measurements during stretching revealed that the crystallinity decreased with increasing PVDF content and further with crosslinking, without the strain-induced crystallization of ACM. This correlation suggested that the local break of the crystalline lamella dissipated the concentrated stress, affording a high strain at break, which in turn led to a high tensile strength due to the stretch of ACM and thus a high toughness.