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 (T
m) 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 T
m, 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.