ma6b01521_si_001.pdf (2.75 MB)
Toughened Isotactic Polypropylene: Phase Behavior and Mechanical Properties of Blends with Strategically Designed Random Copolymer Modifiers
journal contribution
posted on 2016-08-26, 16:52 authored by Jun Xu, Vikas Mittal, Frank S. BatesA series of poly(cyclohexylethylene-ran-ethylene)
(CE) copolymers were synthesized with statistical segment lengths
designed to match that of isotactic poly(propylene) (iPP). Melt blending the CE compounds containing 50–70 wt %
cyclohexylethylene repeat units with iPP at
loadings between 5 and 20 wt % resulted in a dispersion of CE droplets
with number-average diameters between 150 and 500 nm as determined
by scanning electron microscopy. Linear dynamic mechanical elastic
(G′) and loss (G″)
moduli data were fit to the Palierne model providing estimates for
the interfacial tension between iPP and CE, which
was interpreted based on enthalpic (χH) and entropic
(χS) contributions to the overall segment–segment
interaction parameter, χ = χH + χS, attributed to density and statistical segment length differences,
respectively. The small particle sizes are explained by a reduced
interfacial tension, driven by minimization of χS (≈0), counterbalanced by χH > 0, establishing
an optimal balance between phase separation and dispersion during
blending at practical molecular weights. The optically clear blends
exhibit superior tensile mechanical properties, with the strain at
break increasing from 20% for iPP to 400% at a loading
of 5 wt %, attributable to shear yielding of the matrix triggered
by cavitation of the uniformly dispersed CE copolymer particles.