Mechanical consequences of molecular composition on failure in polyolefin composites containing glassy, elastomeric, and semicrystalline components

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Abstract

In order to gain insights into the mechanisms of deformation and ultimate failure in a homologous series of lamellae-forming polyolefin block copolymers comprised of glassy poly(cyclohexylethylene) (C), elastomeric poly(ethylene-alt-propylene) (P), and semicrystalline poly(ethylene) (E), the anisotropic tensile properties of samples in which the microphase separate structure is oriented on a macroscopic length scale were probed. Reciprocating shear processing of monodisperse CPCPC and CPEPC-ξ polymers having mass fraction wC ∼ 0.39-0.44 and 0 ≤ ξ ≤ 1, where ξ = wE/(wE + wP), produces "single-grain" polymer samples with perpendicular-oriented lamellae. Tensile deformation studies in which the strain axis coincides with the lamellar normal direction yield varied mechanical responses ranging from brittle fracture for CEC (ξ = 0) to ductile behavior for CPEPC (ξ > 0) and CPCPC. Tandem small- and wide-angle X-ray scattering analysis of samples undergoing deformation shows that application of strain along the lamellar normal in the CPEPC materials results in formation of a folded lamellar structure or "chevron" morpohology within which the E crystals cant relative to the strain direction. Since the ultimate failure mechanism for materials strained in this direction is chain pullout in the glassy domains, a simple mechanical model applied to the data enables quantitation of the stress required for chain pullout at ∼4 MPa. Additionally, the mechanical properties of miscible blends of CEC and CPC polymers with matched segregation strengths are shown to mimic those of the covalently linked CPEPC pentablock copolymer.

Original languageEnglish (US)
Pages (from-to)1341-1351
Number of pages11
JournalMacromolecules
Volume41
Issue number4
DOIs
StatePublished - Feb 26 2008

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