Abstract
The mechanical properties of a homologous series of polyolefin block copolymers comprised of glassy poly(cyclohexylethylene) (C), elastomeric poly(ethylene-alt-propylene) (P), and semicrystalline poly(ethylene) (E) are documented. Monodisperse CPEPC, CPE, and CEPEC with mass fractions wC ∼ 0.39−0.44 and 0 ≤ ξ ≤ 1, where ξ = wE /(wE + wP), were synthesized by sequential anionic polymerization of styrene, isoprene, and butadiene followed by catalytic hydrogenation. These materials hierarchically microphase separate into lamellae, within which templated crystallization-induced segregation occurs. As ξ increases, the unoriented, polydomain CPEPC materials exhibit monotonically increasing elastic moduli and yield stresses, comparable ultimate tensile strengths, and decreasing failure strains. Cold drawing the CPEPC polymers yields high-strength materials, the structures of which are examined by small- and wide-angle X-ray scattering. Drawn CPEPC-70 (ξ = 0.70) exhibits improved toughness with an ultimate tensile strength σfail = 75 ± 10 MPa and elongation at break of εfail = 1.22 ± 0.22, as compared to σfail = 92 ± 21 MPa and εfail = 0.86 ± 0.18 for drawn CEC (ξ = 1.00). Elasticity measurements on the drawn samples demonstrate that materials with ξ > 0 exhibit low degrees of stress softening, while smaller permanent sets and higher failure strains are observed as ξ decreases.
Published Version
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