| Abstract
| - The effects of molecular architecture on the fracture properties of semicrystalline polymerswere probed at diblock copolymer-reinforced interfaces between polystyrene (PS) and polyethylene (PE).The PE used for this study was a model ethylene−butene copolymer which was chosen for its compatibilitywith hydrogenated 1,4-polybutadiene. This compatibility allowed the use of hydrogenated poly(styrene-b-1,4-tetradeuteriobutadiene) as the block copolymer. For a series of these diblock copolymers, the arealchain density (Σ) and the molecular weight of the PE block (Mn) were varied systematically to observetheir effects on the interfacial fracture energy (Gc). At low Σ, Gc stayed relatively constant, and was roughly1 J/m2. Above a critical value of Σ, the fracture energy climbed rapidly. This critical value decreased withincreasing Mn. The detection of deuterium on the fracture surfaces indicated that pullout of the PE blockwas the predominant failure mechanism when Mn ≤ 30 kg/mol. Only when the molecular weight of thePE block reached 85 kg/mol was failure by chain scission observed. Since the entanglement molecularweight of PE is approximately 1 kg/mol, interfacial reinforcement does not appear to depend on theformation of entanglements for this system. The critical Mn coincides instead with the point at which theroot-mean-square end-to-end length of the PE block exceeds the long period of the PE crystal lamellae(L). The preceding observation is consistent with the decrease in Gc with increasing L near the criticalmolecular weight.
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