Molecular‐Weight‐Controlled Brittle‐to‐Semiductile‐to‐Ductile Transition in S‐(S/B)‐S Triblock Copolymers

Abstract

Toughness enhancement of S‐(S/B)‐S triblock copolymers via a molecular‐weight‐controlled pathway is demonstrated. The post‐yield crack toughness behavior of the triblock copolymers uniquely reveal a brittle‐to‐semiductile‐to‐ductile transition with increasing $\overline M _{\rm w}$ while keeping the basic molecular architecture fixed. TEM and SAXS investigations indicated three distinct morphologies as a function of χeffN as a consequence of the increase in $\overline M _{\rm w}$: (i) a homogeneous structure without phase‐separation, (ii) a weakly segregated structure, and (iii) a lamellar structure. The increase in crack toughness is also reaffirmed from kinetic and strain field analysis studies concerning dynamics of crack growth in block copolymers with high PS content.magnified image

Influence of Controlled Epoxidation of an Asymmetric Styrene/Butadiene Star Block Copolymer on Structural and Mechanical Properties

“…Due to the covalent bonds between the two components, microphase-separated morphologies in the nanometer range are formed, resulting in the transparency of these materials [3][4][5][6][7]. Changing the molecular architecture, relative chemical composition, and nature of monomers the properties of the BCPs can be adjusted over a wide range covering a material portfolio from thermoplastic elastomers [8,9] to toughened thermoplastics [10][11][12][13][14][15]. In addition to their use as components in medical equipment, household technology, and automotive industry or the information technology (IT) sector, SB-based BCPs are also used, for example, in adhesives and sealants and asphalt formulations [16][17][18][19].…”