Dynamic Monte Carlo simulations of strain-induced crystallization in multiblock copolymers: Effects of microphase separation

Semicrystalline multiblock copolymers holding alternatingly crystallizable and noncrystallizable blocks are good thermoplastic elastomers that are commonly processed through strain-induced crystallization. The crystalline microdomains play the role of physical crosslinks in the network of noncrystallizable blocks for high elasticity, and meanwhile their size diversity determines high toughness. We scheduled three integrated steps to study three physical effects of the coexisting noncrystallizable components, i.e. dilution, microphase separation and asymmetric block rigidity, on the size diversity of crystalline microdomains yielded by strain-induced crystallization in multiblock copolymers. We firstly considered the dilution effects in the extremely concentrated and diluted cases presumably generated by concentration fluctuations of crystallizable blocks, as responsible for the large-end and small-end crystalline microdomains, respectively. Our dynamic Monte Carlo simulations of strain-induced crystallization of the extremely concentrated and diluted crystallizable blocks in diblock and tetrablock copolymers demonstrated the dilution effects that the concentrated cases exhibit crystallization similar with bulk homopolymers, but the diluted cases make smaller crystalline microdomains than the cases without stretching, thus strain-induced crystallization in these two cases enhances the size diversity of crystalline microdomains (DOI: 10.1039/D2SM00193D). Hereby in the second step, we further compared the concentrated and diluted cases of strain-induced crystallization with and without microphase separation, and observed that microphase separation influences little to the concentrated cases, but makes more rather than smaller crystalline microdomains in the diluted cases, thus enhances their size diversity in a way different from the dilution effects. Higher extents of microphase separation will however weaken this enhancement. Our observations paved the way towards a better understanding of strain-induced crystallization in thermoplastic elastomers.