Hierarchical Self-Assembly of Polyethylene Midblock Copolymers in Hot Steam: Key Role of Crystalline and Topological Structure

A series of linear-shaped, H-shaped, and dumbbell-shaped semi-crystalline triblock copolymers (E-1, E-2 and E-3) is prepared, which contains polyethylene (PE) midblock and poly(methyl methacrylate) (PMMA) endblocks. The molecular design in this study is focused on the variation of the length and number of PMMA chains, with a fixed PE midblock (M-n = 16 000 g mol(-1)) and approximate composition (wt(PE)%:wt(PMMA) approximate to 1:1), upon which the hierarchical self-assembly behavior in solvent vapor annealing (SVA) process is investigated. The dumbbell-shaped E-3, which contains the most and shortest PMMA chains, shows a drastic reduction of the T-m and crystallinity of PE midblock. It is attributed to the plasticization effects by the dumbbell architecture, which disturbed the chain folding of PE block. The variation of the topological structure of copolymers not only accelerates the transformation of morphologies from spherical to network, but also leads to the formation of new morphologies. After repeated annealing, both E-1 and E-2 form crossed network, columnar and flower-like morphologies by higher-level assembly from preassembled vermicular micelles. By comparison, the dumbbell-shaped E-3 assembled into lamellar or stacks of lamellar morphologies. The hierarchical self-assembly can be governed by the combination of the driving forces of PE crystallization and the topologies structure.

Automated summary

A series of different shaped semi-crystalline triblock copolymers were prepared and studied for their self-assembly behavior during solvent vapor annealing. The dumbbell-shaped polymer showed plasticization effects on the PE midblock, affecting chain folding and reducing crystallinity. The hierarchical self-assembly process was influenced by both PE crystallization and copolymer topological structures.