Poly(methyl methacrylate-block-vinyl-m-triphenylamine): synthesis by RAFT polymerization and melt-state self-assembly

Block copolymers (BCP)s containing electro-active hole-transport components such as triphenylamine-based polymers are attractive for organic electronic applications in which well-defined nanoscale structures are desirable. In this work, we synthesized poly(methyl methacrylate-block-vinyl-m-triphenylamine) (PMMA-b-PVmTPA) BCPs via reversible addition-fragmentation chain transfer (RAFT) polymerization and subsequently explored their melt-state self-assembly in the PMMA-rich phase regime. A library of diblock copolymers was generated by chain-extending several different poly(methyl methacrylate) (PMMA) macroinitiators with vinyl-m-triphenylamine monomer (VmTPA). These PMMA-b-PVmTPA diblock copolymers self-assembled into a variety of well-defined nanostructures over the studied compositional range (PVmTPA volume fractions [fPVmTPA] from 0.25 to 0.33), forming hexagonally packed cylinders (HEX) at fPVmTPA of 0.27 and below, network-like hexagonally perforated lamellae (HPL) at an intermediate fPVmTPA = 0.29, and lamellae (LAM) at fPVmTPA of 0.30 and above, as determined by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) analyses. Additionally, we found a thermally reversible order-order transition (OOT) from HPL to HEX upon heating, indicating that the HPL morphology likely was stable at lower temperatures for this system. Finally, we present an experimental phase diagram based on the assigned nanostructures as a function of PMMA-b-PVmTPA molecular weight and fPVmTPA. These results provide valuable guidance for targeting desirable morphologies in functional nanomaterials that incorporate the TPA functional group.