Direct Visualization of Polymerization-Induced Self-Assembly of Amphiphilic Copolymers

The ability to have precise control over the designed structure and properties of molecular self-assemblies is critical for tailoring the quality and efficacy of their functionality, yet the underlying mechanisms governing the evolution from molecules into self-assembled structures are not fully resolved. Here, we employed the graphene liquid cell (GLC) transmission electron microscopy (TEM) approach to observe nucleation and evolution of individual nanoscale micelles during polymerization-induced self-assembly. We speculate that the electron beam induces radical formation by homolytic cleavage of the poly(glycerol methacrylate)-thiocarbonylthio (PolyGMA-thiocarbonylthio) macro-chain-transfer agent (macroCTA), at which it initiates the polymerization of HPMA monomer in aqueous solution. Chain growth of the hydrophobic block, PolyHPMA, and subsequent instability of the resulting block copolymer in the solution trigger the formation of the nanoscale polymer self-assemblies. The spinodal decomposing mechanism is proposed here for the formation and evolution of the polymer assemblies. Such in-situ visualization of polymeric micelle formation, devoid of metal-ion labeling, provides new insights into understanding the complex mechanism of the self-assembly process in amphiphilic molecules.