Preparation of multicompartment micelles from amphiphilic linear triblock terpolymers by pH-responsive self-assembly

Multicompartment micelles, as an intriguing class of self-assembled aggregates with subdivided solvophobic cores, show high potentials for various applications. Their unique morphologies and sequestration properties depend highly on structure and chemical composition of the building blocks as well as self-assembly environments. To further understand their relationships, a series of well-defined amphiphilic triblock terpolymers poly(methyl methacrylate)-block-poly(2-(cinnamoyloxy)ethyl methacrylate)-block-poly(2-dimethylaminoethyl methacrylate) (PMMA-b-PCEMA-b-PDMAEMA) was synthesized via sequential atom transfer radical polymerization (ATRP) followed by selective modification of the middle block, and the self-assembly of PMMA-b-PCEMA-b-PDMAEMA via direct dispersing in water and step-wise procedures through solvent exchange was studied, respectively. Dynamic laser scattering (DLS) studies showed the existence of large-sized aggregates formed through direct self-assembly of PMMA-b-PCEMA-b-PDMAEMA triblock terpolymers in water, and the aqueous solutions were found to exhibit the surface tension reduction. This is probably caused by the frozen micelles adsorbed on the air/water interface which play the role of Pickering emulsifiers. However, PMMA-b-PCEMA-b-PDMAEMA multicompartment micelles could be successfully prepared by the step-wise self-assembly method, inhibiting the formation of frozen micelles and large aggregates. Prepared from different PMMA-b-PCEMA-b-PDMAEMA triblock terpolymers, the homogeneously nano-sized multicompartment micelles of oval morphologies with distinct subdivided core domains were confirmed by transmission electron microscope (TEM). Besides, various morphologies of the multicompartment micelles were obtained simply by altering the pH value of water. This multicompartment micelle system with adjustable pH response holds potential for therapeutic delivery of multiple incompatible drug payloads and is believed to contribute to enriching the research field of tunable polymer self-assemblies.