Block copolymers comprising chemically incompatible blocks that undergo microphase separation have to date been largely explored for nano-structured films. This process is mainly governed by the Flory-Huggins interaction parameter (χ) and degree of polymerization (N), whereby the MW of the comprising blocks must be sufficiently high for microphase separation to occur. Such microphase separation can also be observed within particles prepared in heterogeneous systems, which results in nano-engineered particles displaying sophisticated morphologies. Recently we reported an environmentally friendly approach for the preparation of multiblock copolymers via sequential RAFT emulsion polymerization. The compartmentalization effect, i.e. how the radicals propagate within the particles reducing the termination rate, was exploited not only to obtain rate enhancement of the system, but also to generate chains with high-degree of chain end fidelity. Amphiphilic block copolymer of low MW was initially prepared via RAFT solution polymerization. After purification and solubilization in water, macroRAFT-assisted emulsion polymerization of hydrophobic monomers (styrene (S) or butyl methacrylate (BMA)) was then performed, generating polymeric nanoparticles (“nanoreactors”). Successive sequential RAFT polymerizations of different monomers were subsequently performed, generating a wide range of multiblock copolymer particles (Fig. 1). Due to the compartmentalization effect, polymers exhibiting high MW (&gt;100.000 g mol-1) could be synthesized in a relatively short period of time (~6h). Furthermore, given that the RAFT-moieties are located in the core of the particle, the successive growth of incompatible block copolymers from within the particle centre leads to the formation of multilayered particles. In addition, the number and the composition of each layer was readily controlled due to the great versatility of RAFT polymerization and the judicious choice of monomers. This demonstrates how RAFT conducted in emulsion polymerization can be a very powerful tool for the preparation of tailored-made multilayered particles.

Nano-engineered multiblock copolymer particles via RAFT emulsion polymerization

ACS Spring Meeting 2021

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