Polymerization-Induced Self-Assembly of All-Acrylic Diblock Copolymers via RAFT Dispersion Polymerization in Alkanes

Abstract

A series of all-acrylic poly(lauryl acrylate)–poly(benzyl acrylate) (PLA–PBzA) diblock copolymer nanoparticles are prepared by reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of benzyl acrylate in n-heptane, n-dodecane, or isohexadecane. As the PBzA block grows from the soluble PLA block it eventually becomes insoluble, which drives in situ polymerization-induced self-assembly (PISA). High monomer conversions (>99%) can be achieved and high blocking efficiencies are observed using 1H NMR spectroscopy and gel permeation chromatography, respectively. However, final Mw/Mn values range from 1.36 to 2.10, which suggests that chain transfer to polymer occurs in these all-acrylic PISA formulations. The soft, film-forming nature of these all-acrylic nanoparticles makes conventional TEM studies problematic. However, inspecting the visual appearance of these dispersions combined with DLS studies allows the construction of a phase diagram, which has been validated by cryo-TEM studies of selected copolymers. The latter technique confirms that spherical, worm-like or vesicular morphologies can be obtained depending on the copolymer concentration, mean degree of polymerization of the core and stabilizer blocks, and choice of solvent. Oscillatory rheology studies indicate that PLA–PBzA worms form free-standing worm gels at 20 °C with relatively low moduli (G′ ∼ 20 Pa). Moreover, reversible thermal transitions are observed below ∼15 °C and above ∼67 °C. Finally, worm gels that exhibit critical gelation concentrations as low as 2.5% w/w at 20 °C can be prepared at up to 40% w/w solids using a convenient one-pot protocol. In summary, this new PISA formulation represents a cost-effective, facile synthesis route to all-acrylic nano-objects in non-polar solvents.