Recently, polymerization-induced self-assembly (PISA) has become widely recognized as a robust and efficient route to produce block copolymer nanoparticles of controlled size, morphology, and surface chemistry. Several reviews of this field have been published since 2012, but a substantial number of new papers have been published in the last three years. In this Perspective, we provide a critical appraisal of the various advantages offered by this approach, while also pointing out some of its current drawbacks. Promising future research directions as well as remaining technical challenges and unresolved problems are briefly highlighted.

■ ACKNOWLEDGMENTS S.P.A. acknowledges the EPSRC for an Established Career Particle Technology Fellowship (EP/R003009), which provided postdoctoral support for N.J.W.P. C.B. thanks the Australian Research Council for his Future Fellowship (FT12010096).

In situ SAXS studies reveal the evolution of copolymer morphology during the PISA synthesis of diblock copolymer nano-objects in mineral oil.

Various carboxylic acid-functionalized poly(N,N-dimethylacrylamide) (PDMAC) macromolecular chain transfer agents (macro-CTAs) were chain-extended with diacetone acrylamide (DAAM) by reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization at 70 °C and 20% w/w solids to produce a series of PDMAC–PDAAM diblock copolymer nano-objects via polymerization-induced self-assembly (PISA). TEM studies indicate that a PDMAC macro-CTA with a mean degree of polymerization (DP) of 68 or higher results in the formation of well-defined spherical nanoparticles with mean diameters ranging from 40 to 150 nm. In contrast, either highly anisotropic worms or polydisperse vesicles are formed when relatively short macro-CTAs (DP = 40–58) are used. A phase diagram was constructed to enable accurate targeting of pure copolymer morphologies. Dynamic light scattering (DLS) and aqueous electrophoresis studies indicated that in most cases these PDMAC–PDAAM nano-objects are surprisingly resistant to changes in either solution pH or temperature. However, PDMAC40–PDAAM99 worms do undergo partial dissociation to form a mixture of relatively short worms and spheres on adjusting the solution pH from pH 2–3 to around pH 9 at 20 °C. Moreover, a change in copolymer morphology from worms to a mixture of short worms and vesicles was observed by DLS and TEM on heating this worm dispersion to 50 °C. Postpolymerization cross-linking of concentrated aqueous dispersions of PDMAC–PDAAM spheres, worms, or vesicles was performed at ambient temperature using adipic acid dihydrazide (ADH), which reacts with the hydrophobic ketone-functionalized PDAAM chains. The formation of hydrazone groups was monitored by FT-IR spectroscopy and afforded covalently stabilized nano-objects that remained intact on exposure to methanol, which is a good solvent for both blocks. Rheological studies indicated that the cross-linked worms formed a stronger gel compared to linear precursor worms.

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A series of water-soluble diblock copolymers containing 2-(dimethylamino)ethyl methacrylate and various alkyl methacrylates has been synthesized using group transfer polymerization. These hydrophilic−hydrophobic copolymers have been characterized with respect to chemical composition and molecular weight by NMR spectroscopy, elemental microanalyses, and gel permeation chromatography. Block copolymers containing methyl methacrylate as the hydrophobic component were water-soluble provided that the hydrophilic monomer content was greater than 60 mol % of the overall block copolymer. Quaternization of the DMAEMA block with methyl iodide was near-quantitative and considerably enhanced the water-solubility of the copolymers. NMR studies, surface tension measurements, and photon correlation spectroscopy all indicated that the PDMAEMA-b-MMA block copolymers form micelles in deionized water. However, in acidic solution (pH 2), copolymer micellization occurred only in the presence of added electrolyte. The block copolymer micelles initially increased in size on addition of added electrolyte at pH 9.5. Further electrolyte addition led to macroscopic precipitation.

With appropriate choice of reaction composition and conditions, copolymerisation of methyl methacrylate and ethylene glycol dimethacrylate using Cu-based ATRP or GTP methodologies yields soluble branched polymers in facile one-pot reactions.

Sodium methacrylate is polymerised directly via atom transfer radical polymerisation (ATRP) in aqueous media using a poly(ethylene oxide)-based macro-initiator; the resulting poly(ethylene oxide-block-sodium methacrylate) copolymers were obtained in good yield and have narrow molecular weight distributions as evidenced by aqueous GPC.