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.

http://pubs.acs.org/doi/pdf/10.1021/acs.macromol.5b02602

A Critical Appraisal of RAFT-Mediated Polymerization-Induced Self-Assembly.

Polymerization-induced self-assembly of block copolymer nanoparticles via RAFT non-aqueous dispersion polymerization

Photomediated controlled radical polymerization

In this Perspective, we summarize recent progress in polymerization-induced self-assembly (PISA) for the rational synthesis of block copolymer nanoparticles with various morphologies. Much of the PISA literature has been based on thermally initiated reversible addition–fragmentation chain transfer (RAFT) polymerization. Herein, we pay particular attention to alternative PISA protocols, which allow the preparation of nanoparticles with improved control over copolymer morphology and functionality. For example, initiation based on visible light, redox chemistry, or enzymes enables the incorporation of sensitive monomers and fragile biomolecules into block copolymer nanoparticles. Furthermore, PISA syntheses and postfunctionalization of the resulting nanoparticles (e.g., cross-linking) can be conducted sequentially without intermediate purification by using various external stimuli. Finally, PISA formulations have been optimized via high-throughput polymerization and recently evaluated within flow reactors for facile scale-up syntheses.

Emerging trends in polymerization-induced self-assembly

After a brief history that positions polymerization-induced self-assembly (PISA) in the field of polymer chemistry, this Review will cover the fundamentals of the PISA mechanism. Furthermore, this Review will also give an overview of some of the features and limitations of RAFT-mediated PISA in terms of the choice of the components involved, the nature of the nanoobjects that can be obtained and how the syntheses can be controlled, as well as some potential applications.

https://hal.archives-ouvertes.fr/hal-03085063/document

RAFT‐mediated polymerization‐induced self‐assembly

We report the use of visible light to mediate a RAFT dispersion polymerization in the absence of external catalyst or initiator to yield nanoparticles of different morphologies according to a polymerization-induced self-assembly (PISA) mechanism. A POEGMA macro-chain transfer agent (macro-CTA) derived from a 4-cyano-4-((dodecylsulfanylthiocarbonyl)sulfanyl)pentanoic acid (CDTPA) RAFT agent can be activated under blue (460 nm, 0.7 mW/cm2) or green (530 nm, 0.7 mW/cm2) light and act simultaneously as a radical initiator, chain transfer agent, and particle stabilizer under ethanolic dispersion conditions. In particular, the formation of worm-like micelles was readily monitored by the increase of reaction viscosity during the polymerization; this method was shown to be particularly robust to different reaction parameters such as macro-CTAs of varying molecular weight. Interestingly, at high monomer conversion, different morphologies were formed depending on the wavelength of light employed, which may be due t...

Visible Light-Mediated Polymerization-Induced Self-Assembly in the Absence of External Catalyst or Initiator

Poly(stearyl methacrylate) (PSMA) homopolymers, prepared by RAFT radical polymerization, have been employed in the RAFT dispersion polymerization (RAFTDP) of 3-phenylpropyl methacrylate (PPMA) in n-tetradecane. RAFTDPs yielded block copolymers with narrow molecular weight distributions and tunable compositions and allowed for ready access to different polymorphic nanoparticle phases. Polymerization of PPMA at 20 wt %, for a fixed PSMA average degree of polymerization (Xn) of 19, allowed for the in situ preparation of soft matter nano-objects with spherical, worm, and vesicular morphologies. For a fixed block copolymer composition increasing total solids (from 10 to 40 wt %) favored the formation of nanoparticles with higher ordered morphologies. For block copolymer samples that formed soft physical gels at ambient temperature, a macroscopic thermoreversible degelation–gelation phenomenon was observed. The fundamental reason for this was a worm-to-sphere morphology transition that was facilitated, in part...

RAFT Dispersion Polymerization in Nonpolar Media: Polymerization of 3-Phenylpropyl Methacrylate in n-Tetradecane with Poly(stearyl methacrylate) Homopolymers as Macro Chain Transfer Agents

Poly(stearyl methacrylate) (PSMA) homopolymers with average degrees of polymerization (n) ranging from 18–30 have been prepared by homogeneous RAFT radical polymerization in toluene and subsequently employed as macro-chain transfer agents (CTAs) in non-polar RAFT dispersion formulations with 3-phenylpropyl methacrylate (PPMA) as the comonomer in n-octane at 70 °C. With PSMA18 or PSMA19 macro-CTAs in n-octane at 20 wt%, a series of PSMAx–PPPMAy block copolymers are readily accessible in situ that form the full range of common nanoparticle morphologies, with the complexity of the nano-objects increasing (spheres-to-worms-to-vesicles) with increasing n of the PPPMA block as clearly evidenced by transmission electron microscopy (TEM). An evaluation of the effect of total solids for the preparation of block copolymers of common composition indicated that polymerizations conducted at higher concentrations favoured the formation of nanoparticles with more complex morphologies. In the case of block copolymers prepared with a PSMA30 macro-CTA the only accessible morphology was spheres regardless of compositional asymmetry. However, the size of the spheres increased monotonically with increasing PPPMA block length. Formulations that yielded (essentially) pure worm phases, such as PSMA18-b-PPPMA71, formed physical gels at ambient temperature. Heating the physical gels to (or beyond) a critical temperature resulted in a macroscopic transformation to a free flowing solution. The fundamental reason for the transformation, as evidenced by TEM, was a morphological transition from worm to sphere nanoparticles facilitated, in part, by a change in solvation of the PPPMA core-forming block with increasing temperature. DLS analysis indicated that the morphology transitions were fully reversible.

Synthesis of poly(stearyl methacrylate-b-3-phenylpropyl methacrylate) nanoparticles in n-octane and associated thermoreversible polymorphism

pH-, thermo- and electrolyte-responsive polymer gels derived from a well-defined, RAFT-synthesized, poly(2-vinyl-4,4-dimethylazlactone) homopolymer via one-pot post-polymerization modification

Odilia R. Sugita

Papers

Visible Light-Mediated Polymerization-Induced Self-Assembly in the Absence of External Catalyst or Initiator

RAFT Dispersion Polymerization in Nonpolar Media: Polymerization of 3-Phenylpropyl Methacrylate in n-Tetradecane with Poly(stearyl methacrylate) Homopolymers as Macro Chain Transfer Agents

Synthesis of poly(stearyl methacrylate-b-3-phenylpropyl methacrylate) nanoparticles in n-octane and associated thermoreversible polymorphism

pH-, thermo- and electrolyte-responsive polymer gels derived from a well-defined, RAFT-synthesized, poly(2-vinyl-4,4-dimethylazlactone) homopolymer via one-pot post-polymerization modification