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

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 to differing degrees of polymerization control. Finally, the in situ encapsulation of the model hydrophobic drug, Nile Red, was demonstrated, suggesting applications of this facile process for the synthesis of nanoparticles for drug delivery applications

Polymerization-Induced Self-Assembly Using Visible Light Mediated Photoinduced Electron Transfer–Reversible Addition–Fragmentation Chain Transfer Polymerization

The ruthenium-based photoredox catalyst, Ru­(bpy)₃Cl₂, was employed to activate reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization via a photoinduced electron transfer (PET) process under visible light (λ = 460 nm, 0.7 mW/cm²). Poly­(oligo­(ethylene glycol) methyl ether methacrylate) was chain extended with benzyl methacrylate to afford in situ self-assembled polymeric nanoparticles with various morphologies. The effect of different intrinsic reaction parameters, such as catalyst concentration, total solids content, and cosolvent addition was investigated with respect to the formation of different nanoparticle morphologies, including spherical micelles, worm-like micelles, and vesicles. Importantly, highly pure worm-like micelles were readily isolated due to the in situ formation of highly viscous gels. Finally, “ON/OFF” control over the dispersion polymerization was demonstrated by online Fourier transform near-infrared (FTNIR) spectroscopy, allowing for temporal control over the nanoparticle morphology

Visible Light-Mediated Polymerization-Induced Self-Assembly Using Continuous Flow Reactors

We present the synthesis of polymeric nanoparticles of targeted morphology in a continuous process via visible light-mediated aqueous RAFT polymerization-induced self-assembly (PISA). A trithiocarbonate-derived poly­(ethylene glycol) (PEG) macroRAFT was activated in the presence of hydroxypropyl methacrylate (HPMA) at 37 °C under blue light irradiation (460 nm), leading to the formation of PEG-<i>b</i>-P­(HPMA) nanoparticles. The method is attractive in its simplicityspheres, worms, and vesicles can easily be obtained in a continuous fashion with higher control in comparison to conventional batch procedures. This allows for more accurate production of particle morphologies and scalable synthesis of these nano-objects. The versatility of this process was demonstrated by the <i>in situ</i> encapsulation of an active compound

2‑(Methylthio)ethyl Methacrylate: A Versatile Monomer for Stimuli Responsiveness and Polymerization-Induced Self-Assembly in the Presence of Air

In this communication, we investigate the photoinduced electron/energy transfer–reversible addition–fragmentation chain transfer (PET-RAFT) polymerization of 2-(methylthio)­ethyl methacrylate (MTEMA) using 5,10,15,20-tetraphenylporphine zinc (ZnTPP) as a photocatalyst under visible red light (λ_max = 635 nm). Interestingly, the polymerization kinetics were not affected by the presence of air as near identical polymerization kinetics were observed for non-deoxygenated and deoxygenated systems, which is attributed to the singlet oxygen quenching ability of MTEMA. In both cases, well-defined polymers were obtained with good control over the molecular weight and molecular weight distribution (MWD). Furthermore, we have demonstrated that MTEMA can undergo the polymerization-induced self-assembly (PISA) process from a poly­(oligo­(ethylene glycol) methyl ether methacrylate) (POEGMA) macromolecular chain transfer agent (macro-CTA) to yield well-defined polymeric nanoparticles of various morphologies. These nanoparticles were rapidly disassembled after exposure to visible light due to the formation of singlet oxygen by the encapsulated ZnTPP and subsequent rapid oxidation of the thioether group

Copolymers with Controlled Molecular Weight Distributions and Compositional Gradients through Flow Polymerization

We report a novel semicontinuous method for producing polymer mixtures with tailored molecular weight distributions (MWDs) and chemical compositions. In contrast to recent methods disclosed for the production of tailored MWDs, the current approach allows the MWD to be tailored at any point in a multistep process. Optimization of a photoflow polymerization process has been performed, where polymer fractions with variable compositions can be produced and independently processed downstream. This independent processing allows complex and tedious operations to be significantly simplified and the polymer structure to be manipulated by varying the production conditions. To illustrate the versatility of our approach, we prepared low dispersity block copolymer mixtures with tailored composition gradients through PET-RAFT polymerization, using a facile one-pass flow technique

An Efficient and Highly Versatile Synthetic Route to Prepare Iron Oxide Nanoparticles/Nanocomposites with Tunable Morphologies

We report a versatile synthetic method for the <i>in situ</i> self-assembly of magnetic-nanoparticle-functionalized polymeric nanomorphologies, including spherical micelles and rod-like and worm-like micelles and vesicles. Poly­(oligoethylene glycol methacrylate)-<i>block</i>-(methacrylic acid)-<i>block</i>-poly­(styrene) (POEGMA-<i>b</i>-PMAA-<i>b</i>-PST) triblock copolymer chains were simultaneously propagated and self-assembled via a polymerization-induced self-assembly (PISA) approach. Subsequently, the carboxylic acid groups in the copolymers were used to complex an iron ion (Fe^II/Fe^III) mixture. Iron oxide nanoparticles were then formed in the central block, within the polymeric nanoparticles, via alkaline coprecipitation of the iron­(II) and (III) salts. Nanoparticle morphologies, particle sizes, molecular weights, and chemical structures were then characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), size exclusion chromatography (SEC), and ¹H NMR measurements. TEM micrographs showed that the average size of the magnetic nanoparticles was ∼7 nm at the hydrophobic/hydrophilic nexus contained within the nanoparticles. In addition, XRD was used to confirm the formation of iron oxide nanoparticles. Importantly, the polymeric nanoparticle morphologies were not affected by the coprecipitation of the magnetic nanoparticles. The hybrid nanoparticles were then evaluated as negative MRI contrast agents, displaying remarkably high transverse relaxivities (<i>r</i>₂, greater than 550 mM^–1 s^–1 at 9.4 T); a result, that we hypothesize, ensues from iron oxide nanoparticle clustering at the hydrophobic–hydrophilic interface. This simple synthetic procedure is highly versatile and produces nanocarriers of tunable size and shape with high efficacy as MRI contrast agents and potential utility as theranostic delivery vectors