Synthesis of Amphiphilic Poly(acrylic acid)-b-poly(n-butyl acrylate-co-acrylic acid) Block Copolymers with Various Microstructures via RAFT Polymerization in Water/Ethanol Heterogeneous Media

Macromolecular Engineered Multifunctional Room-Temperature Phosphorescent Polymers through Reversible Deactivation Radical Polymerization

Despite the intensive research in room-temperature phosphorescent (RTP) polymers, the synthesis of RTP polymers with well-defined macromolecular structures and multiple functions remains a challenge. Herein, reversible deactivation radical polymerization was demonstrated to offer a gradient copolymer (GCP) architecture with controlled heterogeneities, which combines hard segment and flexible segment. The GCPs would self-assemble into a multiphase nanostructure, featuring tunable stretchability, excellent RTP performance, and intrinsic healability without compromising light emission under stretching. The mechanical performance is tunable on demand with elongation at break ranging from 5.0% to 221.7% and Young's modulus ranging from 0.5 to 225.0 MPa.

Synthesis of ABA triblock copolymer nanoparticles by polymerization induced self-assembly and their application as an efficient emulsifier

ABA triblock copolymer nanoparticles of PHPMA-b-PS-b-PHPMA were synthesized by PISA and demonstrated to be an efficient emulsifier.

Photoactive rose bengal-based latex via RAFT emulsion polymerization-induced self-assembly

Rose bengal shell- or core-functionalized acrylic latex synthesized by RAFT emulsion PISA: interfacial photosensitized ¹O₂ production under visible light.

One polymer composition, various morphologies: the decisive influence of conditions on the polymerization-induced self-assembly (PISA) of N-acryloyl thiomorpholine

Polymerization-induced self-assembly (PISA) represents a powerful technique for the preparation of nanostructures comprising various morphologies. Herein, we demonstrate that the recently introduced monomer N-acryloylthiomorpholine (NAT) features a unique self-assembly behaviour during an aqueous PISA. The one-pot, aqueous RAFT dispersion polymerization starting from short poly(N-acryloylmorpholine) (PNAM) enables access to all common solution morphologies including spheres, worms, vesicles and lamellae, at very low molar masses (< 8 kDa). Moreover, all these structures can be obtained for the same polymer composition and size by the variation of the polymerization temperature and concentration of the monomer. This exceptional self-assembly behavior is associated with the combination of a high glass transition temperature, excellent water solubility of the monomer, and the early onset of aggregation during the polymerization, which stabilizes the morphology at different stages. This PISA system opens up new opportunities to reproducibly create versatile, functional nanostructures and enables an independent evaluation of morphology-property relationships, as it is exemplarily shown for the oxidative degradation of spherical and wormlike micelles, as well as vesicles.

Metathesis Cyclopolymerization Triggered Self-Assembly of Azobenzene-Containing Nanostructure

Azobenzene (AB) units were successfully introduced into poly(1,6-heptadiyne)s in order to ensure smooth synthesis of double- and single-stranded poly(1,6-heptadiyne)s (P1 and P2) and simultaneously realize the self-assembly by Grubbs-III catalyst-mediated metathesis cyclopolymerization (CP) of AB-functionalized bis(1,6-heptadiyne) and 1,6-heptadiyne monomers (M1 and M2). Monomers and polymers were characterized by 1H NMR, mass spectroscopy, and GPC techniques. The double-stranded poly(1,6-heptadiyne)s exhibited a large scale of ordered ladder nanostructure. This result was attributed to the π-π attractions between end groups along the longitudinal axis of the polymers and van der Waals interactions between the neighboring polymeric backbones. While the Azo chromophore connected in the side chain of P2 induced conformation of micelles nanostructure during the CP process without any post-treatment. Furthermore, the photoisomerization of Azo units had an obviously different regulatory effect on the conjugated degree of the polymer backbone, especially for the single-stranded P2, which was attributed to the structural differences and the interaction between AB chromophores in the polymers.

Amphiphilic poly(caprolactone-b-N-hydroxyethyl acrylamide) micelles for controlled drug delivery

To increase the bioavailability and water solubility of hydrophobic medicine, an amphiphilic block copolymer, polycaprolactone-block-polyhydroxyethyl acrylamide (PCL-b-PHEAA), was synthesized.

CO2-Triggered and temperature-switchable crystallization-driven self-assembly of a semicrystalline block copolymer in aqueous medium

The synthesis of a semicrystalline block copolymer comprising a hydrophilic poly(acrylic acid) pure block and an amphiphilic poly(acrylic acid)-r-poly(octadecyl acrylate) random block by nitroxide-mediated polymerization is reported.

Critical Dependence of Molecular Weight on Thermoresponsive Behavior of Diblock Copolymer Worm Gels in Aqueous Solution

Reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate was used to prepare three poly(glycerol monomethacrylate) x -poly(2-hydroxypropyl methacrylate) y (denoted G x -H y  or PGMA-PHPMA) diblock copolymers, namely G37-H80, G54-H140, and G71-H200. A master phase diagram was used to select each copolymer composition to ensure that a pure worm phase was obtained in each case, as confirmed by transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS) studies. The latter technique indicated a mean worm cross-sectional diameter (or worm width) ranging from 11 to 20 nm as the mean degree of polymerization (DP) of the hydrophobic PHPMA block was increased from 80 to 200. These copolymer worms form soft hydrogels at 20 °C that undergo degelation on cooling. This thermoresponsive behavior was examined using variable temperature DLS, oscillatory rheology, and SAXS. A 10% w/w G37-H80 worm dispersion dissociated to afford an aqueous solution of molecularly dissolved copolymer chains at 2 °C; on returning to ambient temperature, these chains aggregated to form first spheres and then worms, with the original gel strength being recovered. In contrast, the G54-H140 and G71-H200 worms each only formed spheres on cooling to 2 °C, with thermoreversible (de)gelation being observed in the former case. The sphere-to-worm transition for G54-H140 was monitored by variable temperature SAXS: these experiments indicated the gradual formation of longer worms at higher temperature, with a concomitant reduction in the number of spheres, suggesting worm growth via multiple 1D sphere-sphere fusion events. DLS studies indicated that a 0.1% w/w aqueous dispersion of G71-H200 worms underwent an irreversible worm-to-sphere transition on cooling to 2 °C. Furthermore, irreversible degelation over the time scale of the experiment was also observed during rheological studies of a 10% w/w G71-H200 worm dispersion. Shear-induced polarized light imaging (SIPLI) studies revealed qualitatively different thermoreversible behavior for these three copolymer worm dispersions, although worm alignment was observed at a shear rate of 10 s-1 in each case. Subsequently conducting this technique at a lower shear rate of 1 s-1 combined with ultra small-angle x-ray scattering (USAXS) also indicated that worm branching occurred at a certain critical temperature since an upturn in viscosity, distortion in the birefringence, and a characteristic feature in the USAXS pattern were observed. Finally, SIPLI studies indicated that the characteristic relaxation times required for loss of worm alignment after cessation of shear depended markedly on the copolymer molecular weight.

Recent advances in RAFT-mediated surfactant-free emulsion polymerization

We summarized the RAFT-mediated surfactant-free emulsion polymerization using various RAFT agents and the polymerization types for the preparation of organic/inorganic hybrid materials.

ROMPISA: Ring-Opening Metathesis Polymerization-Induced Self-Assembly

Herein we report a polymerization-induced self-assembly (PISA) process with ring-opening metathesis polymerization (ROMP). We utilize a peptide-based norbornenyl monomer as a hydrophobic unit to provide a range of nanostructures at room temperature yet at high solids concentrations of 20 wt % in combination with an oligoethylene glycol based norbornenyl monomer. Evaluation of the polymerizations under mild conditions highlight that good control is maintained along with high monomer conversion of greater than 99%, indicating that the living polymerization is unaffected during the PISA process. The demonstration broadens the scope of the PISA process to a new living polymerization methodology toward the development of easily accessible and highly functionalized nanostructures in situ.

H2O2 Enables Convenient Removal of RAFT End-Groups from Block Copolymer Nano-Objects Prepared via Polymerization-Induced Self-Assembly in Water

RAFT-synthesized polymers are typically colored and malodorous due to the presence of the sulfur-based RAFT end-group(s). In principle, RAFT end-groups can be removed by treating molecularly dissolved copolymer chains with excess free radical initiators, amines, or oxidants. Herein we report a convenient method for the removal of RAFT end-groups from aqueous dispersions of diblock copolymer nano-objects using H2O2. This oxidant is relatively cheap, has minimal impact on the copolymer morphology, and produces benign side products that can be readily removed via dialysis. We investigate the efficiency of end-group removal for various diblock copolymer nano-objects prepared with either dithiobenzoate- or trithiocarbonate-based RAFT chain transfer agents. The advantage of using UV GPC rather than UV spectroscopy is demonstrated for assessing both the kinetics and extent of end-group removal.

RAFT polymerization to form stimuli-responsive polymers

Stimuli-responsive polymers respond to a variety of external stimuli, which include optical, electrical, thermal, mechanical, redox, pH, chemical, environmental and biological signals. This paper is concerned with the process of forming such polymers by RAFT polymerization.

Guidelines for the Synthesis of Block Copolymer Particles of Various Morphologies by RAFT Dispersion Polymerization

This article presents the recent developments of radical dispersion polymerizaton controlled by reversible addition fragmentation chain transfer (RAFT) for the production of block copolymer particles of various morphologies, such as core-shell spheres, worms, or vesicles. It is not meant to be an exhaustive review but it rather provides guidelines for non-specialists. The article is subdivided into eight sections. After a general introduction, the mechanism of polymerization-induced self-assembly (PISA) through RAFT-mediated dispersion polymerization is presented and the different parameters that control the morphology produced are discussed. The next two sections are devoted to the choice of the monomer/solvent pair and the macroRAFT agent. Afterwards, post-polymerization morphological order-to-order transitions (i.e. morphological transitions triggered by extrinsic stimuli) or order-to-disorder transitions (i.e. disassembly of chains) are discussed. Assemblies based on more complex polymer architectures, such as triblock copolymers, are presented next, and finally the possibility to stabilize these structures by crosslinking is reported. The manuscript ends with a short conclusion and an outlook.

Determining the effect of side reactions on product distributions in RAFT polymerization by MALDI-TOF MS

RAFT polymerization has emerged as one of the most versatile reversible deactivation radical polymerization techniques and is capable of polymerizing a wide range of monomers under various conditions.

Exploiting nucleobase-containing materials – from monomers to complex morphologies using RAFT dispersion polymerization

The synthesis of nucleobase-containing polymers was successfully performed by RAFT dispersion polymerization in both chloroform and 1,4-dioxane and self-assembly was induced by the polymerizations.

Asymmetrical vesicles: convenient in situ RAFT synthesis and controllable structure determination

Asymmetrical vesicles of a block copolymer were prepared, and the vesicle structure was found to be dependent on the degree of polymerization of solvophilic blocks.

RAFT dispersion polymerization: a method to tune the morphology of thymine-containing self-assemblies

The synthesis and self-assembly of thymine-containing polymers were performed using RAFT dispersion polymerization.

Dispersion RAFT polymerization: comparison between the monofunctional and bifunctional macromolecular RAFT agents

The dispersion RAFT polymerizations mediated with monofunctional and bifunctional macro-RAFT agents were comparatively studied, in which different block copolymer morphologies were detected.