Protected Poly(3-sulfopropyl methacrylate) Copolymers: Synthesis, Stability, and Orthogonal Deprotection

Because of their permanent charge, strong polyelectrolytes remain challenging to characterize, in particular, when they are combined with hydrophobic features. For this reason, they are typically prepared through a postmodification of a fully hydrophobic precursor. Unfortunately, these routes often result in an incomplete functionalization or otherwise require harsh reaction conditions, thus limiting their applicability. To overcome these problems, in this work a strategy is presented that facilitates the preparation of well-defined strong polyanions by starting from protected 3-sulfopropyl methacrylate monomers. Depending on the chemistry of the protecting group, the hydrophobic precursor could be quantitatively converted into a strong polyanion under nucleophilic, acidic, or basic conditions. As a proof of concept, orthogonally protected diblock copolymers were synthesized, selectively deprotected, and allowed to self-assemble in aqueous solution. Further conversion into a fully water-soluble polyanion was achieved by deprotecting the second block as well.

RAFT-Based Polymers for Click Reactions

The parallel development of reversible deactivation radical polymerization and click reaction concepts significantly enriches the toolbox of synthetic polymer chemistry. The synergistic effect of combining these approaches manifests itself in a growth of interest to the design of well-defined functional polymers and their controlled conjugation with biomolecules, drugs, and inorganic surfaces. In this review, we discuss the results obtained with reversible addition-fragmentation chain transfer (RAFT) polymerization and different types of click reactions on low- and high-molar-mass reactants. Our classification of literature sources is based on the typical structure of macromolecules produced by the RAFT technique. The review addresses click reactions, immediate or preceded by a modification of another type, on the leaving and stabilizing groups inherited by a growing macromolecule from the chain transfer agent, as well as on the side groups coming from monomers entering the polymerization process. Architecture and self-assembling properties of the resulting polymers are briefly discussed with regard to their potential functional applications, which include drug delivery, protein recognition, anti-fouling and anti-corrosion coatings, the compatibilization of polymer blends, the modification of fillers to increase their dispersibility in polymer matrices, etc.

Polymer ligand binding to surface-immobilized gold nanoparticles: a fluorescence-based study on the adsorption kinetics

We report on a simple, fluorescence-based method for the investigation of the binding kinetics of polystyrene ligands, dispersed in an organic solvent, to substrate supported gold nanoparticles. For this purpose, we develop a protocol for the immobilization of gold nanoparticles on glass substrates, that yields sub-monolayers of randomly distributed particles with excellent homogeneity and reproducibility. Using fluorescently labeled polystyrene, we monitor the ligand concentration in bulk dispersion in real time and follow the binding to the particle-decorated substrates. The influence of the ligand molecular weight on the binding kinetics is investigated. We correlate the reaction rates with the diffusion coefficients of the different ligands and are able to describe the molecular weight dependency with a simple kinetic model. Both the diffusion and the activation step appear to contribute to the effective reaction rates.

Versatile Route toward Hydrophobically Polymer-Grafted Gold Nanoparticles from Aqueous Dispersions

Stabilization of gold nanoparticles in organic solvents is a key challenge in making them available for a wider range of material applications. Polymers are often used as stabilizing ligands because they also allow for the introduction of new properties and functionalities. Many of the established synthesis protocols for gold nanoparticles are water-based. However, the insolubility of many synthetic polymers in water renders the direct functionalization of aqueous particle dispersions with these ligands difficult. Here, we report on an approach for the functionalization of gold nanoparticles, which were prepared by aqueous synthesis, with hydrophobic polymer ligands and their characterization in nonpolar, organic dispersions. Our method employs an auxiliary ligand to first transfer gold nanoparticles from an aqueous to an organic medium. In the organic phase, the auxiliary ligand is then displaced by thiolated polystyrene ligands to form a dense polymer brush on the particle surface. We characterize the structure of the ligand shell using electron microscopy, scattering techniques, and ultracentrifugation and analyze the influence of the molecular weight of the polystyrene ligands on the structure of the polymer brush. We further investigate the colloidal stability of polystyrene-functionalized gold nanoparticles in various organic solvents. Finally, we extend the use of our protocol from small, spherical gold nanoparticles to larger gold nanorods and nanocubes.

Manganese phosphinocarbodithioate for RAFT polymerisation with sunlight-induced chain end post-treatment

A new manganese complex of the formula Cp(CO)₂MnP(Ph)₂C(S)SCH(CH₃)Ph is an efficient RAFT agent for the preparation of SH-terminated polymers by simple visible light photocleavage of the organometallic end-group.

RAFT polymer cross-coupling with boronic acids

The ability to modify the thiocarbonylthio end-groups of RAFT polymers is important for applications where an inert or highly functionalised material is required. Here we report a copper promoted cross-coupling reaction between RAFT polymer end-groups and aryl boronic acids. This method gives high conversion to the modified polymers, and is compatible with a wide variety of functional molecules.

Desulfurization-bromination: direct chain-end modification of RAFT polymers

We report a simple and efficient transformation of thiol and thiocarbonylthio functional groups to bromides using stable and commercially available brominating reagents. This procedure allows for the quantitative conversion of a range of small molecule thiols (including primary, secondary and tertiary) to the corresponding bromides under mild conditions, as well as the facile chain-end modification of polystyrene (PS) homopolymers and block copolymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. Specifically, the direct chain-end bromination of PS prepared by RAFT was achieved, where the introduced terminal bromide remained active for subsequent modification or chain-extension using classical atom transfer radical polymerization (ATRP). This transformation sets the foundation for bridging RAFT and ATRP, two of the most widely used controlled radical polymerization (CRP) strategies, and enables the preparation of chain-end functionalized block copolymers not directly accessible using a single CRP technique.

Cleavage of macromolecular RAFT chain transfer agents by sodium azide during characterization by aqueous GPC

Accurate and reliable analysis of polymers by GPC is vital in the field of controlled radical polymerisation.

One-pot synthesis of poly(vinylidene fluoride) methacrylate macromonomers via thia-Michael addition

A comparison of two one-pot methods to prepare methacrylate PVDF-macromonomers and the synthesis of PVDF-containing block copolymers.