In this Perspective, we discuss the recent development of polymerization-induced self-assembly mediated by reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization. This approach has quickly become a powerful and versatile technique for the synthesis of a wide range of bespoke organic diblock copolymer nano-objects of controllable size, morphology, and surface functionality. Given its potential scalability, such environmentally-friendly formulations are expected to offer many potential applications, such as novel Pickering emulsifiers, efficient microencapsulation vehicles, and sterilizable thermo-responsive hydrogels for the cost-effective long-term storage of mammalian cells.

Polymerization-Induced Self-Assembly of Block Copolymer Nano-objects via RAFT Aqueous Dispersion Polymerization

Transmetalation of Unsaturated Carbon Nucleophiles from Boron-Containing Species to the Mid to Late d-Block Metals of Relevance to Catalytic C−X Coupling Reactions (X = C, F, N, O, Pb, S, Se, Te)

Benzyl methacrylate (BzMA) is polymerized using a poly(lauryl methacrylate) macromolecular chain transfer agent (PLMA macro-CTA) using reversible addition–fragmentation chain transfer (RAFT) polymerization at 70 °C in n-dodecane. This choice of solvent leads to an efficient dispersion polymerization, with polymerization-induced self-assembly (PISA) occurring via the growing PBzMA block to produce a range of PLMA–PBzMA diblock copolymer nano-objects, including spheres, worms, and vesicles. In the present study, particular attention is paid to the worm phase, which forms soft free-standing gels at 20 °C due to multiple inter-worm contacts. Such worm gels exhibit thermo-responsive behavior: heating above 50 °C causes degelation due to the onset of a worm-to-sphere transition. Degelation occurs because isotropic spheres interact with each other much less efficiently than the highly anisotropic worms. This worm-to-sphere thermal transition is essentially irreversible on heating a dilute solution (0.10% w/w) bu...

Thermo-responsive Diblock Copolymer Worm Gels in Non-polar Solvents

Publisher Summary This chapter discusses boranes in organic chemistry, diborane as a reducing agent, volatile compounds of uranium, the alkali metal hydride approach to diborane, and alkali metal borohydrides. The search for solvents led to the discovery of sodium borohydride's being an excellent reducing agent for aldehydes and ketones. The search for catalysts to enhance the reducing power of sodium borohydride led to an anomalous result in the reduction of ethyl oleate. Investigation of this anomalous result led to the discovery of hydroboration. Hydroboration made the organoboranes readily available for the first time. This led to a systematic exploration of the chemistry of the organoboranes and established the fact that they constitute the most versatile organometallic available currently. The chapter describes molecular addition compounds and steric strains, steric assistance in solvolysis, the nonclassical ion problem, selective reductions, hydroboration, and versatile organoboranes. On the theoretical side, study of the dissociation of addition compounds of amines with trimethylborane, boron trifluoride, and borane provides a new quantitative approach to steric strains. These studies quickly removed doubts as to the importance of steric effects in chemical behavior and led to the study of related carbon compounds and the establishment of steric effects as an important factor in their behavior. One phase of these studies involved steric assistance to ionization in highly branched tertiary halides and related derivatives.

Boranes in Organic Chemistry

The preparation of nanoparticles in a soap-free system is highly attractive, as surfactants may influence and deteriorate subsequent applications. Thereby, the assembly of solid particles on droplets/particles is well known as Pickering-type stabilization. The resulting hybrid nanocomposites offer in general a rough surface and are highly intriguing for potential drug delivery systems, coating applications, and so forth. This review highlights developments in production and application of Pickering-type nanoparticles synthesized via heterophase polymerization techniques in emulsion, miniemulsion, dispersion, and suspension. We will focus our discussion on systems, wherein stabilization of the final nanometer-sized hybrids is exclusively accomplished via particle stabilizers. In case surfactants are used during preparation, they only serve as pre-treating agents to modify the surface properties of the particle stabilizer, and not being employed for the purpose of droplet/particle stabilization.

Pickering-type stabilized nanoparticles by heterophase polymerization

A convenient non-catalytic conversion of olefinic derivatives into saturated compounds through hydroboration and protonolysis

The adsorption of small silica particles onto large sterically stabilized poly(2-vinylpyridine) [P2VP] latex particles in aqueous solution is assessed as a potential route to nanocomposite particles with a “core−shell” morphology. Geometric considerations allow the packing efficiency, P, to be related to the number of adsorbed silica particles per latex particle, N. Making no assumptions about the packing structure, this approach leads to a theoretical estimate for P of 86 ± 4%. Experimentally, dynamic light scattering is used to obtain a plot of hydrodynamic diameter against N, which indicates the conditions required for monolayer coverage of the latex by the silica particles. Transmission electron microscopy confirmed that, at approximately monolayer coverage, calcination of these nanocomposite particles led to the formation of well-defined hollow silica shells. This is interpreted as strong evidence for a contiguous monolayer of silica particles surrounding the latex cores. On this basis, an experiment...

Packing efficiency of small silica particles on large latex particles: a facile route to colloidal nanocomposites.

Addition of excess sterically stabilized P2VP latex to a colloidal dispersion of P2VP-silica nanocomposite particles (with silica shells at full monolayer coverage) leads to the facile redistribution of the silica nanoparticles such that partial coverage of all the P2VP latex particles is achieved. This silica exchange, which is complete within 1 h at 20 °C as judged by small-angle x-ray scattering, is observed for nanocomposite particles prepared by heteroflocculation, but not for nanocomposite particles prepared by in situ copolymerization. These observations are expected to have important implications for the optimization of nanocomposite formulations in the coatings industry.

Unexpected Facile Redistribution of Adsorbed Silica Nanoparticles Between Latexes

Small angle X-ray scattering (SAXS) is a powerful characterization technique for the analysis of polymer-silica nanocomposite particles due to their relatively narrow particle size distributions and high electron density contrast between the polymer core and the silica shell. Time-resolved SAXS is used to follow the kinetics of both nanocomposite particle formation (via silica nanoparticle adsorption onto sterically stabilized poly(2-vinylpyridine) (P2VP) latex in dilute aqueous solution) and also the spontaneous redistribution of silica that occurs when such P2VP-silica nanocomposite particles are challenged by the addition of sterically stabilized P2VP latex. Silica adsorption is complete within af ew seconds at 20 � C and the rate of adsorption strongly dependent onthe extent of silica surface coverage. Similar very short time scales for silica redistribution are consistent with facile silica exchange occurring as a result of rapid interparticle collisions due to Brownian motion; this interpretation is consistent with a zeroth-order Smoluchowski-type calculation.

Time-resolved small-angle X-ray scattering studies of polymer-silica nanocomposite particles: initial formation and subsequent silica redistribution.

Communications. Protonolysis and Deuterolysis of Tri-2-norbornylborane- Evidence for the Retention of Configuration in the Protonolysis of Organoboranes.

Kenneth A. Murray

Papers

A convenient non-catalytic conversion of olefinic derivatives into saturated compounds through hydroboration and protonolysis

Packing efficiency of small silica particles on large latex particles: a facile route to colloidal nanocomposites.

Unexpected Facile Redistribution of Adsorbed Silica Nanoparticles Between Latexes

Time-resolved small-angle X-ray scattering studies of polymer-silica nanocomposite particles: initial formation and subsequent silica redistribution.

Communications. Protonolysis and Deuterolysis of Tri-2-norbornylborane- Evidence for the Retention of Configuration in the Protonolysis of Organoboranes.