Metal-complex-bearing star polymers by metal-catalyzed living radical polymerization: Synthesis and characterization of poly(methyl methacrylate) star polymers with Ru(II)-embedded microgel cores

Solvent-Free Templated Synthesis of Core-Crosslinked Star-Shaped Polymers in Supramolecular Body-Centered Cubic Phase

This study reports the exploration of a solvent-free supramolecular templated synthesis strategy toward highly core-cross-linked star-shaped polymers (CSPs). To achieve this, a kind of cross-linkable giant surfactant, based on a functionalized polyhedral oligomeric silsesquioxanes (POSS) head tethered with a diblock copolymer tail containing reactive benzocyclobutene groups, is designed and prepared. By varying the volume fraction of linear block copolymer tail, these giant surfactants can self-assemble into a body-centered cubic (BCC) structure in bulk, in which the supramolecular spheres are composed of a core of POSS cages, a middle shell of crosslinkable poly(4-vinylbenzocyclobutene) (PBCB) blocks, and a corona of inert polystyrene (PS) blocks. The solvent-free thermally induced cross-linking reaction of the benzocyclobutene groups can be finished in 5 min upon heating, resulting in well-defined polymeric spheres with over 90 linear chains surrounding the cross-linked cores. The outer PS blocks serve as the protection corona to ensure that cross-linking of giant surfactants occurs in each supramolecular spherical domain. Given the modular design and diversity of the POSS-based giant surfactants, it is believed that the strategy may enable access to a wide range of CSPs.

Rhodium nanoparticles inside well-defined unimolecular amphiphilic polymeric nanoreactors: synthesis and biphasic hydrogenation catalysis

Rhodium nanoparticles (Rh NPs) embedded in different amphiphilic core-crosslinked micelle (CCM) latexes (RhNP@CCM) have been synthesized by [RhCl(COD)(TPP@CCM)] reduction with H₂ (TPP@CCM = core-anchored triphenylphosphine). The reduction rate depends on temperature, on the presence of base (NEt₃) and on the P/Rh ratio. For CCMs with outer shells made of neutral P(MAA-co-PEOMA) copolymer chains (RhNP@CCM-N), the core-generated Rh NPs tend to migrate toward the hydrophilic shell and to agglomerate depending on the P/Rh ratio and core TPP density, whereas the MAA protonation state has a negligible effect. Conversely, CCMs with outer shells made of polycationic P(4VPMe⁺I^-) chains (RhNP@CCM-C) maintain core-confined and well dispersed Rh NPs. All RhNP@CCMs were used as catalytic nanoreactors under aqueous biphasic conditions for acetophenone, styrene and 1-octene hydrogenation. Styrene was efficiently hydrogenated by all systems with high selectivity for vinyl reduction. For acetophenone, competition between benzene ring and carbonyl reduction was observed as well as a limited access to the catalytic sites when using CCM-C. Neat 1-octene was also converted, but the activity increased when the substrate was diluted in 1-nonanol, which is a better core-swelling solvent. Whereas the molecular Rh^I center was more active than the Rh⁰ NPs in 1-octene hydrogenation, the opposite trend was observed for styrene hydrogenation. Although Rh NP migration and agglomeration occurred for RhNP@CCM-N, even at high P/Rh, the NPs remained core-confined for RhNP@CCM-C, but only when toluene rather than diethyl ether was used for product extraction before recycling.

Star Polymers

Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

Coordination Chemistry Inside Polymeric Nanoreactors: Interparticle Metal Exchange and Ionic Compound Vectorization in Phosphine-Functionalized Amphiphilic Polymer Latexes

Stable latexes of hierarchically organized core-cross-linked polymer micelles that are functionalized at the core with triphenylphosphine (TPP@CCM) have been investigated by NMR spectroscopic analysis at both natural (ca. pH 5) and strongly basic (pH 13.6) pH values after core swelling with toluene. The core-shell interface structuring forces part of the hydrophilic poly(ethylene oxide) (PEO) chains to reside inside the hydrophobic core at both pH values. Loading the particle cores with [Rh(acac)(CO)2 ] (acac=acetylacetonate) at various Rh/P ratios yielded polymer-supported [Rh(acac)(CO)(TPP)] (TPP=triphenylphosphine). The particle-to-particle rhodium migration is very fast at natural pH, but slows down dramatically at high pH, whereas the size distribution of the nanoreactors remains unchanged. The slow migration at pH 13.6 leads to the generation of polymer-anchored [Rh(OH)(CO)(TPP)2 ], which is also generated immediately upon the addition of NaOH to the particles with a [Rh(acac)(CO)] loading of 50 %. Similarly, treatment of the same particles with NaCl yielded polymer-anchored [RhCl(CO)(TPP)2 ]. Interparticle coupling occurs during these rapid processes. These experiments prove that the major contribution to metal migration is direct core-core contact. The slow migration at the high pH value, however, must result from a pathway that does not involve core-core contact. The facile penetration of the polymer cores by NaOH and NaCl results from the presence of shell-linked poly(ethylene oxide) methyl ether functions both outside and inside the polymer core-shell interface.

Coordination Chemistry inside Polymeric Nanoreactors: Metal Migration and Cross-Exchange in Amphiphilic Core-Shell Polymer Latexes

A well-defined amphiphilic core-shell polymer functionalized with bis(p-methoxy-phenylphosphino)phenylphosphine (BMOPPP) in the nanogel (NG) core has been obtained by a convergent RAFT polymerization in emulsion. This BMOPPP@NG and the previously-reported TPP@NG (TPP = triphenylphosphine) and core cross-linked micelles (L@CCM; L = TPP, BMOPPP) having a slightly different architecture were loaded with [Rh(acac)(CO)₂] or [RhCl(COD)]₂ to yield [Rh(acac)(CO)(L@Pol)] or [RhCl(COD)(L@Pol)] (Pol = CCM, NG). The interparticle metal migration from [Rh(acac)(CO)(TPP@NG)] to TPP@NG is fast at natural pH and much slower at high pH, the rate not depending significantly on the polymer architecture (CCM vs. NG). The cross-exchange using [Rh(acac)(CO)(BMOPPP@Pol)] and [RhCl(COD)(TPP@Pol)] (Pol = CCM or NG) as reagents at natural pH is also rapid (ca. 1 h), although slower than the equivalent homogeneous reaction on the molecular species (<5 min). On the other hand, the subsequent rearrangement of [Rh(acac)(CO)(TPP@Pol)] and [RhCl(COD)(TPP@Pol)] within the TPP@Pol core and of [Rh(acac)(CO)(BMOPPP@Pol)] and [RhCl(COD)(BMOPPP@Pol)] within the BMOPPP@Pol core, leading respectively to [RhCl(CO)(TPP@Pol)₂] and [RhCl(CO)(BMOPPP@Pol)₂], is much more rapid (<30 min) than on the corresponding homogeneous process with the molecular species (>24 h).

Fluorinated microgel star polymers as fluorous nanocapsules for the encapsulation and release of perfluorinated compounds

Fluorinated microgel star polymers work as fluorous nanocapsules to efficiently capture and thermo-responsively release perfluorinated guest compounds.

Development of star polymers as unimolecular containers for nanomaterials

Star polymers containing one central core surrounded by multiple radiating arms represent an intriguing type of globular platform to be used as unimolecular containers and reactors. The core domain can encapsulate guest "cargos", whereas protective shell and chain ends can be functionalized with reactive groups and ligands. This Feature Article highlights the recent development on using core-shell structured amphiphilic star polymers as unimolecular containers for applications in drug delivery, catalysis, and template of hybrid nanomaterials. As compared with dendrimers, star polymers enjoy advantages of facile synthesis, flexible compositions, and tunable sizes, which allow them being able to carry more and multiple "cargos" within one molecule.