Synthetic route-dependent intramolecular segregation in heteroarm core cross-linked star polymers as Janus-like nanoobjects

Polymerization-induced intramolecular segregation can be realized during the “in–out” synthesis of heteroarm core cross-linked star polymers to facilitate well-defined microphase separation.

Brush-First and ROMP-Out with Functional (Macro)monomers: Method Development, Structural Investigations, and Applications of an Expanded Brush-Arm Star Polymer Platform

The efficient synthesis of complex functional polymeric nanomaterials is often challenging. Ru-initiated ring-opening metathesis polymerization (ROMP) of multivalent macromonomers followed by cross-linking to form brush-arm star (BASP) polymers enables access to well-defined nano-structures with diverse functionality. This "brush-first" method leaves active Ru in the BASP microgel core, which could potentially be used in a subsequent "ROMP-out" (RO) step to introduce further modifications to the BASP structure via the addition of (macro)monomers. Here, we study this RO approach in depth. The efficiency of RO is assessed for a variety of BASP compositions using a combination of inductively coupled plasma mass spectrometry and gel permeation chromatography. To demonstrate the modularity of the RO process, arylboronic acid-functionalized BASPs were prepared; uptake of these RO-BASPs into hypersialylated cancer cells was enhanced relative to non-functionalized BASPs as determined by flow cytometry and fluorescence microscopy. In addition, the self-assembly of miktoarm BASPs prepared via brush-first and RO with different macromonomers is demonstrated. The combination of brush-first ROMP with RO provides a simple, modular strategy for access to a wide array of functional nanomaterials.

Boron “stitching” reaction: a powerful tool for the synthesis of polyethylene-based star architectures

Taking advantage of the “stitching” reaction, which transforms the “unstable” boron junction to “stable” carbon, we were able to synthesize novel star block copolymers. This strategy is general and opens new horizons towards unprecedented PE-based materials.

Toward Maximizing the Mechanical Property of Interconnected Macroporous Polystyrenes Made from High Internal Phase Emulsions

Macroporous materials polymerized from high internal phase emulsions (PolyHIPEs) possess well-defined interconnected porous structures and tunable device shapes. This provides interesting property characteristics well-suited for a variety of applications. However, such materials also demonstrate poor mechanical performances, which limit their potential use. As will be demonstrated, this results from the high surfactant content required by PolyHIPEs. Herein, a new approach is introduced for designing a highly efficient polymeric surfactant, which generates interconnected pores in PolyHIPEs through designing an incompatible surfactant and skeleton material. The surfactant also possesses a hyperbranched topology, which combines the strong amphipathy of small molecular surfactants and the nanosphere structure of Pickering emulsifiers to provide an excellent colloidal stability to HIPEs. A hyperbranched polyethylene having pendant sodium sulfonate groups (HBPE-SO₃Na) was thus designed and synthesized via chain walking copolymerization of ethylene and 2-trimethylsilyloxyethyl acrylate followed by sulfonation. Stable HIPEs of styrene/divinylbenzene and water at a weight ratio of 1 to 5 were obtained with using HBPE-SO₃Na. The polymerization of HIPEs produced interconnected macroporous polystyrenes (PSs) at a substantially lower surfactant content, for example, 0.5 wt % HBPE-SO₃Na. The compressive Young's moduli of PolyHIPEs reached 104-111 MPa with 0.5-2 wt % HBPE-SO₃Na, which is the first reported case of a PS-based PolyHIPE achieving its theoretical modulus. The PolyHIPE was used to support Au nanoparticles and embed in a column for oxidation of dimethylphenylsilane. A complete conversion of dimethylphenylsilanol was achieved with low column back pressure in a 50 h continuous reaction with no degradation of PolyHIPE integrity and mechanical property.

"Living" Polymerization of Ethylene and 1-Hexene Using Novel Binuclear Pd⁻Diimine Catalysts

We report the synthesis of two novel binuclear Pd–diimine catalysts and their unique behaviors in initiating “living” polymerization of ethylene and 1-hexene. These two binuclear catalysts, [(N^N)Pd(CH₂)₃C(O)O(CH₂)_mO(O)C(CH₂)₃Pd(N^N)](SbF₆)₂ (3a: m = 4, 3b: m = 6) (N^N≡ArN=C(Me)–(Me)C=NAr, Ar≡2,6–(iPr)₂C₆H₃), were synthesized by simply reacting [(N^N)Pd(CH₃)(N≡CMe)]SbF₆ (1) with diacrylates, 1,4-butanediol diacrylate and 1,6-hexanediol diacrylate, respectively. Their unique binuclear structure with two identical Pd–diimine acrylate chelates covalently linked together through an ester linkage was confirmed by NMR and single crystal XRD measurements. Ethylene “living” polymerizations were carried out at 5 °C and under ethylene pressure of 400 and 100 psi, respectively, with the binuclear catalysts, along with a mononuclear chelate catalyst, [(N^N)Pd(CH₂)₃C(O)OMe]SbF₆ (2), for comparison. All the polyethylenes produced with both binuclear catalysts show bimodal molecular weight distribution with the number-average molecular weight of the higher molecular weight portion being approximately twice that of the lower molecular weight portion. The results demonstrate the presence of monofunctional chain growing species resembling catalyst 2, in addition to the expected bifunctional species leading to bifunctional “living” polymerization, in the polymerization systems. Both types of chain growing species exhibit “living” characteristics under the studied conditions, leading to the simultaneous linear increase of molecular weight in both portions. However, when applied for the “living” polymerization of 1-hexene, the binuclear catalyst 3a leads to polymers with only monomodal molecular weight distribution, indicating the sole presence of monofunctional chain growing species. These two binuclear catalysts are the first Pd–diimine catalysts capable of initiating bifunctional ethylene “living” polymerization.

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.

Preparation of CO2-switchable graphene dispersions and their polystyrene nanocomposite latexes by direct exfoliation of graphite using hyperbranched polyethylene surfactants

Herein the preparation of CO₂-switchable graphene dispersions by noncovalent exfoliation of graphite in water using a CO₂-switchable star copolymer surfactant is described.

Synthesis of polystyrene-based Y-shaped asymmetric star by the combination of ATRP/RAFT and its thermal and rheological properties

A₂A′-type asymmetric stars and A₂B-type miktoarm star polymers were prepared by the combination of atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT) using the designed initiator.

Synthesis of ABB′ and ABC star copolymers via a combination of NMRP and ROP reactions

Well-defined miktoarm star copolymers (ABB′ and ABC) were synthesized via a combination of NMRP and ROP using N-(2-hydroxyethyl)maleimide as the branching molecule.

Controlled Formation of Star Polymer Nanoparticles via Visible Light Photopolymerization

A recently developed visible light mediated photocontrolled radical polymerization technique using trithiocarbonates (i.e., conventional RAFT agents) as the sole control agent in the absence of additional photoinitiators or catalysts is utilized for the synthesis of core cross-linked star (CCS) polymer nanoparticles. The attractive features of this photopolymerization system, including high end-group fidelity at (near) complete monomer conversion, are exploited to facilitate a high-yielding, one-pot pathway toward well-defined star polymer products. Moreover, reinitiation of the photoactive trithiocarbonate moieties from within the star core is demonstrated to form (pseudo)miktoarm stars via an "in-out" approach, showing extremely high initiation efficiency (95%).

New polymethylene-based AB2 star copolymers synthesized via a combination of polyhomologation of ylides and atom transfer radical polymerization

Polymethylene-based AB₂ star copolymers were synthesized. PM-b-(PS)₂ porous films and particles were fabricated via static breath-figure process and electrospraying, respectively.