Topologically Induced Heterogeneity in Gradient Copolymer Brush Particle Materials

Organic nanoparticles with tunable size and rigidity by hyperbranching and cross-linking using microemulsion ATRP

Unlike inorganic nanoparticles, organic nanoparticles (oNPs) offer the advantage of "interior tailorability," thereby enabling the controlled variation of physicochemical characteristics and functionalities, for example, by incorporation of diverse functional small molecules. In this study, a unique inimer-based microemulsion approach is presented to realize oNPs with enhanced control of chemical and mechanical properties by deliberate variation of the degree of hyperbranching or cross-linking. The use of anionic cosurfactants led to oNPs with superior uniformity. Benefitting from the high initiator concentration from inimer and preserved chain-end functionality during atom transfer radical polymerization (ATRP), the capability of oNPs as a multifunctional macroinitiator for the subsequent surface-initiated ATRP was demonstrated. This facilitated the synthesis of densely tethered poly(methyl methacrylate) brush oNPs. Detailed analysis revealed that exceptionally high grafting densities (~1 nm-2) were attributable to multilayer surface grafting from oNPs due to the hyperbranched macromolecular architecture. The ability to control functional attributes along with elastic properties renders this "bottom-up" synthetic strategy of macroinitiator-type oNPs a unique platform for realizing functional materials with a broad spectrum of applications.

Synthesis of Mechanically Robust Very High Molecular Weight Polyisoprene Particle Brushes by Atom Transfer Radical Polymerization

Linear polyisoprene (PI) and SiO2-g-PI particle brushes were synthesized by both conventional and activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). The morphology and solution state study on the particle brushes by transmission electron microscopy (TEM) and dynamic light scattering (DLS) confirmed the successful grafting of PI ligands on the silica surface. The presence of nanoparticle clusters suggests low grafting density (associated with the limited initiation efficiency of ARGET for PI). Nevertheless, particle brushes with very high molecular weights, Mn > 300,000, were prepared, which significantly improved the dispersion of silica nanoparticles and also contributed to excellent mechanical performance. The reinforcing effects of SiO2 nanofillers and very high molecular weight PI ligands were investigated by dynamic mechanical analysis (DMA) as well as computational simulation for the cured linear PI homopolymer/SiO2-g-PI particle brush bulk films.

The Importance of Bulk Viscoelastic Properties in "Self-Healing" of Acrylate-Based Copolymer Materials

"Self-healing" has emerged as a concept to increase the functional stability and durability of polymer materials in applications and thus to benefit the sustainability of polymer-based technologies. Recently, van der Waals (vdW)-driven "self-healing" of sequence-controlled acrylate-based copolymers due to "key-and-lock"- or "ring-and-lock"-type interactions has generated considerable interest as a viable route toward engineering polymers with "self-healing" ability. This contribution systematically evaluates the time, temperature, and composition dependence of the mechanical recovery of acrylate-based copolymer and homopolymer systems subject to cut-and-adhere testing. "Self-healing" in n-butyl acrylate/methyl methacrylate (BA/MMA)- or n-butyl acrylate/styrene (BA/Sty)-based copolymers with varying composition and sequence is found to correlate with the bulk viscoelastic properties of materials and to follow a similar trend as other tested acrylate-based homo- and copolymers. This suggests that "self-healing" in this class of materials is more related to the chain dynamics of bulk materials rather than composition- or sequence-dependent specific interactions.

Composition-Orientation Induced Mechanical Synergy in Nanoparticle Brushes with Grafted Gradient Copolymers

Gradient poly(methyl methacrylate/n-butyl acrylate) copolymers, P(MMA/BA), with various compositional ratios, were grafted from surface-modified silica nanoparticles (SiO2-g-PMMA-grad-PBA) via complete conversion surface-initiated activator regenerated by electron transfer (SI-ARGET) atom transfer radical polymerization (ATRP). Miniemulsion as the reaction medium effectively confined the interparticle brush coupling within micellar compartments, preventing macroscopic gelation and enabling complete conversion. Isolation of dispersed and gelled fractions revealed dispersed particle brushes to feature a higher Young's modulus, toughness, and ultimate strain compared with those of the "gel" counterparts. Upon purification, brush nanoparticles from the dispersed phase formed uniform microstructures. Uniaxial tension testing revealed a "mechanical synergy" for copolymers with MMA/BA = 3:2 molar ratio to concurrently exhibit higher toughness and stiffness. When compared with linear analogues of similar composition, the brush nanoparticles with gradient copolymers had better mechanical properties, attributed to the synergistic effects of the combination of composition and propagation orientation, highlighting the significance of architectural design for tethered brush layers of such hybrid materials.

Smart nanoparticles for cancer therapy

Smart nanoparticles, which can respond to biological cues or be guided by them, are emerging as a promising drug delivery platform for precise cancer treatment. The field of oncology, nanotechnology, and biomedicine has witnessed rapid progress, leading to innovative developments in smart nanoparticles for safer and more effective cancer therapy. In this review, we will highlight recent advancements in smart nanoparticles, including polymeric nanoparticles, dendrimers, micelles, liposomes, protein nanoparticles, cell membrane nanoparticles, mesoporous silica nanoparticles, gold nanoparticles, iron oxide nanoparticles, quantum dots, carbon nanotubes, black phosphorus, MOF nanoparticles, and others. We will focus on their classification, structures, synthesis, and intelligent features. These smart nanoparticles possess the ability to respond to various external and internal stimuli, such as enzymes, pH, temperature, optics, and magnetism, making them intelligent systems. Additionally, this review will explore the latest studies on tumor targeting by functionalizing the surfaces of smart nanoparticles with tumor-specific ligands like antibodies, peptides, transferrin, and folic acid. We will also summarize different types of drug delivery options, including small molecules, peptides, proteins, nucleic acids, and even living cells, for their potential use in cancer therapy. While the potential of smart nanoparticles is promising, we will also acknowledge the challenges and clinical prospects associated with their use. Finally, we will propose a blueprint that involves the use of artificial intelligence-powered nanoparticles in cancer treatment applications. By harnessing the potential of smart nanoparticles, this review aims to usher in a new era of precise and personalized cancer therapy, providing patients with individualized treatment options.

Copolymer Brush Particle Hybrid Materials with "Recall-and-Repair" Capability

The effect of sequence structure on the self-healing and shape-memory properties of copolymer-tethered brush particle films was investigated and compared to linear copolymer analogs. Poly(n-butyl acrylate-co-methyl methacrylate), P(BA-co-MMA), and linear and brush analogs with controlled gradient and statistical sequence were synthesized by atom transfer radical polymerization (ATRP). The effect of sequence on self-healing in BA/MMA copolymer brush particle hybrids followed similar trends as for linear analogs. Most rapid restoration of mechanical properties was found for statistical copolymer sequence; an increase of the high Tg (MMA) component provided a path to raise the material's modulus while retaining self-heal ability. Creep testing revealed profound differences between linear and brush systems. While linear copolymers featured substantial viscous deformation when exposed to constant stress in the linear regime, brush analogs displayed minimal permanent deformation and featured shape restoration. The reduction of flow was interpreted to be a consequence of slow cooperative relaxation due to the complex microstructure of brush particle hybrids in which long-range motions are constrained through entanglements and slow-diffusing particle cores. The rubbery-like response imparts BA/MMA copolymer brush material systems concurrent "shape-memory" and "self-heal" capability. This ability to "recall-and-repair" could find application in the design of functional hybrid materials, for example, for soft robotics.

Alternating Methyl Methacrylate/n-Butyl Acrylate Copolymer Prepared by Atom Transfer Radical Polymerization

Poly(methyl methacrylate/n-butyl acrylate) [P(MMA/BA)] copolymer with an alternating structure was synthesized via an activator regenerated by electron transfer (ARGET) atom transfer radical (co)polymerization (ATRP) of 2-ethylfenchyl methacrylate (EFMA) and n-butyl acrylate (BA) with subsequent postpolymerization modifications (PPM). Due to the steric hindrance of the bulky pendant group of EFMA, as well as the low reactivity ratio of BA in copolymerization with methacrylates, copolymerization of EFMA and BA generated a copolymer with a high content of alternating dyads. A subsequent PPM procedure of the alternating EFMA/BA copolymer was comprised of the hydrolysis of a tertiary ester by trifluoroacetic acid and methylation by (trimethylsilyl)diazomethane. After the modifications, the architecture of the obtained alternating MMA/BA copolymers was compared with gradient and statistical copolymers with overall similar compositions, molecular weights, and dispersities. ¹³C NMR indicated the absence of either MMA/MMA/MMA or BA/BA/BA sequences, in contrast to an abundance of homotriads in either the statistical or especially in the gradient copolymer. All three copolymers had similar glass transition temperatures, as measured by differential scanning calorimetry (DSC), but the alternating copolymer had the narrowest range of glass transition.