Synthesis of star-brush polymer architectures from end-reactive molecular bottlebrushes

Diblock brush-arm star copolymers via a core-first/graft-from approach using γ-cyclodextrin and ROMP: a modular platform for drug delivery

Water-soluble diblock brush-arm star copolymers using γ-CD-based core-first ring-opening metathesis polymerization, allowing for anticancer drug delivery via host–guest interaction.

Synthesis and properties of a stimulus-responsive block polymer

In this study, the synthesis of small molecules and use of an improved “one-pot” method to synthesize the reversible addition–fragmentation chain transfer polymerization (RAFT) reagents have been reported. By comparing with the RAFT reagents synthesized by the traditional “step-by-step” method, it was observed that the reagents synthesized by the two methods had the same structure, however, the improved “one-pot” preparation method results in a significantly higher yield. Subsequently, two different macromolecular CTA segments (PVP-CTA-PVP and PDMAEMA-CTA-PDMAEMA) were prepared by RAFT polymerization, followed by the synthesis of the block polymer PDMAEMA-b-PVP-CTA-PVP-b-PDMAEMA. Through FITR, NMR, GPC and DLS analysis of the block polymer, it was observed that the isotacticity gradually became dominant as the degree of polymerization increased. Further, using NMR spectroscopy to study the effect of pH on the block polymer, the ionization degree of the synthesized polymer in the tumor tissue environment was observed to range between 86.32% to 99.50%, which proved that the synthesized polymers exhibit significant prospects in the medical application.

In this study, two different macromolecular CTA segments (PVP-CTA-PVP and PDMAEMA-CTA-PDMAEMA) were prepared by RAFT polymerization, followed by the synthesis of the block polymer PDMAEMA-b-PVP-CTA-PVP-b-PDMAEMA.

Molecular Bottlebrushes Featuring Brush-on-Brush Architecture

Molecular bottlebrushes featuring brush-on-brush (BoB) architecture were prepared by combining azide-alkyne click chemistry, ring-opening polymerization (ROP), and atom transfer radical polymerization (ATRP). Primary side chains of diblock copolymers with a poly(ε-caprolactone) (PCL) block and a poly(α-bromo-ε-caprolactone) (P(CL-Br)) block were synthesized by ROP and then grafted onto PCL backbone by the click reaction. Then the secondary side chains of poly(oligo(ethylene glycol) acrylate) (POEGA) were grafted from the P(CL-Br) block by ATRP, yielding an amphiphilic core/shell structure. Imaging of individual macromolecules by atomic force microscopy (AFM) demonstrated dramatically thickened wormlike formation with distinct hairy side chains. Interestingly, for the BoB molecular bottlebrushes with enough long primary and secondary side chains, sufficient tension can be generated along the backbone and thus lead to its cleavage.

Synthesis of naturally-derived macromolecules through simplified electrochemically mediated ATRP

The flavonoid-based macroinitiator was received for the first time by the transesterification reaction of quercetin with 2-bromoisobutyryl bromide. In accordance with the "grafting from" strategy, a naturally-occurring star-like polymer with a polar 3,3',4',5,6-pentahydroxyflavone core and hydrophobic poly(tert-butyl acrylate) (PtBA) side arms was synthesized via a simplified electrochemically mediated ATRP (seATRP), utilizing only 78 ppm by weight (wt) of a catalytic CuII complex. To demonstrate the possibility of temporal control, seATRP was carried out utilizing a multiple-step potential electrolysis. The rate of the polymerizations was well-controlled by applying optimal potential values during preparative electrolysis to prevent the possibility of intermolecular coupling of the growing polymer arms. This appears to be the first report using on-demand seATRP for the synthesis of QC-(PtBA-Br)5pseudo-star polymers. The naturally-derived macromolecules showed narrow MWDs (Đ = 1.08-1.11). 1H NMR spectral results confirm the formation of quercetin-based polymers. These new flavonoid-based polymer materials may find applications as antifouling coatings and drug delivery systems.

Performances and working mechanism of a novel polycarboxylate superplasticizer synthesized through changing molecular topological structure

A novel star-shaped polycarboxylate superplasticizer (SPCE) was synthesized through a simple two-step method. ¹H Nuclear Magnetic Resonance (¹H NMR) and Infrared Spectroscopy (IR) measurements were used for structural characterization. SPCE and comb-shaped polycarboxylate superplasticizer (CPCE) with same molecular weights were designed and synthesized. The cement paste containing SPCE exhibited better fluidity, fluidity retention, water reduction, 25% lower saturated dosage of PCE, 10% longer setting time, lower hydration heat, more delayed hydration heat evolution and lower amount of hydration products at early ages. Furthermore, the adsorption behavior of SPCE and CPCE in cement pastes and the zeta potential were investigated, and then the working mechanism of SPCE was theoretically explained. It is interesting that changing topological structure from comb-shape to star-shape can achieve the optimization of dispersion effect, and further improve the working effectiveness. The aims of this study are to provide a new avenue to synthesize superplasticizer with novel structure achieving the chemical diversity of superplasticizer structure, and to verify the contribution of optimizing molecular shape. This new type of superplasticizer can be used as a rheology modifying agent in fresh cement-based materials.

Mesoporous Polymer Frameworks from End-Reactive Bottlebrush Copolymers

Reticulated nanoporous materials generated by versatile molecular framework approaches are limited to pore dimensions on the scale of the utilized rigid molecular building blocks (<5 nm). The inherent flexibility of linear polymers precludes their utilization as long framework connectors for the extension of this strategy to larger length scales. We report a method for the fabrication of mesoporous frameworks by using bottlebrush copolymers with reactive end blocks serving as rigid macromolecular interconnectors with directional reactivity. End-reactive bottlebrush copolymers with pendant alkene functionalities were synthesized by a combination of controlled radical polymerization and polymer modification protocols. Ru-catalyzed cross-metathesis cross-linking of bottlebrush copolymers with two reactive end blocks resulted in the formation of polymer frameworks where isolated cross-linked domains were interconnected with bottlebrush copolymer bridges. The resulting materials were characterized by a continuous network pore structure with average pore sizes of 9-50 nm, conveniently tunable by the length of the utilized bottlebrush copolymer building blocks. The materials fabrication strategy described in this work expands the length scale of molecular framework materials and provides access to mesoporous polymers with a molecularly tunable reticulated pore structure without the need for templating, sacrificial component etching, or supercritical fluid drying.

Quantitatively monitoring polymer chain growth and topology formation based on monodisperse polymers

In this work, a novel technique for monitoring polymer chain growth and topology formation was demonstrated by precision synthesis of monodisperse polymers, which opened a novel avenue for obtaining real-time polymer structure information.