Preparation of ABA triblock copolymer assemblies through “one-pot” RAFT PISA

Poly(N,N-dimethyl acrylamide)-block-poly(styrene)-block-poly(N,N-dimethyl acrylamide)(PDMAc-bPSt-b-PDMAc)amphiphilic triblock copolymer micro/nano-objects were synthesized through reversible addition-fragmentation chain transfer(RAFT)dispersion polymerization of St mediated with poly(N,Ndimethyl acrylamide)trithiocarbonate(PDMAc-TTC-PDMAc)bi-functional macromolecular RAFT agent.It is found that the morphology of the PDMAc-b-PSt-b-PDMAc copolymer micro/nano-objects like spheres,vesicles and vesicle with hexagonally packed hollow hoops(HHHs)wall can be tuned by changing the solvent composition.In addition,vesicles with two sizes(600 nm,264 nm)and vesicles with HHHs features were also synthesized in high solid content systems(30 wt%and 40 wt%,respectively).Besides,as compared with typical AB diblock copolymers(A is the solvophilic,stabilizer block,and B is the solvophobic block),ABA triblock copolymers tend to form higher order morphologies,such as vesicles,under similar conditions.The finding of this study provides a new and robust approach to prepare block copolymer vesicles and other higher order micelles with special structure via PISA.

Recent progress on DNA block copolymer

DNA has gained great attention because of its unique structure,excellent molecular recognition property,and biological functions.When married with versatile synthetic polymers,the DNA conjugated polymer hybrids,known as DNA block copolymers（DBCs）,have been launched and well developed for the syntheses of new materials and nanostructures with different functions in the past several decades.Compared to conventional synthetic block copolymers,using DNA as a building block provides several advantages over other polymer candidates,such as molecular recognition,programmable self-assembly,biocompatibility,and sequence-encoded information.In this review,recent developments in this area will be summarized and meaningful breakthroughs will be highlighted.We will discuss representative examples of recent progress in the syntheses,structure manipulations,and applications of DBCs.

Organic Templates for Inorganic Nanocrystal Growth

Nanocrystals provide a variety of size and shape-dependent properties with applications in a wide range of areas, gaining much attention in the past few years. However, due to the nature of the kinetic nanocrystal growth, the procedures often require strict experimental conditions and the shape and size of nanocrystals are difficult to control. In such context, organic templates, which are artificially modified or synthesized, can direct inorganic nanocrystal nucleation and growth to achieve desired shape, size and ultimately properties. In this review article, two general categories of organic templates used for making inorganic nanomaterials are discussed:biotemplates(e.g., peptide, lipid, DNA, and capsid) and block copolymer templates(e.g., block copolymer micelles, star-like block copolymer unimicelles). The goal of this review is to bridge these gaps and help foster a greater awareness of the range and applicability of different organic templating techniques within the field of nanotechnology.

Control on the Morphology of ABA Amphiphilic Triblock Copolymer Micelles in Dioxane/Water Mixture Solvent

This work offers a typical understanding of the factors that govern the nanostructures of poly（4-vinyl pyridine）-b-polystyrene-bpoly（4-vinyl pyridine）（P4 VP-b-PS-b-P4 VP） block copolymers（BCs） in dioxane/water, in which water is a selective solvent for the P4 VP block. It is achieved through an investigation of the amphiphilic triblock copolymer micelles by variation of three different factors, including water content（above CWC but under the immobile concentration）, temperature（ranging from 20 °C to 80 °C）, and copolymer composition（low and high PS block length）. Transition of bead-like micelles to vesicles is observed with the increase of water content due to the increase of interfacial energy between the copolymer and the solvent. Effect of temperature superposed on that of water content results in various morphologies, such as beads, fibers, rods, capsules, toroids, lamellae, and vesicles. The interfacial tension between the BC and the solvent increases with the increase of water content but decreases with the increase of temperature, indicating that the micellar morphologies are resulted from the competitive interplay between the temperature and the water content and always change in a direction that decreases the interfacial energy. Based on the micellar structures obtained in this work and the effects of temperature superposed on water concentration, a diagram of phase evolution of different micellar morphologies is illustrated here, covering the temperature range from 20 °C to 80 °C and the water content changing from 20 vol% to 35 vol%. For the investigation of BC composition, morphological transition of vesicle-to-fiber, for high PS length, is observed as compared with bead-to-capsule for low PS length, as the temperature changes from 20 °C to 80 °C. Our research complements the protocols to control over the morphologies and the phase diagram describing P4 VP-b-PS-b-P4 VP micellar nanostructures in aqueous solution.

A Dual Ligand Targeted Nanoprobe with High MRI Sensitivity for Diagnosis of Breast Cancer

Antibody targeted delivery is an effective strategy to improve the diagnostic imaging outcome of nanoscale imaging agents in the focal areas. Dual targeting micelles encapsulating superparamagnetic iron oxide were prepared from the amphiphilic block copolymer poly（ethylene glycol）-poly（e-caprolactone） （PEG-b-PCL） with different targeting ligands cRGD and scFv-ErbB single chain antibody conjugated to the distal ends of PEG block. The breast cancer animal model was established by subcutaneous injecting the BT474 cells into the BALB/c-nu female nude mice and then employed to assess the potential of the dual ligand targeted magnetic micelles as a novel MRI contrast agent on a 1.5 T clinical MR/scanner. The T2 signal intensity of the tumor in animals receiving the dual ligand targeted magnetic micelles via tail vein decreased more significantly than the single ligand targeted and nontargeted magnetic micelles. These results indicate that the dual ligand targeted magnetic micelles, cRGD/scFv-ErbB-PEG-PCL-SPION, have great potential to act as a new type of effective nanoscale MRI contrast agent for early diagnosis of breast cancer.

Morphology and Thermoresponsive Behavior of Hybrid Micelles of Polystyrene-b-Poly((N-isopropyl acrylamide)-co-(4-vinylbenzyl chloride)) with Prussian Blue

The hybrid micelles of polystyrene-b-poly（（N-isopropyl acrylamide）-co-（4-vinylbenzyl chloride）） block copolymer（PS-b-P（NIPAM-co-VBC）） with Prussian blue（PB） in the corona were prepared by reaction of pentacyano（4-（dimethylamino）-pyridine）ferrate（Fe-DMAP）-attached PS-b-P（NIPAM-co-VBC） with Fe Cl3. The formation of the PB framework inside the micelles was verified by UV-Vis, FTIR and TGA. The morphology of the hybrid micelles was studied by TEM and compared with that of the neat and Fe-DMAP-attached PS-b-P（NIPAM-co-VBC）. It is found that attachment of Fe-DMAP may change the short rod-like micelles of the neat PS-b-P（NIPAM-co-VBC） into spherical ones and lead to a smaller micelle size. The morphology of the hybrid micelles may be altered or remain unchanged after formation of the PB framework, depending on the chain structure of PS-b-P（NIPAM-co-VBC） and starting concentration. The thermoresponsive behavior of different micelles was studied using DLS. It is observed that attachment of Fe-DMAP can improve the hydrophilicity of the P（NIPAM-co-VBC） block, leading to weaker hysteresis of the micelle size during the heating and cooling cycle. However, the crosslinked PB framework in the micellar corona may result in a more evident hysteresis phenomenon and blur the two-stepwise change of the micellar size with temperature.