Local environment influence on the optical properties of block copolymers containing an epoxy-based azo-prepolymer

The aim of this contribution was the study of the influence of polymer matrix on the photo-induced orientation of azobenzene groups. Notably, an azo-prepolymer bearing hydroxyl groups was selectively confined in self-assembled phases of different block copolymers, randomly-epoxidized polystyrene-b-polybutadiene-b-polystyrene (SBSep) and polystyrene-b-poly-4-vinylpyridine (S4VP). The formation of hydrogen bonds between the azo-prepolymer and poly-4-vinylpyridine block, as well as the effect of the local environment surrounding the azo-prepolymer were investigated by Fourier transform infrared and ultraviolet–visible spectroscopies. In addition, the reversible optical storage properties of the developed materials were also studied. Birefringent properties of the systems based on S4VP were strongly enhanced by intermolecular interactions with the azo-prepolymer. Specifically, the maximum birefringence level attained by a system containing 13 wt% of azobenzene was around 2.3 × 10⁻² and its remaining birefringence was nearly three times higher than that of the neat azo-prepolymer. Furthermore, a morphological analysis of the designed materials was carried out by atomic force microscopy. Taking into account that the control of the microdomains ordering in block copolymer films is of current interest, special attention was focused on the influence of different variables on the arrangement of the block copolymer microdomains.     

Self-assembly and aggregation of ATRP prepared amphiphilic BAB tri-block copolymers contained nonionic ethylene glycol and fluorescent 9,10-di(1-naphthalenyl)-2-vinyl-anthracene/1-vinyl-pyrene segments

Two novel amphiphilic BAB-type block copolymers, ADN-PEG3400-ADN and Py-PEG3400-Py containing deep blue and bluish-green fluorescent moieties were prepared using atom transfer radical polymerization (ATRP) (where, ADN = poly(9,10-di(1-naphthalenyl)-2-vinylanthracene), Py = poly(1-vinyl pyrene) and PEG3400 = poly(ethylene glycol) with M_n = 3400 g/mol). The GPC number averaged molecular weights (MW) of the block copolymers were M_n = 9600 and 13,800 g/mol, respectively, based on polystyrene MW standards. The PEG3400 segment has a melting temperature (T_m peak) at 64–65 °C, whereas the glass transition temperatures (T_g midpoint) of the ADN and Py segments were found to be 230 °C and 193 °C, respectively, and are similar to their respective homopolymers indicating complete microphase segregration. The photoluminescence (PL) emission of the copolymers ADN-PEG3400-ADN exhibited two maxima at 423.5 nm and 441.5 nm while Py-PEG3400-Py has a maximum at 488.5 nm. Both copolymers form individual spherical micelles with diameter from 30 to 90 nm for Py-PEG3400-Py and 40–160 nm for ADN-PEG3400-ADN. The micelles, however, transform into cross-linked pearl-necklace-like aggregates at polymer concentrations above 1000 ppm, which may be attributed to the physical cross-linking between adjacent spherical micelles caused by the PEG3400 segments.     

Block Synthesis of Streptococcus pneumoniae Type 14 Capsular Polysaccharide Structures*

Synthesis of a thioglycoside tetrasaccharide block, β‐D‐Galp‐(1→4)‐β‐DGlcp‐(1→6)‐[β‐D‐Galp‐(1→4)]‐β‐D‐GlcNPhthp‐(1→SEt, corresponding to the repeating unit of Streptococcus pneumoniae serotype 14 CPS is described. Coupling of this block with a spacer followed by removal of an isopropylidene acetal yielded an acceptor, which was elongated with the donor block to give a protected dimer of the repeating unit. Iteration of this methodology yielded the trimer. Deprotection then produced an octa and a dodecasaccharide derivative ready for conjugation to proteins to afford immunoactive glycoconjugates.     

Water-dispersible non-aqueous emulsions stabilized by a poly(butadiene)-b-poly(2-vinylpyridine) block copolymer

Submicron non-aqueous emulsions, of interest for biomedical and cosmetic formulations, were developed for the system comprising poly(ethylene glycol) (PEG) 400 and Miglyol 812, an enzymatic degradable liquid glycerine ester. These emulsions, with PEG 400 as continuous phase and Miglyol 812 droplets, in the size range of 200 nm, were stabilized by a poly(butadiene)-b-poly(2-vinylpyridine) (PBut-b-P2VP) block copolymer with a composition close to 50/50 wt%. The droplet size, stability and the rheological characteristics were examined as a function of the copolymer concentration. An original aspect of these anhydrous emulsions, with a water miscible continuous phase, is their water dispersibility without additional surfactant. In fact, the initial anhydrous emulsion is sterically stabilized and after water addition at low pH, the protonated P2VP sequence of the copolymer provides the electro-steric stabilization. This oil-in-water emulsion is characterized by sub micron sized Miglyol 812 droplets in an aqueous phase of PEG 400 and water at pH 1.     

Block Copolymer Supported Gold Nanoparticles Assemblies with Exposed Gold Surface

Polymer-involved nanoparticles or nanoparticle assemblies are now facing a crossroad, where the exposure of nanoparticle and multiple nanoparticles cannot be obtained at the same time. Therefore, a new series of nanoparticle clusters is synthesized, where multiple gold nanoparticles assemble with amphiphilic block copolymers supporting inside. The exposure of gold nanoparticles of the structure is confirmed and increases the reduction rate of 4-nitrophenol by 60%. The assemblies can also be used as surface enhanced Raman scattering(SERS) probes with an enhancement factor(EF) as high as 3×10³.     

pH-Sensitive Wettability Induced by Topologicaland Chemical Transition on the Self AssembledSurface of Block Copolymer简

pH-sensitive wettability of polystyrene-b-poly（4-vinylpyridine） （PS-b-P4VP） self assembled films, exhibiting superoleophobicity under water and hydrophilicity at low pH value, and oleophobicity under water and hydrophobicity at neutral condition, has been realized. The wettability properties resulted from the surface topological and chemical transition, which were confirmed by in situ AFM measurements under water at different pH. At low pH, P4VP chains, which were confined in the hexagonal-packed nanodomains, got protonated into a swollen state, while at high pH, P4VP chains were deprotonated into a collapsed state. The reversible protonation/deprotonation procedure on the molecular scale leads to surface topological and chemical transition, thereby pH-sensitive wettability.     

Influence of different inorganic salts on crystallization-driven morphological transformation of PCL-b-PEO micelles in aqueous solutions

Different inorganic salts, including NaSCN, NaCl, MgCl2 and Na2SO4, were added into the aqueous solution containing poly(ε-caprolactone)-b-poly(ethylene oxide)(PCL-b-PEO) semicrystalline micelles. The effects of inorganic salt on the micellar size and morphology were investigated with TEM and DLS. It is found that addition of NaSCN leads to increase of the micellar size, but the micelles remain to be spherical. By contrast, the other three inorganic salts can induce sphere-to-cylinder or sphere-to-lamella transformations of the PCL-b-PEO semicrystalline micelles. The alteration rate of the micellar size with the time after addition of the inorganic salts decreases in the following order: Na2SO4 NaCl ≈ MgCl2 NaSCN. These results were interpreted in terms of the "salting-out" ability of the cations and anions. The anions SO42- and Cl- have a stronger "salting-out" ability, driving the morphological transformations of the micelles and leading to a rapid change in micellar size. By contrast, SCN- has a weaker salting-out" ability. The cations Na+ and Mg2+ may associate with the PEO blocks, leading to a "salting-out" effect as well. However, the "salting-out" ability of cations is weaker than that of SO42- and Cl- anions, and the "salting-out" abilities of Na+ and Mg2+ are similar.     

两嵌段共聚物反相溶剂中组装结构转变动力学的模拟研究

利用耗散粒子动力学方法,分别研究了不同结构的组装体在改变溶剂的选择性后,在溶液及界面上的结构演变动力学.模拟结果表明,在改变溶剂的选择性后,大球形胶束在溶液中转变形成反向球形胶束,而在界面上则转变形成反向环状胶束,当前模拟结果与已有的实验结果一致.此外,模拟结果还预测出,在改变溶剂的选择性后,环状胶束在溶液中转变形成反向环状胶束,而在界面处受限形成反向的支化蠕虫状胶束;蠕虫状胶束则在溶液中转变形成反向环状胶束,而在界面处受限形成多层纳米球结构;囊泡在溶液中转变形成分散的小胶束聚集体,而在界面处受限形成球形的补丁纳米粒子.     

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.     

Hierarchical porous nanofibers of carbon@nickel oxide nanoparticles derived from polymer/block copolymer system

The triblock copolymer (PAA-b-PAN-b-PAA) is prepared by reversible addition-fragmentation chain-transfer polymerization, and then blended with polymer (PAN) and metal hydroxide (Ni(OH)₂) as a precursor for heat-treatment. A composite material of hierarchical porous nanofibers and nickel oxide nanoparticles (HPCF@NiO) is prepared by electrospinning combined with high-temperature carbonization. The effects of the ratio of PAA and PAA-b-PAN-b-PAA on the internal structure of nanofibers and their electrochemical properties as positive electrode materials are investigated. The experimental results show that when the ratio of PAA to PAA-b-PAN-b-PAA is 1.3 to 0.4, it has good pore structure and excellent electrochemical performance. At the current density of 1 A/g, the specific capacitance is 188.7 F/g and the potential window is −1 V to 0.37 V. The asymmetric supercapacitor assembled with activated carbon as the negative electrode materials has a specific capacitance of 21.2 F/g in 2 mol/L KOH and a capacitance retention of 85.7% after 12,500 cycles at different current density.