光学活性三嵌段刚柔共聚物的合成和在二氧六环/水中的自组装

刚柔嵌段聚合物作为多层次有序高级结构的构筑单元正受到广泛的关注．与仅由柔性链段连接而成的嵌段聚合物相比,一方面,刚性链段和柔性链段的相分离与刚性链段倾向于有序取向间的竞争,使其自组装能力增强;另一方面,可在刚性链段引入某些功能基团,从而赋予超分子聚集体识别、传感、催化、光电等特殊的性质．     

Cleavage of polystyrene‐b‐poly(ethylene oxide) block copolymers with a trithiocarbonate linkage in solutions

In this work, the polystyrene‐b‐poly(ethylene oxide) (PS‐b‐PEO) block copolymers with a trithiocarbonate group between the blocks were prepared by polymerization of styrene in the presence of a trithiocarbonate reversible addition fragmentation chain transfer (RAFT) agent connected with PEO. Decomposition of the trithiocarbonate group by UV irradiation was investigated in three different types of solvent: tetrahydrofuran (THF, common solvent for both blocks), cyclohexane/dioxane mixture (selective solvent for the PS block) and N,N‐dimethylformamide (DMF)/ethanol mixture (selective solvent for the PEO block). It is found that cleavage of the block copolymers can take place in all these three solvents and the cleavage ratio ranges from 76 to 86%. The micellar morphologies in selective solvents before and after cleavage were examined. It is observed that the size of the micelles is reduced after cleavage and sometimes aggregation of the micelles occurs due to removal of the corona of micelles. It shows that this work provides a facile and general method for synthesis of cleavable block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3834–3840, 2010     

Polystyrene-b-poly(acrylic acid) vesicle size control using solution properties and hydrophilic block length

Polymeric vesicles have attracted considerable attention in recent years, since they are a model for biological membranes and have versatile structures with several practical applications. In this study, we prepare vesicles from polystyrene-b-poly(acrylic acid) block copolymer in dioxane/water and dioxane/THF/water mixtures. We then examine the ability of additives (such as NaCl, HCl, or NaOH), solvent composition, and hydrophilic block length to control vesicle size. Using turbidity measurements and transmission electron microscopy (TEM) we show that larger vesicles can be prepared from a given copolymer by adding NaCl or HCl, while adding NaOH yields smaller vesicles. The solvent composition (ratio of dioxane to THF, as well as the water content) can also determine the vesicle size. From a given copolymer, smaller vesicles can be prepared by increasing the THF content in the THF/dioxane solvent mixture. In a given solvent mixture, vesicle size increases with water content, but such an increase is most pronounced when dioxane is used as the solvent. In THF-rich solutions, on the other hand, vesicle size changes only slightly with the water concentration. As to the effect of the acrylic acid block length, the results show that block copolymers with shorter hydrophilic blocks assemble into larger vesicles. The effect of additives and solvent composition on vesicle size is related to their influence on chain repulsion and aggregation number, whereas the effect of acrylic acid block length occurs because of the relationship among the block length, the width of the molecular weight distribution, and the stabilization of the vesicle curvature.     

Synthesis and properties of self organising semiconducting and luminescent polymers and model compounds

Oligothiophene‐PEO‐block‐co‐polymers and related model compounds have been synthesised and characterised. In the polymers well‐defined oligothiophene blocks (with from two to six α,α‐linked thiophene sequences) were alternated with poly(ethylene oxide) blocks of narrow polydispersity. Model α,α‐linked sexithiophenes were prepared carrying chiral, achiral, mono and narrow polydispersity monomethyl PEO substituents at their terminal alpha positions. All the products were soluble in common organic solvents and organic/aqueous solvent mixtures. UV/vis and fluorescence studies in solution indicated that the oligothiophene segments were molecularly dissolved in good solvents like chloroform. Aggregation of the oligothiophenes occurred in dioxane/water mixtures, consistent with observed shifts of the UV absorption maxima towards the blue and quenching of the fluorescence. An oligothiophene length of three thiophenes (terthiophene) was necessary for aggregation to be observed. The materials formed well‐organised transferable monolayers at the air water interface.     

Dendrimer-influenced supramolecular structure formation of block copolymers

The water content-dependent supramolecular structure formation of polystyrene-block-poly(acrylic acid) (PS-b-PAA) copolymer in the presence of a fourth-generation amine-terminated poly(amido amine) dendrimer (PAMAM) is investigated by dynamic light scattering, turbidity measurements, and transmission electron microscopy. The solvent system for this study is a mixture of dioxane/THF and water. A very complex turbidity profile is observed with increasing water content in the system and is explained by the presence of various aggregated structures based on strong interactions between the amine-containing dendrimers and the poly(acrylic acid) blocks of the polymer. The onset of the self-assembly of single chains of PS-b-PAA (primary structure) into single and multiple dendrimer core inverse micelles (secondary structure) is detected as very low water contents of cw < 2% wt (cwc). These micelles consist of dendrimers coated with PAA blocks, which are connected to the corresponding PS chains that form the corona. Further addition of water leads to an association of these micelles into compound multiple dendrimer core inverse micelles (tertiary structure) in the range of cw = approximately 6 to approximately 10% wt. At still higher water content, some of the acrylic acid chains of the block copolymer move from the vicinity of the dendrimer to the outside of the aggregates, resulting in a decrease in the size of the formed structures and the acquisition of progressively increasing hydrophilic character of the aggregates. Multiple dendrimer core inverse onion micelles are formed, which agglomerate into compound multiple dendrimer core inverse onion micelles at cw = approximately 12 to approximately 18% wt. Above this water content, vesicular structures are formed. The complexity is unusual for block copolymer systems and illustrates the importance of strong interactions in structure formation.     

Amphiphilic ABC triblock copolymer-assisted synthesis of core/shell structured CdTe nanowires

A new type of amphiphilic ABC triblock copolymer, poly(acrylic acid)(33)-poly(styrene)(47)-poly(ethylene oxide)(113) (PAA(33)-PS(47)-PEO(113)), was designed to assist the synthesis of core/shell structured CdTe nanowires via a one-step synthetic route. The PAA block was adopted to capture cadmium ions as the precursor of CdTe. Due to the bivalent coordination of Cd(2+), the copolymer in dioxane/H(2)O formed micelles with Cd(2+)-polychelate cores. Then CdTe nanocrystals were obtained within the micelles after introduction of NaHTe into the micelle solution. Transmission electron microscopy experiments revealed that the CdTe nanocrystals obtained simultaneously formed "pearl-necklace" aggregates in solution possibly driven by dipole interactions between neighboring particles, and then single crystalline CdTe nanowires upon reflux. Accompanying this morphology change, a phase transition from cubic zinc blende to wurtzite structure was observed by selected-area electron diffraction. The aggregation of the PS block in dioxane with a certain amount of H(2)O enabled the PS blocks to form a densely packed shell on the CdTe nanowires whose typical size is 700-800 nm in length and 15-20 nm in width. The third block of PEO was employed to render the finally formed CdTe nanowires dispersibility.     

Self‐assembly of oligo(p‐phenylenevinylene)‐block‐poly(ethylene oxide) in polar media and solubilization of an oligo(p‐phenylenevinylene) homooligomer inside the assembly

Rod–coil amphiphilic diblock copolymers, consisting of oligo(p‐phenylenevinylene) (OPV) as a rod and hydrophobic block and poly(ethylene oxide) (PEO) as a coil and hydrophilic block, were synthesized by a convergent method. The aggregation behavior of the block copolymers in a selective solvent (tetrahydrofuran/H₂O) was probed with the absorption and emission of the OPV block. With increasing H₂O concentration, the absorption maximum was blueshifted, the emission from the molecularly dissolved OPV decreased, and that from the aggregated OPV increased. This indicated that the OPV blocks formed H‐type aggregates in which the OPV blocks aligned in a parallel orientation with one another. The transmission electron microscopy observation revealed that the block copolymers with PEO weight fractions of 41 and 62 wt % formed cylindrical aggregates with a diameter of 6–8 nm and a length of several hundreds nanometers, whereas the block copolymer with 79 wt % PEO formed distorted spherical aggregates with an average diameter of 13 nm. Furthermore, the solubilization of an OPV homooligomer with the block copolymer was studied. When the total polymer concentration was less than 0.1 wt %, the block copolymer solubilized OPV with a 50 mol % concentration. The structure of the aggregates was a cylinder with a relatively large diameter distribution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1569–1578, 2005     

Control of the PEO chain conformation on nanoparticles by adsorption of PEO-block-poly(L-lysine) copolymers and its significance on colloidal stability and protein repellency

The physical adsorption of PEO(n)-b-PLL(m) copolymers onto silica nanoparticles and the related properties of poly(ethylene oxide) (PEO)-coated particles were studied as a function of the block copolymer composition. Copolymers adopt an anchor-buoy conformation at the particle surface owing to a preferential affinity of poly(L-lysine) (PLL) blocks with the silica surface over PEO blocks when a large excess of copolymer is used. The interdistance between PEO chains at particle surface is highly dependent on the size of PLL segments; a dense brush of PEO is obtained for short PLL blocks (DP = 10), whereas PEO chains adopt a so-called interacting "mushroom" conformation for large PLL blocks (DP = 270). The size of the PEO blocks does not really influence the copolymer surface density, but it has a strong effect on the PEO layer thickness as expected. Salt and protein stability studies led to similar conclusions about the effectiveness of a PEO layer with a dense brush conformation to prevent colloidal aggregation and protein adsorption. Besides, a minimal PEO length is required to get full stabilization properties; as a matter of fact, both PEO(45)-b-PLL(10) and PEO(113)-b-PLL(10) give rise to a PEO brush conformation but only the latter copolymer efficiently stabilizes the particles in the presence of salt or proteins.     

Polystyrene‐graft‐poly(ethylene oxide) copolymers prepared by macromonomer technique in dispersion. I. Liquid chromatographic separation of product mixtures

Products of the radical dispersion copolymerization of methacryloyl‐terminated poly(ethylene oxide) (PEO) macromonomer and styrene were separated and characterized by size exclusion chromatography (SEC), full adsorption‐desorption (FAD)/SEC coupling and eluent gradient liquid adsorption chromatography (LAC). In dimethylformamide, which is a good solvent for PEO side chains but a poor solvent for polystyrene (PS), amphiphilic PS‐graft‐PEO copolymers formed aggregates, which were very stable at room temperature even upon substantial dilution. The aggregates disappeared at high temperature or in tetrahydrofuran (THF), which is a good solvent for both homopolymers and for PS‐graft‐PEO. FAD/SEC procedure allowed separation of homo‐PS from graft‐copolymer and determination of both its amount and molar mass. Effective molar mass of graft‐copolymer was estimated directly from the SEC calibration curve determined with PS standards. Presence of larger amount of the homo‐PS in the final graft‐copolymer products was also confirmed with LAC measurements. The results indicate that there are at least two or maybe three polymerization loci; namely the continuous phase, the particle surface layer and the particle core. The graft copolymers are produced mainly in the continuous phase while PS or copolymer rich in styrene units is formed mostly in the core of monomer‐swollen particles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2284–2291, 2000     

The role of intrachain and interchain interactions of regioregular poly(3-octylthiophene) chains on the optical properties of a new amphiphilic conjugated random copolymer in solution

The synthesis of a random copolymer through free radical copolymerization of a properly vinyl monofunctionalized regioregular poly(3-octylthiophene) (rrP3OT) macromonomer and N,N'-dimethylacrylamide (DMAM) is presented. The optical properties of the copolymer in water and in several organic solvents of varying polarity, as well as in THF/water and THF/methanol mixtures, were explored using UV-vis and photoluminescence spectroscopy. It is demonstrated that the rrP3OT chains adopt a coil conformation in solvents such as tetrahydrofuran (THF) and chloroform with the appearance of the absorption and emission maxima at 439 and 565 nm, respectively. On the contrary, the rrP3OT chains are organized on a single chain packing form (intrachain interactions) in polar solvents such as ethanol and methanol, as it is verified with the observation of the characteristic three vibronic features of the absorption spectra of the copolymer with maxima at 513, 550, and 603 nm and emission maxima at 560 nm. However, when water is used as solvent, the rrP3OT chains self-assemble into a stacklike structure due to the increased interchain interactions, as confirmed by the different aggregation process of the rrP3OT chains in the THF/water mixture, the broader absorption spectrum in water compared to those recorded in ethanol and methanol, and the 80 nm red-shifted emission maximum, centered at 640 nm.     

Effect of Pluronic F127 on the pore structure of macrocellular biodegradable polylactide foams

Thermally induced phase separation technique was utilized to fabricate biodegradable poly(l ‐lactic acid) (PLLA) macrocellular foams which were capable of being applied in tissue engineering. The block copolymer Pluronic F127 composed of (polyethyleneoxide)‐(polypropyleneoxide)‐(polyethyleneoxide) [(PEO)‐(PPO)‐(PEO)] was used as a porogen. Water/dioxane mixtures with different volume ratios were used as solvents. The addition of Pluronic F127 could induce an appearance of large pores (50–200 μm) besides small pores (10–20 μm) or a change from a solid–liquid phase separation to a liquid–liquid phase separation. The role of Pluronic F127 depends on the water/dioxane ratios in the PLLA/dioxane/water system. The X‐ray diffraction patterns and porosity measurement results showed that Pluronic F127 was crystallized and existed on the pore wall. The effect of Pluronic F127 on changing pore structure is attributed to the occurrence of the interaction of the lipophilic PPO blocks in Pluronic F127 with PLLA clews, consequently, this results in PLLA aggregation and early phase separation on cooling. Copyright © 2004 John Wiley & Sons, Ltd.     

Rupturing polymeric micelles with cyclodextrins

Small-angle neutron scattering has been used to investigate the associative structures formed by triblock copolymers of poly(ethylene oxide) (PEO)-polypropylene oxide (PPO)-poly(ethylene oxide) (PEO) (also known as Pluronics) and to monitor the structural changes occurring upon complexation with heptakis(2,6-di-O-methyl)-beta-cyclodextrin (hbeta-CD) over the temperature range from 5 to 70 degrees C. At low temperature, the Pluronics are dispersed as unimers. Close to ambient temperature, the hydrophobicity of PPO causes the aggregation of the polymers into spherical micelles with core sizes between 40 and 50 A and a high inclusion of solvent. The aggregation number increases with temperature as the hydrophobicity of the core is gradually enhanced. hbeta-CD spontaneously forms pseudopolyrotaxanes with the triblock copolymers either when in their unimer form or micellized. The complexation results in an increase in the effective critical micellar concentration. It is suggested that the cyclodextrins thread onto the polymer backbone to localize preferentially on the central PPO block, therefore improving its water solubility. At temperatures where the polymers exist in micellar form, complexation with hbeta-CD gives rise to a complete disruption of the aggregates. These processes are highly temperature-dependent. Above 50 degrees C, the break-up of the aggregates is inhibited, and large-scale aggregation is observed.     

Morphological transitions in aggregates of thermosensitive poly(ethylene oxide)‐b‐poly(N‐isopropylacrylamide) block copolymers prepared via RAFT polymerization

Double hydrophilic poly(ethylene oxide)‐b‐poly(N‐isopropylacrylamide) (PEO‐b‐PNIPAM) block copolymers were synthesized via reversible addition‐fragmentation chain transfer (RAFT) polymerization, using a PEO‐based chain transfer agent (PEO‐CTA). The molecular structures of the copolymers were designed to be asymmetric with a short PEO block and long PNIPAM blocks. Temperature‐induced aggregation behavior of the block copolymers in dilute aqueous solutions was systematically investigated by a combination of static and dynamic light scattering. The effects of copolymer composition, concentration (C_p), and heating rate on the size, aggregation number, and morphology of the aggregates formed at temperatures above the LCST were studied. In slow heating processes, the aggregates formed by the copolymer having the longest PNIPAM block, were found to have the same morphology (spherical “crew‐cut” micelles) within the full range of C_p. Nevertheless, for the copolymer having the shortest PNIPAM block, the morphology of the aggregates showed a great dependence on C_p. Elongation of the aggregates from spherical to ellipsoidal or even cylindrical was observed. Moreover, vesicles were observed at the highest C_p investigated. Fast heating leads to different characteristics of the aggregates, including lower sizes and aggregation numbers, higher densities, and different morphologies. Thermodynamic and kinetic mechanisms were proposed to interpret these observations, including the competition between PNIPAM intrachain collapse and interchain aggregation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4099–4110, 2009     

PS-b-PEO-b-PS三嵌段共聚物在选择性溶剂中的胶束化

应用原子转移自由基聚合,制备了一组窄分布的PS-b-PEO-b-PS三嵌段共聚物。用^1HNMR和TEM表征了它们在选择性溶剂中的胶束化行为。^1HNMR结果表明,共聚物苯环上的质子峰出现在良溶剂(CHCl~3)中,而在选择性溶剂水中消失,证明上述三嵌段共聚物在选择性溶剂水中可逆自组装成以PS为核、PEO为壳的胶束。通过TEM考察了胶束的形状及大小,发现体系胶束尺寸呈多分散、粒径大,对形成的原因也提出了可能的解释。     

CRYSTALLIZATION AND MELTING OF POLY（ETHYLENE OXIDE） CONFINED IN NANOSTRUCTURED PARTICLES WITH CROSS-LINKED SHELLS OF POLYBUTADIENE

Small fixed aggregates of a poly(ethylene oxide)-block-polybutadiene diblock copolymer(PEO-b-PB)in THFsolution were obtained by adding a selective solvent for PB blocks,followed by cross-linking the PB shells.Themorphologies of the nanostructured particles with a cross-linked shell were investigated by atomic force microscopy andtransmission electron microscopy.The average behaviors of the PEO crystallization and melting confined within thenanostructured particles were studied by using differential scanning calorimetry experiments.For the deeply cross-linkedsample(SCL-1),the crystallization of the PEO blocks was fully confined.The individual nanoparticles only crystallized atvery low crystallization temperatures(T_cs),wherein the homogenous primary nucleation determined the overallcrystallization rate.For the lightly cross-linked sample(SCL-2),the confinement effect was T_c dependent.At T_c(?)42℃,thecrystallization and melting behaviors of SCL-2 were similar to those of the pure PEO-b-PB diblock copolymer.At T_c>42℃,SCL-2 could form PEO lamellae thicker than those of the pure PEO-b-PB crystallized at the same T_c.     

Fabrication of well‐developed nano‐ribbons composed of hierarchically grown isotactic poly(methyl methacrylate) crystals on substrates

Well‐developed nano‐ribbons composed of isotactic poly(methyl methacrylate) (it‐PMMA) were successfully fabricated on mica via a simple solution‐casting method. Typical morphologies with about 0.6 nm thickness and 30–40 nm widths, thermal stability, and alternative structural analyses suggested that nano‐ribbons were composed of two‐dimensional folded chain crystals of it‐PMMA. Typically, nano‐ribbons were developed by incubating tetrahydrofuran (THF) solutions at 20 °C for at least 2 months, more than equi‐amounts of water were added to incubated THF solutions, and solutions were cast onto mica. It was found that, after the aforementioned incubation of THF solutions, it‐PMMA chains adopted trans‐trans (tt) conformations, which are precursors for it‐PMMA crystals, suggesting that THF is a unique solvent for it‐PMMA. By adding water, a poor solvent for it‐PMMA, to THF solutions, it‐PMMA aggregates formed with several hundreds of nanometer sizes, further promoting an increase in the population of the tt conformation. Nano‐ribbons were similarly formed on silicon wafer substrates, suggesting that hydrophilic substrates were essential for the formation of nano‐ribbons. Interestingly, a modulation of the above described method, with the slight evaporation of THF from a THF/water solution before casting onto mica, succeeded in the development of epitaxially adsorbed nano‐ribbons. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3098–3110, 2009     

Amphiphilic polylactide-poly(ethylene oxide)-poly(propylene oxide) block copolymers: Self-assembly behavior and cell affinity

Polylactide (PLA) is a biodegradable polyester recognized for its potential use as a biomedical material. Poly(ethylene oxide) (PEO) and copolymers based on PEO and poly(propylene oxide) (PPO) are biocompatible polyethers widely applied in the biomedical field, particularly as macromolecular nonionic surfactants. In this work, PLA blocks were attached to the PEO and to the PEO and PPO-based triblock copolymer PEO–PPO–PEO, through ring-opening polymerization of racemic lactide (rac-LA) to obtain the amphiphilic triblock PLA–PEO–PLA and pentablock PLA–PEO–PPO–PEO–PLA copolymers containing hydrophilic/hydrophobic blocks with variable block mass ratios. The copolymers were evaluated for chemical composition, molar mass, and thermal properties, and they were used to prepare self-assemble aggregates in water from tetrahydrofuran polymer solutions. The combination of scattering light experiments and microscopy techniques revealed the spherical morphology of the aggregates with diameters around 180–200 nm, which comprises a hydrophobic PLA core and a hydrophilic polyether shell. The aggregates are nontoxic to human cervical cancer cell line — HeLa cells, as determined by MTS assay, and the aggregates are potential candidates to be applied in the encapsulation of hydrophobic compounds. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2203–2213     

Cadmium sulphide quantum dots in morphologically tunable triblock copolymer aggregates

Cadmium sulfide (CdS) quantum dots (QDs) are formed within poly(ethylene oxide)-block-polystyrene-block-poly (acrylic acid) (PEO-b-PS-b-PAA) triblock copolymer aggregates of different architectures. These structures are obtained starting with the same ionically cross-linked primary micelles consisting of a cadmium acrylate core, a PS shell, and a PEO corona. One morphology is a worm-shaped micelle prepared in tetrahydrofuran (THF) in which the CdS QDs are surrounded by the PAA and aligned as a loose necklace in the PS matrix. The PEO serves as a corona around the PS rod. Another structure is a multicore spherical (ca. 50 nm) water soluble PS micelle, surrounded by PEO chains. The CdS particles within these two latter structures are formed by the reaction of cadmium ions present in the acrylate cores with hydrogen sulfide. In a third structure, the CdS QDs are located on the surface of PS micelles. A fourth spherical single-core micelle structure is postulated to exist in dilute THF solutions. The dimensions in all the aggregates can be controlled by the block length.