Monolayer films of PS-b-PEO diblock copolymers at the air/water- and an oil/water-interface

 Amphiphilic diblock copolymers consisting of a hydrophobic polystyrene block (PS) and a hydrophilic poly(ethylene oxide) block (PEO) with block sizes of 1000 or 3000 g/mol for both blocks were studied at the air/water and toluene/water interface. Measurements of the film pressure π of spread monolayers at the water surface reveal two limiting regimes of the π−a _m isotherms, in which the mean molecular area a _m is determined either by the size of the hydrophilic or the hydrophobic blocks of the PS-PEO molecules. The interfacial activity of the block copolymers at the toluene/water interface was studied by measuring the interfacial tension σ over a wide range of concentrations. Pronounced differences in the temperature dependence of the interfacial tension were observed, depending mostly on the block length of the hydrophilic PEO block. From the temperature dependence of σ it is inferred that for the block copolymers with the PEO block size of 3000 g/mol the phase inversion temperature (PIT) is well above 60 °C while for those with a PEO block size of 1000 g/mol the PIT is below or near 25 °C in the toluene/water system. Received: 5 February 1998 Accepted: 16 February 1998     

New amphiphilic diblock copolymers: surfactant properties and solubilization in their micelles

Several series of amphiphilic diblock copolymers are investigated as macrosurfactants in comparison to reference low-molar-mass and polymeric surfactants. The various copolymers share poly(butyl acrylate) as a common hydrophobic block but are distinguished by six different hydrophilic blocks (one anionic, one cationic, and four nonionic hydrophilic blocks) with various compositions. Dynamic light scattering experiments indicate the presence of micelles over the whole concentration range from 10(-4) to 10 g x L(-1). Accordingly, the critical micellization concentrations are very low. Still, the surface tension of aqueous solutions of block copolymers decreases slowly but continuously with increasing concentration, without exhibiting a plateau. The longer the hydrophobic block, the shorter the hydrophilic block, and the less hydrophilic the monomer of the hydrophilic block is, the lower the surface tension is. However, the effects are small, and the copolymers reduce the surface tension much less than standard low-molar-mass surfactants. Also, the copolymers foam much less and even act as anti-foaming agents in classical foaming systems composed of standard surfactants. The copolymers stabilize O/W emulsions made of methyl palmitate as equally well as standard surfactants but are less efficient for O/W emulsions made of tributyrine. However, the copolymer micelles exhibit a high solubilization power for hydrophobic dyes, probably at their core-corona interface, in dependence on the initial geometry of the micelles and the composition of the block copolymers. Whereas micelles of copolymers with strongly hydrophilic blocks are stable upon solubilization, solubilization-induced micellar growth is observed for copolymers with moderately hydrophilic blocks.     

Adsorption of hydrophilic-hydrophobic block copolymers on silica from aqueous solutions

Adsorption of a water-soluble diblock copolymer, poly(t-butylstyrene)-sodium poly(styrene sulfonate) (PtBS-NaPSS), on silica surfaces in aqueous solutions was studied using ellipsometry and atomic-force microscopy (AFM). Molar masses of 87 000 and 160 000 g/mol were used. The block copolymers used were compositionally asymmetric, with large, hydrophilic, PSS blocks and small, hydrophobic, PtBS blocks. Adsorption could not be observed in pure water without added salt. When the NaCl concentration was increased to 1 mol/L, adsorption could be readily observed. The measured adsorbed amount at long times was significantly larger for the 87 000 diblock compared with that for a polyelectrolyte homopolymer of comparable molecular size, demonstrating the role played by the uncharged block in anchoring the diblock at the solid surface. The kinetics of adsorption showed a two-stage process, an initial diffusion-limited stage, followed by a slower buildup of surface coverage in a brush-limited stage. The number density of molecules at the surface was smaller for the higher molecular weight species, in agreement with simple scaling arguments.     

丙烯酰胺-苯乙烯双亲嵌段共聚物的微结构及水溶液行为

通过改变丙烯酰胺(AM)与苯乙烯(St)的投料比、苯乙烯与表面活性剂的加入量之比及引发剂加入量,在微乳液中制备了分子链微结构系列变化的丙烯酰胺-苯乙烯双亲嵌段共聚物(PAM-b-PSt),用荧光探针法与表面活性测定法详细地研究了共聚物中PSt嵌段长度、含量及分子量等微结构因素对共聚物在水溶液中的疏水缔合性与表面活性的影响.结果表明,当共聚物水溶液的浓度高于临界缔合浓度时,PAM-b-PSt的疏水缔合作用以分子间的缔合为主.若共聚物中PSt嵌段含量及分子链长一定时,随着PSt疏水嵌段长度增长,PAM-b-PSt的疏水缔合性增强,而对共聚物的表面活性影响很小.若共聚物中PSt疏水嵌段长度及分子链长一定时,PAM-b-PSt的疏水缔合性随着PSt嵌段含量的变化而变化,当PSt嵌段含量一定时,使大分子链之间产生最强的疏水缔合作用;而其表面活性则随着PSt嵌段含量的增大而增强.若共聚物中PSt疏水嵌段长度及含量一定时,分子量对其表面活性有较大的影响,分子量越高,表面活性越差;同时,在较稀的溶液浓度范围内,分子量对PAM-b-PSt的疏水缔合性的影响则很小.     

Click cyclization of linear triblock copolymers at block junctions under high concentration due to end-block shielding

Linear triblock copolymers of poly(N-isopropylacrylamide) (PNIPAM) and poly(ethylene glycol) (PEG) with two azide groups at both block junctions (PNIPAM-N3-PEG-N3-PNIPAM) are click reacted with dipropargyl oxalylate under high polymer concentration (250 g/L). Benefiting from rapid feature of alkyne-azide click reaction and spatial shielding of PNIPAM end blocks, PEG center block of PNIPAM-N3-PEG-N3-PNIPAM remains separated although PNIPAM end blocks keep in contact under this high concentration. Therefore, PNIPAM-N3-PEG-N3-PNIPAM undergoes self-cyclization at block junctions to form tadpole-shaped architecture while N3-PEG-N3 without PNIPAM end blocks inter-connects linearly. The influence of block lengths of PEG and PNIPAM on the unusual cyclization under high polymer concentration is studied.     

Formation of large PEE domains in PEE212-PEO112 diblock copolymer monolayers: shift of the PEO-desorption transition

PEE212-PEO112 diblock copolymer monolayers are studied at the air/water interface. At large molecular areas, with X-ray reflectivity, PEE domains are observed, which are partly immersed into the water. The domain thickness increases on compression (28 to 40 A). With off-specular X-ray reflectivity, an average domain radius of 750 A is found, but there are also smaller domains. Due to these space constraints, most PEO blocks form a brush beneath the PEE domains. Only a few PEO blocks form a corona surrounding the domains and adsorb flatly onto the air/water interface. The PEO desorption transition is observed at the typical pressure of 9 mN/m, when the flatly adsorbed PEO is compressed at a domain fraction of 95%. It occurs at 6 A2/EO monomer, about half the value found for lipopolymers or diblock copolymers with NPEE approximately NPEO or NPEE < NPEO. Apparently, the thickness of the PEE domains is determined by the forces from the two interfaces, not by the PEO block, for which flat adsorption beneath the domain would be more favorable instead of formation of a PEO brush.     

Determination of long-lived radionuclides in concrete matrix by laser ablation inductively coupled plasma mass spectrometry

A laser ablation system using a Nd:YAG laser was coupled both to a quadrupole inductively coupled plasma (ICP) mass spectrometer and to a double-focusing sector field ICP mass spectrometer. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was applied for the determination of long-lived radionuclides in a concrete matrix. The investigated samples were two laboratory standards with a concrete matrix, which we doped with different long-lived radionuclides (e.g. ⁹⁹Tc, ²³²Th, ²³³U, ²³⁷Np) from the ng g⁻¹ to μ g⁻¹ concentration range and an undoped concrete material (blank). Detection limits for long-lived radionuclides in the 10 ng g⁻¹ range are reached for LA-ICP-MS using the quadrupole mass spectrometer. With double-focusing sector field ICP-MS, the limits of detection are in general one order of magnitude lower and reach the sub ng g⁻¹ range for ²³³U and ²³⁷Np. A comparison of mass spectrometric results with those of neutron activation analysis on undoped concrete sample indicates that a semiquantitative determination of the concentrations of the minor and trace elements in the concrete matrix is possible with LA-ICP-MS without using a standard reference material.     

Poly(ethylene glycol)--oligolactates with monodisperse hydrophobic blocks: preparation, characterization, and behavior in water

Methoxypoly(ethylene glycol)-b-oligo-L-lactate (mPEG-b-OLA) diblock oligomers with monodisperse OLA blocks were obtained by fractionation of polydisperse block oligomers using preparative HPLC. The fractionated oligomers were composed of an mPEG block with a molecular weight of 350, 550, or 750 and an OLA block with a degree of polymerization of 4, 6, 8, or 10. The diblock oligomers with a low PEG content were fully amorphous, with glass transition temperatures ranging from -60 to -20 degrees C, indicating that the blocks were miscible. Upon heating aqueous dispersions of the block oligomers, cloud points, depending on the PEG/OLA ratio of the block oligomer, were observed at temperatures above 40 degrees C. The monodispersity of the hydrophobic block enabled the amphiphilic molecules to form nanoparticles in water with a hydrodynamic radius of 130-300 nm, at concentrations above the critical aggregation concentration (0.4-1 mg/mL), whereas polydisperse mPEG-b-OLAs gave formation of large aggregates. Static light scattering measurements showed that the nanoparticles have a low density (0.6-25 mg/mL), indicating that the particles are highly hydrated. In agreement herewith, the (1)H NMR spectra of nanoparticles in D2O closely resembled spectra in a good solvent for both blocks (CDCl3). It is therefore suggested that the nanoparticles contain a hydrated core of mPEG-b-OLA block oligomers, stabilized by a thin outer PEG layer. The particles were stable for two weeks, except for the mPEG350 series and mPEG750-b-OLA4, indicating that both the PEG block size and the PEG weight fraction of the oligomers determine their stability. The evident self-emulsifying properties of mPEG-b-oligo-l-lactates with monodisperse hydrophobic blocks as demonstrated in this study, together with their expected biocompatibility and biodegradability, make these systems well suitable for pharmaceutical applications.     

Polyimidothioether–polysulfide block polymers

The synthesis of a new class of block polymers that contain alternating polyimidothioether “hard” blocks and polysulfide elastomer “soft” blocks is described. Compositions with 70% and greater polysulfide component are solvent-resistant, thermoplastic elastomers exhibiting room temperature tensile strengths of up to 1500 psi and ultimate elongations of nearly 800%. The physical properties are a strong function of test temperature due to relatively short polyimidothioether blocks, 850 ≤ M?_n ≤ 3500 g/mole. These short polyimidothioether blocks were necessary to minimize degradation of the polysulfide elastomer blocks during thermal processing at temperatures ～100°C above the “hard” block domain T_g.     

Engineering Mechanical Strong Biomaterials Inspired by Structural Building Blocks in Nature

The intricate multiscale architectures in natural structural building blocks provide many sources of inspiration for the designs of artificial biomaterials. In nature, the assembly of highly ordered molecular crystals and amorphous aggregates often derives from inter- and intra-molecular interactions of biomacromolecules, e.g., proteinaceous materials. The structural biomaterials derived from the protein self-assembly behave with remarkable mechanical performance. However, there is still a grand challenge to mimic the mechanical properties of natural protein-based biomaterials in a rational design fashion to yield comparable man-made synthetic ensembles. In this review, a brief perspective on current challenges and advances in terms of bioinspired structural materials is presented. We outline a framework for mimicking protein self-assembly of natural building blocks across multiscale and highlight the critical role of synthetic biology and chemical modifications in material biosynthesis. Particularly, we focus on the design and promising applications of protein-based fibers, adhesives, dynamic hydrogels and engineered living materials, in which natural mechanical functions are effectively reproduced.     

Two-dimensional self-assembly of linear poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers at the air-water interface

The interfacial properties of amphiphilic linear diblock copolymers based on poly(ethylene oxide) and poly(epsilon-caprolactone) (PEO-b-PCL) were studied at the air-water (A/W) interface by surface pressure measurements (isotherms and hysteresis experiments). The resulting Langmuir monolayers were transferred onto mica substrates and the Langmuir-Blodgett (LB) film morphologies were investigated by atomic force microscopy (AFM). All block copolymers had the same PEO segment (Mn = 2670 g/mol) and different PCL chain lengths (Mn = 1270; 2110; 3110 and 4010 g/mol). Isothermal characterization of the block copolymer samples indicated the presence of three distinct phase transitions around 6.5, 10.5, and 13.5 mN/m. The phase transitions at 6.5 and 13.5 mN/m correspond to the dissolution of the PEO segments in the water subphase and crystallization of the PCL blocks above the interface similarly as for the corresponding homopolymers, respectively. The phase transition at 10.5 mN/m was not observed for the homopolymers alone or for their blends and arises from a brush formation of the PEO segments anchored underneath the adsorbed hydrophobic PCL segments. AFM analysis confirmed the presence of PCL crystals in the LB films with unusual hairlike/needlelike architectures significantly different from those obtained for PCL homopolymers.     

Fluorinated bis(phenoxyketimine)titanium complexes for the living, isoselective polymerization of propylene: multiblock isotactic polypropylene copolymers via sequential monomer addition

A series of bis(phenoxyketimine)titanium dichloride complexes were synthesized and evaluated as catalysts for living, isoselective propylene polymerization upon activation with methylaluminoxane (MAO). Catalysts bearing phenoxyketimine ligands with different substituents at the ortho and para positions of the phenolate ring and substituents at the ketimine carbon were investigated. The identity of the ketimine substituent had the largest effect on the activity and isoselectivity of propylene polymerization. Complex 12/MAO promoted the living, isoselective polymerization of propylene ([m4] = 0.73, alpha = 0.94). This catalyst system was used for the synthesis of a number of block copolymers featuring isotactic polypropylene semicrystalline blocks and poly(ethylene-co-propylene) amorphous blocks. Several triblock samples with varying block lengths, a pentablock, and a heptablock copolymer were synthesized. Mechanical testing has revealed that each is elastomeric with elongations at break between approximately 790-1000%.     

Selective ordering of surfactant modified gold nanoparticles in a diblock copolymer

Ordered aggregation of thiol-passivated Au nanoparticles in a diblock copolymer polystyrene-b-poly(methyl methacrylate) has been observed. The morphology of the diblock copolymer/Au-nanocomposite was dependent on the composition of the thiol modifier. For the thiol modifier that does not preferentially interact with one of the blocks, a perpendicular (relative to the substrate) lamellar morphology is maintained. However, for a thiol with a surfactant structure similar to one of the blocks, we observed a parallel lamellar morphology and speculate that the nanoparticles have localized at the microdomain interface. These conclusions are based on transmission electron microscopy, angle-dependent X-ray photoelectron microscopy and tensiometry. These results are consistent with theoretical predictions on the hybrid systems composed of block copolymers and nanoparticles.     

The Crystallization and Melting Behaviors of PDLA-b-PBS-b-PDLA Tri-block Copolymers

In this study,the poly(D-lactide)-block-poly(butylene succinate)-block-poly(D-lactide)(PDLA-b-PBS-b-PDLA)triblock copolymers with a fixed length of PBS and various lengths of PDLA are synthesized,and the crystallization behaviors of the PDLA and PBS blocks are investigated.Although both the crystallization behaviors of PBS and PDLA blocks depend on composition,they exhibit different variations.For the PDLA block,its crystallization behaviors are mainly influenced by temperature and block length.The crystallization signals of PDLA block appear in the B-D 2-2 specimen,and these signals get enhanced with PDLA block length.The crystallization rates tend to decrease with increasing PDLA block lendth during crystallizing at 90 and 100°C.Crystallizing at higher temperature,the crystallization rates increase at first and then decrease with block length.The crystallization rates decrease as elevating the crystallization temperature.The melting temperatures of PDLA blocks increase with block lengths and crystallization temperatures.For the PBS block,its crystallization behaviors are mainly controlled by the nucleation and confinement from PDLA block.The crystallization and melting enthalpies as well as the crystallization and melting temperatures of PBS block reduce as a longer PDLA block has been copolymerized,while the crystallization rates of the PBS block exhibit unique component dependence,and the highest rate is observed in the B-D 2-2 specimen.The Avrami exponent of PBS crystallites is reduced as a longer PDLA block is incorporated or the sample is crystallized at higher temperature.This investigation provides a convenient route to tune the crystallization behavior of PBS and PLA.     

Insertion mechanism of a poly(ethylene oxide)-poly(butylene oxide) block copolymer into a DPPC monolayer

Interactions between amphiphilic block copolymers and lipids are of medical interest for applications such as drug delivery and the restoration of damaged cell membranes. A series of monodisperse poly(ethylene oxide)-poly(butylene oxide) (EOBO) block copolymers were obtained with two ratios of hydrophilic/hydrophobic block lengths. We have explored the surface activity of EOBO at a clean interface and under 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayers as a simple cell membrane model. At the same subphase concentration, EOBO achieved higher equilibrium surface pressures under DPPC compared to a bare interface, and the surface activity was improved with longer poly(butylene oxide) blocks. Further investigation of the DPPC/EOBO monolayers showed that combined films exhibited similar surface rheology compared to pure DPPC at the same surface pressures. DPPC/EOBO phase separation was observed in fluorescently doped monolayers, and within the liquid-expanded liquid-condensed coexistence region for DPPC, EOBO did not drastically alter the liquid-condensed domain shapes. Grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XRR) quantitatively confirmed that the lattice spacings and tilt of DPPC in lipid-rich regions of the monolayer were nearly equivalent to those of a pure DPPC monolayer at the same surface pressures.     

Influence of molecular architecture of S–S/B–S triblock copolymers on rheological properties

The influence of middle and outer block composition of symmetric triblock copolymers consisting of a polystyrene–polybutadiene (S/B) random middle block and two polystyrene (PS) outer blocks on morphology and rheological behavior has been investigated. Master curves are obtained by shifting the experimental data measured at different temperatures using time‐temperature superposition principle, the validity of which was confirmed in the linear viscoelastic regime. The rheological properties are observed to be strongly influenced by the relative composition of the S‐SB‐S triblock copolymers. Increasing the S/B ratio from 1:1 to 1:2 in the middle block has lead to a change in morphology from wormlike to lamellar, which is also accompanied with broad and sharp tan δ peaks in the dynamic mechanical measurements, respectively. The storage and loss modulus have been observed to increase with the increase in PS contents in the outer blocks and PB content in the middle block. The triblock copolymer with wormlike structure showed terminal linear viscoelastic behavior, whereas the ones with lamellar morphology showed nonterminal flow behavior in the similar low‐frequency regime. The relaxation modulus (G_t) has been observed to increase four times when the S/B ratio is increased from 1:1 to 1:2, whereas it increases threefold when the PS‐content in the outer block was increased by just 8 wt %. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2776–2788, 2006     

Theoretical and experimental studies on the surface structures of conjugated rod-coil block copolymer brushes

A combined theoretical and experimental investigation of conjugated rod-coil block copolymer brushes is reported. The theoretical study for the surface structures of rod-coil block copolymer brushes was established based on the simulation method of dissipative particle dynamics. The effects of solvent stimuli, grafting density, and rod-coil block ratio of the polymer brushes on the surface structures were examined. The rod blocks of polymer brushes were found to be well-dispersed on the surface in their good solvents. On the other hand, aggregative domains of the rod blocks were formed in their poor solvents with the conformations of isolated islands or worm-like structures depending on the grafting density of the polymer brushes. The aggregative domains tend to stay on top of the coil blocks for small rod-to-coil block ratio. However, the submergence of the aggregative domains into the coil blocks is thermodynamically preferred for large enough rod-to-coil block ratio. New multifunctional amphiphilic rod-coil block copolymers, poly-[2,7-(9,9-di-n-hexylfluorene)]-block-poly-[poly(ethylene glycol) methyl ether methacrylate]-block-poly-[3(tripropoxysilyl)propyl methacrylate] (PF-b-PPEGMA-b-PPOPS), with two different block ratios were synthesized and used to prepare the corresponding polymer brushes via the grafting- method. The effects of stimuli factors on the surface structures characterized by the atomic force microscopy images were consistent with the theoretical results. Furthermore, the photophysical properties of PF-b-PPEGMA-b-PPOPS brushes were significantly varied by the solvent stimuli. The emission peaks originated from the aggregation and/or excimer formation of PF blocks were observed after methanol treatment. The photoluminescence intensity and its efficiency were well correlated to the surface structure and the methanol content in mixed solvents. Our study demonstrates how the surface structures and photophysical properties of rod-coil block copolymer brushes response to environmental stimuli.     

Coupling of hydrodynamically closed large bore capillary isotachophoresis with electrospray mass spectrometry

Capillary isotachophoresis with coupled columns provides efficient means for rapid electrophoretic analysis of sample volumes of up to 10 μl or more. Commercially available instruments are commonly equipped with conductivity and UV absorbance detectors; however, their on-line coupling with electrospray mass spectrometry is highly desirable. In this work we have modified the commercial coupled column isotachophoresis system for direct connection to an ion trap mass spectrometer. The design included attachment of an elution block with a short capillary transfer line directing the separated zones towards the mass spectrometer. The modification further included separation of the injection and electrode blocks from the separation columns by semipermeable membranes eliminating unwanted fluid movements in the wide bore fluoropolymer separation capillaries. Fused silica capillaries with varying internal diameter were connected as a transfer line between the elution block and mass spectrometer. The transfer line served also as the ESI tip of the sheathless electrospray interface. During the analysis the first, wide bore preseparation capillary with 0.8 mm internal diameter served for removal of the bulk sample components and preseparation of the potentially interfering analytes. After the electronic column switching the separation was finished in a 0.3 mm internal diameter capillary and the separated ITP zones were transferred in-line by a spray liquid towards the mass spectrometer. The instrumentation was tested for determination of vitamins in whole blood analysis and separation of tryptic peptides.     

pluronics和卵磷脂混合载药乳化膜的稳定性

单滴法;pluronics;卵磷脂;混合界面吸附膜;乳状液稳定性     

Morphologies of multicompartment micelles formed by triblock copolymers

Multicompartment micelles are desirable for advanced applications such as drug delivery. Recently, core-shell-corona (CSC) and segmented-worm (SW) micelles formed by ABC triblock terpolymers with three mutually immiscible blocks are observed in experiments. We have performed dissipative particle dynamics simulations to study the effects of molecular architecture, block length, and solution concentration on the morphologies of ABC triblock terpolymers. The formation of CSC and SW micelles for linear and miktoarm star ABC terpolymers is confirmed in this work. In addition, we predict that different multicompartment micellar morphologies (e.g., incomplete skin-layered micelles and segmented worms) can be formed by linear copolymer with different arrangements of the three blocks.