Star-like Block Research Articles

Comparison of the Surface Dilational Properties of Block Copolymers and Sodium Oleate Using the Oscillating Bubble Method

The surface dilational modulus of the star-like block copolymer AP432 and linear block copolymer L64 was studied using the oscillating bubble method at an accessible frequency range of 0.05 to 2 Hz, which was compared with anionic surfactant sodium oleate (C17H33COONa) and the influence of inorganic salt NaNO3 on the surface dilational modulus of AP432 and L64 was also studied. The results indicate that for AP432 and L64 the dilational modulus varies slightly, just decrease gradually with concentrations increasing and never reaches high values with the dilational frequency increasing, but the dilational modulus of C17H33COONa increases gradually with the increase of dilational frequency and pass through the maximum values with increasing concentration. The properties of AP432, L64, and C17H33COONa at the air/water interface were also observed by surface tension measurement. Based on these experimental results, a simple possible adsorption model of these molecules at air/water interface is proposed.

Synthesis, Characterization, and Properties of Starlike Poly(n-butyl acrylate)-b-poly(methyl methacrylate) Block Copolymers

A series of 10- and 20-arm starlike block copolymers containing inner soft poly(n-butyl acrylate) (PBA) block and outer hard poly(methyl methacrylate) (PMMA) block were synthesized by atom transfer radical polymerization (ATRP). Short macroinitiators for preparation of starlike copolymers, poly(2-bromoisobutyryloxyethyl acrylate) (PBiBEA) with degree of polymerization DP = 10 and 20, was prepared by ATRP of trimethylsilyloxyethyl acrylate (HEATMS) and subsequently esterified. Partial star coupling during the star extension with PMMA blocks was observed, and the coupling increased with increasing number of arms and arm length. Phase-separated morphologies of cylindrical hard PMMA block domains arranged in the soft PBA matrix were observed by atomic force microscopy and small-angle X-ray scattering. The mechanical and thermal properties of the copolymers were also thoroughly characterized, and their thermoplastic elastomer behavior was studied. Tensile strength of the starlike copolymers was considerably higher compared to linear and three-arm stars with similar compositions.

Amphiphilic Polystyrene-b-poly(p-hydroxystyrene-g-ethylene oxide) Block−Graft Copolymers via a Combination of Conventional and Metal-Free Anionic Polymerization

This work presents the synthesis of polystyrene-block-poly(p-hydroxystyrene-graft-ethylene oxide), PS-b-(PHOS-g-PEO), amphiphilic block−graft copolymers. The backbone diblock copolymers (PS-b-PHOS) were prepared by lithium-based anionic polymerization, followed by postpolymerization acid hydrolysis of the poly(p-tert-butoxystyrene), PtBOS, precursor block. The PEO side chains were synthesized by metal-free anionic ring-opening polymerization of ethylene oxide (EO), using the phosphazene base (t-BuP4) and the phenolic hydroxyl groups (PhOH) in the backbones as the complex multifunctional initiating system. In all cases, starlike block−graft copolymers with high molecular weights and low polydispersities were synthesized. Well-controlled polymerization was achieved even with the molar ratio of t-BuP4 to PhOH being equal to 0.2. Dynamic and static light scattering and fluorescence spectroscopy studies were carried out to investigate the solution behavior of the amphiphilic block−graft copolymers, including t...

Dispersing Carbon Nanotubes in Aqueous Solutions by a Starlike Block Copolymer

The ability of dispersing carbon nanotubes (CNTs) in aqueous solutions by a starlike amphiphilic block copolymer with PPO−PEO segments (AP432) was investigated in detail. For comparison, two commercially available linear amphiphilic block copolymers, Pluronics L64 and F127, were also selected. It was found that AP432 and F127 can get good CNT dispersions, while L64 was proved to be unable to disperse CNTs. AP432 with five branches could disperse CNTs efficiently at much lower concentrations compared with the linear F127, although it has a smaller molecular weight and shorter terminal EO groups. This indicated clearly that, once branched, copolymers would get a much better ability to disperse CNTs. Increasing concentration of AP432 or F127 would disperse more CNTs, but at high copolymer concentrations the aggregation of dispersed CNTs was observed, which may be related to the free micelles formed by AP432 or F127 around CNTs. Other influencing factors such as the mass ratio of CNTs to copolymers and sonication time and strength were also discussed. From the molecular dynamics simulation results, it can be found that copolymers with five branches can gain better steric repulsions between adjacent CNTs, which is consistent with the experimental results.

Interaction between star-like block copolymer and sodium oleate in aqueous solutions

The interaction between a star-like block copolymer (AP432) and an anionic surfactant sodium oleate (C 17H 33COONa) was investigated in detail both at the air/water interface and in bulk aqueous solutions. The results of surface tension show that AP432 and C 17H 33COONa could form mixed micelles. The results obtained from the oscillating barrier measurements at low dilational frequencies (0.01–0.1 Hz) reveal that the maximum values of the dilational modulus for AP432/C 17H 33COONa mixed system moved to lower concentrations compared to those of single AP432 or C 17H 33COONa aqueous solutions. Steady-state fluorescence measurements indicate that after mixing, the I 1/ I 3 values of AP432/C 17H 33COONa system above the cmc are higher than those of single AP432 or C 17H 33COONa solutions. This is probably due to a looser pack of the molecules within micelles for the AP432/C 17H 33COONa mixture, which is also consistent with the results obtained from TEM observations. For comparison, the interaction between a commercially available linear PEO–PPO–PEO copolymer (Pluronics L64) and C 17H 33COONa was also studied. All experimental results give clear evidence that the interaction between L64 and C 17H 33COONa is different from that between AP432 and C 17H 33COONa.

Syntheses and characterization of statistical and block fluorinated copolymers with linear and star-like architectures via ATRP

The synthesis of a fluorinated macroinitiator for copper-catalyzed atom transfer radical polymerization (ATRP) is reported, as well as its use for the controlled living polymerization of poly(propylene glycol) methacrylate (PPGM) in MEK at 80 °C. The ATRP system used was efficient for polymerization of the functionalized monomer and the molecular weight of the polymer estimated by NMR spectroscopy was in close agreement with the theoretical molecular weight, as expected for controlled processes. The statistical copolymerization of PPGM or methyl ether poly(ethylene glycol) methacrylate (MPEGMA) with a perfluoroalkyl ethyl methacrylate by copper-mediated ATRP was also investigated and led to copolymers with essentially random incorporation of monomers. The syntheses and characterization of star-like homopolymers of MPEGMA or the fluorinated monomer via ATRP are also reported, as well as an amphiphilic star-like block copolymer containing ethyleneglycol units as the core and fluorinated moieties in the shell. The micellar behavior of this copolymer was investigated as a function of the external environment.

Synthesis of Stars and Starlike Block Copolymers from a Trialkoxyamine Used as Initiator

This study investigates the efficiency of a novel trifunctional alkoxyamine (1) based on N-tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide (SG1) (2) as initiator for the controlled radical polymerization of styrene (S) and n-butyl acrylate (nBuA). Three factors, namely the concentration of SG1 initially introduced in excess, the monomer conversion, andin the specific case of PS samplesthe monomer autopolymerization, were found to control the quality of the star samples obtained. Well-defined T-(PBuA-b-PS)3 star block copolymers could also be synthesized by sequential copolymerization using the same trifunctional initiator.

Starlike Block Copolymers with Amphiphilic Arms as Models for Unimolecular Micelles

Starlike Block Copolymers with Amphiphilic Arms as Models for Unimolecular Micelles

Characterization of Polyisoprene-b-Poly(methyl methacrylate) Diblock Copolymer Micelles in Acetonitrile

In acetonitrile, polyisoprene-b-poly(methyl methacrylate) (PI−PMMA) diblock copolymers form starlike micelles with a dense core of the insoluble PI blocks and a soft solvent-swollen corona of the soluble PMMA blocks. Static and dynamic light scattering experiments in combination with viscosity measurements show that these micelles behave hydrodynamically as hard spheres. The block copolymers are labeled at the block junction, with a single fluorescent dye, either a donor chromophore (phenanthrene) or an acceptor chromophore (anthracene). These dyes are confined to the interface during self-assembly. Fluorescence energy-transfer experiments on molecularly mixed micelles of donor- and acceptor-labeled copolymers provide a core radius of 7.6 ± 0.8 nm and a number-average aggregation number ( ) of 98 ± 22 under the assumption that the energy transfer takes place on a surface of a sphere. Simulations in terms of a Helfand−Tagami junction distribution profile confirm that the core−corona interface of the PI−PMMA micelles is thin (ca. 0.9 nm) and that almost all of the energy transfer occurs within a narrow interfacial region. From the static light scattering measurements of the mixed micelles a weight-average aggregation number ( ) of 127 ± 6 is obtained. The ratio / = 1.3 agrees with size polydispersity of the micelles obtained from the analysis of dynamic light scattering data. The experimental corona thicknesses are in good agreement with those calculated from expressions describing starlike block copolymer micelles. (Less)

Coronal Structure of Star-Like Block Ionomer Micelles: An Investigation by Small-Angle Neutron Scattering

The coronal structure of starlike block ionomer micelles has been probed directly by small-angle neutron scattering (SANS), using specific contrast labeling of different regions of the corona. Solutions of PS-b-dPS-b-PS-b-PACs starlike block ionomer micelles in toluene are studied; contrast is provided by perdeuterated polystyrene labels situated at different distances from the ionic core. For deuterated labels situated at 390 PS units from the core, the scattered intensity is found to scale as I ∼ q-1.7 at intermediate q, suggesting a semidilute environment for the labels and local swollen coil behavior. For labels 180 PS units from the core, steric perturbations are more extensive than those found under semidilute conditions, such that single chain scaling is not observed at any length scale; scattered intensity is found to scale as I ∼ q-1.3 at intermediate q. The stiffness of coronal chains next to the core is even greater, as indicated by I ∼ q-1.0 scaling for dPS labels attached directly to the ioni...