Influence of the solvent and the end groups on the morphology of cross-linked amphiphilic poly(1,2-butadiene)-b-poly(ethylene oxide) nanoparticles

The phase diagrams of nanoparticles based on self-assembled amphiphilic poly(1,2-butadiene)-b-poly(ethylene oxide) diblock copolymers (PB-b-PEO) and subsequent intra-micellar cross-linking in methanol and water show that the obtained morphology of the nanoparticles depends on: (i) the block ratio; (ii) the block length; (iii) the solvent; and (iv) the PEO-sided end group. Depending on these parameters, spherical, cylindrical and vesicle-like nanoparticles are synthesized. The PEO-sided end group is found to have an influence on the morphology of the nanoparticles and in addition, it has an impact on the characteristic dimension of the polymeric nanoparticles.     

Preparation of diblock copolymer based on poly(4-n-butyltriphenylamine) via palladium coupling polymerization

A self-condensing monomer 4-(4′-bromophenyl)-4″-n-butyldiphenylamine (1) was synthesized, and successfully converted to poly(4-n-butyltriphenylamine) (PBTPA) by arylamination using palladium catalyst. PBTPAs can be functionalized at both terminals separately by adding an aryl bromide or arylamine derivatives as a terminator, which enabled us to prepare the diblock copolymer PBTPA-block-PEO. Polymer characterization was performed by ¹H NMR, ¹³C NMR, and DSC, which confirmed that the PEO segment was successfully introduced at the terminal of PBTPA. The surface morphology in a thin film of PBTPA-block-PEO was examined by AFM, revealing that a microphase-separated structure or cup-shaped structure with PEO sphere domains formed when the film was spin-cast from 1,1,2,2-tetrachloroethane solutions of different concentrations.     

Clustered assembly of Au nanoparticles from spherical diblock copolymer micelles encapsulating Au nanoparticle

Superstructures composed of diblock copolymer micelles and inorganic nanoparticles are quite interesting because the specific arrangement of inorganic nanoparticles within the micellar structure can reveal interesting opportunities in many field of science. In this perspective, we report a simple method to produce clustered assembly of Au nanoparticles in the micelles in attempt to induce plasmonic coupling among multiple Au nanoparticles in the assembled structures. Here, we utilized polystyrene‐block‐poly(acrylic acid), PS‐PAA, micelles containing single Au nanoparticle in the core (Au@PS‐PAA micelles) as building materials to initiate next‐level assembling process. In particular, the addition of HCl to the solution of Au@PS‐PAA micelles affected the overall equilibrium condition as well as kinetic process in the micellar solution. As a result, individual Au@PS‐PAA micelles could be merged together to form more large micelles with inclusion of multiple nanoparticles in the core, the process of which was accompanied with plasmonic coupling of Au nanoparticles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44693.     

Aggregation behaviour of well defined amphiphilic diblock copolymers with poly(N-isopropylacrylamide) and hydrophobic blocks

Series of amphiphilic diblock copolymers with poly(N-isopropylacrylamide) as a hydrophilic block and a hydrophobic block consisting of either polystyrene or poly(tert-butyl methacrylate) were synthesised using RAFT polymerisations. Differential scanning calorimetry showed the chemically different blocks being phase separated in dry polymers. Light scattering and microcalorimetry studies were performed on aqueous solutions to investigate the phase behavior of the diblock copolymers. By carefully transferring the polymers from an organic solvent to water, either micellar particles or large aggregates were obtained depending on the relative lengths of the blocks. Large aggregates collapsed upon heating, whereas collapse occurred slowly within a broad temperature range in the case of micelle like structures. However, microcalorimetrically the collapse of the PNIPAM chains was observed to take place in all samples, suggesting that the shells of the micellar particles are crowded in a way which hinders the compression of the poly(N-isopropylacrylamide) chains.     

Nanoscale localization of poly(vinylidene fluoride) in the lamellae of thin films of symmetric polystyrene-poly(methyl methacrylate) diblock copolymers

We employed thin film blends of diblock copolymers with functional homopolymers as a simple strategy to incorporate organic functional materials into nanodomains of diblock copolymers without serious synthesis. A blend pair of polystyrene-poly(methyl methacrylate) (PS-PMMA) diblock copolymers and poly(vinylidene fluoride) (PVDF) was selected as a model demonstration because PVDF is a well-known ferroelectric polymer and completely miscible with amorphous PMMA. Thin films of symmetric PS-PMMA copolymers provided the nanometer-sized PMMA lamellae, macroscopically parallel to the substrate, in which PVDF chains were dissolved. Thus, amorphous PVDF chains were effectively confined in the PMMA lamellae of thin film blends. The location of PVDF chains in the PMMA lamellae was investigated by the dependence of the lamellar period on the volume fraction of PVDF, from which we found that PVDF chains were localized in the middle of the PMMA lamellae. After the crystallization of PVDF, however, some of PVDF migrated to the surface of the film and formed small crystallites.     

Fluorescence studies of pyrene-labelled, pH-responsive diblock copolymer micelles in aqueous solution

Fluorescence spectroscopic techniques, and time-resolved anisotropy measurements (TRAMS) in particular, have provided valuable information regarding micelle formation in luminescently labelled pH-responsive diblock copolymers of 2-(diethylamino)ethyl methacrylate (DEA) and 2-(dimethylamino)ethyl methacrylate (DMA). A pyrenyl derivative, located at the DEA block, allowed motion of this site to be monitored via TRAMS in aqueous solution: a significant reduction in the mobility of this label was apparent at concentrations in excess of the critical micelle concentration, CMC, of the diblock copolymer. This is consistent with the labelled DEA block being located in the core of the micelles. At concentrations below the CMC, unimers were detected in solution. The micelle size estimated from TRAMS is approximately half of that determined from dynamic light scattering measurements. This suggests that the chain ends of the block copolymer are not “frozen” into position but that limited motion may occur due to fluidity within the micelle core. This is reasonable given the low T_g of the DEA block. Alternatively, a model is proposed which suggests that the interior of the micelle is a hard sphere, surrounded by flexible, fast-moving corona, which imparts little viscous drag on the core.     

A study of the versatile micropatterns of diblock copolymer micelles: the effect of copolymer concentration, substrate, film thickness and micelles morphology

We report the novel use of polystyrene-block-poly(acrylic acid) (PS-b-PAA) diblock copolymer micelles as the nano-building blocks in fabricating orderly aligned three-dimensional micropatterns with high regularity through a one-step evaporation-induced cracking process. Crack patterns of square, rectangular, stripe-like and mesh-like structures in micron scale were obtained. The effect of the concentration of diblock copolymer, the properties of the substrates, the thickness of the drying layer, and the morphology of the micelles on the regularity of the crack patterns was studied. By regulating the above factors, we achieved micropatterns of various structures. We further developed a cheap, fast, and simple method for fabricating micromolded structures using the crack patterns as templates.     

Crystallization, melting, and morphology of a poly(ethylene oxide) diblock copolymer containing a tablet-like block of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene}

A poly(ethylene oxide) diblock copolymer containing a short block of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PEO-b-PMPCS) has been successfully synthesized via atom transfer radical polymerization (ATRP) method. The number average molecular weights (M_n) of the PEO and PMPCS blocks are 5300 and 2100 g/mol, respectively. Combining the techniques of differential scanning calorimetry (DSC), optical microscopy (OM), wide angle X-ray diffraction (WAXD), and small angle X-ray scattering (SAXS), we have found that the PMPCS blocks, which are tablet-like, can significantly affect the crystallization and melting of the diblock copolymer. The sample studied can form the crystals with a monoclinic crystal structure identical to that of the homo-PEO. The melting temperature (T_m) of the diblock copolymer increases monotonically with crystallization temperature (T_c), which is remarkably similar to the behavior of long period. On the basis of Gibbs-Thomson relationship, the equilibrium T_m of the diblock copolymer is estimated to be 65.4 °C. In a wide undercooling (ΔT) range (14 °C<ΔT<30 °C), the isothermal crystallization leads to square-shaped crystals. The PEO-b-PMPCS crystallization exhibits a regime I→II transition at ΔT of 19 °C. The PEO blocks are non-integral folded (NIF) in the crystals, and the PMPCS blocks rejected to lamellar fold surfaces prevent the NIF PEO crystals from transforming to integral folded (IF) ones. Furthermore, the PMPCS tablets may adjust their neighboring positions up or down with respect to the lamellar surface normal, forming more than one PMPCS layer to accompany the increase in the PEO fold length with increasing T_c.     

Influence of diblock copolymer on the morphology and properties of polystyrene/poly(dimethylsiloxane) blends

Blends of polystyrene (PS) and poly(dimethylsiloxane) (PDMS), with and without diblock copolymers (PS‐b‐PDMS), were prepared by melt mixing. The melt rheology behavior of the blends was studied with a capillary rheometer. The morphology of the blends was examined with scanning electron microscopy. The miscibility of the blends was studied with differential scanning calorimetry. The morphology of PS/PDMS blends was modified by the addition of PS‐b‐PDMS copolymers and investigated as a function of the molar mass of the diblock copolymers, viscosity ratios and the processing conditions. As investigated, the observed morphology of the melt‐blended PS/PDMS pair unambiguously supported the interfacial activity of the diblock copolymers. When a few percent of the diblock copolymers blended together with the PS and PDMS homopolymers, the phase size was reduced and the phase dispersion was firmly stabilized against coalescence. The compatibilizing efficiency of the copolymers was strongly dependent on its molar mass. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2747–2757, 2004     

Electrodeposition of Co-Pt continuous films and nanowires within diblock copolymer template

Patterned media for future ultrahigh-density magnetic data storage can be prepared by electrodeposition into ordered arrays of nanostructured templates. Diblock copolymer templates have been proposed as a promising alternative to alumina templates. They possess smaller feature sizes than alumina and thereby allow for higher storage densities. Templates with pore diameters of ∼8 nm have been fabricated by dip-coating a conducting substrate into a solution of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and 2-(4′-hydroxybenzeneazo) benzoic acid (HABA). A vapor annealing step was interposed for better ordering. The pores are opened by dissolving the HABA from the supramolecular assembly and afterwards filled by electrodeposition.Fe-Pt and Co-Pt alloys are the materials of choice for filling the pores due to their hard magnetic properties like high coercivity and anisotropy. Co-rich Co₈₀Pt₂₀ was chosen for this study because it does not require post annealing as in the case of ordered L1₀ CoPt or FePt. Continuous films have been deposited in order to identify the optimum deposition conditions and the influence of deposition current density on chemical composition, growth morphology, and structural and magnetic properties has been studied systematically. The first results on templates electrochemically filled with Co-Pt are presented together with an analysis of their magnetic properties.     

Synthesis of poly(vinyl acetate) containing diblock copolymer by DPE method

Diblock copolymer poly(methyl methacrylate)‐b‐poly(vinyl acetate) (PMMA‐b‐PVAc) was prepared by 1,1‐diphenylethene (DPE) method. First, free‐radical polymerization of methyl methacrylate was carried out with AIBN as initiator in the presence of DPE, giving a DPE containing PMMA precursor with controlled molecular weight. Second, vinyl acetate was polymerized in the presence of the PMMA precursor and AIBN, and PMMA‐b‐PVAc diblock copolymer with controlled molecular weight was obtained. The formation of PMMA‐b‐PVAc was confirmed by ¹H NMR spectrum. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to detect the self‐assembly behavior of the diblock polymer in methanol. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The vesicle formation in a binary amphiphilic diblock copolymer/homopolymer solution

The formation of vesicles in a binary blend of an amphiphilic diblock copolymer AB/homopolymer C was studied in a dilute solution using the real space two-dimensional self-consistent field theory (SCFT). Special attention was played to the role played by the homopolymer C in controlling the vesicle formation. In the simulations, it was found that as the averaged volume fraction of homopolymer C was decreased while keeping the total averaged volume fraction of block copolymer AB and homopolymer C unchanged, there was a morphological transition from the bilayer vesicles to rod-like/circle-like micelles. The compound vesicle structure was observed in the simulations. When the averaged volume fraction of block copolymer AB was further increased while the total averaged volume fraction of AB and C remained unchanged, the compound vesicle structure became less favored entropically than the unilamellar vesicle structure. The effect of the degree of polymerization of the homopolymer C on the vesicle formation of the amphiphilic system was examined. By reducing the degree of polymerization of the homopolymer C to unity, the component C became a small solvent molecule immiscible with the bulk solvent. It was found that the small solvent C exerted no influence on the morphological stability of the vesicles.     

Size-controllable gold nanoparticles stabilized by PDEAEMA-based double hydrophilic graft copolymer

Poly(N-isopropylacrylamide)-b-[poly(ethyl acrylate)-g-poly(2-(diethylamino)ethyl methacrylate)] (PNIPAM-b-(PEA-g-PDEAEMA)) double hydrophilic graft copolymers were employed to prepare stable colloidal gold nanoparticles in situ with controllable size in aqueous media without any external reducing agent. PDEAEMA side chains served as reduction agent and stabilizer and PNIPAM segment acted as a hydrated layer to enhance the stability of gold nanoparticles. These gold nanoparticles showed a remarkable colloidal stability without any observable flocculation or aggregation for at least 2 months and they were characterized by UV-vis, XRD, TEM and AFM in detail. The size of gold nanoparticles can be tuned by adjusting the length of PDEAEMA side chains and the molar ratio of [DEAEMA]/[AuCl₄⁻]. Both the increasing of the length of PDEAEMA side chains and the decreasing of [DEAEMA]/[AuCl₄⁻] molar ratio resulted in the fall of size.     

Nanostructures from photo-cross-linked amphiphilic poly(ethylene oxide)-b-alkyl diblock copolymers

Poly(ethylene oxide) monomethylether was functionalized by alkyl chains of various lengths (l=10-19 methylene groups) bearing a polymerizable methacrylate moiety. Each synthesis step on the polymer gives quantitative functionalization rates. The self-assembly of the amphiphilic polymers in water was studied by light scattering for various end-groups. Sterical and polar effects were shown to influence the micellization step. The cores of the micelles formed by PEO-C_l-methacrylate were irreversibly cross-linked by UV irradiation. Star polymers that are stable under dilution in good solvent are obtained after 1-min irradiation. The hydrodynamic radius and the molar mass of the nanoparticles depend on the amount of photoinitiator introduced in the cores.     

Double-responsive core-shell-corona micelles from self-assembly of diblock copolymer of poly(t-butyl acrylate-co-acrylic acid)-b-poly(N-isopropylacrylamide)

Self-assembly of poly(t-butyl acrylate-co-acrylic acid)-b-poly(N-isopropylacrylamide) [P(tBA-co-AA)-b-PNIPAM], which was obtained from part hydrolysis of PtBA-b-PNIPAM synthesized by sequential atom transfer radical polymerization (ATRP) was studied. Thermo- and pH-responsive core-shell-corona (CSC) micelles with different structures were formed from (PtBA-co-PAA)-b-PNIPAM in aqueous solution. At pH 5.8 and 25 °C, the block copolymer self-assembled into spherical core-shell micelles with hydrophobic PtBA segments as the core, hydrophilic PAA/PNIPAM segments as the mixed shell. Increasing temperatures, core-shell micelles converted into CSC micelles with PtBA as the core, collapsed PNIPAM as the shell and soluble PAA as the corona. Moreover, decreasing pH at 25 °C, PAA chains collapsed onto the core resulting in CSC micelles with PtBA as the core, PAA as the shell and PNIPAM as the corona.     

Crystallization-induced order in polystyrene-poly(ethylene oxide) metallo-supramolecular diblock copolymer

The solid-state morphology of polystyrene-poly(ethylene oxide) metallo-supramolecular diblock copolymer PS₂₀-[Ru]-PEO₇₀, has been investigated by small-and wide-angle X-ray scattering and atomic force microscopy. Above the melting point of PEO the metal-ligand complexes and their associated counter ions are known to form aggregates within the still disordered polymer matrix of PS and PEO. Crystallization of PEO induces microphase separation between the PS and the PEO blocks. In addition, the metal-ligand aggregates are forced out of the crystalline PEO part and subsequently order at the interface in the amorphous PS block into a (short-range) square lattice.     

Synthesis, reactivity, and pH-responsive assembly of new double hydrophilic block copolymers of carboxymethyldextran and poly(ethylene glycol)

Double hydrophilic block copolymers (DHBC) were prepared by end-to-end coupling of two biocompatible water-soluble homopolymers: the polysaccharide dextran (M_w 8300 or 14,700 g mol⁻¹) and ω-amino poly(ethylene glycol) (PEG-NH₂, M_w 3000 or 7000 g mol⁻¹). The synthesis involved, first, specific oxidation of the dextran terminal aldehyde group and, second, covalent linkage of PEG-NH₂ via a lactone aminolysis reaction. The diblock copolymers dextran-PEG (DEX-PEG) were converted in high yield into the corresponding carboxymethyldextran-PEG (CMD-PEG) derivatives with control over the degree of substitution, from 30 to 85 mol% CH₂COOH groups per glucopyranosyl unit. Further modifications of a CMD-PEG block copolymer led to N-(2-aminoethyl)carbamidomethyldextran-PEG yielding a pair of oppositely-charged DHBC of identical charge density, chain length, and neutral block/charged block content. The properties of CMD-PEG in aqueous solutions were studied by static and dynamic light scattering as a function of solution pH, providing evidence of the pH-sensitive assembly of the copolymers driven by inter- and intra-chain hydrogen-bond formation.     

Cationic fluorene-thiophene diblock copolymers: Aggregation behaviour in methanol/water and its relation to thin film structures

Optical spectroscopy and photophysical measurements on cationic fluorene-thiophene diblock copolymers in solution show distinct properties for the two blocks, with clear indications of singlet exciton migration from the polyfluorene to polythiophene blocks. Electrical conductivity measurements and small angle X-ray scattering studies show that different aggregates are formed in water and methanol. This may be associated both with different solubilities of the two blocks and with the effect of solvent on the degree of dissociation of the ionic part. Atomic force microscopy (AFM) shows that different nanostructures are deposited from the two solvents, with large, vesicular structures deposited on mica from methanolic solution. Aggregation behavior is also found to be modulated, and to lead to more rigid thiophene blocks, by addition of the oppositely charged surfactant sodium dodecylsulfate.     

TEM characterization of diblock copolymer templated iron oxide nanoparticles: Bulk solution and thin film surface doping approach

The morphology of a novel diblock copolymer, poly(norbornene methanol)-b-poly(norbornene dicarboxylic acid), was investigated before and after metal oxide doping by transmission electron microscopy (TEM) using a novel iodine vapor staining method to image the undoped polymer. A lamellar morphology was observed by TEM after staining the undoped diblock copolymer with iodine vapor. Thin film surface doping resulted in a confinement of the iron oxide nanoparticles within the lamellar domains. Spherical nanoparticle aggregates were observed through a bulk solution doping method. It was observed that the particles were templated by the underlying lamellar structure of the copolymer when the thin film surface doping method was used.     

Stabilization of nano-TiO2 aqueous dispersions with poly(ethylene glycol)-b-poly(4-vinyl pyridine) block copolymer and their incorporation in photocatalytic acrylic varnishes

In this work, TiO₂ nanoparticles were dispersed and stabilized in water using a novel type of dispersant based on tailor-made amphiphilic block copolymers of poly(ethylene glycol)-block-poly(4-vinyl pyridine) (mPEG-b-P4VP) prepared by atom transfer radical polymerization (ATRP). The performance of this new block copolymer as dispersant was compared to a polyelectrolyte dispersant commonly used for TiO₂, sodium salt of polyacrylic acid (Na-PAA). The effect of dispersion technique and type and amount of dispersant on deagglomeration and stability of the TiO₂ aqueous suspensions were studied. After incorporation in a standard waterborne acrylic varnish formulation, dry film transparency, photocatalytic activity, and nanoparticle cluster size were also evaluated. The results show that mPEG-b-P4VP copolymer with appropriate block lengths can have a better performance than Na-PAA in terms of aqueous dispersion stabilization and cluster size reduction in the acrylic matrix. This translates into higher film transparency and photocatalytic performance.