Functionalization of shaped polymeric nanoobjects via bulk co-self-assembling gelable block copolymers with silane coupling agents

Hairy polymer nanoobjects (PNOs) of different shapes can be easily obtained by cross-linking the discontinuous microphases of bulk block copolymers followed by dispersing in a solvent. Herein we report a general approach to functionalize the shaped PNOs by bulk microphase separation of poly(3-(triethoxysilyl)propyl methacrylate)-block-polystyrene (PTEPM-b-PS) copolymers in the presence of functional silane coupling agents. The silanes like (3-mercaptopropyl)trimethoxysilane and (3-chloropropyl)trimethoxysilane were enriched into the PTEPM discontinuous microdomains selectively. The microphase structures were characterized by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) of microtomed slices. For the PTEPM₇₈-b-PS₃₄₈ which had a lamellar structure, its blending mixtures with MMS and CMS whose content reached up to 50 wt% still remained as a lamellar structure. When small amount of MMS or CMS was added, the PTEPM₇₁-b-PS₇₈₀ as hexagonally packed cylinders remained its structure. However, the morphology changed into lamellae at higher content of the silanes. For PTEPM₄₆-b-PS₁₆₆₉, its spherical structure remained but the size distribution became broad gradually with increase of silanes. By inducing gelation and then dispersing in a good solvent of PS phases, hairy PNOs having lamellar, cylindrical or spherical shape with their cores being functionalized with the groups from co-gelated silanes were obtained.     

pH responsive nanoplates from bulk self-assembly of UV-crosslinkable poly(tert-butyl acrylate)-block-poly(2-cinnamoyloxyethyl methacrylate)

We report the dispersed nanoplates prepared from bulk self-assembly of diblock copolymer poly(tert-butyl acrylate)-block-poly(2-cinnamoyloxyethyl methacrylate) (PtBA-b-PCEMA) with PCEMA as a UV-crosslinkable segment and PtBA as a hydrolysable segment. PtBA-b-P(HEMA-TMS) was synthesized through a two step ATRP and functionalized to PtBA-b-PCEMA. The diblock copolymer with 55.7 % weight ratio of PCEMA bulk was assembled into lamellar morphology and characterized by small-angle X-ray scattering (SAXS). After UV-crosslinking, the dispersed nanoplates were prepared by dispersing the crosslinked bulk self-assembly in a good solvent of the PtBA segment and characterized by transmission electron microscopy (TEM). The dispersed nanoplates have crosslinked PCEMA as the cores and the solubilized PtBA as the coronas. After hydrolysis of the PtBA segment into poly(acrylic acid) (PAA), the crosslinked nanoobjects could be dispersed in water and showed reversible pH-responsibility.     

Selective distribution of interacting magnetic nanoparticles into block copolymer domains based on the facile inversion of micelles

We demonstrate a simple methodology to incorporate interacting magnetic nanoparticles (mNPs) into cylinder forming block copolymer templates. Poly(styrene-block-isoprene) (PS-b-PI) with PI cylinders and poly(styrene-block-4vinylpyridine) (PS-b-P4VP) with PS cylinders were used as the block copolymer templates and γ-Fe₂O₃ NPs coated with oleic acids were pre-synthesized for the interacting mNPs. Regardless of the template block copolymers, the selective location of mNPs and the size of mNP aggregates are clearly altered by changing casting solvents. When good solvents for both blocks were used as casting solvents, mNPs are readily aggregated during the solvent evaporation. In contrast, under selective casting solvents for the minor blocks, the mNPs were selectively trapped into the cylinder domains through the facile inversion of micelles during solvent evaporation. The interplay between mNPs and block copolymers was also tested with different molecular weights of block copolymers.     

Synthesis of poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene triblock copolymers by two-step atom transfer radical polymerization

The synthesis of ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) via atom transfer radical polymerization (ATRP) is reported. First, a PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of halo-terminated poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers under ATRP conditions. Then PEO-b-PMMA-b-PS triblock copolymer was synthesized by ATRP of styrene using PEO-b-PMMA as a macroinitiator. The structures and molecular characteristics of the PEO-b-PMMA-b-PS triblock copolymers were studied by FT-IR, GPC and ¹H NMR.     

Exfoliation of organoclay nanocomposites based on polystyrene-block-polyisoprene-block-poly(2-vinylpyridine) copolymer: Solution blending versus melt blending

Exfoliated nanocomposites based on polystyrene-block-polyisoprene-block-poly(2-vinylpyridine) (SI2VP triblock) copolymer were prepared by solution blending and melt blending. Their dispersion characteristics were investigated using transmission electron microscopy, X-ray diffraction, and small-angle X-ray scattering (SAXS). For the study, SI2VP triblock copolymers with varying amounts of poly(2-vinylpyridine) (P2VP) block (3, 5, and 13 wt%) and different molecular weights were synthesized by sequential anionic polymerization. In the preparation of nanocomposites, four different commercial organoclays, treated with a surfactant having quaternary ammonium salt, were employed. It was found from SAXS that the microdomain structure of an SI2VP triblock copolymer having 13 wt% P2VP block (SI2VP-13) transformed from core-shell cylinders into lamellae when it was mixed with an organoclay. It was found further that the solution-blended nanocomposites based on a homogeneous SI2VP triblock copolymer having 5 wt% P2VP block (SI2VP-5) gave rise to an exfoliated morphology, irrespective of the differences in chemical structure of the surfactant residing at the surface of the organoclays, which is attributable to the presence of ion-dipole interactions between the positively charged N⁺ ion in the surfactant residing at the surface of the organoclay and the pyridine rings in the P2VP block of SI2VP-5 and SI2VP-13, respectively. Both solution- and melt-blended nanocomposites based on microphase-separated SI2VP-13 having an order-disorder transition temperature (T_ODT) of approximately 210 °C also gave rise to exfoliated morphology. However, melt-blended nanocomposite based on a high-molecular-weight SI2VP triblock copolymer having a very high T_ODT (estimated to be about 360 °C), which was much higher than the melt blending temperature employed (200 °C), gave rise to very poor dispersion of the aggregates of organoclay. It is concluded that the T_ODT of a block copolymer plays a significant role in determining the dispersion characteristics of organoclay nanocomposites prepared by melt blending.     

Corona structure on demand: Tailor-made surface compartmentalization in worm-like micelles via random cocrystallization

We present a straightforward approach to well-defined 1D patchy particles utilizing crystallization-induced self-assembly. A polystyrene-block-polyethylene-block-poly(methyl methacrylate) (PS-b-PE-b-PMMA) triblock terpolymer is cocrystallized in a random fashion with a corresponding polystyrene-block-polyethylene-block-polystyrene (PS-b-PE-b-PS) triblock copolymer to yield worm-like crystalline-core micelles (wCCMs). Here, the corona composition (PMMA/PS fraction) can be easily adjusted via the amount of PS-b-PE-b-PMMA triblock terpolymer in the mixture and opens an easy access to wCCMs with tailor-made corona structures. Depending on the PMMA fraction, wCCMs with a mixed corona, spherical PMMA patches embedded in a continuous PS corona, as well as alternating PS and PMMA patches of almost equal size can be realized. Micelles prepared by cocrystallization show the same corona structure as those prepared from neat triblock terpolymers at identical corona composition. Thus, within a certain regime of desired corona compositions the laborious synthesis of new triblock terpolymers for every composition can be circumvented.     

Suspension polymerization stabilized by triblock copolymer with CdS nanoparticles

In this paper, a new method to prepare polymer colloid particles stabilized by triblock copolymer with CdS nanoparticles was described. Poly(ethylene glycol-block-styrene-block-2-(dimethylamino) ethyl methacrylate) (PEG-b-PS-b-PDMAEMA) triblock copolymer was synthesized by sequential ATRP method. Micelles with CdS nanoparticles in the corona were prepared by “in situ” reaction of hydrogen sulfide with cadmium ion clusters in the corona of the micelles. The size of the CdS nanoparticles is affected by molar ratio of DMAEMA to cadmium ions and polymer concentration in the solution. When introduced into o/w emulsion the micelles reassemble on the surface of styrene oil droplets. PS colloid particles stabilized by triblock copolymer with CdS nanoparticles were achieved by suspension polymerization. TEM image indicates that CdS nanoparticles locate at the surface of the PS colloid particles.     

Self-organized thermosets involving epoxy and poly(?-caprolactone)-block-poly(ethylene-co-ethylethylene)-block-poly(?-caprolactone) amphiphilic triblock copolymer

In this work, we investigated the self-assembly behavior of poly(?-caprolactone)-block-poly(ethylene-co-ethylethylene)-block-poly(?-caprolactone) (PCL-b-PEEE-b-PCL) triblock copolymer in epoxy thermosets. The PCL-b-PEEE-b-PCL triblock copolymer was synthesized via the ring-opening polymerization of ?-caprolactone with a hydroxyl-terminated poly(ethylene-co-ethylethylene) as the macromolecular initiator. The hydroxyl-terminated poly(ethylene-co-ethylethylene) was prepared with the hydrogenation reaction of a hydroxyl-terminated polybutadiene. The triblock copolymer was incorporated into the precursors of epoxy to obtain the nanostructured thermosets. It was found that the self-organized nanophases were formed in the mixture before curing reaction and the nanostructures can be further fixed via curing reaction. The self-assembly behavior of the triblock copolymer in epoxy thermosets was investigated by means of atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and dynamic mechanical thermal analysis (DMTA). Differential scanning calorimetry (DSC) shows that the formation of the self-organized nanophase in the thermosets caused that a part of poly(?-caprolactone) subchains were demixed from epoxy matrix with the occurrence of curing reaction; the fractions of demixed PCL blocks were estimated according to the T_g-composition relation of the model binary blends of epoxy and PCL.     

Synthesis of amphiphilic triblock copolymers and application for morphology control of calcium carbonate crystals

A series of amphiphilic triblock copolymers poly(ethylene glycol)-block-poly(acrylic acid)-block-poly(n-butyl acrylate) (PEG-b-PAA-b-PnBA) differing only in the relative block lengths were synthesized by the acid-catalyzed elimination of the tert-butyl groups from poly(ethylene glycol)-block-poly(tert-butyl acrylate)-block-poly(n-butyl acrylate) (PEG-b-PtBA-b-PnBA), which was synthesized by atom-transfer radical polymerization (ATRP). The degree of polymerization, molecular weight and percentage of hydrolysis of the product PEG-b-PAA-b-PnBA were studied by gel permeation chromatography (GPC), NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF-MS). Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to study the aggregation states of copolymers in water solution. The radii of the copolymer micelles shrink as Ca²⁺ is introduced into the solutions. The crystallization behaviors of calcium carbonate controlled by copolymer 1 (PEG₁₁₂-b-PAA₈₆-b-PnBA₆₀) and copolymer 2 (PEG₁₁₂-b-PAA₄₀-b-PnBA₇₂) differing mainly in the length of PAA block were systematically studied. It was found that the crystallization products are composed of calcite and vaterite, and the ratio of vaterite to calcite increases with increasing the concentration of copolymer 1. For copolymer 2, however, only calcite is obtained at all the concentration range investigated in this work.     

Thermoresponsive core-shell-corona micelles of poly(ethyleneglycol)-b-poly(N-isopropylacrylamide)-b-polystyrene

Core-shell-corona micelles with a thermoresponsive shell self-assembled by triblock copolymer of poly(ethyleneglycol)-b-poly(N-isopropylacrylamide)-b-polystyrene (PEG₄₅-b-PNIPAM₁₆₈-b-PS₄₆) are studied by ¹H NMR, light scattering and atomic force microscopy. The thermoresponsive triblock copolymer, which has a relatively short hydrophobic PS block, can disperse in water at room temperature to form core-shell-corona micelles with the hydrophobic PS block as core, the thermoresponsive PNIPAM block as shell and the hydrophilic PEG block as corona. At temperature above lower critical solution temperature (LCST) of the PNIPAM block, the PNIPAM chains gradually collapse on the PS core to shrink the size and change the structure of the resultant core-shell-corona micelles with temperature increasing. It is found that there possibly exists an interface between the PNIPAM shell and PEG corona of the core-shell-corona micelles at temperature above LCST of the PNIPAM block.     

Synthesis and characterization of polystyrene/poly(4‐vinylpyridine) triblock copolymers by reversible addition–fragmentation chain transfer polymerization and their self‐assembled aggregates in water

Reversible addition–fragmentation chain transfer polymerization (RAFT) was developed for the controlled preparation of polystyrene (PS)/poly(4‐vinylpyridine) (P4VP) triblock copolymers. First, PS and P4VP homopolymers were prepared using dibenzyl trithiocarbonate as the chain transfer agent (CTA). Then, PS‐b‐P4VP‐b‐PS and P4VP‐b‐PS‐b‐P4VP triblock copolymers were synthesized using as macro‐CTA the obtained homopolymers PS and P4VP, respectively. The synthesized polymers had relatively narrower molecular weight distributions (M_w/M_n < 1.25), and the polymerization was controlled/living. Furthermore, the polymerization rate appeared to be lower when styrene was polymerized using P4VP as the macro‐CTA, compared with polymerizing 4‐vinylpyridine using PS as the macro‐CTA. This was attributed to the different transfer constants of the P4VP and PS macro‐CTAs to the styrene and the 4‐vinylpyridine, respectively. The aggregates of the triblock copolymers with different compositions and chain architectures in water also were investigated, and the results are presented. Reducing the P4VP block length and keeping the PS block constant favored the formation of rod aggregates. Moreover, the chain architecture in which the P4VP block was in the middle of the copolymer chain was rather favorable to the rod assembly because of the entropic penalty associated with the looping of the middle‐block P4VP to form the aggregate corona and tailing of the end‐block PS into the core of the aggregates. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1017–1025, 2003     

Preparation,characterization, and thermal properties of polystyrene‐block‐quaternized poly(4‐vinylpyridine)/Montmorillonite nanocomposites

Polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) was synthesized by two steps of reversible addition‐fragmentation transfer (RAFT) polymerization of styrene (St) and 4‐vinylpyridine (4VP) successively. After P4VP block was quaternized with CH₃I, PS‐b‐quaternized P4VP/montmorillonite (PS‐b‐QP4VP/MMT) nanocomposites were prepared by cationic exchange reactions of quaternary ammonium ion in the PS‐b‐QP4VP with ions in MMT. The results obtained from X‐ray diffraction (XRD) and transmission electron microscopy (TEM) images demonstrate that the block copolymer/MMT nanocomposites are of intercalated and exfoliated structures, and also a small amount of silicates' layers remained in the original structure; differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) results show that the nanocomposites displayed higher glass transition temperature (T_g) and higher thermal stability than that of the corresponding copolymers. The blending of PS‐b‐QP4VP/MMT with commercial PS makes MMT to be further separated, and the MMT was homogeneously dispersed in the polymer matrix. The enhancement of thermal stability of PS/PS‐b‐QP4VP/MMT is about 20°C in comparison with commercial PS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1950–1958, 2006     

A new approach in the study of tethered diblock copolymer surface morphology and its tethering density dependence

A poly(l-lactic acid)-block-polystyrene-block-poly(methyl methacrylate) (PLLA-b-PS-b-PMMA) triblock copolymer was synthesized with a crystalline PLLA end block. Single crystals of this triblock copolymer grown in dilute solution could generate uniformly tethered diblock copolymer brushes, PS-b-PMMA, on the PLLA single crystal substrate. The diblock copolymer brushes exhibited responsive, characteristic surface structures after solvent treatment depending upon the quality of the solvent in relation to each block. The chemical compositions of these surface structures were detected via the surface enhanced Raman scattering technique. Using atomic force microscopy, the physical morphologies of these surface structures were identified as micelles in cyclohexane and “onion”-like morphologies in 2-methoxyethanol, especially when the PS-b-PMMA tethered chains were at low tethering density.     

Water-induced morphology evolution of block copolymer micellar thin films

Morphology evolution of diblock copolymer polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) micellar thin film in the presence of water was investigated. Surface holes with nanoscale cavities in hexagonal order could be induced by water treatment for certain periods. The nanoscale surface cavities could be transformed into isolated nanospheres in a dry environment or back to protruding densely packed spheres by toluene (a selective solvent for PS coronae) treatment. The morphology evolution of micellar thin film strongly depended on the slow evaporation of toluene solvent, the swelling of P4VP cores in the humid environment, and the subsequent movement of PS chains induced by air and toluene. The incompatibility between solvent and block, and that between the unlike blocks also played an important role in the morphology evolution.     

A facile way to prepare crystalline platelets of block copolymers by crystallization-driven self-assembly

Poly(ε-caprolactone)-block-poly[2-(dimethylamino)ethyl methacrylate] (PCL-b-PDMAEMA) block copolymers were applied to fabricate elongated polymer platelets with axial length of 5–20 μm and thickness of ca. 10 nm by crystallization-driven self-assembly (CDSA). The block copolymer platelets composed of a crystallized PCL layer sandwiched between two PDMAEMA layers were obtained spontaneously by adding methanol, a selective solvent of PDMAEMA, into the block copolymer solution of THF at 25 °C. Therefore, this is a facile approach to generate lamellar nanoobjects of block copolymers. Effects of the block copolymer compositions on the morphologies of platelets were investigated. The presence of PDMAEMA segments along the lamellar surfaces was further confirmed by loading gold nanoparticles. Moreover, PEO-b-PCL-b-PDMAEMA triblock terpolymer could form spindle platelets by this approach. The crystalline platelets were characterized by the transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD).     

Nanostructure and hydrogen bonding in interpolyelectrolyte complexes of poly(?-caprolactone)-block-poly(2-vinyl pyridine) and poly(acrylic acid)

Nanostructured poly(?-caprolactone)-block-poly(2-vinyl pyridine) (PCL-b-P2VP)/poly(acrylic acid) (PAA) interpolyelectrolyte complexes (IPECs) were prepared by casting from THF/ethanol solution. The morphological behaviour of this amphiphilic block copolymer/polyelectrolyte complexes with respect to the composition was investigated in a solvent mixture. The phase behaviour, specific interactions and morphology were investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, optical microscopy (OM), dynamic light scattering (DLS) and atomic force microscopy (AFM). Micelle formation occurred due to the aggregation of hydrogen bonded P2VP block and polyelectrolyte (PAA) from non-interacted PCL blocks. It was observed that the hydrodynamic diameter (D_h) of the micelles in solution decreased with increasing PAA content up to 40 wt%. After 50 wt% PAA content, D_h again increased. The micelle formation in PCL-b-P2VP/PAA IPECs was due to the strong intermolecular hydrogen bonding between PAA homopolymer units and P2VP blocks of the block copolymer. The penetration of PAA homopolymers into the shell of the PCL-b-P2VP block copolymer micelles resulted in the folding of the P2VP chains, which in turn reduced the hydrodynamic size of the micelles. After the saturation of the shell with PAA homopolymers, the size of the micelles increased due to the absorption of added PAA onto the surface of the micelles.     

Photophysical properties and self-assembly of triblock copolymer with complexes of positively charged PDMAEMA and oppositely charged chromophores

The self-assembly and photophysical properties of a triblock copolymer with complex mid-block in THF and aqueous solution were investigated in this research. Poly(poly(ethylene glycol) methyl ether methacrylate)-block-poly(2-(dimethylamino ethyl methacrylate)-block- poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA–b–PDMAEMA–b–PPEGMA) triblock copolymer was synthesized by subsequent atom transfer radical polymerizations (ATRP) of DMAEMA and PEGMA. The PDMAEMA blocks were quaternized by a reaction with iodomethane. The complex of the positively charged PDMAEMA chain unit and sodium salt of 1-pyrenebutyric acid was prepared by mixing equimolar amount of the two components in THF/water mixture. Transmission electron microscopy and fluorescence technique results show that the triblock copolymer chains self-assemble into micelles in THF at high concentration. The critical aggregation concentration (CAC) of the triblock copolymer in THF determined by fluorescence technique is 6.8 × 10^?5 M. The triblock copolymer was also able to self-assemble into micelles in water. The value of CAC of the triblock copolymer in water is 2.0 × 10^?5 M. The photophysical properties and self-assembly structures of the triblock copolymer in aqueous solutions were influenced by added sodium chloride. After salt addition, a transition of the assembled structures from micelles to hollow structures was observed.     

Structural effect of emulsifiers on the emulsion stability of a water/benzene mixture

Core–shell‐type microspheres with microphase‐separated shells of polystyrene (PS) and poly(ethylene glycol) (PEG) (microsphere_block: molar ratio: PS/PEG 49.1/45.9 mol %; M_w: PS chain: 1.07 × 10⁴, PEG chain 1.0 × 10⁴; the ratio of arm numbers of PEG to PS: 1.0; microsphere_graft: molar ratio: PS/PEG 33.8/55.9 mol %; M_w: PS chain: 1.54 × 10⁴, PEG chain 1.0 × 10⁴, the ratio of arm numbers of PEG to PS: 2.55) were synthesized by crosslinking of spherical domains of poly(2‐hydroxyethyl methacrylate) (PHEMA) and poly(4‐vinyl pyridine) (P4VP) of the microphase‐separated films of poly(ethylene glycol)‐block‐poly(2‐hydroxyethyl methacrylate)‐block‐polystyrene triblock terpolymer (M_n: 2.18 × 10⁴; molar ratio: PS 49.1 mol %, PHEMA 5.0 mol %, PEG 45.9 mol %) and polystyrene‐block‐[poly(4‐vinyl pyridine)‐graft‐poly(ethylene glycol)] block–graft copolymer (M_n: 4.56 × 10⁴; molar ratio: PS 33.8 mol %, P4VP 10.3 mol %, PEG 55.9 mol %; branch number of PEG: 2.55), respectively. The structures of microphase‐separated films were investigated by transmission electron microscopy and small‐angle X‐ray scattering. The effects of the arm number ratio of PS to PEG and the total arm number on the stability of the water/benzene emulsion were investigated. The emulsion stability of oil in water was improved by using the microsphere synthesized with the microsphere_graft. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 321–331, 2004