Cross-linking of polybutadiene at the air/water interface: Toward an easy access to two-dimensional polymeric materials

A novel approach to two-dimensionally crosslink polydienes at the air/water interface is proposed. The acid-catalyzed condensation of the triethoxysilane pendant groups of triethoxysilane-functionalized polybutadiene chains at the air/water interface successfully led to the formation of an insoluble crosslinked material which could be directly removed from the water surface. The efficiency of the cross-linking reaction was demonstrated through surface pressure measurements such as surface pressure-mean molecular area isotherms recorded at different reaction times and isobar experiments for different subphase pH values. The evolution of the monolayer topography during cross-linking was studied by atomic force microscopy imaging of the Langmuir-Blodgett films. © 2007 Elsevier Inc. All rights reserved

Two-dimensional polymeric nanomaterials through cross-linking of polybutadiene-b-poly(ethylene oxide) monolayers at the air/water interface

Two-dimensional polymeric nanomaterials consisting of a continuously cross-linked polybutadiene (PB) two-dimensional network with poly(ethylene oxide) (PEO) domains of controlled sizes trapped within the PB network were synthesized. To reach that goal, novel (PB(Si(OEt)(3))-b-PEO)(3) star block copolymers were designed by hydrosilylation of the pendant double bonds of (PB-b-PEO)(3) star block copolymer precursors with triethoxysilane. The (PB(Si(OEt)(3))-b-PEO)(3) star block copolymers were characterized by H-1 NMR and IR spectroscopy. Self-condensation of the triethoxysilane pendant groups under acidic conditions led to a successful cross-linking of the polybutadiene blocks directly at the air/water interface without any additives or reagents. This strategy was found more efficient than radical cross-linking of (PB-b-PEO)(3) with AIBN to get a homogeneously cross-linked monolayer of controlled and fixed morphology as demonstrated by the easy mechanical removal of the cross-linked Langmuir film from the water surface. As shown by AFM imaging, this strategy allows the accurate control of the PEO "pore" size depending on the monolayer surface pressure applied during the cross-linking reaction. The subphase pH and surface pressure influence on the cross-linking kinetics and monolayer morphologies were investigated by Langmuir trough studies (isotherm and isobar experiments) and AFM imagin

Two-dimensional polymeric nanomaterials through cross-linking of polybutadiene-b-poly(ethylene oxide) monolayers at the air/water interface

Two-dimensional polymeric nanomaterials consisting of a continuously cross-linked polybutadiene (PB) two-dimensional network with poly(ethylene oxide) (PEO) domains of controlled sizes trapped within the PB network were synthesized. To reach that goal, novel (PB(Si(OEt)3)-b-PEO) 3 star block copolymers were designed by hydrosilylation of the pendant double bonds of (PB-b-PEO)3 star block copolymer precursors with triethoxysilane. The (PB(Si(OEt)3)-b-PEO)3 star block copolymers were characterized by 1H NMR and IR spectroscopy. Self-condensation of the triethoxysilane pendant groups under acidic conditions led to a successful cross-linking of the polybutadiene blocks directly at the air/water interface without any additives or reagents. This strategy was found more efficient than radical cross-linking of (PB-b-PEO)3 with AIBN to get a homogeneously cross-linked monolayer of controlled and fixed morphology as demonstrated by the easy mechanical removal of the cross-linked Langmuir film from the water surface. As shown by AFM imaging, this strategy allows the accurate control of the PEO pore size depending on the monolayer surface pressure applied during the cross-linking reaction. The subphase pH and surface pressure influence on the cross-linking kinetics and monolayer morphologies were investigated by Langmuir trough studies (isotherm and isobar experiments) and AFM imaging. © 2007 American Chemical Society

Cross-linking of polybutadiene at the air/water interface: Toward an easy access to two-dimensional polymeric materials

A novel approach to two-dimensionally crosslink polydienes at the air/water interface is proposed. The acid-catalyzed condensation of the triethoxysilane pendant groups of triethoxysilane-functionalized polybutadiene chains at the air/water interface successfully led to the formation of an insoluble crosslinked material which could be directly removed from the water surface. The efficiency of the cross-linking reaction was demonstrated through surface pressure measurements such as surface pressure-mean molecular area isotherms recorded at different reaction times and isobar experiments for different subphase pH values. The evolution of the monolayer topography during cross-linking was studied by atomic force microscopy imaging of the Langmuir-Blodgett films. (C) 2007 Elsevier Inc. All rights reserve

Synthesis and investigation of surface properties of dendrimer-like copolymers based on polystyrene and poly(tert-butylacrylate)

The synthesis of well-defined second-generation PS(n)PtBA(2n) dendrimer-like copolymers based on polystyrene (PS) and poly(tert-butylacrylate) (PtBA) is described. The synthetic procedure involves a combination of atom transfer radical polymerization (ATRP) using multifunctional initiators and chain end modification reactions. These structures are composed of a PS core with 2, 4, 6, or 8 arms and a corona of PtBA with 4, 8, 12, or 16 arms, respectively. Third-generation PS(n)PS(2n)PtBA(4n) dendrimer-like copolymers were also derived by repetition of chain end modification and ATRP. Characterization was carried out by size exclusion chromatography online with multiangle laser light scattering and by H-1 NMR spectroscopy. PS(n)PAA(2n) amphiphilic structures based on PS and poly(acrylic acid) (PAA) were subsequently generated by hydrolysis of the tert-butylester groups. Langmuir monolayer studies of PS(n)PtBA(2n) showed the formation of stable films. AFM images demonstrated a significant change in morphology upon increasing surface pressures

Langmuir and langmuir-blodgett films of polye(thylene oxide)-b-Poly(ε- caprolactone) star-shaped block copolymers

Self-assembly of poly(ethylene oxide)-block-poly(ε-caprolactone) five-arm stars (PEO-b-PCL) was studied at the air/water (A/W) interface. The block copolymers consist of a hydrophilic PEO core with hydrophobic PCL chains at the star periphery. All the polymers have the same number of ethylene oxide repeat units (9 pet arm), and the number of ε-caprolactone repeat units ranges from 0 to 18 per arm. The Langmuir monolayers were analyzed by surface pressure/mean molecular area isotherms, compression-expansion hysteresis experiments, and isobaric relaxation measurements, and the Langmuir-Blodgett (LB) films\u27 morphologies were investigated by atomic force microscopy (AFM). PCL homopolymers crystallize directly at the A/W interface in a narrow surface pressure range (11-15 mN/m). In the same pressure region, the star-shaped block copolymers undergo a phase transition corresponding to the collapse and the crystallization of the PCL chains as shown by the presence of a pseudoplateau in the isotherms. The LB films were prepared by transferring the Langmuir monolayers onto mica substrates at various surface pressures. AFM imaging confirmed the formation of PCL crystals in the LB monolayers of the PCL homopolymers and of the copolymers, but also showed that the PCL segments can undergo additional crystallization after monolayer transfer during water evaporation. The PCL crystal morphologies were also strongly influenced by the surface pressure and by the PEO segments. © 2006 American Chemical Society

Polystyrene-b-poly(tert-butyl acrylate) and polystyrene-b-poly(acrylic acid) dendrimer-like copolymers: Two-dimensional self-assembly at the air-water interface

The two-dimensional self-assembly at the air/water (A/W) interface of two dendrimer-like copolymers based on polystyrene and poly(tert-butyl acrylate) (PS-b-PtBA) or poly(acrylic acid) (PS-b-PAA) was investigated through surface pressure measurements (isotherms, isochores, and compression-expansion hysteresis experiments) and atomic force microscopy (AFM) imaging. The two dendrimer-like block copolymers have an 8-arm PS core (Mn = 10 000 g/mol, ∼12 styrene repeat units per arm) with a 16-arm PtBA (M0 = 230 000 g/mol, ∼112 tert-butyl acrylate repeat units per arm) or PAA (Mn = 129 000 g/mol, ∼112 acrylic acid repeat units per arm) corona. The PS-b-PtBA sample forms stable Langmuir monolayers and aggregates into circular surface micelles up to a plateau observed in the corresponding isotherm around 24 mN/m. Beyond this threshold, the monolayers collapse above the interface, resulting in the formation of large and irregular desorbed aggregates. The PS-b-PAA sample has ionizable carboxylic acid groups, and its A/W interfacial self-assembly was therefore investigated for various subphase pH values. Under basic conditions (pH = 11), the carboxylic acid groups are deprotonated, and the PS-e-PAA sample is therefore highly water-soluble and does not form stable monolayers, instead irreversibly dissolving in the aqueous subphase. Under acidic conditions (pH = 2.5), the PS-b-PAA sample is less water-soluble and becomes surface-active. The pseudoplateau observed in the isotherm around 5 mN/m corresponds to a pancake-to-brush transition with the PAA chains dissolving in the water subphase and stretching underneath the anchoring PS cores. AFM imaging revealed the presence of circular surface micelles for low surface pressures, whereas the biphasic nature of the pseudoplateau region was confirmed with the gradual aggregation of the micellar PS cores above the PAA chains. The aggregation numbers for both samples were estimated around 3-5 dendrimer-like copolymers per circular surface micelle. These rather low values confirmed the tremendous influence of molecular architecture on the two-dimensional self-assembly of block copolymers. © 2007 American Chemical Society

Electrochemical and spectroscopic characterization of organic compound uptake in silica core-shell nanocapsules

Oil-filled silica nanocapsules consisting of a hydrophobic liquid core and a silicate shell have been shown to efficiently extract hydrophobic compounds from aqueous media. With a view toward quantifying the selectivity of these systems, a series of electrochemical and spectroscopic measurements was performed. Uptake and kinetics experiments were carried out through electrochemical measurements by using solutions of lipophilic electroactive molecules of different sizes and with different affinities for silica. Other solutions with fluorescent probes were used for spectrophotometry measurements. In this work we report the environment where the lipophilic compounds studied end up after absorption and the kinetics of their uptake by the oil-filled silica nanocapsules with different shell thicknesses. © 2006 American Chemical Society