Synthesis and properties of 4-arm star-shaped amphiphilic macromolecules

The major goal of this research was to understand the role of number of branching molecular weight and hydrophilic balance of chains segments on star polymer morphology. The present work was focused on synthesis of linear and star-shaped macromolecules with specific topology, using different types of polymerization methods, such as anionic and atom transfer radical polymerization (ATRP). After synthesis of a series of amphiphilic star macromolecules, the chemical composition of the polymers was confirmed by nuclear magnetic resonance (NMR), Fourier transform infra-red (FTIR) spectroscopy, and gel permeation chromatography (GPC). Then, the physical properties of the polymers were analyzed by differential scanning calorimetry (DSC) and X-ray diffraction techniques. X-ray data showed that the degree of crystallinity decreased for PEO star homopolymer. It was due to a junction of the branches of the star polymers. For heteroarmed PEO[subscript n]-b-PS[subscript m], where n+m=4, star polymers, the degree of crystallinity depends not only on architecture, but also on a ratio of PEO and PS segments. Finally, the behavior of the amphiphilic macromolecules at the air/water interface and on a solid surface was characterized by atomic force microscopy (AFM). As observed, all amphiphilic star polymers formed stable monolayers at the air/water interface, which later can be successfully transferred on a silicon substrate. The amphiphilic star polymers spontaneously aggregated after spreading the polymer solution on the surface of water. At the small surface pressure, the amphiphilic star polymers form monolayers with circular micellar structures. In the case of PEO-b-PS3 star polymer with higher content of PEO, the aggregates move closer together without increase in size with increasing surface pressure until layer collapsed. The PEO-b-PS3 star polymer with lower PEO content, aggregates are collapse in lamellar structures when surface pressure reached 5 mN/m. Also, the specific kind of star polymer, containing alkyl terminated hydrophilic hyperbranched core, was synthesized. AFM studies were applied to determine the role of amphiphilic core-shell balance on the aggregation of the polymer in the monolayer at the interface

Amphiphilic branched block copolymers as responsive materials

The ultimate goal of this project is to understand the fundamental relationships between the architecture and chemical design of highly branched multifunctional block copolymers and their supramolecular organization, physical behavior, and microscopic properties at surfaces and interfaces. The present work is focused on synthesis of linear and branched macromolecules with specific topology, using different types of polymerization methods, such as anionic, atom transfer radical polymerization (ATRP), nitroxide mediated polymerization (NMP) and reversible addition-fragmentation chain transfer polymerization (RAFT). The chemical composition of the macromolecules is confirmed by nuclear magnetic resonance (NMR), Fourier transform infra-red (FTIR) spectroscopy, and gel permeation chromatography (GPC). The physical properties of the polymers are analyzed with differential scanning calorimetry (DSC) and X-ray diffraction techniques. The behavior of the amphiphilic macromolecules at the air-water interface and on a solid surface is characterized by X-ray reflectivity and atomic force microscopy (AFM). As concluded in this research for star block copolymers with low number of arms, increasing the number of PS arms stabilized the circular morphology of the Langmuir monolayer. Introducing of ionic amino or carboxyl terminal groups of arms is found to be effective in creating stable and very fine circular domain morphology. Furthermore, adding ionic blocks containing tertiary amino groups allowed tuning their surface properties by changes in both pH and temperature. On the other hand, different surface morphologies ranging from peculiar stripes and net-like patterns to a highly ordered 2D assembly of fine circular domains and peculiar dendritic superstructures were observed for the multiarm star polymers with high number of arms (16-38). Finally, for the hyperbranched block copolymers, AFM revealed morphology transition from very smooth monolayer to formation of nonuniform bilayer structure followed by second collapse and creation of uniform polymeric multilayers. As an outcome of research, fundamental relationships between architecture/chemical composition and resulting structures are suggested. This research expands a range of potential technologies to improve the control over interfacial behavior of the nanoscale polymeric films

Thermoresponsive reversible behavior of multistimuli pluronic-based pentablock copolymer at the air-water interface

Surface behavior of the pH- and thermoresponsive amphiphilic ABCBA pentablock copolymer has been studied with respect to the environmental conditions. We demonstrate that the pentablock copolymer poly((diethylaminoethyl methacrylate)-b-(ethylene oxide)-b-(propylene oxide)-b-(ethylene oxide)-b-(diethylaminoethyl methacrylate)) possesses reversible temperature changes at the air-water interface in a narrow pH range of the water subphase. Significant diversity in the surface morphology of pentablock copolymer monolayers at different pH and temperatures observed were related to the corresponding reorganization of central and terminal blocks. Remarkable reversible variations of the surface pressure observed for the Langmuir monolayers at pH 7.4 in the course of heating and cooling between 27 and 50°C is associated with conformational transformations of terminal blocks crossing the phase line in the vicinity of the lower critical solution temperature point. The observed thermoresponsive surface behavior can be exploited for modeling of the corresponding behavior of pentablock copolymers adsorbed onto various biointerfaces for intracellular delivery for deeper understanding of stimuli-responsive transformations relevant to controlled drug and biomolecules release and retention

Synthesis and properties of 4-arm star-shaped amphiphilic macromolecules

The major goal of this research was to understand the role of number of branching molecular weight and hydrophilic balance of chains segments on star polymer morphology. The present work was focused on synthesis of linear and star-shaped macromolecules with specific topology, using different types of polymerization methods, such as anionic and atom transfer radical polymerization (ATRP). After synthesis of a series of amphiphilic star macromolecules, the chemical composition of the polymers was confirmed by nuclear magnetic resonance (NMR), Fourier transform infra-red (FTIR) spectroscopy, and gel permeation chromatography (GPC). Then, the physical properties of the polymers were analyzed by differential scanning calorimetry (DSC) and X-ray diffraction techniques. X-ray data showed that the degree of crystallinity decreased for PEO star homopolymer. It was due to a junction of the branches of the star polymers. For heteroarmed PEO[subscript n]-b-PS[subscript m], where n+m=4, star polymers, the degree of crystallinity depends not only on architecture, but also on a ratio of PEO and PS segments. Finally, the behavior of the amphiphilic macromolecules at the air/water interface and on a solid surface was characterized by atomic force microscopy (AFM). As observed, all amphiphilic star polymers formed stable monolayers at the air/water interface, which later can be successfully transferred on a silicon substrate. The amphiphilic star polymers spontaneously aggregated after spreading the polymer solution on the surface of water. At the small surface pressure, the amphiphilic star polymers form monolayers with circular micellar structures. In the case of PEO-b-PS3 star polymer with higher content of PEO, the aggregates move closer together without increase in size with increasing surface pressure until layer collapsed. The PEO-b-PS3 star polymer with lower PEO content, aggregates are collapse in lamellar structures when surface pressure reached 5 mN/m. Also, the specific kind of star polymer, containing alkyl terminated hydrophilic hyperbranched core, was synthesized. AFM studies were applied to determine the role of amphiphilic core-shell balance on the aggregation of the polymer in the monolayer at the interface.</p

Amphiphilic branched block copolymers as responsive materials

The ultimate goal of this project is to understand the fundamental relationships between the architecture and chemical design of highly branched multifunctional block copolymers and their supramolecular organization, physical behavior, and microscopic properties at surfaces and interfaces. The present work is focused on synthesis of linear and branched macromolecules with specific topology, using different types of polymerization methods, such as anionic, atom transfer radical polymerization (ATRP), nitroxide mediated polymerization (NMP) and reversible addition-fragmentation chain transfer polymerization (RAFT). The chemical composition of the macromolecules is confirmed by nuclear magnetic resonance (NMR), Fourier transform infra-red (FTIR) spectroscopy, and gel permeation chromatography (GPC). The physical properties of the polymers are analyzed with differential scanning calorimetry (DSC) and X-ray diffraction techniques. The behavior of the amphiphilic macromolecules at the air-water interface and on a solid surface is characterized by X-ray reflectivity and atomic force microscopy (AFM). As concluded in this research for star block copolymers with low number of arms, increasing the number of PS arms stabilized the circular morphology of the Langmuir monolayer. Introducing of ionic amino or carboxyl terminal groups of arms is found to be effective in creating stable and very fine circular domain morphology. Furthermore, adding ionic blocks containing tertiary amino groups allowed tuning their surface properties by changes in both pH and temperature. On the other hand, different surface morphologies ranging from peculiar stripes and net-like patterns to a highly ordered 2D assembly of fine circular domains and peculiar dendritic superstructures were observed for the multiarm star polymers with high number of arms (16-38). Finally, for the hyperbranched block copolymers, AFM revealed morphology transition from very smooth monolayer to formation of nonuniform bilayer structure followed by second collapse and creation of uniform polymeric multilayers. As an outcome of research, fundamental relationships between architecture/chemical composition and resulting structures are suggested. This research expands a range of potential technologies to improve the control over interfacial behavior of the nanoscale polymeric films.</p

Bimetallic nanocobs: Decorating silver nanowires with gold nanoparticles

A study was conducted to demonstrate a novel design of hybrid and bimetallic silver-gold core-double-shell nanowires with greatly enhanced surface-enhanced Raman scattering (SERS) ability. The study demonstrated the novel design, in which gold nanoparticles decorate the surface of silver nanowires, utilizing a three-arm star polymer with functional terminal groups as a linker. It was found that the gold nanoparticles form an effective and hybrid shell of 13 nm thickness with 4 nm gold nanoparticles embedded within the polymer shell around a 65 nm silver core. It was also demonstrated that such hybrid silver-gold nanowires possess significant SERS activity, exceeding the Raman scattering observed from isolated silver nanowires. The SERS is also observed to be much higher than that at the gap between two neighboring silver nanowires.close787

Thermoresponsive reversible behavior of multistimuli pluronic-based pentablock copolymer at the air-water interface

Surface behavior of the pH- and thermoresponsive amphiphilic ABCBA pentablock copolymer has been studied with respect to the environmental conditions. We demonstrate that the pentablock copolymer poly((diethylaminoethyl methacrylate)-b-(ethylene oxide)-b-(propylene oxide)-b-(ethylene oxide)-b-(diethylaminoethyl methacrylate)) possesses reversible temperature changes at the air-water interface in a narrow pH range of the water subphase. Significant diversity in the surface morphology of pentablock copolymer monolayers at different pH and temperatures observed were related to the corresponding reorganization of central and terminal blocks. Remarkable reversible variations of the surface pressure observed for the Langmuir monolayers at pH 7.4 in the course of heating and cooling between 27 and 50°C is associated with conformational transformations of terminal blocks crossing the phase line in the vicinity of the lower critical solution temperature point. The observed thermoresponsive surface behavior can be exploited for modeling of the corresponding behavior of pentablock copolymers adsorbed onto various biointerfaces for intracellular delivery for deeper understanding of stimuli-responsive transformations relevant to controlled drug and biomolecules release and retention.Reprinted with permission from Langmuir 23 (2007), pp.25-30, doi: 10.1021/la061547f. Copyright 2007 American Chemical Society.</p