Showing papers in "Macromolecular Chemistry and Physics in 2011"

A Convenient Method to Produce Close- and Non-close-Packed Monolayers using Direct Assembly at the Air-Water Interface and Subsequent Plasma-Induced Size Reduction

Abstract: An extremely facile approach to produce close-packed colloidal monolayers over large areas using direct assembly at the air–water interface is presented. The influence of small amounts of sodium dodecyl sulfate (SDS) as well as the influence of the pH value of the subphase on the quality of the resulting monolayer is investigated. It is found that small amounts of SDS at the interface influence capillary forces and form a soft barrier that facilitates the crystallization process. Increased electrostatic repulsion arising from a higher pH of the subphase induced a higher order using carboxylic acid functionalized particles. The deposited close-packed monolayers were subjected to plasma treatment in order to shrink the colloids and produce non-close packed monolayers with lattice spacing and symmetry reflecting the order of the initial close-packed monolayer. A detailed examination of etching conditions and their influence on the shrinkage of the particles was performed, including effects of plasma power, composition, flow rates as well as polymeric- and substrate material. The monolayers exhibit vivid coloration, which is determined by their size and packing density. UV–Vis–NIR spectroscopy was used to investigate the change of monolayer color during the size reduction of the individual particles. A simple theoretical model was elaborated to explain the optical properties. Finally, the non-close-packed monolayers were used as masks to produce gold nanostructures to exemplify the versatility of the monolayer architectures in nanosphere lithography.

Poly(propylene)/Graphene Nanoplatelet Nanocomposites: Melt Rheological Behavior and Thermal, Electrical, and Electronic Properties

Abstract: Poly(propylene) polymer nanocomposites containing graphene nanoplatelets (GnPs) with different loadings are fabricated via a facile ex-situ solution approach. Improved thermal stability and higher crystallinity are observed in the PNCs. Both electrical conductivity and real permittivity increase with increasing GnP loading. Electrical conductivity percolation is observed at 12.0wt%GnP. The rheological behavior of the PNC melts are also investigated. It is found that the modulus and viscosity are reduced at small GnP loadings and increased above a critical loading.

Alkyl‐Substituted N‐Vinylimidazolium Polymerized Ionic Liquids: Thermal Properties and Ionic Conductivities

Abstract: Structure-property relationships for polymerized ionic liquids (PILs) relate chemical structure to ionic conductivity and reveal the importance of glass transition temperature (Tg) and the energy associated with an ion-hopping mechanism for ion conduction for a series of alkyl-substituted vinylimidazolium PILs. The alkyl-substituted vinylimidazolium-based PILs with varying lengths of n-alkyl substituents provide diverse precursors with exchangeable anions to further enhance thermal stability and ionic conductivity. As the anion size increases, regardless of alkyl substituent length, Tg decreases and the onset of weight loss, TD, increases. As the length of the alkyl substituent increases, Tg decreases for PILs with Br− and BF4− counteranions. Ionic conductivity increases over an order of magnitude upon exchange of the counteranion from TfO− < Tf2N−.

Studies on Photoinduced ATRP in the Presence of Photoinitiator

Abstract: Photoinduced reverse and simultaneous reverse and normal initiation (SR&NI) atom transfer radical polymerization (ATRP) of methyl methacrylate are investigated. Compared to the photoinduced reverse ATRP, SR&NI ATRP allows for better control over molecular weight with narrow molecular weight distributions.

Determination of Solubility Parameters for Organic Semiconductor Formulations

Abstract: The concept of Hansen solubility parameters (HSP) is applied to organic semiconductors in order to determine and predict their solubility behavior, which is essential for the design of functional and environmentally friendly ink formulations for organic photovoltaics. Two different conjugated polymers, one semicrystalline and one dominantly amorphous, and one fullerene derivative are selected as prototype candidates to evaluate the applicability of the HSP concept for organic semiconductors. The method for determining the solubility parameters is described and the quality of the HSP fits as well as their suitability for designing of organic electronic inks are discussed in detail.

Synthesis and Gas Permeation Properties of Spirobischromane-Based Polymers of Intrinsic Microporosity

Abstract: Polymers of intrinsic microporosity (PIMs) possess molecular structures composed of fused rings with linear units linked together by a site of contortion so that the macromolecular structure is both rigid and highly non-linear. For PIM-1, which has previously demonstrated encouraging gas permeability data, the site of contortion is provided by the monomer 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane. Here we describe the synthesis and properties of a PIM derived from the structurally related 6,6′,7,7′-tetrahydroxy-4,4,4′,4′-tetramethyl-2,2′-spirobischromane and copolymers prepared from combination of this monomer with other PIM-forming biscatechol monomers, including the highly rigid monomer 9,10-dimethyl-9,10-ethano-9,10-dihydro-2,3,6,7-tetrahydroxyanthracene. Generally, the polymers display good solubility in organic solvents and have high average molecular masses () in the range 80 000–200 000 g · mol−1 and, therefore, are able to form robust, solvent-cast films. Gas permeability and selectivity for He, H2, N2, O2, CO2, and CH4 were measured for the polymers and compared to the values previously obtained for PIM-1. The spirobischromane-based polymers demonstrate enhanced selectivity for a number of gas pairs but with significantly lower values for permeability. The solubility coefficient for CO2 of two of the copolymers exceed even that of PIM-1, which previously demonstrated the highest value for a membrane-forming polymer. Therefore, these polymers might be useful for gas or vapor separations relying on solubility selectivity.

Solid‐State Dye‐Sensitized Solar Cells with Conjugated Polymers as Hole‐Transporting Materials

Abstract: DSCs are a promising alternative to conventional silicon-based solar cells owing to their low cost and relatively high efficiency. However, the utilization of a liquid electrolyte containing the iodine/iodide redox couple in traditional DSCs brings practical problems for their long-term application, which leads to rapid development of SDSCs based on inorganic p-type semiconductors or organic HTMs. In this review, we summarize the current research on SDSCs using conjugated polymer as HTM. Special attention is paid to understand the effects of polymer HTM structure and deposition process on SDSC performance. The limiting factors for SDSC energy conversion efficiency are discussed and strategies to improve device performance are proposed.

Poly(propylene) Nanocomposites Containing Various Carbon Nanostructures

Abstract: PP nanocomposites containing different carbon nanofillers (CNTs, CNFs, GnPs, CB) are fabricated and further processed by hot compression molding. A high level of nanofiller dispersion is found. The NCs exhibit improved thermal stability and higher crystallinity. Both electrical conductivity and real permittivity increase with increasing nanofiller loading. A strongly aspect ratio dependent electrical conductivity percolation is observed at loadings of 15.0, 12.0, 5.0, and 3.0 wt% for CB, GnPs, CNFs, and CNTs, respectively. The rheological behavior of the NC melts is also investigated. A small concentration of the nanofillers is found to affect the modulus and viscosity of the PP melts significantly.

Synthesis and characterization of polyurethane-based shape-memory polymers for tailored Tg around body temperature for medical applications

Abstract: Various polyurethane-based SMPUs were synthesized using five types of polyols as soft segments and two different diisocyanates as hard segments. The effects of diisocyanate concentration on material properties such as crystallinity, transition temperature, shape-memory effect and tensile strength were investigated. SMPUs with a maximum strain near 1 000%, recovery rate up to ≈98%, fixity up to ≈90% and Tgs of 35–45 °C were obtained. A high MDI content results in SMPUs with better shape-memory effect, whereas increasing IPDI content leads to a weaker shape-memory effect. High IPDI concentration seems to prevent or restrict chemical reactions and crosslinks between the polyols and the hard segments, leading to large phase separation and coexistence of soft and hard segments in the macrophases.

SAXS/DSC Analysis of the Lamellar Thickness Distribution on a SSA Thermally Fractionated Model Polyethylene

Abstract: Successive self-nucleation and annealing (SSA) is applied to thermally fractionate a model hydrogenated polybutadiene SSA produces discrete and well-separated thermal fractions with distinct melting peaks The samples are studied by SAXS as a function of temperature The SAXS profile displays only one scattering peak associated with the interlamellar correlation and is unable to discriminate the multimodal distribution of lamellar thicknesses in the samples The average lamellar thickness associated with each melting fraction can be estimated from SAXS data at different temperatures A modified Gibbs-Thomson equation is employed to predict the lamellar thickness from DSC data, giving results consistent with those derived from SAXS

Improving the Stability in Aqueous Media of Polymer Brushes Grafted from Silicon Oxide Substrates by Surface‐Initiated Atom Transfer Radical Polymerization

Abstract: Hydrophilic polymer brushes grown via surface-initiated ATRP from silicon oxide surfaces are susceptible to detachment via hydrolytic cleavage of the anchoring siloxane bond. This paper investigates the influence of the structure of the ATRP initiator on the stability of these brushes and seeks for strategies to further enhance their stability. It is found that increasing the hydrophobicity of the organosilane modified ATRP initiator reduces the susceptibility of the brushes toward cleavage. Robust, hydrophilic polymer brushes are prepared, which are obtained by introducing a short, hydrophobic PMMA or PEHMA block between the silicon oxide substrate and the hydrophilic polymer brush.

Linear Polyethyleneimine: Optimized Synthesis and Characterization - On the Way to ''Pharmagrade'' Batches

Abstract: The synthesis of linear polyethyleneimine (LPEI) by acidic hydrolysis of poly(2-ethyl-2-oxazoline) is studied and optimized to reach the highest degree of hydrolysis within the shortest time range using a microwave synthesizer. In addition, the purification procedure is significantly improved; the fast batch processing combined with an excellent control of the actual heating time represents a well-suited alternative to the conventional synthesis on the way to "pharmagrade" PEI. The developed protocol for the preparation of methyl and proton-initiated LPEIs shows a high reproducibility, and the identity and purity of the LPEIs is proven by means of 1 H NMR and IR spectroscopy as well as MALDI-TOF- and ESI-Q-TOF-MS.

Polymers for Control Freaks: Sequence‐Defined Poly(amidoamine)s and Their Biomedical Applications

Abstract: A novel synthetic strategy towards monodisperse, sequence-defined polymers is presented. This technique was applied for the synthesis of a set of polymer carriers for DNA delivery combining monodisperse, sequence-defined PAA segments with PEO blocks. These precision polymers are sequentially assembled from a library of building blocks, enabling programmed interactions and functions by sequence-specific positioning of different functionalities. Due to the absence of chemical and molecular-weight distributions in the multifunctional segments, exact correlation of the monomer sequence and (bio)properties is attainable. This is demonstrated by the interactions with plasmid DNA, investigating the dsDNA complexation and condensation properties in dependence of the monomer sequence.

Chain-Length-Dependent Termination in Radical Polymerization of Acrylates

Abstract: The technique of SPPLP EPR, which is single-pulse pulsed-laser polymerization (SPPLP) in conjunction with electron paramagnetic resonance (EPR) spectroscopy, is used to carry out a detailed investigation of secondary (chain-end) radical termination of acrylates. Measurements are performed on methyl acrylate, n-butyl acrylate, and dodecyl acrylate in bulk and in toluene solution at -40 °C. The reason for the low temperature is to avoid formation of mid-chain radicals (MCRs), a complicating factor that has imparted ambiguity to the results of previous studies of this nature. Consistent with these previous studies, composite-model behavior for chain-length-dependent termination (CLDT) rate coefficients, ki,it, is found in this work. However, lower and more reasonable values of αs, the exponent for variation of ki,it at short chain lengths, are found in the present study. Most likely this is because of the absence of MCRs, thereby validating the methodology of this work. Family-type termination behavior is observed, with the following average parameter values adequately describing all results, regardless of acrylate or the presence of toluene: αs = 0.79, αl = 0.21 (long chains) and ic≈30 (crossover chain length). All indications are that these values carry over to termination of acrylate chain-end radicals at higher, more practical temperatures. Further, these values largely make sense in terms of what is understood about the physical meaning of the parameters. Variation of the rate coefficient for termination between monomeric radicals, k l,l t , is found to be well described by the simple Smoluchowski and Stokes-Einstein equations. This allows easy prediction of k l,l t for different alkyl acrylates, solvent, and temperature. Through all this the unrivalled power of SPPLP EPR for measuring and understanding (chain-length-dependent) termination rate coefficients shines through.

In situ Foaming Evolution of Flexible Polyurethane Foam Nanocomposites

Abstract: The authors gratefully acknowledge the financial support of the Spanish Ministry of Science and Innovation (MICINN) through project MAT 2010-18749 and the 7th Framework Program of E.U. through HARCANA (NMP3-LA-2008-213277). RV and MMB also acknowledge the Ramon y Cajal and FPI programmes from MICINN, respectively.

Functionalization of Graphene Sheets by Polyacetylene: Convenient Synthesis and Enhanced Emission

Abstract: and so on.However,itisstillabigchallengetomakegraphenesoluble,ordispersewellinsolvents,includingorganicandaqueousmedia, due to aggregation and/or restacking effects,althoughthesolubilization/dispersionofgrapheneenablesthe processing of this material by solvent-assisted techni-ques for the subsequent fabrication of nanocompositematerials, which is crucially important for their practicalapplication.By taking advantage of well-developed technologiesused for dispersing carbon nanotubes,

Synthesis and pH/Temperature-Responsive Behavior of PLLA-b-PDMAEMA Block Polyelectrolytes Prepared via ROP and ATRP

Abstract: Well-defined diblock poly(L-lactide)-block-poly(dimethylamino-2-ethyl methacrylate) (PLLA-b-PDMAEMA) copolymers were synthesized by combining ROP of LLA and ATRP of DMAEMA, from a dual-initiator 2-hydroxylethyl 2-bromoisobutyrate. The molecular characterization of these diblock copolymers was performed using (1)H NMR, FT-IR, and GPC-MALLS analysis. The responsive behavior of these diblock copolymers in aqueous solutions at different pH and temperatures were investigated using DLS. Results show that both higher pH and temperature result in a higher degree of neutralization, weaker hydrogen bonding, and micellar aggregation. As observed by TEM, changes in micellar morphology are in accordance with DLS results.

Click‐Chemistry: An Alternative Way to Functionalize Poly(2‐methyl‐2‐oxazoline)

Abstract: CROP has been used to synthesize well-defined POXZ with a monofunctional (iodomethane) or a bifunctional (1,3-diiodopropane) initiator. POXZ has been functionalized with an azido group at one (α-azido- POXZ n = 3.58 × 10 3 g · mol -1 ) or both ends (α,ω-azido-POXZ, n = 6.21 × 10 3 g · mol -1 ) of the macromolecular chain. The Huisgen 1,3-dipolar cycloaddition has been investigated between azido-POXZ and a terminal alkyne on a small or larger molecule (PEG). In each case, the click reaction has been successful and quantitative. In this way, different telechelic polymers (polymers bearing different functions such as acrylate, epoxide, or carboxylic acid) and block copolymers of POXZ and PEG have been prepared. The polymers have been characterized by means of FTIR, 1 H NM R, and SEC.

Responsive Poly(acrylic acid) and Poly(N-isopropylacrylamide) Monoliths by High Internal Phase Emulsion (HIPE) Templating

Abstract: High internal phase emulsions are used to prepare cross-linked polystyrene/poly(acrylic acid) (PS/PAA) and polystyrene/poly(N-isopropyl acrylamide) (PS/PNIPAM) monoliths with a polystyrene scaffold and acrylic domains inside the cavities of the scaffold. Acrylic acid or NIPAM are included in the aqueous phase of a high internal phase emulsion, while the oil phase includes styrene. Polymerisation of such high internal phase emulsions (HIPEs) yields macroporous polymers (polyHIPEs) with a scaffold composed of cross-linked polystyrene and domains of cross-linked poly(acrylic acid) or cross-linked poly(NIPAM) positioned inside the cavities of the polystyrene skeleton. Monolithic discs are shaped from PS/PAA and PS/PNIPAM polyHIPEs in order to study the dependence of flow resistance through the discs in relation to pH or temperature changes. The amount of acrylic component in the aqueous phase and the degree of cross-linking prove to be the most influential on the pressure drops of columns with monolithic discs. The temperature influences the resistance properties in the case of PS/PNIPAM material. Inverse size exclusion chromatography experiments confirm the pH dependent structure of the polymeric monoliths.

An Intriguing Morphology Evolution of Polyoxometalate‐Polystyrene Hybrid Amphiphiles from Vesicles to Tubular Aggregates

Abstract: The originally synthesized hydrophobic hybrid polymer Bu 4 N + -POM-PS is tuned into a giant amphiphile composed of a hydrophilic H + -POM head and a hydrophobic PS tail through protonation. Immediately, the hybrid amphiphiles self-assemble into vesicles. A further annealing treatment induces an evolution from vesicles to tubular aggregates containing H + -POM nanotubes wrapped with PS coronas. After this transformation, the tubular aggregates grow further and then arrange in a parallel manner to form domains. This interesting morphology evolution provides us an opportunity to understand the intriguing aggregation behavior of the hybrid amphiphiles and, meanwhile, to generate POM nanotubes which might be utilized to create nanomaterials for potential applications.

Efficiency Increase of Poly(ethylene terephthalate-co-isosorbide terephthalate) Synthesis using Bimetallic Catalytic Systems

Abstract: New catalytic systems are developed to increase the transesterification efficiency during the synthesis of poly(ethylene terephthalate-co-isosorbide terephthalate) with the aim of compensating for the lack of reactivity of the isosorbide and to reduce the coloration of the polymer. The combination of antimony oxide with a second metal (lithium-, magnesium-, or aluminium-based compounds) is investigated, leading to the discovery of innovative antimony-based bimetallic catalytic systems that exhibit a higher polymerization efficiency, even at high isosorbide contents (20%) and, in some cases, lower coloration.

Thermofluorescent Conjugated Polymer Sensors for Nano- and Microscale Temperature Monitoring

Abstract: It is shown that due to the inherent irreversible non-fluorescence to fluorescence transition feature of polydiacetylene (PDA) supramolecules that occurs in response to thermal perturbations, PDA vesicles embedded in a host polymer matrix function as nano/microscale temperature indicators. As a result, they are used to monitor temperature gradients on an integrated circuit chip and to uncover submicrometer size filamentary defects in a resistance random access memory (RRAM) device structure. This new methodology should find a wide applicability in carrying out temperature distribution analysis on semiconductor and micro-electromechanical system (MEMS) devices where the detection of local heat deviations of small-scale components is critical.

The Influence of Blend Morphology (Co-Continuous or Sub-Micrometer Droplets Dispersions) on the Nucleation and Crystallization Kinetics of Double Crystalline Polyethylene/Polyamide Blends Prepared by Reactive Extrusion

Abstract: Reactive blending of functionalized polyethylenes (PE) and polyamides (PA) is performed by carefully choosing extrusion conditions and polymeric materials in order to obtain two types of stable morphologies. The first blend type yields a co-continuous morphology and the second type a dispersion of sub-micron droplets of the PA phase in a PE matrix. The crystallization kinetics of the PA change from a sigmoidal classical type (for the co-continuous blend) to first-order kinetics in the case of the sub-micron PA droplets. The results demonstrate an intimate relationship between blend morphology and nucleation and crystallization kinetics of the blend components.

Multifunctional Porous Poly(vinylidene fluoride)-graft-Poly(butyl methacrylate) with Good Li+ Ion Conductivity

Abstract: PnBMA is grafted on PVDF using ATRP in NMP solution at 90 °C and characterized by means of 1D and 2D NMR. 19 F NMR spectra clearly reveal that the attack occurs on the head-head >CF 2 groups. Cast PB films show a honeycomb-patterned porous microstructure, and the "breath-figure" model is used to explain pore formation. FT-IR spectra suggest a supramolecular interaction between >C=O groups of PnBMA and >CF 2 groups of PVDF. Storage modulus, loss modulus and stress at break decrease with graft conversion, but the strain at break increases significantly. The toughness of the copolymers also increases dramatically (882%). The porous materials can be applied as solid-state electrolytes (Li + -doped) with good ionic conductivity (10 -5 S · cm -1 ).