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Microphase Separation (microphase + separation)
Terms modified by Microphase Separation Selected AbstractsPhotoinduced Microphase Separation in Block Copolymers: Exploring Shape Incompatibility of Mesogenic Side GroupsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 11 2010Yi Zhao Abstract Photoinduced microphase separation in block copolymers (BCP) was achieved for the first time, using a rationally designed diblock copolymer composed of two side-chain liquid crystalline polymers (SCLCP). The miscibility of the two blocks was promoted by the miscibility between the two types of mesognic side groups, while upon UV exposure inducing the trans,cis isomerization of azobenzene mesogens on one SCLCP, the shape incompatibility of bent cis isomers with an ordered liquid crystalline phase drove the separation of the two blocks resulting in a microphase separated morphology. This result shows the perspective of using light to process and organize BCP morphology and related nanostructures in a lithography-free manner. [source] Behaviors of self-assembled diblock copolymer with pendant photosensitive azobenzene segmentsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2010Jui-Hsiang Liu Abstract A novel monomer, ethyl 4-[4-(11-methacryloyloxyundecyloxy)phenyl azobenzoyl-oxyl] benzoate, containing a photoisomerizable NN group was synthesized. The monomer was further diblock copolymerized with methyl methacrylate. Amphiphilic diblock copolymer poly(methyl methacrylate- block -ethyl 4-[4-(11-methacryloyloxyundecyloxy)phenyl azobenzoyl-oxyl] benzoate (PMMA - b - PAzoMA) was synthesized using atom transfer radical polymerization. The reverse micelles with spherical construction were obtained with 2 wt % of the diblock copolymer in a THF/H2O mixture of 1:2. Under alternating UV and visible light illumination, reversible changes in micellar structure between sphere and rod-like particles took place as a result of the reversible E-Z photoisomerization of azobenzene segments in PMMA - b - PAzoMA. Microphase separation of the amphiphilic diblock copolymer in thin films was achieved through thermal and solvent aligning methods. The microphases of the annealed thin films were investigated using atom force microscopy topology and scanning electron microscopy analyses. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1142,1148, 2010 [source] Highly Fluorinated Comb-Shaped Copolymers as Proton Exchange Membranes (PEMs): Improving PEM Properties Through Rational Design,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2006B. Norsten Abstract A new class of comb-shaped polymers for use as a proton conducting membrane is presented. The polymer is designed to combine the beneficial physical, chemical, and structural attributes of fluorinated Nafion-like materials with higher-temperature, polyaromatic-based polymer backbones. The comb-shaped polymer unites a rigid, polyaromatic, hydrophobic backbone with lengthy hydrophilic polymer side chains; this combination affords direct control over the polymer nanostructure within the membrane and results in distinct microphase separation between the opposing domains. The microphase separation serves to compartmentalize water into the hydrophilic polymer side chain domains, resulting in effective membrane water management and excellent proton conductivities. [source] Self-Assembled Shape-Memory Fibers of Triblock Liquid-Crystal Polymers,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2006V. Ahir Abstract New thermoplastic liquid-crystalline elastomers have been synthesized using the telechelic principle of microphase separation in triblock copolymers. The large central block is made of a main-chain nematic polymer renowned for its large spontaneous elongation along the nematic director. The effective crosslinking is established by small terminal blocks formed of terphenyl moieties, which phase separate into semicrystalline micelles acting as multifunctional junction points of the network. The resulting transient network retains the director alignment and shows a significant shape-memory effect, characteristic and exceeding that of covalently bonded nematic elastomers. Its plasticity at temperatures above the nematic,isotropic transition allows drawing thin well-aligned fibers from the melt. The fibers have been characterized and their thermal actuator behavior,reversible contraction of heating and elongation on cooling,has been investigated. [source] Effective preparation and characterization of montmorillonite/poly(,-caprolactone)-based polyurethane nanocompositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Eun Hwan Jeong Abstract In this study, montmorillonite (MMT)/poly(,-caprolactone)-based polyurethane cationomer (MMT/PCL-PUC) nanocomposites were prepared and their mechanical properties, thermal stability, and biodegradability were investigated. PCL-PUC has 3 mol % of quaternary ammonium groups in the main chain. The MMT was successfully exfoliated and well dispersed in the PCL-PUC matrix for up to 7 wt % of MMT. The 3 mol % of quaternary ammonium groups facilitated exfoliation of MMT. The 1 wt % MMT/PCL-PUC nanocomposites showed enhanced tensile properties relative to the pure PCL-PU. As the MMT content increased in the MMT/PCL-PUC nanocomposites, the degree of microphase separation of PCL-PUC decreased because of the strong interactions between the PCL-PUC chains and the exfoliated MMT layers. This resulted in an increase in the Young's modulus and a decrease in the elongation at break and maximum stress of the MMT/PCL-PUC nanocomposites. Biodegradability of the MMT/PCL-PUC nanocomposites was dramatically increased with increasing content of MMT, likely because of the less phase-separated morphology of MMT/PCL-PUC. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Mechanistic understanding of degradation in bioerodible polymers for drug deliveryAICHE JOURNAL, Issue 12 2002Domenico Larobina A new model was developed to understand the mechanism of erosion in bioerodible polymers, which is essential to accurately predict drug release and precisely design controlled release devices. This model takes into account the phenomenon of microphase separation observed for polyanhydrides of certain copolymer compositions, and assumes that erosion is dominated by degradation and, thus, in a system with a fast eroding and a slow eroding species, two rate constants,one for each species,essentially control the evolution of the polymer microstructure. Expressions were derived for the fraction of each monomer released, as well as for the porosity in the system. A partition coefficient accounts for thermodynamic partitioning of a drug into the microdomains. The solutions of the model equations were fitted to experimental data on monomer release kinetics from two polyanhydride systems to obtain the erosion rate constants. Drug release kinetics experiments are compared to the model solution for drug release, and the partition coefficient of the drug is obtained from the fits. The comparisons to the data are promising, while pointing out the limitations of the model. The model does not account for oligomer formation prior to monomer release or for the dependence of the rate constants on parameters such as the degree of crystallinity, the local pH, and the polymer molecular weight. [source] Synthesis and properties of novel sulfonated polyimides containing binaphthyl groups as proton-exchange membranes for fuel cellsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2007Yuhan Li Abstract A novel sulfonated diamine monomer, 2,2,-bis(p -aminophenoxy)-1,1,-binaphthyl-6,6,-disulfonic acid (BNDADS), was synthesized. A series of sulfonated polyimide copolymers containing 30,80 mol % BNDADS as a hydrophilic component were prepared. The copolymers showed excellent solubility and good film-forming capability. Atomic force microscopy phase images clearly showed hydrophilic/hydrophobic microphase separation. The relationship between the proton conductivity and degree of sulfonation was examined. The sulfonated polyimide copolymer with 60 mol % BNDADS showed higher proton conductivity (0.0945,0.161 S/cm) at 20,80 °C in liquid water. The membranes exhibited methanol permeability from 9 × 10,8 to 5 × 10,7 cm2/s at 20 °C, which was much lower than that of Nafion (2 × 10,6cm2/s). The copolymers were thermally stable up to 300 °C. The sulfonated polyimide copolymers with 30,60 mol % BNDADS showed reasonable mechanical strength; for example, the maximum tensile strength at break of the sulfonated polyimide copolymer with 40 mol % BNDADS was 80.6 MPa under high moisture conditions. The optimum concentration of BNDADS was found to be 60 mol % from the viewpoint of proton conductivity, methanol permeability, and membrane stability. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 222,231, 2007 [source] Synthesis of a novel hybrid liquid-crystalline rod,coil diblock copolymerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2003Yi Yi Abstract A series of novel rod,coil diblock copolymers on the basis of mesogen-jacketed liquid-crystalline polymer were successfully prepared by atom transfer radical polymerization from the flexible polydimethylsiloxane (PDMS) macroinitiator. The hybrid diblock copolymers, poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene}- block -polydimethylsiloxane, had number-average molecular weights (Mn's) ranging from 9500 to 30,900 and relatively narrow polydispersities (,1.34). The polymerization proceeded with first-order kinetics. Data from differential scanning calorimetry validated the microphase separation of the diblock copolymers. All block copolymers exhibited thermotropic liquid-crystalline behavior except for the one with Mn being 9500. Four liquid-crystalline diblock copolymers with PDMS weight fractions of more than 18% had two distinctive glass-transition temperatures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1799,1806, 2003 [source] Structure and Properties of Poly(, -caprolactone) Networks with Modulated Water UptakeMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 23 2006Jorge L. Escobar Ivirico Abstract Summary: A PCL macromonomer was obtained by the reaction of PCL diol with methacrylic anhydride. The effective incorporation of the polymerizable end groups was assessed by FT-IR and 1H NMR spectroscopy. PCL networks were then prepared by photopolymerization of the PCL macromonomer. Furthermore, the macromonomer was copolymerized with HEA, with the aim of tailoring the hydrophilicity of the system. A set of hydrophilic semicrystalline copolymer networks were obtained. The phase microstructure of the new system and the network architecture was investigated by DSC, IR, DMS, TG, dielectric spectroscopy and water sorption studies. The presence of the hydrophilic units in the system prevented PCL crystallization on cooling; yet there was no effect on the glass transition process. The copolymer networks showed microphase separation and the , relaxation of the HEA units moved to lower temperatures as the amount of PCL in the system increased. Ideal structure, compatible with the experimental results, for the hydrophilized poly(, -caprolactone) networks with modulated water uptake. [source] Photoinduced Microphase Separation in Block Copolymers: Exploring Shape Incompatibility of Mesogenic Side GroupsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 11 2010Yi Zhao Abstract Photoinduced microphase separation in block copolymers (BCP) was achieved for the first time, using a rationally designed diblock copolymer composed of two side-chain liquid crystalline polymers (SCLCP). The miscibility of the two blocks was promoted by the miscibility between the two types of mesognic side groups, while upon UV exposure inducing the trans,cis isomerization of azobenzene mesogens on one SCLCP, the shape incompatibility of bent cis isomers with an ordered liquid crystalline phase drove the separation of the two blocks resulting in a microphase separated morphology. This result shows the perspective of using light to process and organize BCP morphology and related nanostructures in a lithography-free manner. [source] Gelation Rate Modulation of an , -Cyclodextrin and Poly(ethylene glycol)-Grafted Hyaluronic Acid Solution System by Inclusion Complexation of a Microphase-Separated StructureMACROMOLECULAR RAPID COMMUNICATIONS, Issue 6 2004Tsuyoshi Nakama Abstract Summary: The gelation rate of a poly(ethylene glycol)-grafted hyaluronic acid (PEG- graft -HA) solution with adding , -CD was investigated in term of the microphase separation between the grafted PEG and HA. The gelation rate of PEG- graft -HA exhibiting the microphase-separated structure was two times higher than that of PEG- graft -HA showing a homogeneous miscible state. The formation of microphases by PEG- graft -HA contributes to its rapid gelation upon the addition of , -CDs. [source] Investigations of Miscibility in Interpenetrated Systems of Polyurethane and Polystyrene Obtained at Room TemperatureMACROMOLECULAR SYMPOSIA, Issue 1 2004Jean-Michel Widmaier Abstract Interpenetrating polymer systems based on crosslinked polyurethane (PU) and polystyrene (PS) were prepared at room temperature by a one-shot (in situ) method, starting from an initial homogeneous mixture of reagents via non interfering mechanisms. Both polymerizations were performed either simultaneously or one after the other. Crosslinks and/or covalent bonds between components were deliberately introduced by the addition of appropriate monomers, in order to tailor the degree of microphase separation. Depending on the formation process, transluscent or transparent films were obtained, despite the difference in refractive index of the components. The maximum of miscibility, taken as from the glass transition criterion, was obtained for sequential tightly graft interpenetrating networks. [source] One- and Two-Component Bottle-Brush Polymers: Simulations Compared to Theoretical PredictionsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 7 2007Hsiao-Ping Hsu Abstract Scaling predictions for bottle-brush polymers with a rigid backbone and flexible side chains under good solvent conditions are discussed and their validity is assessed by a comparison with Monte Carlo simulations of a simple lattice model. It is shown that typically only a rather weak stretching of the side chains is realized, and then the scaling predictions are not applicable. Also two-component bottle brush polymers are considered, where two types (A,B) of side chains are grafted, assuming that monomers of different kind repel each other. In this case, variable solvent quality is allowed. Theories predict "Janus cylinder"-type phase separation along the backbone in this case. The Monte Carlo simulations, using the pruned-enriched Rosenbluth method (PERM) give evidence that the phase separation between an A-rich part of the cylindrical molecule and a B-rich part can only occur locally. The correlation length of this microphase separation can be controlled by the solvent quality. This lack of a phase transition is interpreted by an analogy with models for ferromagnets in one space dimension. [source] | ||||||||||