Reactive block copolymer modified thermosets : highly ordered nanostructures and improved properties

A highly ordered poly(dimethyl siloxane)-poly(glycidyl methacrylate) (PDMS-PGMA) reactive diblock copolymer was synthesized and used to modify bisphenol A-type epoxy resin (ER). The PDMS-PGMA block copolymer consisted of epoxy-miscible PGMA blocks and an epoxy-immiscible PDMS block. The PGMA reactive block of the block copolymer formed covalent bonds with cured epoxy and was involved in the network formation, and the PDMS block phase separated to give different ordered and disordered nanostructures at different blend compositions. The solvent cast PDMS-PGMA diblock copolymer showed ordered hexagonal cylindrical morphology. A highly ordered morphology consisting of hexagonal cylinders inside the lamellar morphology was observed in the cured PDMS-PGMA block copolymer. In the cured ER/PDMS-PGMA blends, a variety of morphologies including lamellar, cubic and worm-like and spherical nanostructures were detected depending on the blend composition. Moreover, the addition of this reactive diblock copolymer significantly increases the hydrophobicity and the glass transition temperature. It also improves the tensile strength and tensile ductility of the nanostructured thermosets at low diblock copolymer contents.

Competitive hydrogen bonding and self-assembly in Poly(2-vinyl pyridine)-block-Poly(methyl methacrylate)/ Poly(hydroxyether of bisphenol A) blends

Blends of poly(2-vinyl pyridine)-block-poly(methyl methacrylate) (P2VP-b-PMMA) and poly(hydroxyether of bisphenol A) (phenoxy) were prepared by solvent casting from chloroform solution. The specific interactions, phase behavior and nanostructure morphologies of these blends were investigated by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). In this block copolymer/homopolymer blend system, it is established that competitive hydrogen bonding exists as both blocks of the P2VP-b-PMMA are capable of forming intermolecular hydrogen bonds with phenoxy. It was observed that the interaction between phenoxy and P2VP is stronger than that between phenoxy and PMMA. This imbalance in the intermolecular interactions and the repulsions between the two blocks of the diblock copolymer lead to a variety of phase morphologies. At low phenoxy concentration, spherical micelles are observed. As the concentration increases, PMMA begins to interact with phenoxy, leading to the changes of morphology from spherical to wormlike micelles and finally forms a homogenous system. A model is proposed to describe the self-assembled nanostructures of the P2VP-b-PMMA/phenoxy blends, and the competitive hydrogen bonding is responsible for the morphological changes.

Zwitterion effect in polyelectrolyte gels based on lithium methacrylate-N,N-dimethyl acrylamide copolymer

Zwitterionic compounds such as those based on 1-butylimidazolium-3-(n-butanesulfonate) have previously been shown to have positive effects on the transport properties of polyelectrolytes. The addition of the zwitterion has been found to, in some cases, increase the dissociation of the lithium ion and enhance the conductivity by almost an order of magnitude. In this work, we report the effects of adding the above-mentioned zwitterion into the polyelectrolyte gel system poly(lithium methacrylate-co-N,N-dimethyl acrylamide); the anionic group being a stronger base leads to different behaviour for this copolymer compared to previous work. Polyelectrolyte gels based on dimethyl sulfoxide and polyether solvents were investigated to determine the breadth of applicability of the zwitterion in improving lithium ion transport. Impedance spectroscopy and pulse field gradient-NMR diffusion indicate an increase in the number of available charge carriers with zwitterion addition in some gel systems, however, the effect is not universal.

Poly methacrylate-plasticiser-salt blends as solid polymer electrolytes

Methoxy-ethylene glycol methacrylates, CH₂=CMeCOO(CH₂CH₂O)_nMe (n = 1, 2, 3), ethoxy-triethylene glycol methacrylate, CH₂=CMeCOO(CH₂CH₂O)₃Et, and N,N-dimethylaminoethyl methacrylate, CH₂=CMeCOOCH₂CH₂NMe₂, were used to synthesise the corresponding polymers. Conductivities of these polymers complexed with lithium perchlorate were investigated. Tetraethylene glycol dimethyl ether was used as plasticiser to increase the conductivity of the materials. A conductivity of 10⁻⁵ S cm⁻¹ was obtained at room temperature for the plasticised polymer samples. Effects of polymer structure, plasticiser, salt concentration and temperature on conductivity and glass transition temperature of the polymer electrolytes are discussed.

Reinforcement of natural rubber with core-shell structure silica-poly(Methyl Methacrylate) nanoparticles

A highly performing natural rubber/silica (NR/SiO2) nanocomposite with a SiO2 loading of 2 wt% was prepared by combining similar dissolve mutually theory with latex compounding techniques. Before polymerization, double bonds were introduced onto the surface of the SiO2 particles with the silane-coupling agent. The core-shell structure silica-poly(methyl methacrylate), SiO2-PMMA, nanoparticles were formed by grafting polymerization of MMA on the surface of the modified SiO2 particles via in situ emulsion, and then NR/SiO2 nanocomposite was prepared by blending SiO2-PMMA and PMMA-modified NR (NR-PMMA). The Fourier transform infrared spectroscopy results show that PMMA has been successfully introduced onto the surface of SiO2, which can be well dispersed in NR matrix and present good interfacial adhesion with NR phase. Compared with those of pure NR, the thermal resistance and tensile properties of NR/SiO2 nanocomposite are significantly improved.

Polystyrene-b-poly(oligo(ethylene oxide) monomethyl ether methacrylate)-bpolystyrene triblock copolymers as potential carriers for hydrophobic drugs

A simple and effective method is introduced to synthesize a series of polystyrene-b-poly(oligo(ethylene oxide) monomethyl ether methacrylate)-b- polystyrene (PSt-b-POEOMA-b-PSt) triblock copolymers. The structures of PSt-b-POEOMA-b-PSt copolymers were characterized by Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H NMR) spectroscopy. The molecular weight and molecular weight distribution of the copolymer were measured by gel permeation chromatography (GPC). Furthermore£ the self-assembling and drug-loaded behaviours of three different ratios of PSt-b-POEOMA-b-PSt were studied. These copolymers could readily self-assemble into micelles in aqueous solution. The vitamin E-loaded copolymer micelles were produced by the dialysis method. The micelle size and core-shell structure of the block copolymer micelles and the drug-loaded micelles were confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The thermal properties of the copolymer micelles before and after drug-loaded were investigated by different scanning calorimetry (DSC). The results show that the micelle size is slightly increased with increasing the content of hydrophobic segments and the micelles are still core-shell spherical structures after drug-loaded. Moreover, the glass transition temperature (Tg) of polystyrene is reduced after the drug loaded. The drug loading content (DLC) of the copolymer micelles is 70%-80% by ultraviolet (UV) photolithography analysis. These properties indicate the micelles self-assembled from PSt-b- POEOMA-b- PSt copolymers would have potential as carriers for the encapsulation of hydrophobic drugs.

A facile method to fabricate carbon nanostructures via the self-assembly of polyacrylonitrile/poly (methyl methacrylate-b-polyacrylonitrile) AB/B' type block copolymer/homopolymer blends

The self-assembly and high temperature behavior of AB/B′ type block copolymer/homopolymer blends containing polyacrylonitrile (PAN) polymers were studied for the first time. Here, microphase separated nanostructures were formed in the poly(methyl methacrylate-b-polyacrylonitrile) (PMMAN) block copolymer and their blends with homopolymer PAN at various blend ratios. Additionally, these nanostructures were transformed into porous carbon nanostructures by sacrificing PMMA blocks via pyrolysis. Spherical and worm like morphologies were observed in both TEM and AFM images at different compositions. The thermal and phase behavior examinations showed good compatibility between the blend components in all studied compositions. The PAN homopolymer (B′) with a comparatively higher molecular weight than the corresponding block (B) of the block copolymer is expected to exhibit ‘dry brush’ behavior in this AB/B′ type system. This study provides a basic understanding of the miscibility and phase separation in the PMMAN/PAN system, which is important in the nanostructure formation of bulk PAN based materials with the help of block copolymers to develop advanced functional materials.

Surface patterns induced by laser irradiation on thin polymer bilayer films

We report on the preparation of wavelike surface patterns with characteristic wavelengths on thin bilayers of poly(methyl methacrylate) on azobenzene liquid crystalline polymer films (LCP/PMMA) by irradiation of a single polarized pulsed laser beam. The formation of such patterns was influenced by the thickness of the upper layer and the laser fluence. We were also able to guide the wavelike pattern to have a specific orientation by placing an elastic polydimethylsiloxane (PDMS) mold on the surface of bilayer film prior to laser irradiation. Moreover, the property of the laser irradiation, that is, the selectivity through mask-projection systems, allowed us fabricating complicated micropattems for novel microdevices. (c) 2007 Elsevier B.V. All rights reserved.

Ionic conductivity studies of polymeric electrolytes containing lithium salt with plasticizer

New plasticized polymer electrolytes were synthesized based on poly ethylene oxide (PEO), Poly (N,N-dimethylamino-ethyl-methacrylate) (PDMAEMA), LiN(CF₃SO₂)₂ (LITFSI) as the salt and tetraethylene glycol dimethyl ether(tetraglyme) and EC + PC as plasticizers. The preparation and characterization of the polymer electrolytes were investigated as a function of temperature and various concentrations of LITFSI. Impedance spectroscopy and differential scanning calorimeter (DSC) were used to characterize the effects of various temperature, lithium salt concentration and two plasticizers on conductivity. The complex of PDMAEMA/PEO/LiTFSI/tetraglyme (S2) exhibits higher conductivity (4.74 × 10⁻⁴ S cm⁻¹at 25 °C) than PDMAEMA/PEO/LiTFSI/EC + PC (S1).

Polymer-in-ionic-liquid electrolytes

In order to achieve high conductivity in a polymer electrolyte, polymer-in-ionic-liquid electrolytes have been explored. It is found in this study that poly[vinylpyrrolidone-co-(vinyl acetate)] (P(VP-c-VA)) in 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl) amide (EtMeIm+Tf2N−) and poly(N,N-dimethyl acrylamide) (PDMAA) in trimethyl butyl ammonium bis(trifluoromethane sulfonyl) amide (N1114+Tf2N−) produce ion-conducting liquids and gels. The P(VP-c-VA)/ EtMeIm+Tf2N− mixture has a conductivity around 10−3 S · cm−1 at 22 °C, for copolymer concentrations up to 30 wt.-%. Thermal analysis shows that the Tg of the P(VP-c-VA)/ EtMeIm+Tf2N− system is well described by the Fox equation as a function of polymer content. Poly(methyl methacrylate) (PMMA)/ EtMeIm+Tf2N− gel electrolytes were prepared by in-situ polymerisation of the monomer in the ionic liquid. In the presence of 0.5–2.0 wt.-% of a crosslinking agent, these PMMA-based electrolytes displayed elastomeric properties and high conductivity (ca. 10−3 S · cm−1) at room temperature.

In situ photopolymerization of a gel ionic liquid electrolyte in the presence of iodine and its use in dye sensitized solar cells

We report for the first time an in situ photopolymerization of model co-monomers, 2-hydroxyethyl methacrylate (HEMA) and tetra (ethylene glycol) diacrylate (TEGDA), in an IL electrolyte containing I₂ for DSSCs. TiO₂ nanoparticles were used as the photo-initiator and co-gelator in a charge transfer polymerization reaction. The gel-IL polymer obtained was characterized in terms of the diffusion properties of the electrolyte. Preliminary results from DSSCs assembled using the gel-IL electrolyte showed energy conversion efficiency of 3.9% at 1 sun (AM1.5) and 5.0% at 0.39 sun illumination.

Measuring colour and photostability of small fleece wool samples

A convenient method for measuring the clean colour (Y and Y-Z) and photostability Δ(Y-Z) of small samples of fleece wool (0.5 g) is described. Scoured wool samples are compressed to a constant density in disposable polymethyl methacrylate spectrophotometer cells and the wool colour is measured using a standard textile laboratory reflectance spectrophotometer. Packing scoured wool into cells ensures that the irradiated fibre surface is robust and individual fibres are unable to move relative to one another during irradiation and measurement. A UVB (280–320 nm) source was used to ensure all samples regardless of initial yellowness were yellowed following exposure and photobleaching was avoided. An apparatus capable of irradiating up to 48 scoured wool samples in one batch is described. The precision of photostability measurements was assessed and the relative error in Δ(Y-Z) was 5.7%. An initial study on 75 fleece wool samples with a high range of initial yellowness showed a moderate linear correlation (R² = 0.68) between initial yellowness and Δ(Y-Z).

Microengineering of soft functional materials by controlling the fiber network formation

The engineering of soft functional materials based on the construction of three-dimensional interconnecting self-organized nanofiber networks is reported. The system under investigation is an organogel formed by N-lauroyl-L-glutamic acid di-n-butylamide (GP-1) in propylene glycol. The engineering of soft functional materials is implemented by controlling primary nucleation kinetics of GP-1, which can be achieved by both reducing thermodynamic driving force and/or introducing a tiny amount of specific copolymers (i.e., poly(methyl methacrylate comethacrylic acid)). The primary nucleation rate of GP-1 is correlated to the number density of GP-1 spherulites, which determines the overall rheological properties of soft functional materials. The results show that the presence of a tiny amount of the polymer (0.01-0.06%) can effectively inhibit the nucleation of GP-1 spherulites, which leads to the formation of integrated fiber networks. It follows that with the additive approach, the viscoelasticity of the soft functional material is significantly enhanced (i.e., more than 1.5 times at 40 °C). A combination of the thermal and additive approach led to an improvement of 3.5 times in the viscosity of the gel.