Chemical sensing materials based on electrically‐conductive immiscible polymer blends

Two families of electrically‐conductive immiscible polymer blends were studied as liquid sensing materials for an homologous series of alcohols. The systems studied include: multiphase matrices [containing carbon black (CB)] consisting of either polypropylene or high‐impact polystyrene as the major phase and thermoplastic polyurethane as the minor dispersed phase; and polyaniline (PANI) dispersed within a polystyrene matrix. Extruded filaments, produced by a capillary rheometer at various shear‐rate levels were used in the sensing experiments. The electrical resistance of these filaments was selectively sensitive to the various alcohols. Moreover, the responses displayed by these filaments are reproducible and reversible. The sensing behaviour of these blends is determined by the nature of the blend components, the blend composition and the processing conditions. An attempt is made to identify the dominant mechanisms controlling the sensing process in CB‐containing immiscible polymer blends and PANI‐containing blends. In addition, the sensing performances of these blends are compared in the light of their sensing mechanisms. Copyright © 2005 Society of Chemical Industry     

Characteristic molecular weights in the dynamics of polymer melts: n.m.r. and zero-shear viscosity

As shown in previous papers, chain fluctuations in polymer melts can be analysed into three consecutive components (local segment re-orientation, reptation within the tight tube and tube renewal). The intensity function derived on this basis leads to a series of limiting cases, which can be realized by frequency and/or molecular weight variation. The occurrence of the characteristic molecular weights M_AB, M_BC and M_C separating these limits have been verified by the aid of nuclear magnetic relaxation of linear polyethylene and atactic polystyrene melts. The M_C-values are equivalent to the critical molecular weights as known from rheology. An expression for the zero-shear viscosity in the whole range of molecular weights has been derived.     

Thermomechanical analysis of binary polymer blends

Thermomechanical analysis by penetration and extension modes, was performed on polyolefin/polystyrene blends (high density polyethylene, low density polyethylene or isotactic polypropylene with atactic polystyrene) and polyolefin/polyolefin mixtures (high density polyethylene or low density polyethylene with isotactic polypropylene). All the measurements were performed on cylindrical specimens obtained directly by extrusion on which extensive mechanical and morphological studies were previously made. It was found that the addition of small quantities of a polymer to a different polymeric matrix tend to modify the thermomechanical behaviour of the whole system. Furthermore the results showed that such an analysis seems to be a suitable tool to get useful information on the thermal and morphological transitions as well as on the interactions between the components in the blends.     

Latex interpenetrating polymer networks based on high styrene resin

Latex interpenetrating polymer networks based on high styrene resin (“HSR300”) as seed latex and polystyrene as the second polymer have been synthesized in different compositional ratios. The morphology of resultant materials was determined by field emission electron microscopy, atomic force microscopy, transmission electron microscopy, and by dynamic mechanical analysis. A polystyrene (PS) rich shell is observed in the latex particles. At higher second polymer ratios, a PS‐rich shell can be resolved, but in general the majority of the polymer is incorporated as domains within each particle. The two crosslinked polymers are well intermeshed at the microscopic level, as reflected not only by morphology but also by single tan δ peaks in dynamic mechanical analysis (DMA) data. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 622–628, 1999     

Study on polymer solutions in solvent mixtures in the vicinity of the critical point of the solvents: 4. Saturation phenomena

Turbidimetric results have been obtained with the ternary system N,N-dimethylformamide/cyclohexane/polystyrene. The displacement of the heterogeneous region depends on the molecular weight of the polystyrene sample and for each polystyrene sample the displacement changes with the concentration of the polymer. Above a certain molecular weight of the polymer, with a given concentration, the displacement reaches a plateau region. A plateau is also obtained when we change the concentration of the polymer of a given molecular weight. The crossover region, which is determined by the appearance of the plateau region, obeys the scaling laws and is probably the region where the distance between the macromolecular coils is comparable to their diameters.     

Orientation factors and orientation distribution function of anisotropic polymer glasses determined by X-ray scattering: A comparison of different evaluation methods

This paper presents a critical analysis of the available evaluation methods to calculate the chain orientation distribution function and the orientation factors of uniaxially oriented polymer glasses from wide angle X-ray scattering data. Experimental results obtained on a stretched atactic polystyrene sample are used for the calculations.     

Plastic deformation and subsequent crystallization of thin films of isotactic/atactic polystyrene (iPS/aPS) blends

Thin films of crystallized and non crystallized isotactic polystyrene (iPS) and its blends with atactic polystyrene (aPS) were deformed below their glass transition temperature T_g. Deformation occurs in a very narrow ‘deformation zone’ (λ = 4 nm) and the deformed material exhibits long range order independent of the crystallinity of the films till concentrations of aPS up to 15%. Films containing more than 20% aPS do not show long range order within the deformed material even after subsequent annealing above T_g. From these results, which were obtained by transmission electron microscopy and electron diffraction, the conclusion is drawn that the molecular processes of crazing in amorphous polymers and the high local deformation of polymer single crystals are obeying similar mechanisms.     

Orientation and relaxation in uniaxially-stretched poly(2,6-dimethyl 1,4-phenylene oxide) — atactic polystyrene blends

Infra-red measurements of the dichroic ratio of atactic polystyrene and poly(2,6-dimethyl 1,4-phenylene oxide) absorption bands provide a valuable method for the determination of orientation as well as relaxation of chains of both polymers during stretching of their compatible blends. Influence of strain rate, temperature of stretching, and molecular weight of the polymers on orientation of both polymer chains in blends containing up to 35% PPO has been studied. Orientation relaxation for both polymers has been analysed using Lodge's constitutive equation. Master curves have been obtained for PPO and PS in the blends at a reference temperature T₀ = T_g + 10°C. Results are interpreted in terms of an hindrance of relaxation of PS chains induced by interaction with a highly-oriented PPO network which slowly relaxes.     

Dissolution dynamics of some polymers: Solvent-polymer boundaries

A critical angle illumination microscopy technique was used to study the in situ dissolution dynamics of polystyrene, poly (α-methylstyrene) and the two tactic forms of poly (methyl methacrylate), (PMMA), in several solvents. The dissolution characteristics; of polymers were found to be greatly influenced by several factors: type of polymer, processing condition of the sample, type of solvent, and tacticity, Polystyrene was found to exhibit extensive swelling in several solvents while atactic PMMA exhibited extensive cracking on dissolution. Isotactic PMMA, which has a glass temperature of about 70°C lower than the atactic PMMA, showed swelling behavior similar to atactic polystyrene, while the α-methylstyrene showed the cracking phenomena exhibited by atactic PMMA.     

Highly efficient synthesis of cylindrical polymer brushes with various side chains via click grafting-onto approach

Though much attention has been paid to synthesis of cylindrical polymer brushes, it is still not easy to prepare well-defined brushes by a general approach. Herein, well-defined cylindrical polymer brushes with various side chains were synthesized via grafting-onto approach by CuAAC click chemistry. Narrowly dispersed polymer backbones functionalized with azide groups were obtained by post-modification of poly(glycidyl methacrylate) (PGMA) which was prepared by reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerization. The alkyne-terminated side chains, polystyrene, polyacrylates, polymethacrylates and poly(N-alkyl acrylamide)s, were synthesized by RAFT mediated radical polymerization with alkyne-containing chain transfer agents (CTAs). The CuAAC reactions between the backbone and side chain polymers were conducted with an equivalent feed of alkyne-terminated side chains and azide groups under mild conditions. Influences of reaction conditions and chemical composition of polymer side chains on grafting efficiency and molecular weight distribution of the polymer brushes were investigated. It is demonstrated that the side chains of polystyrene, polyacrylates and poly(N-alkyl acylamide)s were grafted at a density above 85% while that of polymethacrylates decreased to ca. 50%. The polymer brushes synthesized under the optimized reaction conditions had well-defined chemical composition and narrow distribution of molecular weight, and their wormlike morphology was visualized by atomic force microscopy (AFM).     

Electrical conductivity of polymer blends containing liquid crystalline polymer and carbon black

This paper presents results of a study of melt‐processed immiscible polymer blends of high impact polystyrene (HIPS), liquid crystalline polymer (LCP) and carbon black (CB). Relationships between composition, electrical resistivity and morphology of the blends produced by Brabender mixing followed by compression molding, extrusion through a capillary rheometer, extrusion through a single‐screw extruder and injection molding were investigated. The LCP phase morphology in the blends was found sensitive to the processing conditions. A blend composition of at least 20 wt% LCP and 2 phr CB is necessary to preserve the conductivity of filaments produced over a wide range of shear rates. Enhancement of conductivity of blends containing CB and 30 wt% or more LCP was observed, under processing at 270°C and increasing levels of shear rate. An important role of the skin region in determining the resisitivy of injection molded samples was found. A good agreement between resistivity values of extruded or injection molded blends with resistivity values of filaments produced at similar conditions by a capillary rheometer was shown. Hence, the study of shear rate effect on resistivity of capillary rheometer filaments may serve as a predictor of resistivity behavior in real processing procedures. Polym. Eng. Sci. 44:528–540, 2004. © 2004 Society of Plastics Engineers.     

Cryogenic relaxations of polystyrene and poly(fluorinated styrenes)

The effect of structural and morphologic modifications of styrene and fluorinated styrene polymers on their internal friction was studied by means of a free-oscillating torsional pendulum at temperatures from 300° to 4.2°K and frequencies of 1 to 2 Hz. Atactic and isotactic polystyrene gave the previously observed δ and β′ loss peaks at 38° and 100°K, respectively. These losses decrease in intensity with crystallinity in isotactic polystyrene but remain relatively unchanged in uniaxially drawn atactic polymer. Atactic polypentafluorostyrene showed an intense δ loss peak at 52°K and a broad shoulder around 100°K, which extends toward the β′ relaxation. In poly-α,β,β-trifluorostyrene, the δ loss peak is largely suppressed, the logarithmic decrement showing only broad maxima at 22° and 100°K. Plasticization of atactic polystyrene with 2% mineral oil gives rise to a sharp loss maximum at 100°K, which does not occur in the pure atactic polymer.     

Porous polystyrene-based monolithic materials templated by semi-interpenetrating polymer networks for capillary electrochromatography

Porous polystyrene-based monolithic columns were engineered through the in-situ generation of poly(?-caprolactone) (PCL)/polystyrene (PS) semi-interpenetrating polymer networks (semi-IPNs), followed by the extraction of the uncrosslinked partner acting as a polymeric porogen. In a first stage, the semi-IPNs were prepared within the confines of fused silica capillaries by UV-initiated free-radical copolymerization of styrene and divinylbenzene, in the presence of PCL oligomers. In a second stage, the quantitative extraction of uncrosslinked oligoesters led to the formation of porous frameworks with a hierarchical porosity, as evidenced by SEM and DSC-based thermoporometry. Such as-obtained porous monoliths could be efficiently used as reversed-phase stationary phases for the separation of alkyl benzene derivatives by capillary electrochromatography (CEC).     

Preparation of styrene-based, magnetic polymer microspheres by a swelling and penetration process

A swelling and penetration process is proposed to prepare magnetic polymer microspheres. Micron-size polystyrene (PS) particles were swollen in an aqueous solution of N-methyl-2-pyrrolidone (NMP) and then mixed with superparamagnetic iron oxide nanoparticles. The magnetic nanoparticles were able to diffuse into polymer microspheres and were entrapped within the polymer microspheres. The saturation magnetization of resultant magnetic polymer microspheres increased as increasing magnetic nanoparticle concentrations were added to the swelling mixture. A higher ratio of NMP-to-water led to a greater swelling but a larger loss of polymer mass due to polymer chain dissolution in the NMP solution. Sodium dodecyl sulfate (SDS) in the NMP aqueous solution significantly enhanced the swelling and penetration process. The use of SDS could not only shorten the process time but also lower the required NMP concentration. The proposed method also worked well in preparing magnetic polymers microspheres with other styrene-based copolymer beads like poly(styrene–glycidyl methacrylate) (PS–GMA).     

Penetrant transport in polyethylene-polystyrene semi-interpenetrating polymer networks

In this study, diffusion behavior is investigated for polyethylene-polystyrene semi-interpenetrating polymer networks (PES-IPN) with toluene and chloroform and for a polyethylene/toluene system. The results show that diffusion in the semi-IPN material consists of a continuous polyethylene phase containing disperse polystyrene and that the transport in this material closely parallels transport in the homogeneous polyethylene. Consequently, the measured diffusion coefficients can be correlated, using the free-volume theory and parameters which characterize the free volume of the continuous phase, as a function of temperature and concentration. In addition, from the diffusivities of toluene in the polyethylene and the solubilities in the polyethylene and polystyrene, the diffusion coefficients of the PES-IPN/toluene system are predicted with an unsteady-state diffusion model developed in this study. Predictions with the new unsteady-state model are comparable with the experimental data. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 51–57, 1997     

Epimerization of isotactic polystyrene

Summary A procedure for epimerizing isotactic polystyrene and a Monte-Carlo computer program for simulating polymer epimerization reactions have been developed. The 300 MHz methine proton resonance patterns of partially epimerized isotactic polystyrene and of free radical initiated polystyrene have been analyzed. The latter polymer is essentially atactic (=0.45±0.05) and has the same nmr spectrum as completely epimerized polystyrene. Conventional polystyrene therefore seems to be at stereochemical equilibrium.     

Microstructure formation in polymer composites prepared with polypropylene and a polyaniline complex

BACKGROUND: Results of a feasibility study to produce elongated structures of an electro‐conductive polyaniline complex (PANICOM) within polymer composites by means of an in situ deformation process are reported. The aim was to find an alternative route to produce fiber‐like polymer materials with potential applications in electrostatic discharge (ESD) protection. PANICOM–polypropylene blends with PANICOM contents ranging from 1 to 50 wt% were capillary extruded. The microstructure was analyzed using optical and scanning electron microscopy. Conductivity measurements were carried out. Tensile mechanical properties were also characterized. RESULTS: PANICOM was deformed into elongated structures, embedded within the polypropylene, preferentially oriented in the extrusion direction. The highest conductivity levels were reached for PANICOM contents of 15 wt% and greater. For contents of PANICOM of about 5 to 10 wt%, the conductivities lay within the optimal ESD range, and the breaking tenacity was only about 25% lower than that of pure polypropylene. CONCLUSION: The results obtained provide further evidence to support the feasibility of producing electrically conductive fibers of PANICOM within a suitable polymer matrix by means of a simple in situ deformation process, so as to allow the fabrication of conducting composites with potential applications in ESD protection. Copyright © 2009 Society of Chemical Industry     

Microcrystallization of Atactic Polystyrene Induced by Photooxidation Aging

Photooxidation aging, hygrothermal aging, and hot-air aging are carried out on atactic polystyrene (aPS) samples formed by injection molding. It is interesting that microcrystals of atactic polystyrene are only found in photooxidation aging. This work proposes that high molecular weight atactic polystyrene can crystallize under photooxidation aging. It is a good addition to the research on the aspect of crystallization of atactic polystyrene.     

Preparation and Characterization of Confined Atactic Polystyrene in Ordered Silica/Polystyrene Composites

Ordered silica/polystyrene composites were prepared via radical polymerization in silica colloidal crystal templates, and ordered macroporous polymers were accordingly obtained after removing the silica templates. The confinement effect of the templates on the polymers in the composites was investigated. NMR results indicated that the polystyrenes formed both inside and outside the template were atactic. The polystyrene inside the template possessed a higher molecular weight and a narrower molecular weight distribution than the bulk one outside the template. The glass transition temperature of the confined polystyrene increased significantly with decreasing silica sphere size of the templates, and so did the contraction of polymer pores. The smaller the silica sphere size of the templates, the more remarkable is the confinement, which could be explained by entropic confinement of the polymer chains within a fixed inorganic meso‐framework (T. P. Russell, Science 2001 , 293, 446).     

Analysis of wide-angle X-ray diffraction patterns of aligned glassy polymers with particular references to polystyrene

Improvement of WAXD patterns from aligned glassy polymers by a numerical desmearing technique is reported. This gives a fibre type diffraction pattern that can be more easily interpreted than radial or cylindrical distribution functions. Application to atactic and quenched isotactic polystyrene shows that the molecular conformations that are found are in agreement with those deduced from i.r. and n.m.r. spectroscopy. For isotactic polystyrene there is significant agreement between the fibre pattern of the aligned glassy polymer and that of the drawn crystalline polymer.