Electrical conductivity of graphite/polystyrene composites made from potassium intercalated graphite

Composites between graphite and polystyrene have been synthesized starting from potassium intercalated graphite and styrene vapor. This in situ polymerization process can be used to make electrically conductive composites containing well-dispersed thin graphite sheets. The conductivities of the composites increase as the number of ordered carbon layers increases. With only 10% graphite in a polystyrene matrix, an electrical conductivity up to 1.3 × 10⁻¹ S/cm can be obtained. The key is synthesizing a material with at least four ordered graphite layers (a stage IV complex) separated by polystyrene. This composite shows an improvement in conductivity over a control composite made by radical polymerization of styrene containing the same amount of dispersed graphite which had a conductivity of 5.0 × 10⁻³ S/cm. Characterization of the complexes by powder X-ray diffraction, scanning electron microscopy and electrical conductivity is presented.     

PS-EG插层复合物制备及其改性聚苯乙烯的研究

通过化学氧化、高温处理将天然鳞片石墨制成膨胀石墨(EG),采用原位聚合法制备了聚苯乙烯-膨胀石墨(PS-EG)插层复合物,并将PS-EG复合物与PS进行熔融共混,研究了PS-EG复合物含量对PS结构及性能的影响。结果表明,PS-EG的加入,使得PS的冲击强度和热性能提高,而拉伸强度下降;当PS-EG含量为9%(质量分数,下同)时,PS的冲击强度提高了63.4%;EG在复合材料中呈蠕虫状分布;PS-EG复合物的存在增加了复合材料的界面效应,冲击断面呈现孔洞式结构。     

Preparation of polystyrene–graphite conducting nanocomposites via intercalation polymerization

In situ polymerization of styrene was conducted in the presence of expanded graphite obtained by rapid heating of a graphite intercalation compound (GIC), to form a polystyrene–expanded graphite conducting composite. The composite showed excellent electrically conducting properties even though the graphite content was much lower than in normal composites. The transition of the composite from an electrical insulator to an electrical semiconductor occurred when the graphite content was 1.8 wt%, which is much lower than that of conventional conducting polymer composites. TEM, SEM and other studies suggest that the graphite was dispersed in the form of nanosheets in a polymer matrix with a thickness of 10–30 nm, without modification of the space between carbon layers and the structure of the graphite crystallites. The composite exhibited high electrical conductivity of 10^?2 S cm^?1 when the graphite content was 2.8–3.0 wt%. This great improvement of conductivity could be attributed to the high aspect ratio (width‐to‐thickness) of the graphite nanosheets. The rolling process strongly affected the conductivity and the mechanical properties of the composite. © 2001 Society of Chemical Industry     

Preparation and characterization of polystyrene/graphite composite prepared by cationic grafting polymerization

A new graphite/polystyrene composite was produced with cationic grafting polymerization of styrene initiated by CO⁺ClO⁻₄ group on the surface of expanded graphite (EG). The structures of EG and the graphite/polystyrene composite were studied with SEM and optical micrograph. The spectra of XRD and IR were used not only for confirming whether the polymerization reaction took place, but also for determining whether the polystyrene in the composite covered the surface of EG particles or intercalated into EG particles. The electrical conductivity, thermal phase transitions and mechanical properties were also discussed.     

Oriented PP-PS composites obtained by polymerization of styrene inside oriented PP matrices. I. Dispersion of PS and the composites' orientation

Dispersion of polystyrene (PS) and the molecular orientation of the polypropylene–polystyrene (PP–PS) composites acquired by the in situ polymerization of styrene in the oriented PP matrices were characterized by microscopic observations, birefringence measurements, and differential scanning calorimetry. It has been shown that applied processing of the “envelope” polymerization leads to obtaining oriented composites with large contents and the specific dispersion of PS. Some composites exhibit a substantial gradient of PS concentration and a gradient of molecular orientation, both strongly dependent on the initial structure of the oriented PP matrix. The modification of the PP structure taking place during processing does not disturb the orientation of the matrices deformed to the higher draw ratios. The structural changes of the oriented PP induced by processing are reflected in the shrinkage behavior and mechanical properties discussed in the second part of this paper. © 1993 John Wiley & Sons, Inc.     

Toughened polystyrene composites by the concentrated emulsion pathway

Rubber–styrene solutions of various compositions and containing a suitable initiator have been polymerized starting from concentrated emulsions in which the above solutions constitute the dispersed phase and solutions of sodium dodecylsulfate in water the continuous phase. Latexes of rubber-modified polystyrene composites have been thus obtained. Solutions of rubber–styrene have been also polymerized by bulk polymerization for comparison purposes. The molecular weights have been determined from intrinsic viscosity measurements, and the mechanical properties of the composites have been studied via tensile testings. Because of the lower mobility of the high-molecular radicals in the concentrated emulsions, higher molecular weights have been obtained by the concentrated emulsion polymerization than by the bulk polymerization method. The tensile properties and toughness of the composites have been determined. While the two polymerization methods provide high, comparable toughness, the concentrated emulsion method generates latexes that can be easily processed in any desirable shape. © 1994 John Wiley & Sons, Inc.     

聚苯乙烯/氧化石墨纳米复合材料的制备

天然石墨在浓硫酸中用高锰酸钾氧化成氧化石墨(GO),在含有氧化石墨的苯乙烯乳液中进行自由基聚合,可以得到层间插入聚苯乙烯(PS)的石墨纳米复合材料。研究发现,在聚合过程中不仅发生了苯乙烯均聚反应,而且存在插入聚合反应,并用FTIR、XRD、TEM等手段进行表征。     

Preparation and structures of ethyl–cyanoethyl cellulose/cross-linked polystyrene composites

Ethyl–cyanoethyl cellulose [(E–CE)C]/cross-linked polystyrene (PS) composites were prepared via polymerization of styrene in (E–CE)C/styrene solution with glycol diacrylate as a cross-linking reagent. The polymerization of the solution, morphology, and miscibility of (E–CE)C/PS composites were studied with polarizing microscopy, small-angle light scattering (SALS), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). It was found that the mixing state of the (E–CE)C/PS system and the thermal stability of composites were modified by cross-linking of PS. In the intensively cross-linked composite prepared from the anisotropic solution, there existed cylindrical domains in which (E–CE)C spherulites were dispersed in PS. © 1994 John Wiley & Sons, Inc.     

Synthesis and properties of polystyrene–clay nanocomposites via in situ intercalative polymerization

Organophilic montmorillonite (MMT) was prepared by ion exchange between Na⁺ ions in the clay and twin benzyldimethyloctadecylammonium bromine cations in an aqueous medium. The organophilic MMT particles were easily dispersed and swollen in styrene monomer. Polystyrene–MMT nanocomposites were prepared by the free‐radical polymerization of styrene containing dispersed clay. The intercalation spacing in the nanocomposites and the degree of dispersion of these composites were investigated with X‐ray diffraction and transmission electron microscopy, respectively. The nanocomposites had higher weight‐average molecular weights, lower glass‐transition temperatures, and better thermal stability (the decomposition temperature was improved by ca. 70°C) than the virgin polystyrene. The rheological behavior of the polystyrene–MMT nanocomposites was also studied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 201–207, 2005     

非共价改性法制备聚苯乙烯/高分散石墨烯复合材料

以工业化石墨烯粉体(IGN)与苯乙烯为原料,聚乙烯醇、磷酸三钙为分散剂,过氧化苯甲酰为引发剂,聚苯乙烯(PS)树脂作为非共价改性组分,通过超声分散、悬浮聚合法制备了聚苯乙烯/高分散石墨烯复合材料,探究了超声分散时间与PS含量对IGN在复合材料中的分散性影响机理。结果表明,PS可提高IGN在苯乙烯(St)单体中的相容性;超声时间30 min,PS添加量为St单体质量的3 %时,复合材料微观形貌较好,IGN分散性较佳;随着PS/IGN中IGN含量的增加,复合材料的外延起始降解温度逐渐提高40 ℃,玻璃化转变温度最大提升7.3 ℃,拉伸强度由43.5 MPa增强至68.3 MPa,提升近65 %。     

Preparation of polystyrene/graphite nanosheet composite

A new process for the dispersion of graphite in the form of nanosheets in a polymer matrix was developed via in situ polymerization of monomer at the presence of sonicated expanded graphite during sonication. Graphite nanosheets prepared via powdering the expanded graphite had a thickness ranging 30-80 nm and a diameter ranging 0.5-20 μm and was an excellent nanofiller for the fabrication of polymer/graphite conducting nanocomposite. The process fabricated electrically conducting polystyrene/graphite nanosheet nanocomposite films with much lower percolation threshold and much higher conductivities than those of composites made by conventional methods.     

Synthesis of Low-Density Heat-Resisting Polystyrene/Graphite Composite Microspheres Used as Water Carrying Fracturing Proppants

Low-density heat resistamt, low-cost polystyrene (PS)/graphite microspheres were successfully synthesized via in situ suspension polymerization. Scanning electron microscopy (SEM) indicated that PS/graphite composite microspheres had good sphericity, and graphite particles were evenly dispersed in microspheres. Furthermore, density analysis illustrated that the density of composites was about 1.025–1.185 g/cm³ with good suitability for carrying water. Thermodynamic testing revealed that the thermostability of the composite was dramatically improved by the introduction of graphite, which is used deep underground. In addition, the percentage of damage decreased to 1.3% with graphite ratio of 2.5% at 68 MPa. Therefore, PS/Graphite composite microspheres possess entirely feasible applications in oil exploitation as pure water carrying petroleum proppants.     

Carbon black/polystyrene composites as candidates for gas sensing materials

Amorphous polymer-based composites consisting of polystyrene and carbon black were developed in the current work as candidates for gas sensing materials. With the help of polymerization filling, i.e., in-situ polymerization of styrene in the presence of carbon black, the composites were provided with low percolation threshold. The experimental results indicated that the composites have selective sensitivity as characterized by high electrical responsivity to the vapors of non-polar and low polar solvents, and low responsivity to high polar solvent vapors as well. Besides conductivity of the composites, absorption characteristics of both the matrix and the fillers exert importance influence on the gas sensitivity of the composites. Therefore, composites’ performance can be tailored by changing filler concentration, molecular weight and molecular weight distribution of matrix polymer, etc. In regard to the fact that most conducting polymer composites as vapor sensing materials are based on crystalline polymer matrices, the approach reported by this paper provides another feasible way to develop new candidates.     

Preparation of polystyrene/montmorillonite nanocomposites in supercritical carbon dioxide

The preparation of polystyrene (PS)/montmorillonite (MMT) composites in supercritical carbon dioxide (SC? CO₂) was studied. Lipophilic organically modified MMT can be produced through an ion‐exchange reaction between native hydrophilic MMT and an intercalating agent (alkyl ammonium). PS/clay composites were prepared by free‐radical precipitation polymerization of styrene containing dispersed clay. X‐ray diffraction and transmission electron microscopy indicated that intercalation of MMT was achieved. PS/clay composites have a higher thermal decomposition temperature and lower glass‐transition temperature than pure PS. The IR spectrum analysis showed that the solvent of SC? CO₂ did not change the structures of the PS molecules, but there were some chemical interactions between the PS and the clay in the composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 22–28, 2005     

Thermal polymerization of styrene in the presence of TEMPO

To investigate aspects of the contribution of (thermal) self-initiation in nitroxide-mediated radical polymerization (NMRP) of styrene, selective styrene polymerizations with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) in the absence of initiator were carried out at 120 and 130 °C. The results of these experiments (including conversion data, molecular weight averages, polydispersity and molecular weight distribution information) were compared with regular thermal polymerization of styrene and NMRP of styrene in the presence of a bimolecular initiator (benzoyl peroxide; BPO). It was observed that although the thermal polymerization of styrene can be controlled to some extent in the presence of TEMPO to provide polystyrene with low polydispersity, the polymerization was never as controlled as that obtained by a BPO-initiated NMRP.     

Polymer characteristics and fracture morphology of radiation-polymerized styrene-impregnated mortar

Mechanical and durability properties and the fracture morphology of polystyrene-impregnated mortar composites prepared by impregnation of styrene and its in situ polymerization by gamma radiation have been studied. Variation of flexural strength of the composites, percent extractable polystyrene, and its molecular weight suggest crosslinking of the impregnated polymer under the influence of prolonged gamma irradiation. Moreover, crosslinking appears to contribute toward the improvement in flexural strength but has little effect on durability properties. SEM micrographs of the composites reveal a very weak cement–polymer interfacial bonding which is believed to be responsible for poor durability properties of the composites.     

Production of micron-size monodisperse polymer particles by seeded polymerization utilizing dynamic swelling method with cooling process

Monodisperse polystyrene particles (6.6 μm diameter) were produced by seeded polymerization utilizing the dynamic swelling method with cooling process as follows. Monodisperse polystyrene seed particles (1.8 μm diameter) were dispersed in ethanol/water (3/4 w/w) medium containing styrene monomer, benzoyl peroxide as initiator and poly(vinyl alcohol) as stabilizer at 65d?C. By lowering the temperature to ?5d?C at a speed of ?1d?C/min the polystyrene seed particles were swollen from 1.8 to 7.7 μm by the absorption of styrene monomer, keeping the high monodispersity. An appropriate amount of water was then added to the dispersion at ?5d?C to depress the redissolution of styrene from the swollen particles into the medium. By elevating the temperature the seeded polymerization was carried out at 70d?C. The production of submicron-size polystyrene new particles as a by-product was depressed by the addition of NaNO₂ to the medium.     

Living dispersion polymerization of styrene in the presence of polystyrene-block-poly(4-trimethylsilylstyrene)

Summary Living polystyrene microparticles with average particle diameters varying between 0.5 and 3.8 m were obtained via sec-butyl lithium-initated anionic polymerization of styrene in n-hexane diluent when polystyrene-block-poly(4-trimethyl-silylstyrene) was added as dispersing agent. The influence of block copolymer molecular architecture and concentration as well as polymerization temperature, monomer concentration and THF addition on polystyrene particle size, molecular weight and molecular weight distribution were investigated. In comparison to anionic styrene polymerization in cyclohexane solution, the anionic styrene dispersion polymerization in n-hexane was markedly slower.     

Evaluation of the potential use of ultrasound during the industrial manufacturing of high impact polystyrene

During the production of high impact polystyrene the rubber particle formation process is very important to control the final physical property balance. Besides the rubber viscosity, the presence of a copolymer to reduce the interfacial tension between the rubber and polystyrene phase is central. Such a copolymer can be added or can be made during the polymerization. In this study, it was attempted to create a block rubber in situ using ultrasound. Polybutadiene dissolved in styrene has been sonicated to create macroradicals. It was anticipated that these macroradicals would initiate the polymerization of styrene thus generating a poly(butadiene‐block‐styrene) acting as emulsifier during the production of high impact polystyrene. No evidence was found for the formation of a block copolymer but the higher reactivity and the resulting rubber particles indicate that besides rubber molecular weight reduction extra functionality was introduced on the rubber. No attempts were made to define the nature of the functionality. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Evaluation of the confinement effect of nanoclay on the kinetics of styrene atom transfer radical polymerization

The grafting through method was employed to study the effect of nanoclay confinement on the atom transfer radical polymerization (ATRP) of styrene. An ammonium salt containing a double bond on its structure was used as a clay modifier. Employing ATRP to polymerize styrene in the presence of modified montmorillonite resulted in a finely well‐defined polystyrene nanocomposite. The gas chromatography (GC) results showed the linear increase of ln(M₀/M) versus time, which indicated the controlled behavior of the polymerization. Another confirmation of the living nature of the polymerization was the linear increase of molecular weight against monomer conversion concluded from the gel permeation chromatography (GPC) data. Nanoclay exerted acceleration on the polymerization of free polystyrene chains. The polydispersity indexes of polymer chains increased by the addition of nanoclay. In the case of clay‐attached polystyrene chains, number and weight‐average molecular weights were lower than that of freely dispersed polystyrene chains. The polydispersity index of the clay‐attached chains was higher in respect to the freely dispersed polystyrene chains. The living nature of polymer chains was more elucidated by Fourier transform infrared spectroscopy (FTIR). Exfoliation of the clay layers in the polymer matrix of polystyrene nanocomposite containing the lowest amount of nanoclay has proven by Transmission Electron Microscopy (TEM). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011