Nascent morphology of syndiotactic polystyrene synthesized over silica-supported metallocene catalyst

The nascent morphology of semi-crystalline syndiotactic polystyrene (sPS) polymerized over silica-supported pentamethyl cyclopentadienyl titanium trimethoxide (Cp^∗Ti(OCH₃)₃) catalyst in a liquid slurry polymerization has been investigated under various reaction conditions. The scanning electron microscopic analysis of nascent polymers reveals that sPS molecules grow as long nanofibrils of 30-50 nm diameter and X-ray diffraction analysis shows the co-crystalline phases including both sPS and low molecular weight guest molecules of monomer and diluent. The energy dispersive X-ray spectroscopy also shows that the disintegration of silica primary particles occurs during the polymerization as evidenced by the uniform dispersion of silicon and aluminum in a polymer particle. The fibrous growth of the polymer inside a polymer particle leads to the shape replication of the original silica particles.     

Polystyrene composites of single‐walled carbon nanotubes‐graft‐polystyrene

Single‐walled carbon nanotubes (SWCNTs) dispersed in N‐methylpyrrolidone (NMP) were functionalized by addition of polystyryl radicals from 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐ended polystyrene (SWCNT‐g‐PS). The amount of polystyrene grafted to the nanotubes was in the range 20‐25 wt% irrespective of polystyrene number‐average molecular weight ranging from 2270 to 49 500 g mol^?1. In Raman spectra the ratios of D‐band to G‐band intensity were similar for all of the polystyrene‐grafted samples and for the starting SWCNTs. Numerous near‐infrared electronic transitions of the SWCNTs were retained after polymer grafting. Transmission electron microscopy images showed bundles of SWCNT‐g‐PS of various diameters with some of the polystyrene clumped on the bundle surfaces. Composites of SWCNT‐g‐PS in a commercial‐grade polystyrene were prepared by precipitation of mixtures of the components from NMP into water, i.e. the coagulation method of preparation. Electrical conductivities of the composites were about 10^?15 S cm^?1 and showed no percolation threshold with increasing SWCNT content. The glass transition temperature (T_g) of the composites increased at low filler loadings and remained constant with further nanotube addition irrespective of the length and number of grafted polystyrene chains. The change of heat capacity (ΔC_p) at T_g decreased with increasing amount of SWCNT‐g‐PS of 2850 g mol^?1, but ΔC_p changed very little with the amount of SWCNT‐g‐PS of higher molecular weight. The expected monotonic decrease in ΔC_p coupled with the plateau behavior of T_g suggests there is a limit to the amount that T_g of the matrix polymer can increase with increasing amount of nanotube filler. Copyright © 2012 Society of Chemical Industry     

Thermal and NMR Studies of Polystyrene Blends

Abstract

The effect of addition of poly (propylene oxide) (PPO) and polystyrene with low molecular weight (LPS) to polystyrene (PS) was investigated blending these polymers in a Haake internal mixer. The PPO and LPS range was established up to 10% by weight. The blends were analysed by differential scanning calorimetry (DSC) and carbon-13 nuclear magnetic resonance spectroscopy at solid state (NMR), using conventional NMR techniques as cross-polarisation/magic angle spinning (CP/MAS) and proton spin-lattice relaxation time in the rotating frame (T ₁ ^H _p ). The addition of 1 and 5% of PPO and 5% of LPS to PS made the blends of PS/PPO and PS/LPS more rigid.     

Influence of Polar Monomers on the Performance of Wood Fiber Reinforced Polystyrene Composites. I. Evaluation of Critical Conditions

Abstract

Wood fibers and nonpolar thermoplastics, e.g. polystyrene, are not the ideal partner for the preparation of composites because of a wide difference in their polarity. In the present study, polarity of the polystyrene was modified by the introduction of a—COOH group, through the reaction with maleic anhydride (MA) in the presence of an initiator (benzoyl peroxide: BPO) in a roll mill at the elevated temperatures. Optimum conditions for the preparation of polar polystyrene have been investigated. The temperature of the roll mill, i.e., the reaction temperature, and reaction time varied between 160–175°C and 10–15 min., respectively. The concentrations of the monomer, (MA) as well as the initiator (BPO), also varied: 0–10% and 0–2% (by weight of polymer), respectively. The mechanical properties of chemithermomechanical pulp (CTMP)-filled modified polystyrenes were evaluated. The effect of 3% coupling agent [e.g. poly(methylene (polyphenyl isocyanate))] (PMPPIC) on the mechanical properties of the same composites was also determined.

Generally, mechanical properties of the composite materials were enhanced when modified polymers were used as base polymers. Moreover, the extent of the improvement in mechanical properties depends on the reaction temperature and time, as well as on the concentrations of the monomer (maleic anhydride) and initiator. Maximum improvements in mechanical properties occur when the temperature was maintained at 175°C for 15 min. In addition, preferred concentrations of both the monomer and initiator were found to be 5% and 1% (by polymer weight), respectively. Once again, properties were further accelarated when coupling agent (e.g. PMPPIC) was used in addition to the modified polystyrene. The improvements in mechanical properties (over those of the original polymer and those of composites containing unmodified polymers) indicate that the compatibility between hydrophilic cellulosic fiber and hydrophobic polymer has increased.     

Polystyrene with half-titanocene/MAO catalysts: Influence of 2,6-diisopropylphenol

Styrene polymerization was carried out by a simple half-titanocene complex [cyclopentadienyltitanium trichloride] (CpTiCl₃) and pentamethyl [cyclopentadienyltitanium trichloride] (Cp*TiCl₃) combined with methylaluminoxane (MAO) as a cocatalyst. The effects of addition of 2,6-diisopropylphenol on the catalytic activity of the above catalytic systems and the microstructure of the resulting polymer were investigated. The results of the above experiments showed that the addition of the 2,6-diisopropylphenol changed the catalytic performance of the above catalytic systems, in terms of catalytic activity of the metal complexes and microstructure, molecular weight and molecular weight distribution of polystyrene synthesized. The yields of polystyrene of the above polymerization reactions indicated that the 2,6-diisopropylphenol enhanced the catalytic activity of both the CpTiCl₃/MAO and Cp*TiCl₃/MAO catalyst systems. Further Soxhlet extraction of the polymer was conducted by boiling acetone for 6 h to get pure syndiotactic polystyrene. The microstructure of polystyrene obtained by the above polymerization reactions was investigated by ¹³C NMR, GPC and DSC. Results indicated the formation of syndiotactic polystyrene in the absence of phenol and in low concentration of phenol. On the other hand, in the presence of excess phenol, the polystyrene produced was found to be completely atactic in nature. The appearance of monomodal peaks and narrow polydispersity in the GPC results of polystyrenes obtained in all the above polymerizations indicated that the polymerization was only coordination in nature.     

Ultrasonic Degradation of Polystyrene for Tailoring Molecular Weight and Polydispersity of Polystyrene Fragments

Ultrasonic degradation of polymers attracts more and more attention in the field of chemical recycling of polymers due to the promising opportunity to tailor molecular weight and polydispersity of the gained polymer fragments. In this work, the influence of solvent, gas atmosphere, and ultrasound amplitude on the ultrasonic degradation process of polystyrene is investigated. Therefore, an experimental procedure to perform ultrasonic degradation of polystyrene under homogeneous temperature conditions in the solvents cyclohexane and toluene under the gas atmospheres CO₂ and N₂ for different ultrasonic amplitudes was designed. It could be shown that a significant effect on the molecular weight and polydispersity of the polymer could only be revealed for N₂ and not for CO₂ atmosphere.     

Synthesis of porous carbon and silica spheres using PEO-PF polymer blends

In this paper, we performed a physical mixture of PEO and PF polymers (i.e. a polymer blend) as an organic template for synthesizing PF-PEO-silica homogeneous composites in a dilute silicate solution at pH = 4.0–5.0. The PF-PEO-silica composites exhibit spherical morphology, in micrometer dimension, and the sphere size is dependent on the pH value of the solution. After undergoing calcination to remove the organic part of the PF-PEO-silica composites with and without the hydrothermal treatment, porous silica spheres of different pore sizes were obtained. Due to the existence of the carbonizing PF polymer in the PF-PEO-silica composite, porous carbon spheres can be conveniently obtained from pyrolysis of the PF-PEO-silica composites under a N₂ atmosphere and HF-etching procedures. TEM images demonstrate that the mesostructures of the mesoporous silica and porous carbons are disordered.     

Polystyrene/EVA melt blends compatibilized with EVA-graft-polystyrene

The influence of poly[(ethylene-co-vinyl acetate)-g-polystyrene] (EVA-g-PS) on the mechanical and morphological properties of polystyrene and the blends with EVA copolymers has been investigated. The melt blends have been performed in a twin-screw extruder. The addition of the graft copolymer enhances the mechanical properties and impact resistance of the PS matrix and PS/EVA (90 : 10 wt %) blends. Better results on impact strength and elongation at break have been achieved by using a EVA-g-PS graft copolymer with a higher EVA proportion by weight. This graft copolymer also contains a lower molecular weight of the PS-grafted segments than the PS matrix. Morphological studies by scanning electron microscopy revealed some interfacial adhesion between the components in the compatibilized polymer blends. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2141–2149, 1997     

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     

Synthesis of porous carbon and silica spheres using PEO-PF polymer blends

In this paper, we performed a physical mixture of PEO and PF polymers (i.e. a polymer blend) as an organic template for synthesizing PF-PEO-silica homogeneous composites in a dilute silicate solution at pH = 4.0–5.0. The PF-PEO-silica composites exhibit spherical morphology, in micrometer dimension, and the sphere size is dependent on the pH value of the solution. After undergoing calcination to remove the organic part of the PF-PEO-silica composites with and without the hydrothermal treatment, porous silica spheres of different pore sizes were obtained. Due to the existence of the carbonizing PF polymer in the PF-PEO-silica composite, porous carbon spheres can be conveniently obtained from pyrolysis of the PF-PEO-silica composites under a N₂ atmosphere and HF-etching procedures. TEM images demonstrate that the mesostructures of the mesoporous silica and porous carbons are disordered.     

Review on Polymer/Carbon Nanotube Composite Focusing Polystyrene Microsphere and Polystyrene Microsphere/Modified CNT Composite: Preparation,Properties, and Significance

In recent times, carbon nanotubes play a promising role in a wide variety of technical applications due to improved structural properties, multifunctional features, mechanical strength, and electrical properties. Initially, problems interrelated to dispersion and alignment of nanotubes inside polymer/carbon nanotubes nanocomposites have been discussed. Fabrication methods and properties of polymer/carbon nanotubes nanocomposites were also highlighted. Main spotlight of the review article was the preparation, properties, and applications of polystyrene microspheres. The carbon nanotubes functionalization and physical/covalent grafting of polystyrene microspheres onto the sidewall of nanotubes is a rousing research spot. The article also evaluates the characteristics and potential applications of polystyrene microsphere-grafted-modified carbon nanotubes.     

A unifying approach for melt rheology of linear polystyrene

Several studies of melt rheological properties of polystyrene have been conducted over the past 50 years. Several approaches, including empirical models, have been developed to understand the behavior of materials using simple equations. The existing melt rheology models are best suited for high‐molecular‐weight polymers whose T_g does not vary. In this work, a semiempirical viscosity equation has been derived, including the effect of T_g dependence on molecular weight, to describe the melt rheology of low‐molecular‐weight polymers. The equation is derived based on a combination of well‐known concepts, such as the effects of free volume and molecular dynamics on polymer rheology. This provides a better understanding of the rheological behavior in the low‐molecular‐weight regime with respect to temperature and molecular weight. Because of the industrial trend towards lower molecular weight materials for applications such as high solids coatings, this unifying approach, based on the free volume theory with a simple expression, is of extreme practical significance. This equation can predict the zero shear viscosity behavior for different molecular weights, including low‐molecular‐weight regions, and temperatures. Viscosity calculations using the empirical equation agree with published experimental data. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2597–2607, 2007     

Influence of temperature,molecular weight,and molecular weight dispersity on the surface tension of PS,PP, and PE. I. Experimental

In this work, the influence of temperature, molecular weight (M?_n), and molecular weight dispersity (MWD) on the surface tension of polystyrene (PS) was evaluated using the pendant drop method. The influence of temperature on the surface tension of isotatic polypropylene (i‐PP) and of linear low‐density polyethylene (LLDPE) was also studied here. It was shown that surface tension decreases linearly with increasing temperature for all the polymers studied. The temperature coefficient ?dγ/dT (where γ is the surface tension, and T, the temperature) was shown to decrease with increasing molecular weight and to increase with increasing MWD. The surface tension of PS increased when the molecular weight was varied from 3400 to 41,200 g/mol. When the molecular weight of PS was further increased, the surface tension was shown to level off. The surface tension was shown to decrease with increasing molecular weight distribution. Contact angles formed by drops of diiomethane and water on films of PS with different molecular weights were measured at 20°C. The surface energies of those polymers were then evaluated using the values of the different pairs of contact angles obtained here using two different models: the harmonic mean equation and the geometric mean equation. It was shown that the values of the surface energy obtained are slightly less than are the ones extrapolated from surface‐tension measurements in the rubbery state. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1907–1920, 2001     

Effect of the chemical characteristics of mesoporous silica MCM‐41 on morphological,thermal, and rheological properties of composites based on polystyrene

Mesoporous silica nanoparticles (MCM‐41) with an average diameter of ～ 20 nm were synthesized by a sol‐gel method using binary surfactant system. Polystyrene (PS) composites containing mesoporous silica nanoparticles were prepared by in situ polymerization of styrene monomers. Similar in situ polymerized PS composites were prepared based on the modified silica functionalized with methyl and vinyl groups. The effects of silylation on thermal and rheological properties of the PS/silica composites are investigated. Of particular importance is that the in situ polymerization of monomers within the mesoporous silica may trap some polymer chains, if not all, thereby affording a greater physical interaction between polymer and the porous fillers, whereas the chemical modification of silica surface promotes the polymer–filler interaction, which in turn enhances the thermal stability of composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of styrene oligomers and polymers on the suspension polymerization behavior and properties of expandable polystyrene

Styrene oligomers are formed by a free‐radical mechanism during the thermal polymerization of styrene in storage. The effects of these compounds on the preparation of expandable polystyrene (EPS) were investigated with respect to suspension polymerization behavior and the properties of the impregnated polystyrene beads produced. Styrene dimers and trimers up to concentrations of 0.2 wt % did not affect the stability of the suspension during the polymerization and impregnation stages. Besides differentiated effects on the particle size distributions of the polymers and on the polymerization rate, no chain‐transfer activity of the oligomers was observed, and this confirmed the assignment of chain transfer to the Diels–Alder dimer in the literature. The investigation of the foaming behavior of the pentane‐impregnated EPS beads indicated a significant reduction of the prefoaming density caused by styrene dimers and trimers. This behavior resulted from a decrease in the glass‐transition temperatures of these polymers. The effects of high‐molecular‐weight polystyrene, formed in addition to oligomers during storage by the thermal polymerization of styrene, on the polymerization behavior and polymer properties of EPS were also investigated. The results showed a significant impact on the suspension stability that was dependent on the concentration of the high‐molecular‐weight polystyrene. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of polymer chain length on the solubility of polystyrene grafted single‐walled carbon nanotubes in tetrahydrofuran

BACKGROUND: While carbon nanotubes are highly interesting materials for a variety of applications, their inherent insolubility limits widespread applications and solution‐phase processing. It is known that chemical functionalization can overcome this insolubility problem, and covalent grafting of polymers to the nanotube surface has been shown to be effective. In this study, the effect of polymer molecular weight on the solubility of polymer–nanotube conjugates was investigated. RESULTS: A series of nitroxide‐capped polystyrene polymers ranging in molecular weight from 2900 to 105 000 g mol^?1 were grafted to single‐walled carbon nanotubes (SWNTs). The resulting polystyrene–SWNT conjugates exhibited different degrees of solubility in tetrahydrofuran. Subsequent thermogravimetric and UV‐visible spectroscopy analyses indicated that carbon nanotube solubility reached a maximum when a polymer sample with a weight‐average molecular weight of 10 000 g mol^?1 was used. Higher and lower molecular weights resulted in reduced solubilities. CONCLUSION: Polymer chains of intermediate length maximize SWNT solubility, while lengths that are too low or too high seem to diminish the ability of the polymer–SWNT conjugates to remain in solution. Copyright © 2008 Society of Chemical Industry     

Polystyrene recycling processes by dissolution in ethyl acetate

This study evaluated the thermal, morphological, chemical, and mechanical properties of virgin and recycled polystyrene. The recycling process was carried out by dissolution of polystyrene (extruded and crystal) in ethyl acetate, followed by two processes for solvent removal: vaporization by direct contact with water at 85 °C in a tubular evaporator and vaporization during the extrusion process. For the samples produced by solvent evaporation in the tubular evaporator, there was practically no degradation on polymer chain, neither reduction in glass transition temperature. For the samples produced by solvent evaporation during the extrusion, a polymer chain degradation was noted by reduction in molar weight and in glass transition temperature. The FTIR evaluation suggests that polymer oxidative degradation, in both samples, was more pronounced in the extruded sample. The removal of plasticizing additives could be evidenced by the glass transition temperature increase in the recycled samples produced in the tubular evaporator. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46208.     

Attributes of Polymer and Silica Nanoparticle Composites: A Review

In this article, polymer microspheres and silica nanoparticles have been discussed as important filler in polymer composites. Their synthesis methods, properties, and application were particularly stressed. Silica is usually used as nucleating agent, surface enhancement mediator, and as templates and cores. Among polymer/silica composites, various categories including polyaniline, polypyrrole, polystyrene, epoxy, rubber, and acrylate polymer were discussed in detail. It was observed that silica nanoparticles enhanced mechanical strength and overall performance of composites. Furthermore, composites having carbon nanotube along with silica particles possess high electrical and mechanical performance. These composites are important in nanoelectronic devices, nanomedicines, and defense-related applications.     

乳液法聚苯乙烯纳米微球的制备

采用十二烷基硫酸钠为乳化剂、过硫酸盐为引发剂、苯乙烯为单体,在低水油比的条件下,采用乳液聚合方法合成了聚苯乙烯纳米微球,探讨了乳化剂用量、乳化时间、反应温度、引发剂用量和反应时间对单体转化率及产物分子量的影响.结果表明:在低水油比条件下,反应参数对苯乙烯的转化率和聚苯乙烯的分子量具有一定的影响.在最优条件下苯乙烯的转化率达到98%、聚苯乙烯的分子量达到32万.激光粒度分布测试结果显示,所得产物为单分散纳米微球.     

The effect of chemical treatment of wood and polymer characteristics on the properties of wood–polymer composites

The physical-mechanical properties and the microscopic structure of caixeta (Chrysophyllum viride) and slash pine (Pinus elliottii) impregnated with polystyrene (PS) were investigated. The influences of a pretreatment with hydrogen peroxide (H₂O₂) solutions utilized in the production of the wood–polymer composites (WPC) and the characteristics of polystyrene formed in situ on the properties of WPC were analyzed. The incorporation of polystyrene improved the compression and static bending properties of slash pine and caixeta. The micrographies confirmed that there were distinct but continuous phases of polymer and wood cell wall which granted the composites a better physical-mechanical behavior. The sensibilizing treatment with dilute hydrogen peroxide solution led to an increase in the viscosity average molecular weight (M _v) of polystyrene, and to the graft polymerization of the monomer, which, in turn, enhanced the stress properties of caixeta–polystyrene composites. Concentrated H₂O₂ solutions degraded caixeta wood, decreasing its tensile properties. Lower initiator concentration favoured higher molecular weight of polystyrene formed in pine wood. A fivefold increase in M _v of PS, however, had little effect on the compression properties of pine–polystyrene composites.