The effects of oxygen diffusion on the surface photooxidation of polystyrene

This paper further illustrates the applicability of multiple internal reflectance infrared spectroscopy to the analysis of near-surface photooxidation. The results are compared with transmission infrared spectra to evaluate compositional gradients resulting from photooxidation and the influence of oxygen diffusion. The sample was a solvent-cast film of atactic, narrow distribution polystyrene, M_w of 100,000, that had been drawn to a ratio of 3.0 at 110°C by solid state coextrusion. Irradiation of these thin films, ～25μm thickness, was performed on exposure to air at 35°C for periods of up to 6 h using a mercury source emitting at 254 nm. On photooxidation, a board peak appears at 3200–3500 cm^?1, attributable to hydroperoxide formation. The most dramatic increase in the infrared spectra is found for a carbonyl band at 1730 cm^?1. It appears to result from an aromatic acid group since it is shifted to 1660 cm^?1 on immersion of the oxidized polystyrene films in aqueous ammonium hydroxide. It is confirmed that the photooxidation of polystyrene occurs preferentially at the surface and that this reaction rate is greatly reduced in the drawn polystyrene film.     

Crazing and the stress dependence of creep in two glassy polymers: Polystyrene and a poly(styrene–acrylonitrile) copolymer

The stress dependences of crazing and of tensile creep were studied at 30.5° and 80°C in polystyrene (M _v = 2.7×10⁵) and in a poly(styrene–acrylonitrile) copolymer (73.5% styrene, M _v = 2.35×10⁵) at four stresses in the interval from 0.6 to 1.5×10⁸ dynes/cm². Material failure was observed in all cases for the polystyrene and in no cases for the copolymer. Crazing was found to occur at all stresses for polystyrene, the spacing between craze lines decreasing with increasing stress and temperature. A much higher stress level for the onset of crazing was found for the copolymer. An inverse stress dependence of the compliance was observed for polystyrene at 30.5°C, i.e., the compliance decreased with increasing stress. This behavior was partially reversed at 80°C below 10² sec and became a positive stress dependence at long times. The stress dependence of the compliance for the SAN copolymer was partially reversed at 30.5°C. At 80°C, the stress dependence was positive for stresses ≥0.9×10⁸ dynes/cm². The present results suggest that in the copolymer there may exist an enhanced local mobility which alters the stress dependence observed in pure polystyrene and which enhances the ability of the material to deform without failure. This concept is discussed further in light of the stress dependence of the compliance and of crazing in these materials and appears to be consistent with our previous studies of the stress dependence of creep and of the stress dependence of whitening in ABS systems.     

Synthesis of Polymer Grafted Magnetite Nanoparticle with the Highest Grafting Density via Controlled Radical Polymerization

Abstract  The surface-initiated ATRP of benzyl methacrylate, methyl methacrylate, and styrene from magnetite nanoparticle is investigated, without the use of sacrificial (free) initiator in solution. It is observed that the grafting density obtained is related to the polymerization kinetics, being higher for faster polymerizing monomer. The grafting density was found to be nearly 2 chains/nm² for the rapidly polymerizing benzyl methacrylate. In contrast, for the less rapidly polymerizing styrene, the grafting density was found to be nearly 0.7 chain/nm². It is hypothesized that this could be due to the relative rates of surface-initiated polymerization versus conformational mobility of polymer chains anchored by one end to the surface. An amphiphilic diblock polymer based on 2-hydroxylethyl methacrylate is synthesized from the polystyrene monolayer. The homopolymer and block copolymer grafted MNs form stable dispersions in various solvents. In order to evaluate molecular weight of the polymer that was grafted on to the surface of the nanoparticles, it was degrafted suitably and subjected to gel permeation chromatography analysis. Thermogravimetric analysis, transmission electron microscopy, and Fourier transform infrared spectroscopy were used to confirm the grafting reaction. Graphical Abstract   Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Viscosities of molten polymer blends

Pairs of four thermoplastic resins, polystyrene, poly(methyl methacrylate), acetal homopolymer, and nylon-12, were intensively melt-blended in nine proportions from 0 to 100 percent. Capillary rheometry at 210°C was done on each blend; melt densities were also measured on most of them. The dependence of shear stress on Rabinowitsch-corrected shear rate was accurately represented, for all the blends, by a simple empirical model. The dependence of viscosity, at particular shear rates between 5 and 1000 s^?1, on blend composition was examined and we fitted two viscosity-composition models to all the systems by least-squares procedures. The character of the dependence of blend viscosity on composition varied widely for the five binary systems studied, two being monotonic over the whole range of shear rate, two exhibiting clear minima and one displaying mixed behavior, with both a minimum and maximum viscosity seen at shear rates near 250 s^?1. The McAl lister three-body model satisfactorily describes the viscositycomposition dependence in all five systems. A simpler blend rule was useful only in the monotonic systems, and even there it was inferior to the McAllister model.     

Thickness variation in the thermoforming of poly(methyl methacrylate) and high-impact polystyrene sheets

The influence of material flow properties on the variation of wall thickness in a thermoformed part was investigated by measuring the thickness reduction at the pole of free-formed axisymmetric domes of poly(methyl methacrylate) and high-impact polystyrene. It was found that at a given pole height, the thickness reduction in poly(methyl methacrylate) was less than in high-impact polystyrene, i.e., the wall thickness in a part formed from poly(methyl methacrylate) will be more uniform than in a part formed from high-impact polystyrene by the same technique. This difference in formability was ascribed to a difference in the dependence of the flow stress σ at the thermoforming temperatures on time. The flow stress of both materials was given by σ = Kt^m′?ⁿ, but whereas n was approximately 1 for both materials, m′ was ?0.052 and ?0.33 for poly(methyl methacrylate) and high-impact polystyrene, respectively. A physical argument and simple analysis led to the conclusion that a large (negative) value of the “stress relaxation index” in a material reduces the degree of uniformity of sheet thickness in a formed part.     

High performance gel permeation chromatography of polystyrene

Microparticulate crosslinked polystyrene packings in short columns have been investigated with high performance liquid chromatography instrumentation. Reliable molecular weight data for six polystyrene standards having narrow molecular weight distributions and for a polystyrene having a broad distribution have been obtained by optimizing the injection procedure, using a constant flow pump, and incorporating an internal standard into each injected solution. Experimental determinations of the dependence of the polydispersity for polystyrene standards on eluent flow rate and polymer diffusion coefficient were in agreement with a relation predicted from theoretical considerations of chromotogram broadening. Because of the dependence of chromatogram broadening on polystyrene molecular weight, high efficiency separations for high polymers were only obtained at low eluent flow rates. For low polymers, high efficiency separations may be performed at fast eluent flow rates. It was concluded that accurate molecular weight distributions can only be determined from chromatograms obtained at low eluent flow rates, which was supported by experimental measurements of polydispersity on polystyrene sample prepared by a radical polymerization at low monomer conversion. A differential weight distribution calculated from an experimental chromatogram for the polydisperse polystyrene determined at the lowest eluent flow rate (0.1 cm³min^?1) was compared with distributions predicted theoretically for polystyrenes prepared by radical polymerization. It was concluded that the experimental distribution contained a small contribution from chromatogram broadening and that most of the radicals in the polymerization of styrene terminated by combination.     

Rheological properties of mixtures of molten polymer and fluorocarbon blowing agent. II. Mixtures of polystyrene and fluorocarbon blowing agent

The viscosities of mixtures of polystyrene and fluorocarbon blowing agent were determined, using the experimental technique described in Paper I of this series. For the study, three commercial grades of polystyrene were used, together with the following fluorocarbon blowing agents, trichlorofluoromethane (FC-11), dichlorodifluoromethane (FC-12), and blends of FC-11 and FC-12. For each combination of polystyrene and blowing agent, blowing agent concentration and melt temperature were varied. We have found that, for all three polystyrenes used, a single correlation exists between the viscosity reduction factor (VRF) and the blowing agent concentration, in which VRF is defined as the ratio of the viscosity of polystyrene-blowing agent mixture to that of polystyrene homopolymer. The correlation was found to be independent of shear rate and temperature, and dependent upon only the type of fluorocarbon blowing agent. It was suggested that such a correlation be used in predicting the bulk viscosity of mixtures of polystyrene and fluorocarbon blowing agent, using information on the viscosity of polystyrene alone.     

Synthesis of a Novel Miktoarm Star Azobenzene Side-Chain Liquid Crystalline Copolymers by Atom Transfer Radical Polymerization

Summary A series of miktoarm star novel azobenzene side-chain liquid crystalline (LC) copolymers were synthesized by combination of atom transfer radical polymerization (ATRP) and chemical modification of the termini of ATRP-derived polymers. These miktoarm star copolymers carrying one polystyrene (PS) arm and two poly [6-(4-methoxy-4-oxy-azobenzene) hexylmethacrylate] (PMMAZO) arms were characterized by ¹H NMR and GPC. The liquid crystailline behavior of these copolymers was studied by DSC and POM. It was found that the miktoarm star copolymers have the similar LC properties to PMMAZO homopolymer, and their thermal stability of the mesophases is increased, while the phase transition enthalpies are reduced.     

Development of elastic and plastic properties of polyoxymethylene during bending fatigue

The development of the plastic and viscoelastic properties and the corresponding failure limits of the acetal homopolymer polyoxymethylene were studied in unidirectional cyclic fatigue. Samples with molecular weights (MWs) ranging from 90 to 142 kg/kmol were tested in displacement‐controlled conditions, resulting in maximum stress amplitudes between 30 and 59 MPa and strain amplitudes between 35.8 and 92.6 με. The zero‐hour material properties and the cycle‐dependent property development were predominantly dictated by deformations in the crystalline regions and showed a negligible dependence on MW. However, the final failure limits were found to be primarily dependent on the length of the amorphous tie chains that connect the crystallites. As such, fatigue life analysis showed a strong dependence on MW. Results are interpreted in light of the primary mechanical failure mechanisms and the corresponding molecular deformations. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40762.     

Polyethylene-polystyrene grafting reaction: effects of polyethylene molecular weight

Blending of different thermoplastic polymers usually results in segregated and low value materials for almost any mixing condition. Nevertheless, a synergetic combination of properties can be obtained by an adequate compatibilization via reactive blending. In this work a Friedel-Crafts alkylation reaction is used to graft polyethylene chains onto polystyrene. The relation between the initial PE molecular weight (MW) and the structure of the compatibilizer copolymer is studied by a combination of size exclusion chromatography and Fourier transform infrared spectroscopy. The amount of copolymer formed is estimated from the amount of polystyrene reacted. The relative lengths of the grafted polyethylene chains are assessed. It is found that lower MW PE produces, upon reaction, a greater amount of short chain length grafted PE onto PS than higher MW PE. The results are in agreement with theories relating the component MW to the reaction localization at the interface.The low cost Friedel-Crafts alkylation results in a convenient reaction for the in situ compatibilization of PE/PS blends. It produces enough graft copolymer to compatibilize the phases without causing PS crosslinking and PE chain scission.     

Pulsed n.m.r. relaxation study of a polystyrene/poly(ethylene oxide) diblock copolymer: evidence for interaction at the phase boundary

Pulsed nuclear magnetic resonance relaxation measurements are presented for a hydrophobic-hydrophilic diblock copolymer of polystyrene and poly(ethylene oxide) along with results for the individual homopolymers. Although observation of the thermal transitions of the homopolymer components in the copolymer reveals a gross incompatibility, the n.m.r. data suggests strong interfacial effects. From the T₁ and T₂ data below the melting point of PEO (T_m = 335K), it was concluded that polystyrene creates localized defects which reduce PEO domain crystallinity to 75% from 93% in the homopolymer. Above T_m in the copolymer three motional domains can be distinguished, isolated rigid polystyrene, isolated molten PEO and an intermediate domain. The composition of the intermediate domain suggests that 23% of the polystyrene is plasticized whereas 80–90% of the molten PEO is motionally constrained. The results are interpreted in terms of a spatial segregation of the homopolymer components with a forced interaction at the phase boundary as a result of the covalent linkages tying the two components together.     

Absorption and emission spectra of Athabasca asphaltene in the visible and near ultraviolet regions

Absorption, excitation and emission spectra in the visible and ultra-violet region were recorded at room temperature for Athabasca (Alberta, Canada) asphaltene and five of its fractions separated according to molecular weight (MW) by gel permeation chromatography (g.p.c.) on Bio-Beads SX-1. Strong concentrations effects were observed on the profiles of all the excitation and emission spectra at concentrations higher than 5.0 mg l⁻¹. The proper excitation and emission spectra were taken at concentrations lower than 5.0 mg l⁻¹ where the profiles are independent of concentration. All the spectra obtained were broad, structureless bands with the exception of that of the lowest MW fraction, which shows the sharp Soret band characteristic of the vanadyl porphyrin complex. The absorbance of the whole asphaltene was found to be equal to the weighted sum of absorbances of the fractions at a given wavelength and a given weight concentration. This additive property was not observed among the intensities in the emission spectra. The profiles of all the excitation and absorption spectra are identical throughout the asphaltene fractions, suggesting that the basic absorbing chromospheres are the same throughout the fractions and independent of MW of the fractions. In addition the absorption spectra are not significantly affected by the Tyndall scattering. From the examination of absorptivity and the position of the absorption band, the average number of aromatic rings in the average absorbing chromophores throughout the fractions was found to consist of approximately two to three. The fluorescence spectra, on the other hand, show a very rapid decrease of intensity at a constant weight concentration and a gradual shift of the band maxima toward longer wavelength with increasing number average MW. The origin of the fluorescence band is considered to be exciplexes. The average rate of non-radiative processes decreases steadily with decreasing MW from fraction 1 to fraction 5. The influence of various solvents was explored on the absorption, excitation and emission spectra of the lowest MW (1200) asphaltene fraction.     

Hydrodynamic characters of co-current operation for SO<Subscript>2</Subscript> absorption in a laboratory packed column

A co-current operation for SO₂ absorption by water was performed in a laboratory-scale packed column. The effects of L/V (liquid-gas ratio) and F (gas phase loading factor) on the SO₂ absorptivity were both investigated. The absorptivity for co-current increased with the increase of L/V and the percentage of absorptivity increase at higher L/V is larger. At lower F, in regular packing there is fluctuation of absorptivity with F increased, but in random packing there is not. With the increase of F, the absorption curve slowed down. It is proposed that in order to obtain a steady desulfurization efficiency, F factor in both kinds of packings should be higher than 4 kg^0.5/m^0.5s. For absorptivity, which could be reached by both co-current and counter-current, it is suggested that co-current is better because of the higher gas velocity.     

Rapid FTIR method for quantification of styrene‐butadiene type copolymers in bitumen

The mid‐IR molar absorptivity for polystyrene (PS) and polybutadiene (PB) blocks were obtained for five styrene‐butadiene‐styrene (SBS) and SB copolymers, including linear, branched, and star copolymers, and their blends with bitumen. The average absorptivity for PS and PB blocks was 277 and 69 L mol⁻¹ cm⁻¹ and it was little affected by the S/B ratio or the copolymer architecture. In the presence of bitumen, Beer's law was obeyed but the respective PS and PB absorptivity was 242 and 68 L mol⁻¹ cm⁻¹, possibly because of weak interactions between the copolymer and bitumen. The absorptivity values were used to calculate the concentration of SB‐type copolymers in blends with bitumen with an accuracy of 10% or better. The method can be used to probe the stability of bitumen–copolymer blends in storage at 165°C, to determine the copolymer concentration in commercial polymer modified bitumen (PMB), and to assess the resistance of PMB to weathering. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1034–1041, 2001     

Softening phenomenon by remilling of styrene–butadiene copolymer rubber–general-purpose polystyrene resin blend

The softening phenomenon by remilling of uncured blends of various commercia styrene—butadiene copolymer rubber (styrene content, 23.5 to 48 wt-%, styrene block 0 to 18 wt-%) with general-purpose polystyrene resin was mainly studied by examining the blend ratio dependence of hardness and compression modulus (in logarithmic form), with special attention to the state of dispersion of the polymers. It was found that the blend of styrene—butadiene copolymer rubber with general-purpose polystyrene resin forms a microheterogeneous polymer blend system and that the hardness and the compression modulus change in S-shaped curves versus blend ratio. However, the degree of softening phenomenon by remilling (roll surface temperature, 70°–90°C) was found to be different for the two blend systems, i.e., random styrene—butadiene copolymer rubber and block styrene—butadiene copolymer rubber. The softening phenomenon is more pronounced in random-type rubbers; and in some block-type rubbers, no softening phenomenon was observed. The influence of the styrene content of the polymer is small. Further discussions have shown us that the strong interaction between the polystyrene block of the copolymer and the styrene homopolymer of the general-purpose polystyrene resin controls the state of dispersion of polymers thereby causing this difference in the softening phenomena among the different kinds of styrene—butadiene copolymer rubbers.     

Photografting of acrylonitrile and methacrylic acid on polyethylene film under air atmosphere

Photografting of acrylonitrile (AN) and methacrylic acid (MAA) on low-density polyethylene film (thickness 70 μm), on which benzophenone was coated earlier, was investigated at 60°C in water medium under air atmosphere. In the case of AN monomer, where grafted polymer was formed predominantly, oxygen in the system promoted the formation of both grafted polymer and homopolymer. With MAA monomer, in which homopolymer was formed preferentially compared to the formation of grafted polymer, the formation of homopolymer was accelerated by the presence of oxygen while suppressing that of grafted polymer. The formation of polyethylene peroxides by photoirradiation seemed to be a factor for the accelerated polymerization under air atmosphere. It was found that additives such as hydrazine and metallic ions (Fe²⁺, Cu²⁺, and Ni²⁺) are useful for enhancing the photografting under air atmosphere. © 1993 John Wiley & Sons, Inc.     

Temperature dependence of dynamics of solutions of triblock copolymer in a selective solvent

The temperature dependence of dynamic properties of solutions of a triblock copolymer with polystyrene outer blocks and a middle block of fully hydrogenated polybutadiene (M_w=7.0×10⁴ gmol⁻¹, mass fraction of PS 0.28) was studied in a selective solvent for the middle block, n-heptane. In dilute solutions, a gradual decomposition of the flower-like micelles was observed on heating. A more complex behavior was observed in semidilute solutions of the copolymer where three dynamic processes can be reliably extracted from the correlation functions. The fast mode corresponds to the collective diffusion mode of physically interconnected micelles, the broad middle mode is probably due to the tracer diffusion of polydispersed clusters (animal-like structures) formed by random association of the triblock copolymer and the slow mode is probably related to the diffusion of aggregates of insoluble polystyrene impurities. The crossover from relaxational to diffusive behavior was found for samples with c>5.5% (w/v). The scattered light intensity measurements revealed a phase transition for the solution with the concentration 4% (w/v) at a temperature of 79±2°C, which was related to the phase separation of polystyrene homopolymer present in a small amount in the copolymer used.     

The production of a new partially biodegradable starch plastic by reactive extrusion

The grafting of polystyrene onto dissolved starch in a twin screw extruder has been studied. This copolymerization was initiated using the thermal initiators benzoyl peroxide and K₂S₂O₈. As end product a mixture containing polystyrene‐grafted starch, homopolymer of polystyrene and starch was obtained. Parameters like screw rotation rate, fully filled length of the extruder, wall temperature and throughput have been varied in order to obtain information about their influence on conversion, graft percentages and molecular weight of the materials formed. To increase the amount of graft points, maleic acid anhydride (MAH) was added resulting in an increased grafting of polystyrene onto starch. Graft percentages of 60% could be achieved. The total conversion of styrene could be controlled by adjusting extruder parameters like barrel temperature, fully filled length and initiator type. Conversions of 95% were found. Molecular weights of the polystyrene formed could be controlled by adding a chain transfer agent (dodecylmercaptan) to the styrene phase. In this way the molecular weight (M_n) of the styrenic part could be varied from 20,000 to 140,000. The experiments with the chain transfer agent showed that the grafting of polystyrene onto starch is a process occurring at the interface between the dissolved starch and the styrene phase.     

Preparation of polystyrene/MMT nanocomposite through in situ RAFT polymerization by new chain transfer agent derived from bisphenol A

Reversible addition‐fragmentation chain transfer (RAFT) polymerization was performed in the presence of a new RAFT agent based on bisphenol A and modified clays and successfully prepared polystyrene/MMT nanocomposite. The structure of RAFT agent was investigated by Fourier transform infrared spectroscopy (FT‐IR) and proton nuclear magnetic resonance spectroscopy (¹H NMR). The polymer had well‐defined molecular weight and narrow polydispersity obtained by gel permeation chromatography (GPC). The morphology of polystyrene/MMT nanocomposite was investigated by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) and was found to be exfoliated. Thermal stability of pure polystyrene and polystyrene/MMT synthesized via RAFT polymerization was also investigated and showed better thermal stability for nanocomposite. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Microwave plasma‐initiated grafting of acrylic acid on Celgard 2500 membrane to prepare alkaline battery separators—Characteristics of process and product

A process of plasma‐initiated grafting of acrylic acid on commercial porous polypropylene membrane was studied. The influence of parameters of the plasma (power, gas pressure, time plasma‐sample distance, sample arrangement) and grafting (solvent composition, monomer concentration, time, inhibitor presence) on the degree of grafting, amount of homopolymer produced and surface electrical resistance was determined. A degree of grafting up to 18 mmol/g was obtained, which resulted in sample resistance as low as 30 mΩ cm². The molecular weight of AAc homopolymer that can be assumed as equal to the MW of grafted chains, ranged from 25,000 to 50,000,000 da. SEM and water permeability measurements show that grafting causes filling of the pores, which, however, does not stop K⁺ ions from penetrating the membrane. The performance of nickel‐cadmium cells with acrylic acid grafted membranes as separator is also presented. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010