Problems associated with the surface characterization of polystyrene latices

It has been shown that polystyrene latices prepared by the surfactant free emulsion polymerization process often contain sufficient residual monomer and possibly low-molecular-weight material and reaction by-products, such as benzaldehyde, which are not efficiently removed by dialysis, to affect their bulk and surface characteristics. These materials have been identified by gel permeation chromatography (GPC) and infrared (IR) spectroscopy studies and their effective removal by steam stripping has been investigated. Steam stripping has proved to be efficient in this process but it led to rapid hydrolysis of the surface sulfate groups and a consequent change in the surface characteristics. The problem of hydrolysis of sulfate groups under various environments has been studied. The problems associated with the identification of weak acid end groups are discussed and several alternative explanations for their occurrence are advanced.     

A novel process for synthesizing polystyrene and polyarylate block copolymers utilizing telechelic polystyrene

A novel process for synthesizing polystyrene (PS) and polyarylate (PAr) block copolymers utilizing telechelic polystyrene was proposed. This process was comprised of three steps. In the first step, carboxyl-terminated telechelic polystyrene (COOH PS COOH) was prepared by free radical polymerization with 4,4′-azobis(cyanovalelic acid) (ACVA). In the second step, COOH PS COOH was reacted with bisphenol-A by the use of triphenylphosphine, hexachloroethane, and triethylamine to convert carboxyl groups into phenol groups (OH PS OH). In the third step, to produce the PS PAr block copolymer, OH PS OH was added to a polyarylate synthesizing system where bisphenol-A and the mixture of tere/isophthaloyl dichloride (1 : 1 mole ratio) were polymerized by solution polycondensation. PS PAr block copolymers were successively obtained with relatively high PS copolymerization ratio. The ratio was over 70%, while there was a wide variety in molecular composition and molecular weight. Furthermore, by this process PS PAr block copolymers can be obtained from step 1 through step 3 consecutively without isolating the intermediates. This method has potential for industrial applications. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2839–2847, 1998     

Reaction of nitrogen dioxide with polystyrene films

The reaction of nitrogen dioxide with thin polystyrene films has been investigated at 35°C with different partial pressures of NO₂ (0.1, 2, 15, 30, and 60 cm Hg) and at several temperatures (25, 35, 45 and 55°C). The films were thin enough (ca. 20 μ) so that the reaction was independent of the diffusion of gas into the polymer. The experimental results can be represented by a chain mechanism. The whole degradation process is controlled by the diffusion of polymer radicals out of cages. This diffusion in turn, is affected by the decrease in viscosity or decrease in weight-average molecular weight as degradation proceeds. This leads to an acceleration of the degradation process. A straight-line relationship between the logarithm of the reciprocal weight-average molecular weight and the logarithm of a reaction–time function was found. The dependence on the rate was substantiated by degrading polymer fractions. The energy of activation for the process is small, in agreement with a diffusion process for chain scission. Nitro and nitrite groups are incorporated along the backbone of polystyrene during exposure. The number of these polar side groups appears to pass through a maximum with time, as is evidenced by aggregation of polymer molecules in benzene solution only during the middle stage of the degradation. The final stage of the process is slowed down by retarder being produced. This retarder can be removed by reprecipitation of exposed polymer films. Degradation in solution is similar to that of films. Isotactic polystyrene shows less irregularities in its degradation curve than the atactic polymer. This is, presumably, due to its more homogeneous morphology, large molecular weight, and broader molecular size distribution. The plot of the degree of degradation versus time for the isotactic polymer can be satisfactorily approximated by a straight line.     

Craze-initiation kinetics in polystyrene

In this study it is shown, for a commercial polystyrene grade, that the strain-rate dependence of craze initiation is equivalent to that of yielding. This implies that the kinetics of craze initiation are determined by the nonlinear flow behavior, and that the actual cavitation process is governed by an additional, apparently rate-independent, criterion. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2066–2073, 2004     

Evidence of formation of radicals in the polystyrene thermodegradation

The formation of radicals in the thermal degradation of polystyrene (PS) in tubes sealed under vacuum has been evidenced by using ESR spectroscopy. The radicals were found to be stable for weeks at room temperature. The rate coefficients of the formation of radicals have been evaluated in the temperature range 350–420°C. The reaction kinetically followed has been related to the initiation step of the multi-step degradation process of PS. The activation energy of this reaction resulted 185 kJ/mol.     

Calorimetric study of the conformational relaxation times in polystyrene

The temperature dependence of the relaxation times of the structural relaxation process of polystyrene is determined by temperature-modulated differential scanning calorimetry (TMDSC) and by conventional differential scanning calorimetry (DSC) in the latter by modelling the experimental heat capacity curves measured in heating scans after different thermal histories. The good agreement between both measuring techniques in the temperature interval just above the glass-transition temperature is a guide for the interpretation of the results of the TMDSC technique in the glass-transition region. In addition, the same model applied to DSC scans is used to simulate the TMDSC experiment and the calculated response is compared with the measured scans. Received: 22 February 1999 Accepted in revised form: 11 June 1999     

Thermal degradation of polystyrene

Molecular weight change studies have shown that the thermal degradation of random copolymers of styrene — namely HIPS, SAN, and ABS-at low temperatures and in air involves random chain scission. The dominant process in the degradation of HIPS is random chain scission due to weak links, whereas in SAN it is intermolecular chain transfer. In ABS, the degradation is initially random scission due to weak links and then mainly intermolecular chain transfer. The infrared spectra show that during degradation the labile weak links are attacked by oxygen and peroxidic free radicals are produced. Via hydrogen abstraction or autoxidation of olefinic links, these free radicals are responsible for the formation of aliphatic ketonic or peroxyester structures, and for isomerization and cyclization. The activation energies of overall degradation of HIPS, SAN, and ABS are 134, 142, and 92 kJ.mol^–1 respectively.Part of the PhD dissertation of Mrs. Jaya Nambiar, University of Gorakhpur, Gorakhpur-273001, 1980.     

‘Weak links’ in polystyrene

A first step in the thermal degradation of polystyrene prepared by radical polymerisation has been isolated by heating the polymer in the temperature range 199–280°C. In this step a chain scission process occurs without formation of volatile products, involving, on average, about one bond between structural units in every 10 000. This gives more direct evidence than hitherto of the presence of ‘weak links’ in polystyrene which are shown to be randomly distributed in the polymer chains, their scission resulting in a single break in the molecule of polystyrene to which they belong.The very low energy of activation for chain scission suggests that more than one rate determining step is involved in the process.     

Benchtop micromolding of polystyrene by soft lithography

Polystyrene (PS), a standard material for cell culture consumable labware, was molded into microstructures with high fidelity of replication by an elastomeric polydimethylsiloxane (PDMS) mold. The process was a simple, benchtop method based on soft lithography using readily available materials. The key to successful replica molding by this simple procedure relies on the use of a solvent, for example, gamma-butyrolactone, which dissolves PS without swelling the PDMS mold. PS solution was added to the PDMS mold, and evaporation of the solvent was accomplished by baking the mold on a hotplate. Microstructures with feature sizes as small as 3 μm and aspect ratios as large as 7 were readily molded. Prototypes of microfluidic chips made from PS were prepared by thermal bonding of a microchannel molded in PS with a flat PS substrate. The PS microfluidic chip displayed much lower adsorption and absorption of hydrophobic molecules (e.g. rhodamine B) compared to a comparable chip created from PDMS. The molded PS surface exhibited stable surface properties after plasma oxidation as assessed by contact angle measurement. The molded, oxidized PS surface remained an excellent surface for cell culture based on cell adhesion and proliferation. To demonstrate the application of this process for cell biology research, PS was micromolded into two different microarray formats, microwells and microposts, for segregation and tracking of non-adherent and adherent cells, respectively. The micromolded PS possessed properties that were ideal for biological and bioanalytical needs, thus making it an alternative material to PDMS and suitable for building lab-on-a-chip devices by soft lithography methods.     

Pressure-jump volume-relaxation studies of polystyrene in the glass transition region

An apparatus has been constructed that permits the measurement of time-dependent changes in pressure near the point of vitrification. The same instrument is used for measuring steady-state PVT properties, which are necessary for a proper analysis of the dynamic measurements. The former experiments are referred to as pressure-jump volume-relaxation (PJVR) measurements and serve as a direct probe of the structural relaxation process that occurs in all glasses. Experiments have been performed on polystyrene from 110 to 150°C and up to 2 kbar using pressure steps of 500 bars. The qualitative observations are analogous to those obtained at atmospheric pressure by rapid changes in temperature, namely (1) nonlinearity, (2) asymmetry, and (3) memory effects associated with complicated temperature or pressure histories. Each of these effects is accounted for semiquantitatively by a phenomenological order-parameter model that has been extended to include the effect of pressure. Deviations between theory and experiment increase as temperature and pressure increase, this being manifest mostly in a predicted recovery curve (expansion isobar) that recovers the equilibrium volume more quickly than the experimental data; the contraction isobars are in most cases predicted within experimental error. The adjustable parameters of the model are found to vary somewhat with pressure and temperature, apparently due to variations in δ and Δκ. The activation volume suggests that 10–20 monomer segments are involved in the recovery process, assuming that the activation volume itself represents only a fraction of the dynamic unit (as observed in molecular glasses).     

Mathematical modeling of the graft reaction between polystyrene and polyethylene

Polystyrene (PS) and polyethylene (PE) are two major components of household plastic waste whose blends are immiscible. Recycling them together is an attractive option that requires a compatibilization process to improve the blend mechanical properties. If a PE/PS copolymer is added or formed in situ, it may act as compatibilizer. The structure and molecular properties of this copolymer are key factors to assure its effectivity as a compatibilizer. In this work, we study the graft copolymerization reaction between polystyrene and polyethylene using the catalytic system composed of AlCl₃ and styrene. We develop a model of this process which considers that PE/PS grafting and PS degradation occur simultaneously. We propose a kinetic mechanism for the whole process and apply the method of moments to solve the mass balance equations. The model is able to calculate average molecular weights as well as the amount of grafted PS. It accurately describes the available experimental data, constituting a valuable tool for simulation and optimization purposes.     

Investigations of the combustion products of flame-protected impact resistant polystyrene

During the decomposition process of the entitled material in presence of air, the degradation products of the flame retardant (deca-bromdiphenyloxide) are produced as well as polystyrene components. In addition compounds were formed resulting from reactions between the devolatilization products of the polymer and the flame retardant, e.g. especially benzyl bromide, brominated styrene derivates, bromoethylbenzene and 4-bromotoluene.The apparatus used, has been described in previous papers (1,2), but additionally an instrumental modification of the buring apparatus has been made according to DIN 4102, this work deals with comparison of the results by use of both, the Bayer-ICI-Shell apparatus and our self-designed burning apparatus.     

Fast-scan chip-calorimeter measurement on the melting behaviors of melt-crystallized syndiotactic polystyrene

We employed fast-scan chip-calorimeter (FSC) measurement (Flash DSC1) to study the melting of syndiotactic polystyrene after melt-crystallized at various cooling rates as well as after isothermally crystallized at various high temperatures. We attributed the observed double melting peak to a melting-recrystallization process of beta-form crystals upon heating, as evidenced by their variations with different cooling and heating rates. Our experiments demonstrated the advantages of FSC techniques in the investigation of crystallization and melting behaviors of polymer materials.     

Spectroscopic evidence of phase transition of monomolecular water in solid polystyrene

Phase transition behavior of monomolecular water in solid polystyrene was examined by temperature variable Fourier transform infrared spectroscopy. Spectral changes showed for the first time that monomolecular water in a polymer matrix (in a closed system) could be condensed and then frozen and also that the ice formed could be grown and diminished by vapor deposition in cooling process and sublimation in heating process, respectively.     

Surface-modified hemispherical polystyrene/polybutyl methacrylate composite particles

Micrometer-sized polystyrene/poly(n-butyl methacrylate) composite particles of hemisphere morphology and narrow size distribution were prepared by a process of single-step swelling of uniform polystyrene template microspheres with emulsion droplets of the monomer n-butyl methacrylate containing the initiator benzoyl peroxide in the presence, or absence, of the co-swelling agent toluene. Butyl methacrylate was then polymerized at 73 degrees C within the template microspheres. Surface and bulk characterization of the particles were performed by methods such as FTIR, elemental analysis, XPS, advancing contact angle, light microscope, SEM, and cross-sectional TEM. Selective surface functionalization of the poly(n-butyl methacrylate) phase of the composite particles was performed by carrying out a similar swelling and polymerization process in the presence of a water-soluble vinylic monomer such as acrylamide.     

Graft copolymerization of acrylonitrile onto polystyrene

It is possible to graft vinyl monomers, such as acrylonitrile, onto polystyrene via anionic processes but not by a radical process. Both homopolymerization of the added acrylonitrile and graft copolymerization in which acrylonitrile units are added to the para position on the benzene ring in styrene occur; the conversion of acrylonitrile into polymer depends upon the time and temperature of the reaction and on the concentration of the anionic initiator, butyllithium. A constant 15–20% of the acrylonitrile is converted to graft copolymer while the remainder is homopolymerized; graft copolymer may be separated from homopolymer by selective precipitation from either N,N′-dimethylformamide or aqueous potassium thiocyanate. Treatment of the mixed graft and homopolymer with aqueous sodium hydroxide converts the nitrile into an acid salt and one may conveniently separate homopolymer from graft copolymer in this way. Each polystyrene chain is grafted with acrylonitrile units. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1275–1282, 1997     

Thermal behavior of polystyrene synthesized in the presence of carboxymethyl cellulose

Summary Study of the decomposition kinetics is an important tool for the development of polymer recycling in industrial scale. In this work, parameters such as activation energy, frequency factor and reaction order, were measured under dynamic conditions. Flynn-Wall-Ozawa, Van Krevelen, Horowitz-Metzger, Coats-Redfern, Madhusudanan and Vyazovkin methods were used to determine the kinetic parameters. The analysis of the results obtained by the Coats-Redfern method shows that the thermal degradation process of LDPE and HDPE corresponds to a phase boundary controlled reaction (mechanism R2). This method shows that the reaction order values of LDPE and HDPE are about 0.7 and 0.6, respectively.     

Investigation of the thermal degradation process of polystyrene brominated on the ring

The results of investigation of the degradation process of polystyrene brominated on the ring via an ionic route have been presented. Using thermogravimetric (TG) and differential thermal analysis (DTA) methods, the course of degradation of polymer samples with different bromine content has been described. Introducing of bromine on the aromatic ring influenced the initial decomposition temperature (IDT) and the temperature corresponding to the maximum of decomposition rate (T _m). The samples have been pyrolyzed at 300°C and some pyrolysis products were identified by means of gas chromatography/mass spectrometry. Finally, the possible mechanism of degradation was presented.     

Template synthesis of functionalized polystyrene in ordered silicate channels

A mesostructured nanocomposite was fabricated by using a novel electroactive, polymerizable surfactant as a template in a sol-gel process, and the first example of well-resolved polystyrene with redoxactive functional group synthesized in silicate matrices was provided.     

Structure formation during isothermal crystallization of oriented isotactic polystyrene

Isothermal crystallization from the glassy state of oriented isotactic polystyrene (iPS) was studied using in situ Fourier transform infrared (FTIR) spectroscopy and in situ wide‐angle X‐ray diffraction (WAXD) studies. The oriented amorphous films of iPS were prepared by rolling the amorphous iPS film to a draw ratio of 3 or 4. In situ FTIR was used to investigate the ordering process of polymer chains prior to crystallization by measuring the change in the dichroic ratio with time, while in situ WAXD studies were used to investigate the development of the crystalline structure. The studies showed that the orientation process and the conformation change preceded crystallization. This observation suggests that polystyrene chains undergo an ordering process during the induction period of crystallization. The degree of orientation markedly increases with time in the induction period, suggesting that heat treatment of oriented amorphous materials under constraint provides a useful method for processing highly oriented materials. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2912–2921, 2000