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.     

Photooxidation of polystyrene: Irradiation at 254 and 365 nm

Studies have been made of the near surface photooxidation of atactic polystyrene films prepared in the absence of air. The samples were photooxidized on exposure to air at two frequencies, 254 and 365 nm, using a calibrated mercury irradiation source with filters. Most studies were made at 40°C and as a function of irradition time with the reactions characterized by changes in molecular weight and composition. The former was evaluated by gel permeation chromatography and the latter by transmission Fourier transform infrared spectroscopy and by multiple-internal-reflectance infrared spectra using different angles and different crystals to evaluate compositions as a function of film depth. Species identified in photooxidation include the generation of hydroperoxides and the appearance of carbonyl bands with the latter identified by the spectral shift asociated with the exposure of the photooxidized polystyrene surface to ammonia. These results suggest that principal products of near-surface oxidation of polystyrene are carboxylic acids.     

Effect of Thermal Aging on the Optical Properties of ABS Plastics

Poly(acrylonitrile/butadiene/styrene) (ABS) is a two-phase material consisting of elastomer particles in a glassy polymer matric of styrene and acrylonitrile (SAN) [1]. The photooxidation of ABS was the subject of several studies [2, 3]. It was suggested that several processes will take place during photooxidation. These changes include the formation of hydroperoxide [4], chain breakage of the polystyrene, and the oxidation of the polymer as it was monitored by IR spectroscopy [4–6]. Also photooxidation affect the polybutadiene in ABS and oxidizes it, which results in the formation of hydroperoxide. There are no data available on the thermal degradation of ABS. In a previous study the thermal aging of recycled high-impact polystyrene was studied using UV-vis spectroscopy [7]. It was found that this method provided very useful information about the degradation of several industrial polymers [8–12]. In this paper thermal degradation of ABS is investigated by UV-vis and IR spectroscopy.     

Mixing of a self-assembled supramolecular polymer and a covalent polymer in organic solutions

We report on a neutron scattering study of the molecular structure of a self-assembled supramolecular polymer composed of a bicopper complex within a solution of a covalent polymer (atactic polystyrene/trans-decalin). The study is achieved by putting two binary phases in contact and allowing for diffusion of both components in either phase. It is shown that the one-dimensional bicopper filaments are compatible to a high extent with the atactic polymer. These results are discussed in the light of a recently devised encapsulation process of the bicopper filaments within the fibrils of a physical network of isotactic polystyrene.     

Transport properties of dichloromethane in glassy polymers. I. Atactic polystyrene films

Sorption and diffusion of dichloromethane vapor were measured in atactic polystyrene films, obtained with different cooling conditions and after controlled aging times at different temperatures. The diffusional behavior is characterized by three zones, depending on temperature and penetrant activity. In Zone I, at low activity, the diffusion coefficient is independent of vapor concentration; Zone II is characterized by concentration-dependent diffusion, whereas in Zone III structural transformations are possible. The study of diffusion at three temperatures allowed building of a temperature-penetrant concentration diagram, which is very useful to visualize the different zones of behavior. The aging at room temperature has no effect on the curve of sorption as a function of vapor activity, whereas it determines two effects on the diffusion: a decrease of the zero concentration diffusion coefficient and a more and more anomalous behavior with the aging time. The aging at 70°C produces the same effects on the diffusion behavior as the aging at room temperature; in addition, a decrease sorption is observed at low penetrant activity. The possible presence of ordered domains, impermeable to the vapor, in the samples stored at 70°C, was suggested on the basis of sorption results.     

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.     

Amorphous phase in atactic polystyrene

Summary Amorphous phase in atactic polystyrene (a-PS) was investigated via its physical aging behavior. It was found that when the samples were quenched rapidly, there were dual amorphous regions with quite different characters: free amorphous region and constrained amorphous region. The former was the normal bulk amorphous region, while the latter was constrained by the internal stress. The dual amorphous regions exhibited as dual endothermic peaks in differential scanning calorimetry (DSC) traces when the samples were physically aged at temperatures well below the glass transition temperature (T_g). The lower peak corresponded to the free amorphous region, and the upper peak to the constrained amorphous region. Received: 10 July 2001/Accepted: 24 July 2001     

Thermal shrinkage of drawn polystyrene

Many papers have reported on the thermal shrinkage mechanism of drawn polymers. The cause of the thermal shrinkage is very complex, because that relates to many factors. In this study, atactic polystyrene, a noncrystalline polymer, was used to eliminate factors related to the melting and crystallization effects, and it is considered that there is a relation between the change of the polymer's structure due to heat treatment and thermal shrinkage. It is observed in a certain temperature range that the thermal shrinkage of drawn polystyrene is not caused by increase of the entropy but results in decrease of the entropy.     

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.     

Thermo-mechanical properties of the blend syndiotactic/atactic polystyrene after crystallization of the syndiotactic polystyrene

The thermo-mechanical properties of the blend syndiotactic polystyrene (sPS)/ atactic polystyrene (aPS) are characterized by studying the concentration depending softening behavior with thermo-mechanical analysis (TMA) and the temperature depending Young's modulus for different concentrations with dynamic mechanical analysis (DMA).     

Reactivity of macromonomer in copolymerization of styrene with styrene-terminated macromonomer by CpTiCl3-MAO catalyst

Summary The copolymerization of styrene (St) and styrene-terminated macromonomers with CpTiCl₃-MAO catalyst was investigated. The contents of the macromonomer in the graft copolymer was found to depend on the miscibility of the macromonomer with the main chain polystyrene formed by copolymerization. miscible system of the syndiotactic polystyrene in the main chain and atactic polystyrene in the side chain was favorable for the incorporation of the macromonomer into the graft copolymer as compared with immiscible system of syndiotactic polystyrene in the main chain and atactic polyisoprene in the side chain. The contents of the SSTM in the graft copolymer was influenced by the MAO/Ti mole ratio and content of the SSTM in the comonomer feed. Received: 9 November 1999/Revised version: 24 November 1999/Accepted: 6 December 1999     

Dielectric constant,optical transmission,and thermal diffusivity monitoring of iodine-impregnated polystyrene films

A simple method for the iodine doping of atactic polystyrene films is described. The marked changes in the physical properties of the polystyrene films, such as dielectric constant, optical absorption coefficient, and thermal diffusivity, are presented as a function of the doping time. The results show strong evidences of the onset of an order–disorder transition as a function of the doping time.     

Surface photostabilization of polystyrene by Tinuvin 1577

The effect of a new hydroxyphenyltriazine additive (Tinuvin 1577) on the surface photooxidation of polystyrene films at various concentrations of the additive was studied using ESCA spectroscopy. The accelerated weathering was run in a Xenotest apparatus to mimic outdoor conditions. The presence of Tinuvin 1577 effectively inhibited the surface photooxidation of polystyrene. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1251–1256, 1998     

Study of the solution properties of tactic polystyrenes

Summary Viscosity measurements are reported for syndiotactic polystyrenes in a molar mass range from 35,000 to 400,000 g/mol and standard fractions of narrowly distributed atactic polystyrenes in a molar mass range from 50,000 to 600,000 g/mol in trichlorobenzene at 135 °C. The correlation between molar mass and intrinsic viscosity of different polystyrene samples was investigated as well as their solution properties. The results demonstrate that the intrinsic viscosity of polystyrene in thermodynamically good solvents is independent of the type of tacticity of the polystyrenes investigated here. The dilute solution properties were compared with those for isotactic and atactic polystyrenes. The small differences in their solution viscosities may occur due to the different molar mass distributions of differently synthesized samples. Received: 14 April 1998/Revised version: 23 June 1998/Accepted: 23 June 1998     

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.     

Thermal transitions in cold-crystallized blends of isotactic and static polystyrene

Solution-cast blends of isotactic and atactic polystyrene were stripped of casting solvent and heated above the glass transition temperature to temperatures below the equilibrium melting point of the respective blends to induce the development of crystallinity of the isotactic polystyrene. The samples, maintained at these crystallization temperatures for various times, were subsequently characterized by differential scanning calorimetry. The amount of crystallinity, the crystalline melting point, and the rate of crystallization were determined for each of the blends from the d.s.c. scans. The development of crystallinity, characterized by increased melting points, resulted from annealing at progressively higher temperatures. The maximum rate of crystallization for each of the blends was observed at a temperature corresponding closely to $\text{8}\text{9}$ of the absolute equilibrium melting temperature. The decrease in the melting point of the isotactic polymer, crystallized in the presence of atactic diluent, resulted primarily from weak enthalpic interactions between isotactic and atactic polystyrene homopolymers. Scanning electron photomicroscopy revealed that atactic-rich blends, immersed in n-hexane at 40°C, developed a non-intercommunicating network of microvoids. Similar solvent treatment of isotactic rich blends had little effect on the samples. D.s.c. measurements confirmed recently published results which indicated that n-hexane, at modest temperatures, does not induce the development of crystallinity in isotactic polystyrene.     

Physical aging behavior of miscible blends containing atactic polystyrene and poly(2,6-dimethyl-1,4-phenylene oxide)

The influence of blend composition on physical aging behavior was assessed for miscible blends of atactic polystyrene (a-PS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO). At aging temperatures of 15 and 30°C below the midpoint glass transition temperature (T_g), the a-PS/PPO blends exhibited volume relaxation rates that were retarded compared to additivity based upon the aging rates for pure a-PS and PPO. This negative deviation diminished with increased undercooling, and eventually the volume relaxation rates displayed a nearly linear trend with respect to composition at the greatest undercooling of 60°C that was employed. The compositional nature of unaged glassy density and secondary relaxation intensity, both influenced by the presence of specific attractive interactions in the blend system, were likely causes for the variation of volume relaxation rate with composition and undercooling. For aging at 30°C below T_g, the dependence of enthalpy relaxation rate on composition was similar to that observed for volume relaxation. Mechanical aging rates determined from time–aging time superposition of creep compliance data showed significantly less than additive behavior for the blends aged at T_g−30°C, but unlike the volume relaxation results, this trend persisted at the 60°C undercooling.     

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.     

Photooxidation of polystyrene. Effect of stabilizers

The effect of commercially available stabilizers such as Tinuvin-327, Tinuvin-770, and Irganox-1024 on the photooxidation of polystyrene (PS) was investigated by following the changes in molecular weight and molecular weight distribution. Structural changes during degradation were studied by ¹H-NMR- and IR-Spectroscopy and by Electron Spectroscopy for Chemical Analysis (ESCA). Neat PS films became very brittle and yellow on exposure to UV light. Tinuvin-770 stabilized the PS films towards discolouration and brittleness. The ESCA studies of surface photooxidation of polystyrene indicate the formation of ketonic and methylene ether groups in the initial stages (? 100 h). At later stages ester and carbonate groups are formed.     

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.