Microstructure Of Polystyrene Research Articles

Nanostructuring of honeycomb-like polystyrene with excimer laser

This paper is aimed on the construction of honeycomb like patterns (HCP) with defined dimensions of pores on activated solid-state substrate. Dip coating technique with improved phase separation was used for pattern preparation, subsequent nanostructuring was realized with an excimer laser. Polystyrene patterns were prepared on perfluorethylenepropylene, which were subsequently treated with laser wavelength 248 nm. The main goal was to prepare honeycomb like pattern and by interaction of such microstructure with an excimer laser to prepare superposed structure. This idea was fully fulfilled, uniform micropattern on perfluorinated polymer was prepared, with several laser fluences and number of pulses to be tested subsequently. Optimal conditions of KrF exposure were determined to be 6000 pulses and interval of laser treatment from 8 to 16 mJ.cm−2, by this combination of input parameters a superposed globular nanostructure was constructed on honeycomb-like polystyrene microstructure. Surface wettability, morphology and chemistry of nanopatterned microstructures were changed significantly, oxygen concentration of treated substrates was significantly increased. Particular stages of globular pattern formation were studied and described in detail by atomic force microscopy, scanning electron microscopy, EDS/EDX and XPS analysis. Elemental mapping was applied for detailed analysis of prepared superposed pattern.

Microstructure of Polymers Prepared in the Presence of Tri-n-butylboron–p-Quinone System

The microstructure of polystyrene, poly(methyl acrylate), and poly(tert-butyl acrylate) obtained in the presence of tri-n-butylboron in combination with naphthoquinone-1,4 and 2,3-dimethylbenzoquinone is studied. The stereoregularity of polymers formed under these conditions may be described in the framework of the first-order Markov chain model. The use of p-quinones in combination with tri-n-butylboron favors an increase in the content of isotactic triads in the polymers. The causes of the observed deviations are discussed.

Electric Field and Gradient Microstructure for Cooperative Driving of Directional Motion of Underwater Oil Droplets

Driving a liquid droplet with control of directional motion on a solid surface, by introducing a surface wettability gradient or external stimuli, has attracted considerable research attention. There still remain challenges, however, due to the slow response rate and slow speed of continuous liquid droplet motion on the structured surface. Here, an approach to continuously drive the underwater oil droplet with control of directional motion by the cooperative effects of an electric field and the gradient of a porous polystyrene microstructure is demonstrated. The gradient microstructure induces the liquid droplet to take on an asymmetrical shape, causing unbalanced pressure on both ends to orient the droplet for motion in a particular direction. Meanwhile, the electric field decreases the contact area and the corresponding viscous drag between the droplet and the gradient‐structured surface. Then, the unbalanced pressure pushes the underwater oil droplet to move directionally and continuously at a certain voltage. This work provides a new strategy to control underwater oil droplets and realize unidirectional motion. It is also promising for the design of new smart interface materials for applications such as electrofluidic displays, biological cell and particle manipulation, and other types of microfluidic devices.

Synthesis and characterization of UV-crosslinkable unsaturated ketone group containing polystyrene films

In this study, as a serial of our previous studies, polystyrene (PS) containing acetyl group (CH3CO) was used as a raw material and condensation reaction was performed in basic medium with aliphatic saturated and unsaturated aldehydes. Synthesized modified polystyrenes (MPSs) were characterized using spectroscopic (1H NMR and IR) and chemical analysis methods. Atomic force microscopy (AFM), has been used to determine the microstructure of PS, APS and MPS with crotonaldehyde, as example. The thermal properties of polymers were investigated after crosslinking by ultraviolet (UV) irradiation. The crosslinking of MPSs was quantitatively estimated from the amount of insoluble polymer as well as the change in the glass transition temperature. As a result, MPSs with crotonaldehyde and cinnamaldehyde had higher thermal properties and crosslinking than others due to two double bonds in their structure. MPSs films were resistant to corrosive mediums. After irradiation, water sorption of MPS decreased 0.65%.

Polymerization of styrene with tetradentate chelated α-diimine nickel(II) complexes/MAO catalyst systems: Catalytic behavior and microstructure of polystyrene

The recently reported N,N,N,N-tetradentate chelated α-diimine Ni(II) complexes 1– 3 were demonstrated to be efficient precatalysts for the polymerization of styrene in the presence of MAO, producing isotactic-enriched heterotactic polystyrenes (isotactic contents in the range 73–75.5%). The corresponding sequence distributions were determined by NMR spectroscopy, and fitted to six probabilistic models of chain propagation. A better conformity to a Bovey–first order Markov chain propagation model was obtained, indicating a chain-end control mechanism. A comparison of the microstructural features with other polystyrenes obtained by several different types of initiation indicates that the polystyrenes are formed by a coordination insertion polymerization mechanism at the nickel centers.

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

Styrene polymerization was carried out by a simple half-titanocene complex [cyclopentadienyltitanium trichloride] (CpTiCl 3) and pentamethyl [cyclopentadienyltitanium trichloride] (Cp*TiCl 3) 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 CpTiCl 3/MAO and Cp*TiCl 3/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.

Effect of ultrasound on the microstructure of polystyrene in cyclohexane: a synchrotron small-angle X-ray scattering study

Synchrotron small-angle X-ray scattering tech- nique has been used to study the effect of ultrasound on the microstructure of polystyrene (PS) in cyclohexane solu- tions. The results show that the intramolecular radius of gyration (Rg) decreases with ultrasound, indicating the shrinkage and collapse of PS chains. There is an exponen- tial relationship between Rg and the molecular weight of PS (Mw), and the exponent changes from 0.5 to 0.417, as the ultrasound time is increased. This means that the shape of PS chain changes from random coil to shrunken form. The Kratky plots also confirm the shape transformation of PS chains induced by ultrasound. Moreover, the intermolecular correlation length increases with the ultrasound time, which is indicative of the entanglement of PS chains.

Styrene polymerization with novel anilido–imino nickel complexes/MAO catalytic system: Catalytic behavior, microstructure of polystyrene and polymerization mechanism

The polymerization of styrene with novel catalytic systems of anilido–imino nickel complexes (Ar 1N = CHC 6H 4NAr 2) NiBr (Ar 1 = Ar 2 = 2,6-dimethylphenyl, 1; Ar 1 = 2,6-dimethylphenyl, Ar 2 = 2,6-diisopropylphenyl, 2; Ar 1 = Ar 2 = 2,6-diisopropylphenyl, 3; Ar 1 = 2,6-diisopropylphenyl, Ar 2 = 2,6-dimethylphenyl, 4) activated by methylaluminoxane was investigated. The influence of reaction parameters (temperature, Al/Ni mole ratio, and polymerization time) on styrene polymerization was evaluated. The influence of the bulkiness of the substituents on polymerization activity and polymer characteristics was also ascertained. The obtained polystyrene was an iso-rich atactic polymer and its weight–average molecular weight reached 70 500. NMR analysis of the end groups further confirmed that styrene polymerization catalyzed by anilido–imino nickel complexes/MAO systems proceeded through a coordination mechanism, and the chain was initiated through styrene secondary insertion into the Ni H and terminated mainly through β-H elimination of styrene producing the chain-end group ( CH CHPh).

Experimental Study of Laser Interaction with Fibrous and Foam‐Like Materials

AbstractNew results obtained in experiments on laser irradiation (I = 1014 W/cm2, λ = 1.055 micrometer) of lowdensity (1–30 mg/cm3) fibrous and foam‐like materials are presented and discussed. Influence of low‐density material microstructure of irradiated plane samples on processes of laser light absorption, X‐ray conversion, energy transport, plasma formation and homogenization was investigated. The pronounced effect of material microstructure on the parameters and dynamics of produced plasma has been found out using the variety of complementary X‐ray and optical methods. The extension of hot plasma region inside irradiated samples as well as the energy transport rate was observed to be several times higher for samples of foam‐like polystyrene than for samples of fibrous agar. The experiments with cascade targets consisting of several mylar films (film thickness and film‐to‐film spacing were varied) were carried out with the aim to model the polystyrene microstructure in a simplified manner. The low‐density fibrous samples with external and internal soft X‐ray sources (converters) were also irradiated. Preferences of either fiber or foam‐like material utilization in target constructions for specific research problems are considered. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Stereospecific anionic polymerization of styrene initiated by R 2Mg/ROMt ‘ate’ complexes

Various ‘ate’ complexes formed by reaction of alkali metal (Li, Na, K) derivatives and alkyl metals (Mg, Al, Zn) were used as initiator for the styrene anionic polymerization in hydrocarbon media and their influence on polystyrene microstructure has been investigated. A strong dependence of the polymer tacticity on both the nature of the alkali metal and of the associated metal alkyl used is observed. Binary systems like potassium derivatives/dialkylmagnesium yield isotactic-rich polystyrene. Eighty-five percent isotactic polystyrene (mm triad) is obtained in methylcyclohexane at −40 °C with the potassium tert-butoxide/ n, s-dibutylmagnesium system. The characteristics of solubility of the stereoregular polystyrenes are in agreement with isotactic polystyrene chains containing some stereostructural defects and suggest that one single type of isospecific propagating centres is operating during the polymerization. When lithium or sodium derivatives are used in association to dialkylmagnesium instead of a potassium derivative, a strong decrease of the isotacticity is observed. The influence, on the extent of stereoregulation, of other parameters of these initiating systems as well as that of the solvent has also been investigated. The stereoregulation mechanisms involved in these styrene anionic polymerizations may be related to styrene insertion into carbon–metal bonds of the ‘ate’ complexes with a covalent character.

Viscoelastic characteristics of pentane-swollen polystyrene beads

Expansion of pentane-swollen polystyrene beads was followed at and above the glass transition by using a very simple optical technique. Measurements allowed a suitable determination of the glass transition temperature and of the viscoelastic characteristics of the pentane-plasticized polystyrene chains inside the beads, at different pentane contents. This was achieved by combining the well-known Williams, Landel, and Ferry approach and some calculations derived from a recent micromechanical modeling of the expanded polystyrene microstructure. The results, analyzed in terms of free volume characteristics, revealed the peculiar plasticizing character of pentane, as compared to the usual polymer diluents. A value of 42°C was found as the lowest temperature for which the dimensional variation of the beads could result from glass transition motions. The relevance of these conclusions was discussed, not just in terms of the changes in dimensions of the individual beads at zero expansion time but also in terms of the dimensional evolution observed in the expanded polystyrene structures. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2463–2472, 1999

The evolution of microstructure of polystyrene following pressure relaxation: a positron study

Positron annihilation lifetime spectra on polystyrene (PS) have been measured as a function of pressure relaxation time ( t = 0–100 h) under the initial uniaxial pressure P = 0, 25 and 50 MPa, respectively. In order to extract the information on the variations in the microstructure and free-volume hole as a function of pressure relaxation time t, we first considered the inhibition of ortho-positromium (o-Ps) formation by positron-irradiation induced free-radicals; second we evaluated the quantity ΔI 3( t), i.e. the difference in the o-Ps formation probability between P = 25 (or 50) and 0 MPa. We observed that ΔI 3( t) dramatically increases with t up to a characteristic time (≈ 5 and 12 h for P = 25 and 50 MPa, respectively) and then tends to a constant level. This result is explained by the evolution of microstructure and free-volume holes in PS during pressure relaxation.