Para-substituted Polystyrenes Research Articles

Correlation between fragility and cooperativity in segmental dynamics of glass-forming para-substituted polystyrenes

To understand the mechanism of the viscous slowdown in supercooled liquids that is responsible for glass transition, we investigate the interrelation between glass transition temperature Tg, fragility and cooperativity in segmental dynamics. Polymeric glass formers having a similar chemical structure are expected to exhibit clear correlations between the above parameters. In this paper, polystyrene (PS) derivatives possessing various para-substituents are studied using calorimetry with regard to the fragility parameter m, dynamic length scale ξ and the number of cooperatively rearranging segments NCRR at Tg. Positive correlations were revealed for both NCRR(Tg) vs m and ξ3(Tg) vs m. Both fragility and cooperativity were found to increase as the bulkiness of the substituent increases. Wide-angle X-ray scattering measurements revealed that the structural correlation between backbone chains is reduced as the bulkiness increases. This may be responsible for the reduced cooperativity. In contrast, for poly(methacrylic acid ester)s, the relations between the above parameters appeared to be less clear. The clear trend observed for the PS system may be due to the rigidity of the phenylene unit, through which the substituent directly affects the backbone dynamics. The estimated activation energy per segment increased consistently with an increase in the para-substituent’s bulkiness. The relations between glass transition temperature, fragility and cooperativity in segmental dynamics were investigated on polystyrene derivatives possessing various para-substituents using calorimetry. A positive correlation was observed between cooperativity and fragility. Both fragility and cooperativity were found to increase as the bulkiness of the substituent increases. Estimated activation energy per segment increased consistently with an increase in the substituent’s bulkiness.

Polymeric Cross-Linked Surface Treatments for Controlling Block Copolymer Orientation in Thin Films

The orientation of cylinder-forming poly(styrene-block-methyl methacrylate) [P(S-b-MMA)] was investigated on two sets of polymeric surface treatments: 10 para-substituted polystyrene derivatives with <10 mol % poly(4-vinylbenzyl azide) and a series of poly(styrene-random-4-vinylbenzyl azide) [P(S-r-VBzAz)] copolymers with 5-100 mol % poly(4-vinylbenzyl azide). The copolymers were spin-coated to form thin films and then cross-linked by heating. The resulting films exhibited a range of surface tensions from 21 to 45 dyn/cm. Perpendicular orientation of P(S-b-MMA) cylinders was achieved with poly(p-bromostyrene) and all the [P(S-r-VBzAz)] copolymer surface treatments, most notably the homopolymer of poly(4-vinylbenzyl azide). Films made from these simple copolymers are as effective as random terpolymer alignment layers commonly made from both block monomers and a cross-linkable monomer.

Decay Lifetimes of Para-Substituted Polystyrene in Solid Films and in Dichloromethane

The fluorescence decay times of polystyrene, poly(4-bromostyrene), poly(4-chlorostyrene), poly(4-methylstyrene), poly(α-methylstyrene), poly(4-methoxystyrene), and poly(4-tert butylstyrene) were measured in solid films and in dichloromethane solution. A detailed analysis of the emission profile performed by nanosecond time resolved fluorescence spectroscopy confirmed the presence of monomer fluorescence as well as excimer fluorescence in both media. Monomer fluorescence decay times gave shorter times compared with that of excimer decay times in dichloromethane solution. Fluorescence from substituted polystyrene was mainly excimer fluorescence with shift of maximum emission to longer wavelength. The ratio of monomer to excimer contributions was found to be dependent on the emission wavelength, but was not affected by polymer concentration. Both monomer and excimer fluorescence lifetimes as well as excimer intensity increase with increasing emission wavelength. An accompanying decrease in monomer contribution is also observed is solution in comparison with that in solid films.

Solvent effect on thermal degradation of plasticized para-substituted polystyrenes

The thermal effect on stability of a series of para-substituted polystyrenes with methyl, methoxy and α-methyl substituents in various solvents was studied in the temperature range of 298–363 K. They gave a monomer fluorescence as a minor part and excimer fluorescence as a major part. Thermal heating of para-substituted polystyrenes shows a decrease in both monomer and excimer fluorescences in all used solvents. Thermal heating causes a small fluorescence quenching effect at lower temperatures in solution but becomes very dominant at higher temperatures. Added terephthalate and phthalate plasticizers to these para-substituted polystyrenes caused a quenching of both monomer and excimer fluorescences without the formation of exciplex emission. The thermal quenching processes of the plasticized polymers were accompanied by a change in the structure of the fluorescence spectra at high heating temperatures. This may indicate that thermodestruction of these polymers starts from a random chain scission. The change in solvent polarity has considerable effect on fluorescence quenching but it has a minor effect on the thermal degradation of these polymers. The binding energies for excimer formation were calculated in the used solvents.

Transport Behavior of Oxygen and Nitrogen through Organasilicon-Containing Polystyrenes by Molecular Simulation

Molecular dynamics (MD) simulations have been used to study the transport properties of oxygen and nitrogen in the para-substituted polystyrenes which possess one to four Si atoms in each substituent. The Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field was used to construct the polymers. Diffusion coefficients were obtained from molecular dynamics (NVT ensemble) with up to 3 ns simulation times. After molecular dynamic simulation, the trajectories of the small molecules in the polymer matrix were obtained. Then diffusion coefficients have been calculated from the Einstein relationship revealing a considerable agreement between the simulated and the experimental data. And solubility coefficients have been calculated by the Grand Canonical Monte Carlo (GCMC) method. The solubility of oxygen increased with increasing Si content in the polymer membrane. The para-substituted polystyrenes with a branched substituent at the alpha-position showed higher permeability than those of the nonbranched ones. The higher the glass transition temperature (T(g)) of the membrane, the larger the diffusion coefficients of oxygen and nitrogen obtained.

Physicochemical properties of complexing para-substituted polystyrene sorbents containing functional amino groups

The acid-base properties of the analytical functional groups of complexing polymer sorbents based on aminopolystyrene and the sorption capacity of the sorbents were investigated. The influence of various substituents on the acid-base properties of the sorbents was studied.

Thermal degradation of para-substituted polystyrenes

The thermal degradation of a series of para-substituted polystyrenes with electron-donating (CH 3, NH 2) and electron-attracting (NO 2,Cl,Br) substituents has been studied in isothermal conditions at 600°C using pyrolysis chromatography/mass spectrometry and in dynamic conditions using thermogravimetry. The pyrolysis of these substituted polystyrenes gives monomer as the main product for all polymers (60–80 wt.%). The other distribution of products supports the view that thermodestruction of these polymers starts from a random chain scission. The main process for all substituted polystyrenes is depolymerization, similar to unsubstituted polystyrene. In the case of para-substituted polystyrenes a good linear dependence was found between T max on the thermogravimetry curve and the Hammett constants of the substituents ( T max =403.5–67.486 σ x ). The results indicate that the Hammett relationship can describe quantitatively the trends in T max and thus thermostability of substituted polystyrenes and that thermostability of these polymers depends only on electronic nature of substituent and their possibility to stabilise macroradicals forming on chain scission.

Para-substituted polystyrenes: Stress relaxation, creep, dynamic mechanical and dielectric analyses

The effects of methyl, ethyl, n-propyl and t-butyl para-substituents on relaxations in polystyrene are characterized via multiple thermal techniques. It is shown that the glass transition temperature T g can be readily obtained from stress relaxation and creep data by locating the intersecting point of the Arrhenius and WLF curves on the logarithm of the shift factor a T vs. temperature plots. The T g thus obtained from stress relaxation data is correlated well with literature values obtained by isochronal dilatometry. The processes of creep and stress relaxation show two regions of distinct molecular motion patterns with different activation energies determined. Rubbery plateaus for stress relaxation moduli due to chain entanglements are observed for polystyrene, poly ( p-methyl styrene) and poly ( p- t-butyl styrene). The flexural storage moduli E′ for the three polymers show a density dependency, which is correlated by the Rao function. The peak width of loss modulus E″ is affected by the molecular weight distribution of each polymer. Two weak sub-glass transition temperature transitions, β and γ, are also observed from dynamic mechanical analysis. The variations in the glass transition temperature and activation energy from dielectric analysis are analyzed with regard to steric hindrance resulting from different alkyl groups.

Gas permeation properties of organosilicon-containing polystyrenes

para-Substituted polystyrenes that possess one to four Si atoms in each substituent were prepared using our original synthetic methods. The gas permeation properties of these polymer membranes were investigated in detail. With an increasing Si content in the polymer membrane, it was determined that the solubility of oxygen increased. The para-substituted polystyrenes with a branched substituent at the α-position showed higher permeability than those of the non-branched ones. With a higher glass transition temperature ( T g) of the membrane, a higher diffusion constant of oxygen was obtained. Consequently, p poly[4-{bis(trimethylsilyl)methyl}styrene] which had the highest T g among the membranes investigated in this study, showed the highest oxygen permeation coefficient (37–45 Barrer). The activation energy of the oxygen permeation in this membrane was 3.0 kcal/mol.

Selective oxidation of para-substituted polystyrenes during surface-enhanced Raman scattering

Influence du substituant sur le mecanisme de photo-oxydation de films de PS sur les substrats d'argent; le premier stade de l'oxydation serait une reaction de Norrish de type II. Lorsque le substituant est electrodonneur (F, Cl, Br, Me), l'oxydation se poursuit rapidement par une reaction de Norrish de type I donnant des acides benzoiques p-substitues. Pour des electroattracteurs, la station de Norrish I est lente et l'oxydation se poursuit par un processus d'addition de Diels-Alder

Dilute solution properties of poly(4-hydroxystyrene)

Light-scattering and viscosity measurements have been carried out on dilute solutions of poly(4-hydroxystyrene) (PHS) fractions, which were obtained by hydrolysis of poly(4-acetoxystyrene) (PAS). The Mark-Houwink-Sakurada equations were determined in dioxane, tetrahydrofuran, isobutyl acetate and ethyl propionate at 25°C. The unperturbed dimension and the thermodynamic interaction parameters for PHS in various solvents were also determined and compared with those previously obtained for PAS. It was concluded that the hindrance potential of rotation around the C-C bond in the main chain of PHS is influenced more than expected solely from the volume effect of side groups, but it is within the same range found for other polar para-substituted polystyrenes. Also, it was found that in contrast to the PAS-solvent system there are significant energetic and entropic interactions between segments of PHS and solvent molecules, arising from the presence of a hydroxyl group in the side chain.

Dipole moments of several para-substituted polystyrenes and poly(.alpha.-methylstyrenes) in various solvents over a wide range of temperature

Moments dipolaires de derives chloro, bromo et fluoro du polystyrene, de derives methoxy, fluoro et bromo du poly-α-methylstyrene et du poly-vinylcarbazole, dans le benzene, le toluene et CCl 4

Application of ESCA to studies of structure and bonding in polymers

Shake-up phenomena in a series of para-substituted polystyrenes have been studied by ESCA. Comparison with other spectroscopic data and with theoretical calculations within the sudden approximation, equivalent cores model, and CNDO SCF MO formalism identifies the shake-up structures arising from π*â†�π transitions involving the highest occupied and lowest unoccupied orbitals of the pendant phenyl groups. The relative intensities of different core levels and associated shake-up satellites are used to investigate the structure and surface morphology of some alkane styrene copolymers and polystyrene-polydimethylsiloxane AB block copolymers.

Electron spin resonance studies of spin-labelled polymers—I segmental relaxation of polystyrene in solution

From an analysis of the widths of the hyperfine lines in the ESR spectrum of a nitroxidelabelled polystyrene in toluene solution, the correlation times for rotational diffusion at three temperatures have been measured. The values agree well with published data from NMR studies of polystyrene in solution. The value of the activation energy for the relaxation process, 4·3 kcal. mole −1, is close to published values for dielectric relaxation of para-substituted polystyrenes. These comparisons provide strong evidence for associating the ESR correlation times with some form of segmental motion of the polymer backbone.