Glass Transition Of Polystyrene Research Articles

The rigid amorphous fraction of isotactic polystyrene prepared by freeze-drying from dilute solutions

The techniques of wide-angle X-ray diffraction, infra-red spectroscopy and differential scanning calorimetry were used to characterize the glass transition and crystallization behavior of freeze-dried isotactic polystyrene (iPS) derived from dilute solutions. It was found that there is a concentration boundary for the original solution: below the boundary, the freeze-dried iPS samples are poorly crystallized but the chains are in a highly ordered 3 1 helix state; above the concentration boundary, the freeze-dried iPS is in a completely disordered amorphous state.

Transitiometric Analysis of Pressure Effects on Various Phase Transitions

A scanning transitiometer has been used in investigations of 1st and 2nd order phase transformations in polymers. It was demonstrated taking as an example fusion of polyethylene at 200 MPa with a temperature scan as inducing variable that by recording simultaneously the rate of heat exchange and the rate of volume variations it is possible to determine in a single experiment the pressure derivative of temperature of this 1st order phase transition. For phase transformations similar to the 2nd order transitions the transitiometric analysis permits simultaneous measurements of pairs of thermodynamic derivatives which permit determination of pressure effects according to the Ehrenfest equations. For the glass transition in polystyrene at high pressures the pressure effect was similar independently of the pair of thermodynamic derivatives used (heat capacity and thermal expansivity or compressibility and thermal expansibility).

Linearity limits of dynamic calorimetric response at the glass transition of polystyrene

The thermal relaxation of polystyrene (PS) in the glass transition region is investigated with both temperature modulated differential scanning calorimetry (TMDSC) and a model calculation based on the dislocation concept. It is shown that the model permits a proper description of the linear and non-linear effects of thermal relaxation. It is well known that the thermal relaxation in the glass transition region can be non-linear. On the other hand a linear analysis of the measured TMDSC curve is common. A resulting property is a complex heat capacity. The affect of the non-linear effects on the measured complex heat capacity is investigated experimentally and with model calculations. Consequently the non-linearity determines two effects: an increase of the amplitude of the heat capacity change at the glass transition temperature and an increase of the fraction of higher harmonics in the periodic heat flow. The limits of the linear response are discussed. It is shown that the linear response approach is applicable at temperature amplitudes up to 1.5 K for Polystyrene.

Synthesis of Poly(styrene−dimethylsiloxane) Block Copolymers: Influence of the Phase-Separated Morphologies on the Thermal Behaviors

Five polystyrene−poly(dimethylsiloxane) di- and triblock copolymers were prepared by two different methods, a classical anionic polymerization and a cationic polymerization of styrene in the presence of a new macromolecular initiator. Spherical, cylindrical, and lamellar phase-separated morphologies were identified. Their sizes were measured by transmission electron microscopy (TEM) on films obtained from bulk and solvent-cast samples. DSC and TEM show that the phase-separated morphologies are strongly segregated with no long range ordering. The specific microphase surface area, obtained by TEM, is strongly correlated with the broadening of the polystyrene glass transition.

Glass Transition Temperature of Polystyrene with Compressed Carbon Dioxide.

Glass transition of polystyrene (PS) with carbon dioxide was studied under high pressures up to 15MPa over the temperature ranges from 305. 2K to 358. 2K. The glass transition temperature (Tg) was determined as a function of pressure P from a change in width of strip PS films in CO2, which depends on a cutting direction of PS films against the extruding direction. The pressure coefficient of the glass transition temperature (∂Tg/∂P) obtained in this work is in agreement with the literature values.

Dynamics of polyisoprene in star block copolymers confined in microstructures: A dielectric spectroscopy study

Dielectric spectroscopy has been employed to study selectively the local and global dynamics of polyisoprene (PI) in three microphase separated star diblock copolymers (SI)4, where PI and polystyrene (PS) form the core and corona, respectively. The thermally induced order-to-disorder transition (ODT) has been identified by rheology and small-angle x-ray scattering (SAXS). All dielectric measurements were made at temperatures well below the ODT and the polystyrene glass transition temperatures, where the four PI chain ends are tethered by the glassy polystyrene domains. The ordered state morphology, studied by SAXS, revealed the formation of PS spheres (fPS=0.25, where fPS is the polystyrene volume fraction), polyisoprene cylinders (fPS=0.68), and a lamellar structure (fPS=0.41) in the three copolymers. In contrast to the local segmental motions, the chain orientational dynamics associated with the amplitude and the characteristic relaxation time are strongly influenced by the spatial confinement. The main effects are the suppressed amplitude and the enhanced chain mobility, which are predicted and found to be stronger if the star topology is accompanied by topological (entanglement) effects of the PI block, irrespective of the ordered star morphology.

Glass transition of polystyrene near the surface studied by slow-positron-annihilation spectroscopy

We have measured the Doppler broadening energy spectra of positron annihilation using a variable monoenergetic positron beam as a function of positron energy and of temperature in polystyrene. The $S$ parameters from the energy spectra versus temperature show that onset temperatures significantly decrease as the positron energy decreases. This result gives direct evidence that the glass-transition temperature is suppressed at a magnitude of 57 \ifmmode^\circ\else\textdegree\fi{}C at the depth of 50 \AA{} from the surface.

Morphology of model three-component three-arm star-shaped copolymers

The microdomain structure of a model three-component, three-arm, star-shaped copolymer consisting of polystyrene (PS), poly(dimethylsiloxane) (PDMS) and poly(tert-butyl methacrylate) (PTBMA), each of them having nearly the same weight fraction, was investigated by means of differential scanning calorimetry (d.s.c.), transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). D.s.c. results exhibiting the glass transition of PS and PTBMA and the crystallization and melting of PDMS strongly suggest the microphase separation of the three components into three microdomains. The microdomain structure is considered to be extremely complicated because the chemical junction points of the three constituent polymers must be confined on the lines where three kinds of interfaces meet. TEM and SAXS results strongly support the existence of a very regular microdomain structure with three-fold symmetry. Each of the three components possibly forms a three-dimensionally continuous network domain resulting in an ordered tricontinuous microdomain structure.

Thermal and mechanical properties of poly (styrene- b-ethylene- co-butylene- b-styrene) triblock copolymers

Styrene- b-ethylene- co-butylene- b-styrene triblock copolymers with variable styrene and ethyl branch contents have been prepared by hydrogenation of the butadiene block in the precursor poly(styrene- b- butadiene- b-styrene)s. Their thermal and mechanical properties and their viscoelastic behaviour have been determined in order to establish the influence of the structure. parameters. Thermal transitions measured by differential scanning calorimetry and dynamic mechanical analysis show, for the first time, the peculiar characteristics of these copolymers, which present two relaxations, α and β corresponding to the glass transition of polystyrene and the relaxation of the elastomeric block, respectively. The nature of the β-relaxation depends on the crystallinity of the system. Below 50% butylene content, it can be related with that found in polyethylene copolymers due to segmental motions in the interfacial regions. Above 50% butylene, the crystallinity has practically disappeared and the -EB- block behaves as an amorphous ethylene-butylene copolymer, and the β-relaxation values can be assigned to the glass transition of this amorphous system. Both styrene and ethyl branch levels determine the ultimate properties. By increasing the styrene content, the modulus at low deformation and the tensile strength at break increase but the abrasion resistance and resilience decrease. The ethyl content does not affect either resilience or hardness, but the tensile properties decrease with increasing the branch level.

Modulated differential scanning calorimetry in the glass transition region, IV. Pseudo-isothermal analysis of the polystyrene glass transition

Abstract The kinetics of the glass transition of Polystyrene is measured by quasi-isothermal, temperature-modulated differential scanning calorimetry (TMDSC) and compared to pseudo-isothermal analyses of standard TMDSC traces. Quasi-isothermal TMDSC is carried out at a series of fixed average temperatures, modulated sinusoidally with an amplitude of ±1.0 K and a period of 100 s. These measurements use, thus only a single time scale defined by the modulation frequency. The standard use of TMDSC adds a second time scale to the experiment, the underlying heating and cooling rates 〈 q 〉 at 1 K min −1 . In the pseudo-isothermal analysis of standard MDSC, the effects of the underlying heating and cooling rates are separated by subtraction of averages over full modulation periods from the modulated temperature and heat flow. The small differences in the reversing, apparent heat capacity between MDSC heating and cooling traces are measured and linked to the kinetic expressions of irreversible thermodynamics and interpreted using the hole theory. As the sample moves away from the equilibrium of the liquid state, the kinetics depends increasingly on the thermal history, and the expected deviations from a first-order kinetic expression are observed.

Glass Transition and Ultrasonic Relaxation in Polystyrene

ABSTRACTWe present measurements of the glass transition and the ultrasonic relaxation modulus in a series of monodisperse polystyrenes. The temperature dependence of the modulus was analyzed using Havriliak-Negami relaxation model (HN) and Vogel-Tammann-Fulcher equation (VTF) for the relaxation time. The results allowed us to determine the fragility index, m, which decreases with increasing molecular weight, Mn. Furthermore, the relaxation time was found to saturate at high molecular weights and varies as Mnp, in the low molecular weight region. The exponent is p≈2 at high temperatures and p ≈ 7 at low temperatures close to Tg.

Modulated differential scanning calorimetry: 2. Studies of physical ageing in polystyrene

Physical ageing in polystyrene (PS) has been studied by means of modulated differential scanning calorimetry (m.d.s.c.). The results show that there exists a characteristic annealing temperature at which relaxation enthalpy has a maximum value. When annealing below 65°C, another relaxation peak has been found. The position of this relaxation peak, which changes with annealing temperature, lies approximately between 54 and 64°C. It has been postulated previously in the literature that the relaxation behaviour involves phenyl ring relaxation. As measured from heat capacity curves, this transition is evident as a shoulder on the glass transition. With increasing annealing temperature, the glass transition of PS increased slightly.

Atomic Force Microscopy Study of Polystyrene Latex Film Morphology: Effects of Aging and Annealing

The surface topography of polystyrene latex thin films (∼1-μm thick) deposited from surfactant-free latex dispersions onto mica was investigated by atomic force microscopy (AFM) as a function of particle size, annealing time and temperature, and aging at ambient temperatures. The films were observed to be polycrystalline, consisting of hexagonal domains of long-range, close-packed particles. Greater particle monodispersity resulted in fewer crystal defects. Films aged at ambient temperatures did not exhibit interparticle fusion, within the resolution limits of the AFM. Limited particle fusion is observed when the films are annealed : the particle heights decreased dramatically but only when heated at temperatures above the glass transition of polystyrene, whereas the interparticle distance between adjacent, close-packed particles was observed to remain constant under all annealing and aging conditions. A smaller particle sized latex resulted in a faster rate of interparticle fusion, thought to be due to a greater capillary force between the smaller particles. Crystal defects at the film surface became larger in size as a result of annealing, but there was no measurable increase in the number of defects.

Poly(styrene‐graft‐ethylene oxide) as a compatibilizer in polystyrene/polyamide blends

AbstractPolystyrene (PS) blends containing a dispersed phase of either polyamide‐6 (PA‐6) or polyamide‐12 (PA‐12) were compatibilized by additions of 1, 3, or 5 wt % poly(styrene‐graft‐ethylene oxide). The graft copolymers were found to have a stabilizing effect on the domain sizes. Weight average radii of PA‐6 domains in compression molded samples were reduced by a factor of 5 with 3 wt % graft copolymer added. The corresponding size reduction for PA‐12 domains was by a factor of 3. Also, the domain sizes were more uniformly distributed in blends containing the graft copolymers. Thermal analysis of the blends revealed that compatibilization retarded the PA crystallization, with some PA crystallizing at the PS glass transition. This retarded crystallization is explained as a result of the domain size reduction and by the presence of graft copolymer at the interface. The graft copolymers had a toughening effect on the blends and the impact strength of a PS/PA‐12 blend was improved by 65% by adding 3 wt % of graft copolymer. Binary blends of the PA and poly(ethylene oxide) (PEO) were investigated in a separate study to verify miscibility of the graft copolymer side chains and the PA. Hydrogen bonding between PA‐6 and PEO was confirmed by IR spectroscopy and partial miscibility was indicated by melting point depressions. © 1995 John Wiley & Sons, Inc.

Boson peak and fast relaxation process near the glass transition in polystyrene

Atactic polystyrene, both side group and main chain deuterated, was investigated by inelastic neutron scattering in a wide temperature range around the glass transition from 2 to 450 K. In the glass the Boson peak position is only very weakly influenced by the deuteration of the phenyl group. In the neighborhood of the glass transition temperatureTg we find a fast relaxation process similar to other glasses. The onset of the fast relaxation in polystyrene, however, is observed already at temperaturesTg — 200 K. Results from partially deuterated polystyrene suggest a change of the phenyl ring dynamics already far belowTg.

Glass transition of atactic polystyrene with less chain entanglements

Atactic polystyrene was dissolved and refluxed in benzene keeping the polymer concentration well below the critical concentration C* value for chain overlap. After rapid freezing of the solution by injecting it directly into liquid nitrogen, the solvent was sublimated so that the expanded chain coils with few entanglements could be obtained. Tg for this material was found to be 11 K lower than the normal polystyrene even after annealing up to 470 K. Comparison of the infrared spectra shows some conformational differences between the freeze-dried and the normal PS. Upon shock-cooling and subsequent freeze-drying, all vibrational bands appear much sharper, indicating an increase in structure regularity.

Thermoplastic interpenetrating polymer networks based on a poly(styrene‐b‐butadiene) copolymer and an ionically‐terminated polybutadiene ionomer

AbstractThermoplastic interpenetrating polymer networks (IPN) are mixtures of two physically crosslinked polymers. Thermoplastic IPNs were prepared by blending an SBS triblock elastomer with a 1,2‐polybutadiene that was ionically‐terminated at both ends. The morphologies of these IPNs were studied using differential scanning calorimetry and dynamic mechanical thermal analysis. It was concluded that the ionomer was incompatible with the SBS elastomer, since the Tgs of both the 1,2‐polybutadiene from the ionomer and the essentially 1,4‐polybutadiene from the SBS component were observable at temperatures that were close to those of the individual components. The addition of the polybutadiene material had, however, an influence on the relaxation processes of the polystyrene blocks. The polystyrene glass transition in the pure SBS copolymer is broadened by the interfacial region between polystyrene and polybutadiene. The low temperature shoulder was much more pronounced when the ion‐terminated polybutadiene was present, indicating it has a preference to be located in these interfacial regions. © 1994 John Wiley & Sons, Inc.

Temperature Effects on Interdiffusion at Glassy/Rubbery Interfaces

Abstract Attenuated total reflection infrared spectroscopy was used to measure interdiffusion at a model glassy/ rubbery interface consisting of polystyrene (PS) below its glass transition temperature in contact with poly(vinyl methyl ether) (PVME). PVME swelled PS at temperatures ranging from 60 to 95°C, corresponding to 41 to 6°C below the glass transition of PS. This swelling was confirmed with dynamic mechanical analysis using glassy crosslinked PS in contact with PVME. The swelling process was characterized by an interfacial velocity as the PVME swelled PS. The relaxation time for the swelling process was determined from the interface velocity as a function of temperature and the results indicated that the swelling process is controlled by the relaxation time of the slowly diffusing component (PS). The relaxation time ranged from 141 min at 60°C to 16.8 s at 95°C. The activation energy for the relaxation of the PS matrix was determined as 40.9/pm 2.6 kcal/mol using the Arrhenius expression, in good a...

Observation of temperature dependent thicknesses in ultrathin polystyrene films on silicon.

The temperature dependent thicknesses of ultrathin polystyrene films under vacuum on Si (111) substrates were investigated via x-ray reflectivity in situ. The contraction of ultrathin polymer films was directly observed for the first time to the author's knowledge. The degree of contraction depends on the initial thickness of the ultrathin polystyrene film, with the magnitude of contraction increasing with decreasing initial film thickness. This contraction ranged from 0--17 % and occurred at temperatures well below the reported bulk polystyrene glass transition temperature.

Use of ATR-FTIR to study interdiffusion in polystyrene and poly(vinyl methyl ether)

ATR-FTIR was used to measure interdiffusion in a polystyrene (PS) and poly(vinyl methyl ether) (PVME) compatible pair below and above the glass transition of PS. At 105°C, corresponding to 5°C above the glass transition of PS, the interdiffusion coefficient was of the order of 1.1x10 -12 cm 2 /s. Interdiffusion was not dominated by either component and it was controlled by the rate of swelling of PS by PVME. At 85°C, the interdiffusion was not-Fickian and time-dependent. A combination of the Fickian and case II models was used to fit the data at 85°C as well as the data at 105°C