Tg Of Polystyrene Research Articles

Mechanical properties of the double gyroid phase in oriented thermoplastic elastomers

We investigate the mechanical properties of triblock copolymers with oriented double gyroid (DG) morphology in poly(styrene-b-isoprene-b-styrene) (SIS) triblock copolymers by deforming textured samples along both the [111] direction and transverse to this direction. The modulus anisotropy for the two directions of this cubic material is approximately a factor of 5. Deformation along [111] causes the sample to form a distinct neck and draw, while the deformation in the transverse direction proceeds without neck formation. In addition, the mechanical hysteresis of the [111] stretch is 50% higher than that transverse to the [111] direction. Upon unloading and annealing above the polystyrene Tg, the DG structure recovers fully, both macroscopically and microscopically. The mechanical properties of the DG are compared to those of the classical block copolymer morphologies to gain insight into the deformation mechanism.

Structure of Waterborne Organic Composite Coatings

The mechanical properties and structure of composite films made of high-Tg polystyrene (PS) nodules dispersed in a low-Tg poly(butyl acrylate) (PBuA) matrix were studied by means of dynamic mechanical spectrometry and small-angle neutron scattering. At temperatures between the Tg of PS and PBuA, the mechanical properties depend drastically on the spatial distribution of the glassy PS domains. For films cast from mixtures of PS and PBuA latexes, an aggregation of PS particles into dense clusters dispersed in the PBuA matrix was observed. As a consequence, a large density of contacts between PS particles in the dry films ensured a strong mechanical reinforcement above a percolation threshold of 30% PS volume fraction. Extensive coalescence of PS particles occurred at their contacts upon annealing the films above the Tg of PS, leading to further mechanical reinforcement. For films cast from core−shell particles, the aggregation phenomenon was prevented, depending on the coverage of the PS core by the PBuA shell. An efficient core encapsulation in the core−shell morphology led to poor contact between PS cores, the elastic moduli were then close to that of the PBuA matrix, and the PS coalescence upon annealing was prevented.

Morphological Changes of a Molten Polymer/Polymer Interface Driven by Grafting

Whether interfacial tension between two molten polymers can be reduced significantly by the formation of copolymer at the interface by chemical reaction of functionalized chains is the question addressed by this paper. To answer it, model experiments are carried out by grafting of benzylamine end-functionalized deuterated polystyrene (dPS−NH2) onto poly(styrene-r-maleic anhydride) (PSMA) random copolymer at an initially planar melt interface between polystyrene (PS) and PSMA. Various volume fractions of dPS−NH2 with polymerization indices N = 33, 55, and 270 were mixed with PS and then reacted with PSMA above the Tg of PS and PSMA. The interfacial excess, z*, of the dPS portion of the graft copolymer formed at the boundary was measured using forward recoil spectrometry. The values of normalized grafting density z*/Rg, where Rg is the radius of gyration of dPS−NH2, are observed to be as large as 40, 9, and 4 for the N = 33, 55, and 270 dPS−NH2 chains, respectively. These large values signal the formation o...

Surface mobility and diffusion at interfaces of polystyrene in the vicinity of the glass transition

Symmetric polydisperse (Mw = 23 × 104, Mw/Mn = 2.84) and monodisperse (Mw = 21 × 104, Mw/Mn < 1.05) polystyrene (PS), and asymmetric polydisperse PS/poly(2,6-dimethyl 1,4-phenylene oxide) (PPO) interfaces have been bonded in the vicinity of the glass transition temperature (Tg) of PS. In a lap-shear joint geometry, strength develops in all cases with time to the fourth power, which indicates that it is diffusion controlled. Strength developing at short times at the polydisperse PS/PS interface, at 90°C, is higher than that at the monodisperse interface, at 92°C (at Tg − 13°C in both cases), presumably due to the contribution of the low molecular weight species. The decrease of strength at the PS/PPO interface when the bonding temperature decreases from 113 to 70°C, i.e., from Tg + 10°C to Tg − 33°C of the bulk PS, indicates a high molecular mobility at the surface as compared to that in the bulk, and can be expressed by a classical diffusion equation, which is valid above Tg (of the surface layer). © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 567–572, 1998

Polystyrene-poly(ethylene oxide) diblock copolymers micelles in water

Micellization in water of polystyrene–poly(ethylene oxide) diblock copolymers is achieved by the stepwise dialysis technique in order to prepare micellar solutions for copolymers with a wide range of molecular parameters. Hydrodynamic radii, determined by quasielastic light scattering, are correlated with the molecular parameters, e.g. molecular weight and composition, and compared with the theory. Two couples of phenanthrene and anthracene labelled copolymers are used to prepare micellar solutions by mixing them before and after dialysis. The non radiative energy transfer is determined on these solutions to prove that polystyrene-poly(ethylene oxide) diblock copolymers micelles in water are "frozen" micelles even when heated near the Tg of polystyrene.

Phase Separation Behaviors Of Polyimide Blends

ABSTRACTWe investigated phase behaviors of polyimide blends such as polyethermide(PEI)/polystyrene(PS), PEI/polyamideimide(PAI), PEI/polyethyleneoxide(PEO), and PAI/PEO systems. Our sample systems exhibited lower critical solution temperature(LCST) phase behaviors. In the PEI/PS system, phase transition occurred near or above the glass transition temperature(Tg) of PS and the critical temperature of the system increased with decreasing molecular weight of PS. For PEI/PAI and PEI/PEO systems, the critical temperature of PEI/PAI system is higher than that of PEI/PEO system. Phase transition temperatures of PAI/PEO systems appeared near or below the melting point of PEO.

Transition and relaxation processes of polyethylene, polypropylene, and polystyrene studied by positron annihilation

Transition and relaxation processes of polyethylene (PE), polypropylene (PP), and polystyrene (PS) were studied by the positron annihilation technique. From measurements of lifetime spectra of positrons as a function of temperature, the lifetime of ortho-positronium, τ3, and its intensity, I3, were found to increase above 260 K for PP. This fact was attributed to a cooperative motion of large segments of molecules above the glass transition temperature, Tg. For PE, above Tg (140 K), the value of τ3 increased, but the temperature coefficient of I3 was negative below 230 K. From this fact, for PE, the molecular motions that cause the glass transition were associated with a rearrangement of molecules by local motions such as kink motions. The discrepancy between the results for PE and PP was attributed to the presence of methyl groups in PP and the resultant suppression of the local motions. For PS (Tg = 340 K), the molecular motions were found to start above 260 K, but those were suppressed by an interphenyl correlation. Detailed annihilation characteristics of positrons in polymers were also discussed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1601–1609, 1997

Synthesis and mechanical properties of poly(styrene‐b‐lsobutylene‐b‐styrene) block copolymer lonomers

AbstractLinear and three‐arm star poly(styrene‐b‐isobutylene‐b‐styrene) (PS‐PIB‐PS) block copolymer ionomers possessing various counterions and levels of sulfonation were synthesized by sulfonating the polystyrene blocks of PS‐PIB‐PS block copolymers. Analysis of compression‐molded films of the ionomers showed that the incorporation of sulfonate groups into the polystyrene blocks of these materials resulted in an increase in tensile strength, a decrease in elongation at break, and a persistence of elastic properties to much higher temperatures as compared with unsulfonated precursors. Among all counterions studied, zinc resulted in the strongest ionomers and potassium yielded the most easily processed ionomers. Dynamic mechanical analysis showed that the block copolymer ionomers possessed a phase‐separated morphology; however, anomalous relaxations observed during the first heating cycle, but that were substantially reduced or completely absent in subsequent cycles, implied that strong ionic interactions were causing reduced processability and the formation of nonequilibrium morphologies. The observed relaxations were interpreted to be domain rearrangements brought about by the thermal energy supplied by the dynamic experiment. Annealing of films of relatively low ionic contents yielded viscoelastic behavior that was consistent with an equilibrium morphology characterized by phase‐separated, partially sulfonated polystyrene domains of the same density and size as the polystyrene domains of the unsulfonated precursor. Compression molded films of high ionic content yielded a higher rubbery plateau modulus than the unsulfonated precursor, suggesting a different morphology. Solution‐cast films of zinc ionomers exhibited two values for the rubbery modulus, a higher values at temperature below the Tg of polystyrene and a lower value at temperature above the Tg of polystyrene. Thermogravimetric analysis revealed the major mass‐loss process of the parent, linear block copolymer at 417°C (mid‐point) and of the tetramethyl ammonium ionomer at 431°C.

Morphology and texture of high-density polyethylene-polystyrene blends deformed by plane-strain compression

The blends of high-density polyethylene (HDPE) with atactic polystyrene (PS) were deformed plastically by plane-strain compression in a channel die. The samples were deformed up to the true strain 1.8 (compression ratio 6) in three temperature regimes: below, near, and above the glass transition temperature of polystyrene component. The morphology and the texture of crystalline component in the deformed blend samples were investigated by means of scanning electron microscopy and wide angle X-ray diffraction (pole figures technique). It was found that the deformation process in the blend of immiscible HDPE and PS does not differ markedly from the deformation of the one-component system from the point of view of the deformation mechanisms involved. The crystalline textures of the blend samples are qualitatively the same as in the plain HDPE deformed under similar conditions. The active deformation mechanisms are the same in deformation of both the plain HDPE and HDPE/PS blend. The mechanism identified are crystallographic slips: (100)[001], (100)[010], and (010[001] supported by the interlamellar slip. The presence of PS in blends modifies to some extent the deformation process and resulting orientation of the crystalline component of HDPE by modification of the stress distribution within HDPE matrix around PS inclusions. This influence is much stronger at low deformation temperatures, when PS is in a glassy state, than at temperatures above Tg of PS. © 1996 John Wiley & Sons, Inc.

Asphalt modified by SBS triblock copolymer: Structures and properties

AbstractMicrostructural transformation of a poly(styrene‐b‐butadiene‐b‐styrene), SBS, triblock copolymer blended with asphalt was studied as the asphalt composition was varied from 0 wt% to 96 wt%. Transmission electron microscopy (TEM), dynamic mechanical spectrometry (DMS), and differential scanning calorimetry (DSC) were used. The blends were made in batch mixers at 200°C, or by solution casting from a nonselective solvent (trichloroethane) at ∼28°C. Asphalt partially solubilizes the polybutadene (PB) midblock of the SBS producing saturated PB microdomains along with macrodomains of asphalt. When the asphalt concentration was varied from 10 to 90 wt%, the asphalt phase separated into a variable number of large domains, while the SBS‐rich regions formed a continuous matrix. Networks of SBS‐rich regions were observed at low magnification; these are referred to as macro‐networks. At higher magnification, networks that are stabilized by polystyrene (PS) microdomains (denoted micro‐networks) are also formed. The presence of a macro‐network is also confirmed by stress relaxation tests. The macro‐network broke down into microgel‐like structures when the asphalt composition exceeded 90 wt%. Examination of the interior of the SBS‐rich regions showed that the shape of the PS microdomains transformed from short cylinders to lamellae, hexagonally perforated lamellae (HPL), back to lamellae, short cylinders, and finally to spheres. DMS and DSC indicate a systematic increase in the PB glass transition temperature (Tg) and negligible change in the Tg of PS as the asphalt content increases. Triblock copolymers that can form a macro‐network at low concentration will be more desirable for highway pavement modification.

Glass Transition Temperature Of Ultrathin Polymer Films On Silicon

AbstractThe glass transition temperature, Tg, of polystyrene (PS) thin films on silicon wafers with different surface preparations was determined in order to explore the effect of interfacial interaction energy on local chain dynamics. To enhance interface behavior, the film thickness included in this work was as low as 50 Å. PS with monodisperse molecular weights was chosen as a model polymer. Two different silicon surfaces were prepared: sulfuric acid-clean and hydrogen passivated. Tg of thin films was determined by monitoring the film thickness as a function of temperature. Tgwas identified as the temperature where the thermal expansion coefficient underwent an abrupt change. X-ray reflectivity was used to determine film thickness with a precision of a few angstroms. Tg of PS was found to depend strongly on the initial film thickness, as well as the substrate surface.

Attempted synthesis of multiblock copolymers of butadiene, styrene, and α‐methylstyrene: Effect of polar additives on copolymerizations

AbstractOwing to the low Tg of polystyrene, the mechanical properties of polystyrene‐block‐poly‐butadiene‐block‐polystyrene (SBS) thermoplastic elastomers drop steeply above 60°C. To overcome this behavior, many research groups have considered the replacement of styrene (S) by α‐methylstyrene (MS). We also attempted the synthesis of copolymers with a central polybutadiene (poly B) block and rigid blocks consisting of polystyrene (poly S) and poly(α‐methylstyrene) (poly MS) blocks. Starting from a dilithium initiator, difunctional poly B's with low 1,2 content (10%) were prepared and toluene was added. After addition of a small amount of styrene, MS was added in the presence of a 15% (in vol) of THF at T ≤ −40°C. The copolymers did not have the expected structure and poor mechanical properties resulted, which were, however, still measurable at 120°C. These results probably resulted from secondary reactions involving the MS carbanions. To identify these reactions and to control the polymer structure, the synthesis of multiblock copolymers was carried out with a monofunctional polybutadienyllithium to which were added successively S and MS (in a mixture of hexane and benzene as solvent). MS was added at low temperature in the presence of small amounts of THF or at room temperature after addition of TMEDA. These attempts were unsuccessful, the copolymer being always multimodal as a result of unwanted coupling reactions involving terminal double bonds. The synthesis of elastomers using a coupling reaction of poly MS–poly S–poly B was also considered but the yield in poly B was low since termination reactions involving the polar additive occurred. © 1994 John Wiley &amp; Sons, Inc.

Structural changes upon annealing in a deformed styrene-butadiene-styrene triblock copolymer as revealed by infrared dichroism

Structural and morphological changes in a deformed styrene-butadienestyrene (SBS) tri- block copolymer were usually studied by means of small-angle X-ray scattering techniques through analysis of scattering patterns which are related to rigid polystyrene (PS) microdomains. In the present study, a different approach was demonstrated. Infrared dichroism was used to elucidate these changes induced by annealing through measurements of molecular orientation of rubbery polybutadiene (PB) chains. This was made possible by the fact that (1) structural rearrangements of PS microdomains are inevitably associated with changes of the PB orientation and (2) strain-induced orientation of the PB chains depends on the arrangement or orientation of the PS microdomains which act as cross-links. Infrared dichroism analysis showed that the relaxation of rigid PS microdomains, which occurs even at annealing temperatures (T,) below the glass transition temperature (T,) of PS, can be studied by observing the relaxation of the PB orientation and that the remaining PB orientation under constant strain at long annealing time (>30 min) characterizes the orientation of rubbery chains required for activating PS plastic flow. Furthermore, it was found that the loss of PB orientation under strain with annealing time is not equally associated with the lost recovery of the sample length after removal of the extensional stress, suggesting the existence of different mechanisms of PB orientation relaxation. Finally, an anisotropic morphology in annealed SBS polymer was revealed by a strain-induced PB orientation which depends on the redrawing direction with respect to the initial stretching direction (SD). These measurements indicate that, at Ta 5 Tg of PS, the PS rearrangement involves essentially rotation of cylindrical microdomains, with the interdomain vector connecting the centers of the cylinders remaining preferentially parallel to the SD; while, at T,, > Tg of PS, the rearrangement process involves more displacement of the PS cylinders, with the interdomain vector oriented perpendicularly with respect to the SD.

Gas solubility and diffusion in a polystyrene–polybutadiene block copolymer

AbstractOver the temperature range of 20 to 90°C, the equilibrium solubility of methane or argon in a star‐branched polystyrene–polybutadiene (SB) block copolymer can be reliably estimated from a volume‐fraction‐weighted average of the homopolymer solubilities; the value of heat of solution for SB block copolymer lies between the two values associated with the constituent homopolymers. Diffusion coefficients for gases in the block copolymer are bracketed by the homopolymer values over the range of temperature employed, but the activation energies for diffusion in SB are higher than either of the homopolymer values. The anomalous temperature dependence and the inability of a computer simulation to reproduce experimental diffusion coefficients supported the concept of a temperature‐dependent restriction on chain mobility in the polybutadiene regions of the block copolymer. This β factor embodies the relative reduction in the rate of gas diffusion through the B regions of the copolymer compared to B homopolymer; β has a value of about 2–3 at room temperature but decreases to unity when the polystyrene chains become mobile at the polystyrene Tg.

Phase rearrangement in two‐stage emulsion polymers of butyl acrylate and styrene: Mechanical properties

AbstractThe mechanical and thermal properties of films from a series of two‐stage emulsion polymers were investigated. The emulsion polymers were made by polymerizng styrene in the presence of a preformed poly(butyl acrylate‐co‐divinyl benzene) seed latex. The effects of seed particle size, seed particle crosslinking via the amount of divinyl benzene, styrene/butyl acrylate ratio, and thermal history on the film properties were studied. Latex particles were characterized by light scattering and film formation behavior. Dried films were characterized by differential scanning calorimetry, dynamic mechanical analysis, and stress‐strain behavior. Although evidence was obtained for nearly complete phase separation between the polystyrene (PS) and poly(butyl acrylate) (PBA) phases, the site of styrene polymerization and thus the PS phase morphology is influenced by seed particle size, seed crosslinking, and S/BA ratio. The morphology of as‐dried films consists of finely dispersed PS domains in a continuous PBA matrix. Thermal annealing above the PS Tg causes coalescence of the PS domains, resulting in significantly improved mechanical properties. The extent of PS phase coalescence is also influenced by the level of seed crosslinking.

Conformational equilibria and the glass transition

Solutions of the conformationally inhomogeneous compounds 2-chlorobutane, chlorocyclohexane and trans-1,2-dichlorocyclohexane in glass-forming liquids (Nujol, butyl chloride and some phthalates) were investigated by i.r. absorption spectra. Freezing the conformational equilibrium at the glass transition of the solutions was observed. The method of using conformationally inhomogeneous compounds as a probe for the determination of the glass transition temperature (Tg) is proposed. The necessity of taking into account the glass transition process in interpreting results obtained for the temperature range T < Tg has been shown. The possibilities of the application of the proposed method to polymers have been explored, and Tg of polystyrene has been determined.

Effects of high‐pressure CO2 on the glass transition temperature and mechanical properties of polystyrene

AbstractHydrostatic pressure usually increases the glass transition temperature Tg of a polymer glass by decreasing its free volume; if the pressurizing environment is soluble in the polymer, however, one might expect an initial decrease in Tg with pressure as the polymer is plasticized by the environment. Just such a minimum in the Tg of polystyrene (PS) is observed as the pressure of CO2 gas is increased over the range 0.1–105 MPa from both ultrasonic (1 MHz) measurements of Young's modulus E and static measurements of the creep compliance J. A time‐temperature‐pressure superposition law is obeyed by PS which allows a master curve for the compliance to be constructed and shift factors to be determined. A master curve for E is then obtained by using the Boltzmann superposition principle. The compliance J reaches a maximum, and E and Tg reach minima, at a CO2 pressure of ca. 20 MPa at both 34 and 45°C, which are above the critical temperature (31°C) of CO2. At the minimum, Tg is 41 at 45°C and 36 at 34°C, the larger depression at 34°C evidently corresponding to the higher solubility of CO2 at the lower temperature. The plasticization effect due to CO2 can be isolated by subtracting the effect of hydrostatic pressure alone from the experimental data. The results leave no doubt that at high pressures CO2 gas is a severe plasticizer for polystyrene.

On the drying of glassy polystyrene

AbstractMany commercial polymers contain water which must be reduced to a lower level for application. The drying behavior of polystyrene (PS), molecular weight 12,000, and flow characteristics suitable for extrusion and injection molding, have been studied. A laboratory tray dryer was used at temperatures below the glass transition temperature of PS (Tg ∼ 373 K). Effects of air flow rate (from 0.5 to 3.5 liters/s), temperature (from 323 to 373K) and relative humidity (from 0.5 to 25 percent) on retained water in PS were measured, and from those effects the effective diffusion coefficients (D) have been deduced as: .

Plasticization effects on environmental craze microstructure

Environmental crazes were grown in thin films of polystyrene (PS) using the homologous series of alcohols, CH3OH, C2H5OH, n-C3H9OH and n-C4H9OH. The films were bonded to copper grids, strained to below the minimum crazing strain in air and exposed to the vapour of the various alcohols. The craze microstructure, as measured quantitatively by transmission electron microscopy, varies significantly along the series. The craze fibril volume-fraction, Vf, decreases monotonically from 0.25 for methanol, which depresses the glass transition temperature, Tg, of PS to 91° C, to 0.09 for n-butanol, which depresses Tg of PS to 71° C. All these slowly-growing vapour crazes thicken by drawing more fibrillar material from the craze surfaces rather than by fibril creep. The large decrease in Vf along the series of alcohols cannot be due to a change in the chain-entanglement molecular weight, as a result of swelling by the alcohols, but must result rather from an easier slippage of molecular entanglements in the drawing glassy fibrils. The large decrease in Vf from methanol to butanol crazes must also enhance the nucleation of cracks within these crazes, as evidenced by the ten-fold decrease in the environmental fatigue life of PS along the series from methanol to butanol.

Thermal Decomposition and Glass Transition Temperature Study of Poly-p-isopropylstyrene

Abstract Thermal decomposition and glass transition temperature studies have been carried out on poly-p-isopropylstyrene (PpiPrS) with a differential scanning calorimeter. The un-decomposed polymer as well as its decomposition products were analyzed by gel permeation chromatography (GPC), infrared spectroscopy (IR) and nuclear magnetic resonance (NMR). During isothermal treatments in the 25–150°C temperature range (α < 3%), the observed increase in M arose primarily from interchain linking between the longer radical-bearing chains. Beyond 315°C (α > 6%), the molecular weight increases result from crosslinking reactions between decomposed polymer and longer undecomposed chains. During interchain linking, the number of isomethyl groups (iso-CH3) increase. In the crosslinking reactions that take place at temperatures beyond 315°C, the number of iso-CH3 and terminal or α-methyl groups (α-CH3) both increase while the number of methylene groups (CH2) decreases. Activation energies of decomposition for various homologs of polystyrene (PS) obey the following order: EPS > EPpiPrS > EPpiPrαMeS ≥ EPαMeS. A comparison of the Tge values of PS with those of PpiPrS, poly-α-methylstyrene (PαMeS) and poly-p-isopropyl-α- methylstyrene (PpiPrαMeS) shows that the presence of the p-isopropyl groups lowers the Tg of PS as well as that of PaMeS by about 30–35° K.