Random Copolymers Of Styrene Research Articles

Electrical conductivity of polymers containing carbon black

AbstractChanges in volume resistivity with temperature of carbon‐black‐filled polymers and a random copolymer of styrene and butyl methacrylate were measured. For polystyrene containing 20 wt % carbon black, of surface area 24 m2/g, the resistivity changes abruptly from 1013 to 106 ohm‐cm above 150°C. Poly(butyl methacrylate) did not show well‐defined changes in resistivity on heating. The random copolymer containing 16.7 or 28.6 wt % carbon black, of surface area 24 m2/g, showed a resistivity exceeding 1013 ohm‐cm, that decreased to about 107 ohm‐cm on heating above 120°C. This Copolymer containing 16.7 wt % carbon black, of surface area 625 m2/g, shows a resistivity of about 108 ohm‐cm that decreases sharply to 103 ohm‐cm by 150°C. Decreases in resistivity on increasing the temperature in the quiescent state are correlated with the observation of a yield stress at low shear rates in rheological studies. It is suggested that carbon black agglomerates at elevated temperature and forms an independent conductive network that prevents flow.

Gas permeation in miscible homopolymer‐copolymer blends: II. Tetramethyl bisphenol‐A polycarbonate and a styrene/acrylonitrile copolymer

AbstractGas sorption and transport properties for He, H2, O2, N2, Ar, CH4, and CO2 at 35°C near atmospheric pressure have been obtained for miscible blends of tetramethyl bisphenol‐A polycarbonate (TMPC) and a random copolymer of styrene with acrylonitrile (SAN) containing 9.5% by weight of acrylonitrile. All gas permeability, diffusion, and solubility coefficients obtained are lower than that calculated from the semilogarithmic additivity rule. These results are qualitatively interpreted by ternary solution theory and activated state theory which have been proposed to describe gas sorption and diffusion in miscible blends. The negative deviation of gas permeabilities for the blends from this rule can be explained semiquantitatively by free volume theory which takes volume contraction on mixing into account. The negative deviation increases with gas molecular size which results in larger ideal gas separation factors than that calculated from the additivity rule. For He/CH4 and H2/CH4 pairs, the permselectivities for the blends are higher than that for either pure TMPC or SAN. The deviation from additivity for gas transport properties of TMPC/SAN blends is the opposite of that observed in the first paper of this series for PMMA/SAN blends. This can be attributed to the stronger interactions in TMPC/SAN blends than in PMMA/SAN blends.

The dielectrical relaxation and liquid-crystalline state in copolymers of 1-methacryloyl-oxybenzoyl-phenylene-4-anisoate with styrene

The relaxational and mesophase phenomena in random copolymers of styrene with 1-methacryloyl-oxybenzoyl-phenylene-4-anisoate having the mesogenic group in the side chain, have been studied. The limits of existence of the LC phase in relation to the quantity of mesogenic component have been determined. The presence of mesophase transitions in the LC composition region was found. A multiplicity of forms of internal motion was demonstrated in the side chains of the mesogenic component.

Effect of pressure on phase behavior in polymer blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide) and poly(styrene‐co‐p‐fluorostyrene) copolymers

AbstractThe effect of pressure on the miscibility of blends of poly(2,6‐dimethyl‐l,4‐phenylene oxide) (PPO) with a random copolymer of styrene and para‐fluorostyrene, P(S‐co‐p‐FS), has been studied by high pressure differential thermal analysis (HPDTA). P(S‐co‐p‐FS) copolymers less than 36 mole % p‐FS are miscible with PPO in all proportions irrespective of pressure up to 200 MPa, using the customary criterion of a single calorimetric glass relaxation. P(S‐co‐p‐FS) copolymers containing 40 to 50 mole % p‐FS undergo phase separation upon annealing at elevated temperatures, indicating the existence of a lower critical solution temperature (LCST). In these blends, pressure displaces the phase boundary associated with the LCST to higher temperatures causing an apparent increase in polymer miscibility. The phase diagram for the blend of PPO and P(S‐co‐p‐FS) containing 46 mole % p‐FS, shows that the critical composition at about 50 wt % PPO does not change with pressure, but the consolute temperature Tc increases with increasing pressure. The pressure dependence of the LCST (dTc/dP) of this system is about 0.35°C/MPa.

Inverse Gas Chromatography on Graft and Random Copolymers of Styrene and 2-Hydroxyethyl Methacrylate

Inverse gas chromatography (IGC) was applied to amphiphilic graft copolymers of poly(2-hydroxyethyl methacrylate) (PHEMA) with polystyrene (PSt) branches using various probes at 160°C. Retention of tetradecane or amylbenzene, which selectively interacts only with PSt phase, suggested that a microphase inversion occurs around 20—30 wt% PSt, below which PSt segments constitute a discontinuous phase (islands). Rather nonselective probes such as dimethyl-formamide and 2-(2-methoxyethoxy)ethanol showed a retention which exceeds that expected from a simple additive relation, suggesting a considerable contribution of their interaction with the interface of the microphase-separated domains. In contrast, random copolymers showed a retention behavior as expected for a statistical distribution of the monomer units. General discussion is given on IGC as a means of characterizing binary polymer systems.

Comparison of the Adhesion and Cohesion of Triblock and Random Copolymers of Styrene and Butadiene

Abstract A substantially greater detachment energy is required to strip a polyethylene tereph-thalate (Mylar) film from a styrene-butadiene-styrene (SBS) triblock copolymer compared to that for peeling from a random styrene-butadiene (SBR) copolymer. This is true even though the intrinsic interaction between the Mylar and each elastomer is expected to be similar because of their virtually identical chemical composition. It is proposed that this difference in peel strength (between the SBS and SBR) is a consequence of the much higher dissipative capacity of the former elastomer. Another manifestation of this is the higher cohesive tear strength of the SBS compared to the SBR. Extents of energy dissipation within each elastomer during detachment of the Mylar adherend are consistent with the hypothesis that the average maximum stress experience before detachment is some similar fraction of each elastomer's tensile strength.

Synthesis and Interfacial Characterization of Graft and Random Copolymers of Styrene and 2-Hydroxyethyl Methacrylate

Polystyrene (PSt) macromonomers with methacrylate end-groups (M1) were copolymerized with 2-hydroxyethyl methacrylate (HEMA, M2) to give amphiphilic graft copolymers with PSt branches. The monomer reactivity ratio of HEMA was estimated as r2=1.7±0.4. The 1H NMR spectrum of a graft copolymer in methanol revealed a micelle formation with a PSt core, while chloroform caused the formation of a reversed micelle with a PHEMA core. The contact angle of water on polymer films suggested that the PSt segments generally dominate the surface properties of graft copolymers, independent of a composition above 15 wt% PSt. In contrast, the random copolymers of St and HEMA showed results as expected for a single-phase structure, both by 1H NMR and contact angle.

Conformational changes of methacrylonitrile-styrene copolymers in diluted solutions

Conformational changes of methacrylonitrile — styrene random copolymers, at different temperatures and in various solvents (dimethylformamide, dioxane and methyl ethyl ketone), have been studied by light scattering measurements.

Thermoplastic interpenetrating polymer networks of a triblock copolymer elastomer and an ionomeric plastic. I. Rheology and morphology

The thermoplastic interpenetrating polymer networks (IPNs) are combinations of two physically crosslinked polymers. Thermoplastic IPNs were prepared by combining polymer I, an SEBS triblock elastomer with polymer II, an ionomer prepared from a random copolymer of styrene, methacrylic acid, and isoprene (90/10/1 by volume). Neutralization of the acid groups to form the ionomer was carried out on a Brabender Plasticorder. Two subclasses of the thermoplastic IPNs were identified. Chemically blended systems, prepared by a sequential polymerization method, were compared with compositionally equivalent mechanically blended systems prepared by melt blending the separately synthesized polymers. The chemically blended thermoplastic IPNs (CBT IPNs) exhibited lower melt viscosities than compositionally equivalent mechanically blended thermoplastic IPNs (MBT IPNs). Moreover, the melt viscosities of many of the CBT IPNs were even lower than that of either homopolymer component, leading to an explanation in terms of an unusually low value of the rubbery modulus front factor. Although both types of thermoplastic IPNs underwent a phase inversion during neutralization of polymer II, the phase inversions were often incomplete. Morphological studies revealed that more equal dual phase continuity existed in the MBT IPNs than in the CBT IPNs after ionomer formation.

Thermoplastic interpenetrating polymer networks of a triblock copolymer elastomer and an lonomeric plastic. II. Mechanical behavior

AbstractThermoplastic interpenetrating polymer networks, IPN's, are defined as combinations of two physically crosslinked polymers. A styrene‐b‐ethylene‐co‐butylene‐b‐styrene (SEBS) triblock elastomer was combined with an ionomer prepared from a random copolymer of styrene, methacrylic acid, and isoprene (90/10/1 by volume), and subsequently neutralized. Two subclasses of the thermoplastic IPN's were identified. A sequential polymerization method yielded the chemically blended thermoplastic IPN's (CBT IPN's). Melt blending of the separately synthesized polymers produced the mechanically blended thermoplastic IPN's (MBT IPN's). Stress‐strain and Rheovibron characterization revealed that the CBT IPN's exhibited greater tensile strength and higher elongation at break, but lower moduli than the MBT IPN materials of the same overall composition. Analysis of moduli data with the theories of Takayanagi, Davies, Budiansky, and Kerner disclosed more equal dual phase continuity for the MBT IPN's than the CBT IPN's at each composition. The low modulus of the more rubbery CBT IPN compositions was attributed to a decrease in the effective chain end‐to‐end distance between crosslinks in the elastomeric (EB) center block, brought about by the synthetic method.

Dielectric study of polymer compatibility: Blends of polystyrene/poly-2-chlorostyrene

Abstract The dielectric constant and loss have been monitored isothermally in the frequency plane in the α relaxation region for a series of amorphous compatible and phase separating polymer blends comprising one polar and one relatively non-polar component. Differential scanning calorimetry has been employed for preliminary assessment of the miscibility of a given pair. The system polystyrene/poly-2-chlorostyrene (PS/PoCS) has been found to exhibit miscibility highly dependent on molecular weight and temperature. High molecular weight blends display wide loss spectra; phase separation above a lower critical solution temperature (LCST) results in the narrowing of the loss curves. Low molecular weight polystyrene yields blends which remain homogeneous up to degradation temperatures and exhibit narrow loss peaks. Comparison between PS/PoCS blends and random copolymers of styrene and 2-chlorostyrene is made.

Modeling of tensile properties of polymer blends: PPO/poly(styrene-c o-p-chlorostyrene)

Young’s modulus, yield (break) strength, and elongation to yield (break) have been measured for blends of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with polystyrene (PS), poly(p-chlorostyrene) (PpClS), and random copolymers of styrene and p-chlorostyrene (pClS). The significant difference between blend compositions is the compatibility of PPO with each styrene polymer. Blends of PPO with PS or copolymers with 67.1 mole% or less pClS are compatible (i.e., one Tg) and show small synergistic maxima in modulus, strength, and elongation as a function of PPO composition. These maxima correspond to observed maxima in packing density as a result of specific interactions contributing to blend compatibility. A rule of mixtures for one-phase systems with an adjustable compatibility parameter gives adequate fit to the observed composition dependence of the modulus. In a narrow composition range between 67.8 and 68.6 mole% pClS, copolymers exhibit partial miscibility with PPO. Two mixed composition phases are present. Moduli of these transitional blends follow the same form of synergistic dependence on blend composition as do the compatible blends but strength and elongation exhibit a sigmoidal relation to blend PPO content. At about 20% PPO, strength (and elongation) reaches a minimum as predicted by a simple composite model for a dispersed phase with good adhesion to the matrix. A maximum is reached at ∼80% PPO at which composition blend test specimens yield prior to failure. Blends of PPO with PpClS and with copolymers of ≳68.6 mole% pClS exhibit a broader minimum in strength (and elongation) but a similar maximum at 80% PPO. Unlike the compatible and transitional blends, moduli follow a nonsynergistic composition dependence adequately represented by the series model for two-phase systems.

Nonequilibrium tensile deformation of amorphous polymers in the rubbery state: Temperature, strain rate, and strain effects. I

Abstract We analyze nonequilibrium tensile deformational behavior of an amorphous uncrosslinked random copolymer of styrene and acrylonitrile stretched above its Tg at various temperatures and constant strain rates. The variable investigated is the force required to pull the specimen to a certain strain level. Our results suggest the deformational behavior in the rubbery state can be incorporated in a universal scheme where strain, strain rate, and temperature effects are all superposed, e.g., the effect of strain is identical to the effect of temperature and strain rate. This unexpected result is true within two contiguous but distinct regimes of strain, on both sides of ca. 40% strain, suggesting that non-equilibrium extension at constant pulling speed in the rubbery state occurs by at least two successive mechanisms. Our results also reveal that the physical parameter which should be used to achieve a true superposition of strain rate and temperature data is not as simple as has long been commonly prop...

Thermally stimulated discharge in polymer electrets: Compatibility and impurity effects

Polymer electrets have been prepared and studied by measuring thermally stimulated discharge currents. Two current maxima have been observed for samples of polystyrene, poly(p-chlorostyrene), and a random copolymer of styrene and p-chlorostyrene. These maxima are attributed to dipole reorientation accompanying the glass transition and to real charge drifts. Poly(2,6 dimethyl-1,4-phenylene oxide) and blends of this polymer with the three aforementioned polymers were also studied. In these systems unresolved and nonreproducible peaks were obtained, and these difficulties have been attributed to impurities present.

Heat capacity of random copolymers of styrene and methacrylates

Differential scanning calorimetry has been used to investigate the thermal behavior of random copolymers of styrene and hexyl methacrylate and of styrene and glycidyl methacrylate in the temperature range of 20° to 150°C. Heat capacities of the copolymers and homopolymers, poly-(hexyl methacrylate), poly(glycidyl methacrylate), and polystyrene have been measured. It is found that the heat capacities of the homopolymers from 60°K to the glass transition temperatures can be adequately obtained by Wunderlich's empirical method. It is also found that the copolymer heat capacities can be adequately represented by addition of homopolymer heat capacities.

Copolymers of Hydrophilic and Hydrophobic Monomers. Benzene and Water Vapor Sorption Equilibria by Random Copolymers of Styrene and Acrylamide

Copolymers of Hydrophilic and Hydrophobic Monomers. Benzene and Water Vapor Sorption Equilibria by Random Copolymers of Styrene and Acrylamide

Segregation and conformational transition in triblock copolymers: Part 2. Light-scattering studies

From light-scattering experiments carried out on a polystyrene (PS) sample, a poly(methyl methacrylate) (PMMA) sample, on a random copolymer of styrene and MMA and on an anionically prepared triblock copolymer PMMA-PS-PMMA, all of the same molecular weight, in various solvents over a range of temperature (18–65°C) it was shown that a conformational transition occurs for the triblock copolymer. At lower temperatures segregation occurs and the second virial coefficient A 2 is the weighted average between the A 2A and A 2B values for the corresponding homopolymers (PS and PMMA). At higher temperatures contacts between chemically unlike parts of the molecule become possible, and the additivity rules are no more valid for A 2 , as well as for the expansion coefficient. This change from a segregated to a ‘pseudo-gaussian’ conformation involves a change in specific volume of the molecule, and it there-fore brings with it an abnormal variation of the refractive index increment, which has been investigated on the same light-scattering diagrams.

Donor-Acceptor Complexes in Copolymerization. XVI. NMR Analyses of Alternating and Random Copolymers of Styrene and α-Methylstyrene with Acrylonitrile and Methacrylonitrile

Abstract An NMR investigation was carried out on random and alternating copolymers of acrylonitrile (AN) with a-methylstyrene (MS) and methacrylonitrile (MAN) with α-methylstyrene and styrene (S). The alternating MS-AN copolymer, prepared by complexation with AlEti1-5Cl1-5, was found to have a predominantly coisotactic configuration which was attributed to the interaction between the CH3 and CN groups. The cotacticity of the alternating copolymer was found to be independent of the temperature of polymerization and the amount of AlEt1-5Cl1-5 used for complexation. The NMR spectra of random MS-AN copolymers of varying compositions indicated a high value (0.85) for the coisotacticity probability parameter (σ). The equimolar random MS-AN copolymer was also found to have essentially alternating sequences which was attributed to their low reactivity ratios. The equimolar alternating MS-MAN copolymer was found to have a random stereochemical configuration in which the coisotactic placement was slightly preferrred over the cosyndiotactic placement. The NMR spectrum of the equimolar free radical initiated MS-MAN copolymer lacked the fine structure observed in the spectrum of the alternating copolymer which was attributed to the presence of other sequences. The equimolar alternating S-MAN copolymer was found to have a high coisotactic configuration similar to that observed in the MS-AN copolymer. The equimolar free radical initiated S-MAN copolymer had a random sequence distribution.

Etude de la degradation accompagnant la metallation de copolymeres statistiques styrene-acenaphtylene

Random copolymers of styrene and acenaphthylene, in THF solution, have been metallated with sodium. At low temperature, the characteristic green solutions of the radical-anion of acenaphthylene (τ) are obtained. The metallated copolymers degrade very rapidly when the temperature is raised above −50° yielding deep-red solutions. The ESR and ultraviolet spectrophotometric studies, as well as molecular weight decrease, give evidence that several mechanisms are involved in this degradation. In a first step, preferential metallation of neighbouring acenaphthylene units occurs and radical-anions are formed. Then an extremely fast chain scission takes place, with disappearance of the radicals and with formation of two anionic acenaphthylene chain-ends. After longer reaction-times, chain scission between isolated acenaphthylene units and styrene units occurs also. This reaction seems to be much slower than the degradation reaction between two neighbouring acenaphthylene units.

Dynamic mechanical properties of two copolymers of styrene and n‐hexyl methacrylate

AbstractThe storage (J′) and loss (J″) shear compliances have been measured for two random copolymers of styrene and n‐hexyl methacrylate with styrene contents of 18% and 30% (by weight) in the frequency range 45–4400 Hz and the temperature range 31–107°C. The data at different temperatures were combined by the method of reduced variables, and the WLF coefficients were calculated from the temperature shift factors by the method of Pierson and Kovacs. The data were compared with earlier data for the two homopolymers. The thermal expansion coefficient of the fractional free volume, and the free volume at the glass transition temperature, varied monotonically with composition, but the fractional free volume at a reference temperature of 100°C appeared to pass through a maximum as a function of concentration. Comparison of isothermal plots of J′ at 100°C, plots of the relaxation spectrum at 100°C, the monomer friction coefficient and its temperature dependence, and isochronal plots of the storage shear moduls at 100 radians/see all show that the properties of poly(n‐hexyl methacrylate) are very slightly affected by incorporation of 18% styrene and only moderately affected by 30% styrene. By contrast, comparison of styrene–butadiene rubber with 1,4‐polybutadiene shows a very large effect of incorporation of 23.5% styrene. These differences may be associated with local packing relations of the comonomer residues and suggest that copolymer properties cannot be readily predicted from those of the component homopolymers.