Search results for "Polystyrene"
showing 10 items of 349 documents
Thermodynamics of pseudo-ternary systems as a tool to predict the morphologies of cellulose acetate/polystyrene blends cast from tetrahydrofuran solu…
2003
Abstract The demixing behavior of the ternary system THF/CA/PS (tetrahydrofuran/cellulose acetate/polystyrene) was investigated at 25 °C. Cloud point measurements show that the system exhibits a large miscibility gap caused by the incompatibility of CA and PS. Both ends of the experimentally determined tie lines are located inside the two-phase area of the phase diagram. By means of the measured critical composition of the ternary system and the Flory–Huggins interaction parameters published for two of the binary subsystems ( χ CA/THF =0.442 and χ PS/THF =0.475) the polymer/polymer interaction parameter was adjusted (directly minimizing the Gibbs energy) to χ CA/PS =0.057. These thermodynam…
Recyclable Heterogeneous and Low-Loading Homogeneous Chiral Imidazolidinone Catalysts for α-Alkylation of Aldehydes
2014
Two polystyrene-supported and six homogeneous MacMillan imidazolidinone catalysts were prepared and tested for the asymmetric α-alkylation of propanal with benzodithiolylium tetrafluoroborate. The chiral imidazolidinone was linked to polystyrene through the N-3 atom or through the phenyl ring and their catalytic activity was compared with that of their unsupported precursors. This comparison has allowed us to find an unsupported catalyst that displays high catalytic activity down to 5 or 2 mol % at room temperature with a high level of enantioselectivity also when used with hexanal and 3-phenylpropanal. In addition, one of the heterogeneous materials was revealed to be highly recyclable for…
Structure relaxation after temperature jumps in homogeneous polystyrene/poly(styrene-co-bromostyrene) blends
1988
Concentration fluctuations in polymer blends and their change after a temperature jump were studied by time-dependent small angle X-ray scattering experiments. Measurements were conducted on homogeneous mixtures of polystyrene and a partially brominated derivative. Structure factors in thermal equilibrium show the form given by the random phase approximation, thus enabling a direct determination of theχ-parameter and the mean radius of gyration. TheT-dependence ofχ can be understood as the result of superposed enthalpic contributions and a free volume term. In theT-jump experiments, samples were quenched to temperatures near Tg. Relaxation occurs on the time scale of minutes and is nonexpon…
Thermochromic Fluorescence from B18H20(NC5H5)2: An Inorganic–Organic Composite Luminescent Compound with an Unusual Molecular Geometry
2017
BH(NCH) is a rare example of two conjoined boron hydride subclusters of nido and arachno geometrical character. At room temperature, solutions of BH(NCH) emit a 690 nm fluorescence. In the solid state, this emission is shifted to 620 nm and intensifies due to restriction of the rotation of the pyridine ligands. In addition, there is a thermochromicity to the fluorescence of BH(NCH). Cooling to 8 K engenders a further shift in the emission wavelength to 585 nm and a twofold increase in intensity. Immobilization in a polystyrene thin-film matrix results in an efficient absorption of pumping excitation energy at 414 nm and a 609 nm photostable fluorescence. Such fluorescence from polystyrene t…
Micromechanics of “raspberry” morphology in PPE/SAN polymer blends compatibilized with linear ABC triblock terpolymers
2015
Abstract The effect of compatibilization with a symmetrical polystyrene- block -polybutadiene- block -poly(methyl methacrylate) (SBM) triblock terpolymer on the morphological and mechanical properties (specifically toughness) of immiscible poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene- co -acrylonitrile) (PPE/SAN) blends with different blend (w/w) ratios is investigated. We study the effect of blend viscosity on the localization of the compatibilizer at the blend interface, influencing the mechanical properties of the macroscopic material. The impact of the specific morphology of the blends, known as “raspberry morphology”, on the final material will be explained using thermomechanica…
Tapered Multiblock Star Copolymers: Synthesis, Selective Hydrogenation, and Properties
2020
Two series of well-defined multiblock four-arm tapered star copolymers with “arms” of the type poly(styrene)-block-poly(isoprene-grad-styrene), (SI/S)₄, were synthesized on a multigram scale with short reaction times. Targeted molecular weight (M) values ranged from 80 to 240 kg mol–¹ with polystyrene (PS) compositions of 40 and 60 wt %. Narrowly distributed (Đ = 1.04–1.12) copolymers were obtained regardless of M and without additional purification beyond precipitation. At sufficiently high M, members of the 40 wt % PS series possessed either a cylindrical or bicontinuous morphology, whereas the 60 wt % PS series yielded lamellae. The star copolymers outperformed their corresponding linear…
Synergistic effects of Janus particles and triblock terpolymers on toughness of immiscible polymer blends
2017
Abstract By influencing both the interfacial adhesion and the morphology, compatibilizers determine the mechanical properties of polymer blends. Here, we study the mechanical properties, in particular the fatigue crack propagation (FCP) of immiscible blends of poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene- co -acrylonitrile) (PPE/SAN), compatibilized with Janus nanoparticles (JPs) and linear polystyrene- block -polybutadiene- block -poly(methyl methacrylate) (SBM) triblock terpolymers. Synergistic effects of a mixture of both compatibilizers improve the FCP behavior and reveal the important role of interface stiffness and flexibility on the mechanical properties of polymer blends. The…
Preparation and nonlinear optics of monodisperse oligo(1,4-phenyleneethynylene)s
2001
Oligo(1,4-phenyleneethynylene)s 1a−e, with solubilizing propoxy side chains, were prepared by use of Hagihara−Sonogashira coupling reactions. The synthetic strategy was based on a building block system and on the use of trimethylsilyl and triisopropylsilyl protecting groups that could be cleaved selectively. The extension of the conjugation with an increasing number of repeat units provokes a bathochromic shift of the long wavelength absorption and a superlinear increase of the second hyperpolarizability |γ|. The corresponding third harmonic generation (THG) measurements were performed using polystyrene matrices and variable laser wavelengths. We conclude that the conjugation length is much…
Dynamic mechanical properties of semi-interpenetrating networks based on poly(styrene-co-maleic anhydride)
1991
Semi-interpenetrating networks based on linear anionic polystyrene (PS) and poly(styrene-co-maleic anhydride) P(ScoMA) of low MA content are prepared by crosslinking the P(ScoMA) with 4,4′-diphenylmethanediamine (DPMDA). It is demonstrated by dynamic mechanical analysis and by DSC that immiscible semi-IPN's are obtained for MA contents greater 5 wt.-%. In miscible semi-IPN's the relaxation of free PS chains is observed as a second maximum in the loss tangent at higher temperatures. The position of this maximum is shifted to higher temperatures for a polystyrene of molecular weight 500000 compared to a polystyrene of molecular weight 150000. The experimental temperature shift is in good agre…
A comparative study on Kθ evaluation from [η]-M data in single and mixed solvents through various excluded volume theories
1991
Abstract By allowing for the dependence of B on molecular weight, through its relationship with A2, modified Flory-Fox-Schaefgen, Kurata-Stockmayer-Roig, Berry and Inagaki-Suzuki-Kurata equations are obtained, relating [η] to A2 and to Kθ. Through these equations, Kθ can be determined from data sets for [η]-A2. Because of the scarcity of these data sets, A2 values have been calculated from experimental data for [η] and trial Kθ values through two parameter theories, namely, through the Flory-Krigbaum-Orofino theory for Ψ. Iterative processes were followed until coincidence was obtained between trial Kθ values and those evaluated from the modified excluded volume equations. The method has be…