Search results for "styrene"

Polymer induced changes of the crystallization scenario in suspensions of hard sphere like microgel particles

2012

We investigated the crystallization scenario of highly cross linked polystyrene particles dispersed in the good solvent 2-ethylnaphtalene and their mixtures with non-adsorbing low molecular weight polysterene polymer using time resolved static light scattering. The samples were prepared slightly below the melting volume fraction of the polymer free system. For the polymer free samples, we obtained polycrystalline solids via crystallization scenario known from hard sphere suspensions with little competition of wall crystal formation. Addition of non-adsorbing low molecular weight polystyrene polymer leads to a considerably slowing down of the bulk crystallization kinetics. We observed a dela…

Hemiesters and hemiamides of maleic and succinic acid: synthesis and application of surfactants in emulsion polymerization with styrene and butyl acr…

1999

Hemiesters and hemiamides of maleic acid with different chain lengths of the hydrophobic alkyl group (R = C8H17, C10H21, C12H25, C16H33) have been synthesized and used as surfactants in the emulsion polymerization of styrene and butyl acrylate. The same polymerization experiments were also carried out using nonreactive surfactants with an analogous succinic structure. The chemical structure of the surfactants was confirmed by 1H nuclear magnetic resonance. The melting point and critical micelle concentration of the reactive surfactants described herein were measured. All of the surfactants studied provided good stability of styrene/butyl acrylate latexes, when compared with a reference late…

A contribution to the kinetics of the polymerization of styrene with CF3SO3H as catalyst

1978

The time dependence of the cationic polymerization of styrene in CH2Cl2 with CF3SO3H as catalyst can be formally described as being first-order with respect to monomer concentration [M]0. The reaction rate shows a third-order dependence in catalyst concentration [C]0. A high polymer and a low polymer polystyrene fraction are found at [M]0>0.2 mole · l−. The reaction rate of the high polymer fraction is proportional to [C] 0 3 , that of the low polymer fraction probably proportional to [C] 0 2 . The polymerization active species may thus be triple ions in the first and ion pairs in the second case.

2018

We report a novel multi-step method for the preparation of ordered mesoporous titania scaffolds and show an illustrative example of their application to solar cells. The method is based on (monolayer) colloidal nanosphere lithography that makes use of polystyrene nanoparticles organised at a water–air interface and subsequently transferred onto a solid substrate. A titania precursor solution (titanium(IV) isopropoxide in ethanol) is then drop-cast onto the monolayer and left to “incubate” overnight. Surprisingly, instead of the expected inverse monolayer-structure, a subsequent calcination step of the precursor yields an ordered monolayer of hollow titania nanospheres with a wall thickness …

Valence Topological Charge-Transfer Indices for Dipole Moments

2003

Valence topological charge-transfer (CT) indices are applied to the calculation of dipole moments. The dipole moments calculated by algebraic and vector semisums of the CT indices are defined. The combination of the CT indices allows the estimation of the dipole moments. The model is generalized for molecules with heteroatoms. The ability of the indices for the description of the molecular charge distribution is established by comparing them with the dipole moment of the valence-isoelectronic series of benzene and styrene. Two CT indices, μ v e c (vector semisum of vertex-pair dipole moments) and μ V v e c (valence μ v e c ) are proposed. μ v e c and μ V v e c are important for the predicti…

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…

Investigation of the porosity of silica and alumina with chemically bonded polystyrene

1996

The effect of modification of porous silica and alumina with a copolymer of styrene and vinylsilane on the porosity of oxides have been investigated by means of low temperature nitrogen sorption. Only small changes of the specific surface area and of the specific pore volume were observed on modification of oxides with non-cross-linked copolymer. The specific surface area significantly increased after the cross-linking of the deposited polymeric layer while the specific pore volume remains almost unaffected. A broad hysteresis loop appears in the nitrogen sorption isotherm for the alumina modified with the cross-linked polymer. The porosity of oxides modified by chemisorption method differe…

Single Particle Motion of Hard-Sphere-Like Polymer Micronetwork Colloids Up to the Colloid Glass Transition

1997

Polymer micronetwork spheres swollen in a good solvent can be regarded as colloids which require no special stabilisation to avoid aggregation. Their interactions can be timed by changing the degree of internal crosslinking. The phase behaviour and the static structure factor demonstrate that crosslink density of 1:10 (inverse number of monomer units between crosslinks) is sufficient to achieve hard sphere behaviour. We designed a host-tracer system consisting of core-shell micronetwork spheres (core: polystyrene; shell: poly-t-butylacrylate) in a host of refractive-indexmatched poly-t-butylacrylate micronetwork colloids. Employing a crosslink density of 1:10 and tuning the polydispersity s…

A system for rapid radiochemical separations from aqueous solutions

1969

Abstract For the study of short-lived fission products, an automatic system has been developed that allows to irradiate aqueous solutions sealed in polystyrene capsules, to separate chemically the radioactive products formed, and to start counting, all within a few seconds. Irradiations are performed in a pneumatic tube system installed in a horizontal beam hole of a reactor. The capsule is projected into a separation apparatus where it breaks by impact. Its content is then sucked through a thin reactive layer that takes up the desired product. The whole sequence of irradiation, transportation, chemical separation, and counting is controlled by automatic timers. The adaption of this techniq…

A Chemical Index Inspired by Biological Plastic Evolution:  Valence-Isoelectronic Series of Aromatics

2004

Plastic evolution is a new perspective of the evolutionary process conjugating the effect, on one hand, of the acquired characters and, on the other, of the relationships that emerge among the principle of evolutionary indeterminacy, the principle of morphologic determination, and natural selection. Plastic evolution is applied to design the coordination index Ic. Ic is used to characterize the valence-isoelectronic series of cyclopentadiene, benzene, toluene, and styrene and compared to charge indices for dipole moment. The parameters needed to calculate Ic are minus the standard enthalpy of formation T, molecular surface area S, and molecular weight W. With the exception of the O heteromo…