Search results for "polystyrene"

Switching of Polymer Brushes

1999

Polymer coatings of brushlike monolayers composed of two different polymers, polystyrene and poly(2-vinylpyridine), are grafted by radical polymerization on the surface of silicon wafers. Thickness, grafting density, molecular weight of grafted chains, and the composition of the coatings were regulated by grafting time, monomer concentration, and additional initiator in solution. A typical dry film thickness is between 10 and 100 nm, and the molecular weights of the components range from 100 to 300 kg/mol. The fabricated coatings turn out to be sensitive to the composition of the environment. For instance after exposition to toluene the layer becomes hydrophobic and the top of the layer is …

DIMENSIONAL STABILITY OF REINFORCED MATRICES.

1983

Particulate fillers are often used to improve the dimensional stability of polymeric items obtained through processing techniques such as injection molding, deep drawing, hot stamping, etc. In these operations the material undergoes large multiaxial deformations which result in molecular orientation and remain as frozen-in stresses during cooling of the material. Once the formed objects are exposed to sufficiently high temperatures, various degrees of spring-back take place and subsequent changes in shape and dimension occur (1).

Hydrophobically directed aldol reactions: polystyrene-supported L-proline as a recyclable catalyst for direct asymmetric aldol reactions in the prese…

2007

A simple synthetic methodology for the preparation of a polystyrene- supported L-proline material is reported, and this material has been used as catalyst in direct asymmetric aldol reactions between several ketones and arylaldehydes to furnish aldol products in high yields and stereoselectivities. Screening of solvents showed that these reactions take place only in the presence of water or methanol, at lower levels of conversion in the latter case. This solvent effect, coupled with the observed high stereoselectivities, has been ex- Introduction In the last decade organocatalysis has became a field of great interest.[1] Organocatalysts are metal-free small organic molecules that are able t…

Collective and self diffusion of PS microgels in solution as observed by thermal diffusion forced Rayleigh scattering

2007

Thermal diffusion in solutions of polystyrene micro-network spheres (microgels) in toluene has been studied by the holographic scattering technique of thermal diffusion forced Rayleigh scattering (TDFRS) and by photon correlation spectroscopy (PCS). Size distributions of microgels of different crosslink ratios are obtained from TDFRS measurements on dilute solutions at very low q-values around 4000cm−1. At low concentrations a single diffusive mode is observed and the diffusion coefficient increases with concentration. It is attributed to the collective diffusion of the microgels and the solvent. At high concentrations an additional slow mode appears whose diffusion coefficient decreases wi…

Synthesis of a polystyrene-arm-polybutadiene-arm-poly(methyl methacrylate) triarm star copolymer

1996

The straightforward synthesis of a polystyrene-arm-polybutadiene-arm-poly(methyl methacrylate) triarm star copolymer has been successfully realized by a sequence of reactions which involves the sequential addition of a living polybutadienyllithium to a polystyrene macromonomer with a terminal 1,1-diphenylethylene unit and subsequent polymerization of methyl methacrylate. The high-molecular-weight polystyrene-arm-polybutadiene-arm-poly(methyl methacrylate) star copolymer shows microphase separation into three phases.

1989

By endcapping of living polystyrene with ethylene oxide and subsequent reaction with bromoacetyl bromide a polymer with a bromoacetoxy endgroup was obtained. This was used as a macroinitiator for the living cationic polymerization of 1-azabicyclo[4.2.0]octane. The structure and composition of the so formed two-block copolymer was elucidated by different methods. The ratio of the two block and their lengths were varied within broad limits.

Vapor Pressures of Polymer Solutions and the Modeling of Their Composition Dependence

2009

Equilibrium vapor pressures, p, are reported for the systems tetrahydrofuran + poly(vinyl methyl ether) and tetrahydrofuran + polystyrene at 20, 40, and 60 °C. These data plus information from the literature serve to demonstrate that the composition dependence of p can be modeled quantitatively for polymer solutions in thermodynamically very different solvents by means of three, physically meaningful parameters.

Toluene self-diffusion in solutions of linear and crosslinked polystyrene

1995

Toluene self-diffusion coefficients in solutions of linear and crosslinked polystyrene (PS) at concentrations up to 30 wt% polymer have been determined over the temperature range 143–230 K using the1H n.m.r. static gradient stimulated echo method. At similar polymer concentrations, the diffusion coefficient values of toluene were higher for mixtures with crosslinked PS than for solutions containing linear PS. On cooling and approaching the solution glass transition, the amplitude decays in diffusion and spin-relaxation measurements become non-exponential and are interpreted in terms of a two-component decomposition. The estimated fraction of the toluene motionally bound to polymer increases…

Poly(styrene-b-methyl methacrylate) block copolymers as compatibilizing agents in blends of poly(styrene-co-acrylonitrile) and poly(2,6-dimethyl-1,4-…

1993

Abstract The influence of the molecular weight of the symmetric block copolymer poly(styrene-b-methyl methacrylate) (P(S-b-MMA)) in blends with high-molecular-weight poly(styrene-co-acrylonitrile) (PSAN) and poly(2,6-dimethyl-1,4-phenylene ether) (PPE) is investigated by dynamic mechanical analysis and transmission electron microscopy. Total molecular weights of the block copolymers vary from 16 up to 275 kg mol−1. Independent of molecular weight, all block copolymers locate to the interface with strong dispersing efficiency. The different block copolymers also showed approximately the same emulsifying efficiency. The degree of segmental mixing of the blocks with the respective phases is ev…

The mechanism of polymer permeation through polymer gel membranes

2007

Polymer gels are capable of producing separation effects on polymers. Applications for fractionation and for osmotic measurements are possible. Investigations are reported concerning the separation properties of polystyrene layers grafted onto a supporting cellulose basis. The permeation for pure solvents and the separating molecular limit for different solvents are tested. Their size depends uniquely on the interaction between the grafted polystyrene and the solvent.