Search results for "Styrene"

Estimation of Number-Average Molecular Weights of Copolymers by Gel Permeation Chromatography−Light Scattering

1996

The true number-average molecular weight, Mn, of copolymers is obtained by GPC coupled with a light-scattering detector even if the composition and therefore the refractive index increment varies with elution volume, provided slices taken are monodisperse with respect to molecular weight and composition. In contrast, only an apparent weight-average molecular weight, can be obtained by the conventional GPC−light scattering combination, even for a perfect chromatographic resolution. The errors in Mn associated with nonhomogeneous slices are estimated. Experimental data with mixtures of linear polystyrene and poly(methyl methacrylate) confirm these estimations and indicate that the error in Mn…

Synthesis and properties of amphiphilic “dumbbell”-shaped grafted block copolymers, 1. Anionic synthesis via a polyfunctional initiator

1994

Two poly(ethylene oxide) stars linked by a long polystyrene chain represent a novel amphiphilic architecture (dumbbell), which is available by anionic grafting of ethylene oxide from a hydroxylated polybutadiene-block-polystyrene-block-polybutadiene triblock copolymer. The short butadiene end-blocks (DPB = 36) of a BSB triblock copolymer with a long styrene middle block (DPS = 650) was first modified by hydroboration and oxidation. A multifunctional alkoxide initiator is thus prepared by titration of the hydroxyl groups of the “polybutadiene” end-block with cumylpotassium. Gelation and precipitation of the polyfunctional initiator in THF could be avoided by complexing the cation (K+) with a…

Water sorption isotherms of molecularly imprinted polymers. Relation between water binding and iprodione binding capacity

2017

International audience; Molecularly imprinted polymers are often used in aqueous medium in order to recognize specifically a target molecule. The molecular recognition is usually based on hydrogen bonding. In this case, water molecule presents a serious competition towards the target molecule. In this study, the water sorption by molecularly imprinted polymers was studied in aqueous medium. The molecularly imprinted polymers were specific for iprodione fungicide and were prepared using a 24 full factorial experimental design. They were synthesized using EGDMA or TRIM as crosslinker, methacrylamide or styrene as functional monomer and using bulk or precipitation polymerization. The water sor…

Investigation of polymer organic deposit formed on nickel phosphate in oxidative dehydrogenation of ethylbenzene

1997

Abstract Several polymer organic deposits (PODS) had been obtained by heating of nickel polyphosphate (NiP) at 720 K for 1, 4, or 10 h in a stream of helium (carrier gas) containing 20% of (ethylbenzene : oxygen= 1: 0.5] mixture. The samples were tested in oxidative dehydrogenation (OD) of ethylbenzene (EB) to styrene, before and after their separation from the inorganic part of NiP as catalysts. Some functional groups or bonds, important for enhancement of styrene yield, have been found in the PODS. The POD obtained after 10-h coking of NiP, containing a mixture of both insoluble fused-ring and soluble-in-pyridine macromolecules, provided with at least two types of catalytically active cen…

Spatial heterogeneity in glassy polystyrene detected by deuteron NMR relaxation

1999

Using deuteron NMR, the dynamics of supercooled polystyrene-d 3 was investigated near the calorimetric glass transition. At these temperatures non-exponential spin lattice relaxation is found, indicating the presence of spatial heterogeneity. With increasing temperature, structural relaxation becomes fast enough to average efficiently over different spatial environments, leading to exponential magnetization decays. A qualitative comparison with toluene as a representative of a low molecular weight glass former is carried out. Indications are found that in polystyrene the observed averaging process is more effective at T g than it is in toluene.

1997

We have determined by forced Rayleigh scattering the diffusion coefficients of photo-labeled polystyrene micronetwork spheres (radii ≤ 10 nm) in melts of linear polyvinylmethylether (M W ≤ 40000 g/mol) at temperatures of 20-80°C. An expected slippage of the spheres through the meshes of the entanglement network appears possible but is still within the experimental uncertainty of our results.

Synthesis of SBC, SC and BC block copolymers based on polystyrene (S), polybutadiene (B) and a crystallizable poly(ɛ-caprolactone) (C) block

1996

The sequential anionic polymerization of polystyrene-block-polybutadiene-block-poly(e-caprolactone) (SBC) triblock copolymers as well as polystyrene-block-poly(e-caprolactone) (SC) and polybutadiene-block-poly(e-caprolactone) (BC) diblock copolymers was achieved in benzene. To initiate the polymerization of the highly reactive e-caprolactone, the nucleophilicity of the carbanion has to be reduced. For this purpose 1,1-diphenylethylene (DPE) was used. To avoid inter- and intramolecular transesterification reactions of the growing caprolactone block, the reaction time of this monomer in the block copolymers was strictly controlled. The reaction between polybutadienyl anions and DPE is too slo…

Atom transfer radical polymerization with different halides (F, Cl, Br, and I): Is the process "living" in the presence of fluorinated initiators?

2016

Atom transfer radical polymerization (ATRP) is often used for grafting from fluorinated polymers. Nevertheless, the possibility to initiate an ATRP from a C-F functionality and the activity of the catalysts in the presence of fluoride anions are essentially unexplored. Therefore, we investigated the thermodynamics and kinetics of C-F bond activation by ATRP catalysts and compared it with other halide systems. The ATRP equilibrium constant was estimated to be small for the reaction between [CuITPMA]+ and benzyl fluoride (TPMA = tris(2-pyridylmethyl)- amine). However, [CuITPMA] + could react with the more active initiator diethyl fluoromalonate (DEFM). With DEFM as initiator and CuIBr/TPMA as…

HPMA copolymers as surfactants in the preparation of biocompatible nanoparticles for biomedical application.

2012

In this work we describe the application of amphiphilic N-(2-hydroxypropyl)methacrylamide (HPMA)-based copolymers as polymeric surfactants in miniemulsion techniques. HPMA-based copolymers with different ratios of HPMA (hydrophilic) to laurylmethacrylate (LMA; hydrophobic) units were synthesized by RAFT polymerization and postpolymerization modification. The amphiphilic polymers can act as detergents in both the miniemulsion polymerization of styrene and the miniemulsion process in combination with solvent evaporation, which was applied to polystyrene and polylactide. Under optimized conditions, monodisperse colloids can be prepared. The most promising results could be obtained by using the…

Interfacial tension and interaction parameters

1994

In view of various contradictory theoretical equations relating the interfacial tension σ between phase-separated polymer solutions to the Flory-Huggins interaction parameter of the system, the idea that σ should depend on the extent of the ‘hump’ in the concentration dependence of the Gibbs energy of mixing was studied. This investigation is based on 12 series of σ( T ) measurements reported in the literature and on additional experiments for the system cyclohexane/polystyrene. To quantify the extent of the ‘hump’, a reduced ‘hump energy’ ɛ was introduced and its value calculated for different temperatures from the measured critical data of the systems. The analysis of the entire experimen…