Search results for "Polystyrene"
showing 10 items of 349 documents
Micelles Formed by Cylindrical Brush-Coil Block Copolymers
2005
Amphiphilic cylindrical brush-coil block copolymers consisting of a polystyrene coil and a cylindrical brush block with poly(acrylic acid) side chains are prepared by ATRP of t-butylacrylate from a block comacroinitiator. Upon acidolysis of the poly(t-butylacrylate), water-soluble polymers were obtained that were observed to form micelles consisting of 4-5 block copolymers on average in aqueous solution. The star-like nature of such micelles was clearly visualized by scanning force microscopy.
Mechanical relaxation in miscible polymer systems: the glass transition regime in poly(vinylmethylether) (PVME)-cross-polystyrene (PS) semi-interpene…
1990
Abstract Miscible semi-interpenetrating polymer networks (semi-IPN) of varying composition are prepared by crosslinking polystyrene containing few maleic anhydride groups with a diamine in the presence of linear poly(vinylmethylether) (PVME). The resulting PVME-c-P(ScoMA) semi-IPNs are characterized by their thermal and thermomechanical behaviour. Comparison with the corresponding uncrosslinked material proves that weak crosslinking has a negligible effect on the location of the glass transition as measured by d.s.c. Both the Tg data and the temperatures of the loss modulus maximum E″ (at 1 rad/s) show the same non-linear curved composition dependence. Contrary to this the tan δ maximum var…
Interpolymer complexes and polymer compatibility.
2012
A reliable method to decide whether two polymers A and B are miscible or incompatible would be very helpful in many ways. In this contribution we demonstrate why traditional procedures cannot work. We propose to use the intrinsic viscosities [η] of the polymer blends instead of the composition dependence of the viscosities as a criterion for polymer miscibility. Two macromolecules A and B are miscible because of sufficiently favorable interactions between the two types of polymer segments. For solutions of these polymers in a joint solvent, this Gibbs energetic preference of dissimilar intersegmental contacts should prevail upon dilution and lead to the formation of interpolymer complexes, …
Sorption of n-hexane in amorphous polystyrene
2014
Sorption properties of pure n-hexane vapor in amorphous polystyrene (PS) were studied at 298 K by thermogravimetry under controlled vapor pressure. Two sorption-desorption cycles were performed by varying the relative pressure between 0 and 0.91. Mixing of PS with n-hexane resulted in a strong plasticization, which was evidenced by quite significant depression in the glass transition temperature of the polymer as shown by differential scanning calorimetry. Maximum quantity of n-hexane sorbed in the PS at 298 K and at a pressure close to saturation was about 12.4 wt %. The thermogravimetry yielded an isotherm with a strong hysteresis loop, explanation of which was hypothesized with the help …
Synthesis and Characterization of Syndiotactic Polystyrene-Polyethylene Block Copolymer
2019
The direct synthesis of syndiotactic polystyrene-block-polyethylene copolymer (sPS-b-PE) with a diblock structure has been achieved. The synthetic strategy consists of the sequential stereocontrolled polymerization of styrene and ethylene in the presence of a single catalytic system: cyclopentadienyltitanium(IV) trichloride activated by modified methylaluminoxane (CpTiCl3/MMAO). The reaction conditions suitable for affording the partially living polymerization of these monomers were identified, and the resulting copolymer, purified from contaminant homopolymers, was fully characterized. Gel permeation chromatography coupled with two-dimensional NMR spectroscopy COSY, HSQC, and DOSY confirme…
Main dielectric relaxation of poly(methyl acrylate)–polystyrene interpenetrating polymer networks
2005
Abstract Two series of poly(methyl acrylate)–polystyrene sequential interpenetrating polymer networks were prepared by free radical polymerization using ethyleneglycol dimethacrylate as cross-linking agent. In one of them the cross-linking density was very low and the IPNs presented phase separation. The main dielectric relaxation appears in the IPNs in the same position in the frequency axis and almost with the same shape as in the pure PMA network. Nevertheless the ratio of the relaxation strength to the weight fraction of PMA in the IPN decreases slightly with the increase of polystyrene content. The other series of IPNs were highly cross-linked, in these IPNs a dielectric relaxation sti…
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 …
Synthesis and large scale fractionation of non-linear polymers: brushes and hyperbranched polymers
2002
Polymer brushes with poly(methyl methacrylate) (PMMA) backbone and polystyrene side chains were synthesized by radical polymerization of ω-methacryloyl-polystyrene macromonomers. Hyperbranched PMMA was obtained by means of self-condensing group transfer copolymerization of methyl methacrylate with an initiator-monomer containing a polymerizable methacryloyl moiety and an initiating silylketeneacetal function. Both non-linear products were fractionated using the method of continuous polymer fractionation, consisting in a particular type of continuous countercurrent extraction. The combination of methyl ethyl ketone (solvent) with acetone (AC) (precipitant) turned out to be suitable for the f…
Self-Diffusion in Concentrated Colloid Suspensions Studied by Digital Video Microscopy of Core−Shell Tracer Particles
1998
Optical video microscopy and digital image processing have been used to study the self-diffusion of colloidal particles with a hard-sphere potential. The colloid particles consist of cross-linked polymers and are dispersed in a good solvent to avoid aggregation. To investigate single particle motion in highly concentrated dispersions, a host−tracer system, consisting of two different kinds of polymer particles, has been designed: the host particles are made of poly-t-butylacrylate (with ethanedioldiacrylate as cross-linker) and have the same refractive index as the employed solvent, 4-fluorotoluene. The tracer particles have a core−shell structure with a polystyrene core (cross-linked with…
Nanowear on Polymer Films of Different Architecture
2007
In this paper, we describe atomic force microscope (AFM) friction experiments on different polymers. The aim was to analyze the influence of the physical architecture of the polymer on the degree and mode of wear and on the wear mode. Experiments were carried out with (1) linear polystyrene (PS) and cycloolefinic copolymers of ethylene and norbornene, which are stabilized by entanglements, (2) mechanically stretched PS, (3) polyisoprene-b-polystyrene diblock copolymers, with varying composition, (4) brush polymers consisting of a poly(methyl methacrylate) (PMMA) backbone and PS side chains, (5) PMMA and PS brushes grafted from a silicon wafer, (6) plasma-polymerized PS, and (7) chemically c…