Search results for "Styrene"
showing 10 items of 561 documents
Polymerization of an activated ester monomer based on 4-vinylsulfonic acid and its polymer analogous reaction
2011
Homopolymers containing sulfonic ester side groups were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization utilizing benzyl dithiobenzoate, cumyl dithiobenzoate, and 4-cyano-4-((thiobenzoyl)sulfanyl)pentanoic acid as chain transfer agents. Likewise diblock copolymers containing poly(styrene), poly(octylstyrene) and poly(pentafluorostyrene) as the second block were synthesized. Additionally, nitroxide mediated polymerization (NMP) was investigated for the synthesis of a homopolymer as well as for a diblock copolymer. Furthermore, the post-polymerization functionalization with various amines to yield the respective sulfonamides was conducted. The conversion …
Half-sandwich molybdenum(III) compounds containing diazadiene ligands and their use in the controlled radical polymerization of styrene
2002
Abstract The reaction of CpMoCl2 with diazadiene ligands RNCHCHNR (R2dad) affords the corresponding paramagnetic complexes CpMoCl2(R2dad) (R=Ph, 1; p-Tol, 2; C6H3Pr2i-2,6, 3; and Pri, 4). All compounds have been characterized by EPR spectroscopy and have been investigated by cyclic voltammetry. They display one-electron oxidation and reduction processes, these being reversible or irreversible depending on the nature of R. The irreversibility of the reduction wave is due to a chemical follow-up process which consists of chloride loss from the reduced product. This phenomenon is suppressed in the presence of excess chloride in solution. An X-ray structure of 3 verifies the mononuclear na…
How the interplay of different control mechanisms affects the initiator efficiency factor in controlled radical polymerization: An investigation usin…
2007
International audience; Compound CpMoI2(iPr2dad) (iPr2dad = iPrNdouble bondCHsingle bondCHdouble bondNiPr), obtained by halide exchange from CpMoCl2(iPr2dad) and NaI, has been isolated and characterized by EPR spectroscopy, cyclic voltammetry, and X-ray crystallography. Its action as a catalyst in atom transfer radical polymerization (ATRP) and as a spin trap in organometallic radical polymerization (OMRP) of styrene and methyl acrylate (MA) monomers has been investigated and compared with that of the dichloro analogue. Compound CpMoCl2(iPr2dad) catalyzes the ATRP of styrene and MA with low efficiency factors f (as low as 0.37 for MA and ethyl 2-chloropropionate as initiator), while it irre…
Half-sandwich Mo(III) complexes with asymmetric diazadiene ligands
2006
The asymmetric 1,4-diazadiene ligands R ∗ N CHCH NR ∗ [R ∗ = ( S )-CH(CH 3 )Ph], R 2 ∗ dad , and 2,2′-bis(4-ethyloxazoline), as-ox, have been used to generate half-sandwich Mo III derivatives by addition to Cp 2 Mo 2 Cl 4 . Ligand R 2 ∗ dad affords a mononuclear, paramagnetic 17-electron product, CpMoCl 2 ( R 2 ∗ dad ) , whereas as-ox leads to the isolation of a dinuclear compound where only one molecule of ligand has been added per two Mo atoms, Cp 2 Mo 2 Cl 4 (as-ox). In the presence of free as-ox, this compound coexists with the paramagnetic mononuclear complex in solution. Both products are capable of controlling the radical polymerization of styrene under typical atom transfer radical…
Wormlike Polystyrene Brushes in Thin Films
1997
Mono- and multilayer films were prepared on mica by solution casting of a high molecular weight polymacromonomer, i.e., a polymethacrylate of about 1000 repeating units each of which was substituted by a polystyrene chain with a molecular weight of about 5000 Da. The films were studied by tapping scanning force microscopy. The material showed a remarkable preference for forming well-defined monolayers of a thickness of 6.5 ± 0.2 nm consistent with the hard core diameter of the collapsed cylindrical brush molecules. When the films were probed with high normal force, the single molecules were observed to organize in a dense nematic-like packing as expected for inherently stiff molecules. In o…
Optical experiments on a crystallizing hard-sphere–polymer mixture at coexistence
2010
We report on the crystallization kinetics in an entropically attractive colloidal system using a combination of time resolved scattering methods and microscopy. Hard sphere particles are polystyrene microgels swollen in a good solvent (radius a=380nm, starting volume fraction 0.534) with the short ranged attractions induced by the presence of short polymer chains (radius of gyration rg = 3nm, starting volume fraction 0.0224). After crystallization, stacking faulted face centred cubic crystals coexist with about 5% of melt remaining in the grain boundaries. From the Bragg scattering signal we infer the amount of crystalline material, the average crystallite size and the number density of cry…
γ-Fe2O3 nanoparticle in NaY-zeolite matrix: Preparation, characterization, and heterogeneous catalytic epoxidation of olefins
2010
Abstract Nano-sized crystals of maghemite iron oxide (γ-Fe 2 O 3 ) were synthesized onto the surface of NaY-zeolite crystals by immobilizing a polynuclear iron complex [Fe 4 O 2 (O 2 CCH 3 ) 7 (bpy) 2 ](ClO 4 ) (bpy = 2,2′-bipyridine) and subsequent calcination of the material in oxygen. Superparamagnetic γ-Fe 2 O 3 particles with sizes ∼5 nm were formed on the surface of the zeolite matrix. The nano-composite, γ-Fe 2 O 3 @NaY has been subsequently subjected for thorough characterization with several spectroscopic techniques as well as magnetic and transmission electron microscopic measurements. This confirms the formation of maghemite nanoparticles on a NaY-zeolite surface. γ-Fe 2 O 3 @NaY…
The impact of growth history and flagellation on the adhesion of variousListeria monocytogenesstrains to polystyrene
2009
International audience; The contribution of growth history and flagella to adhesion of Listeria monocytogenes was analysed. An in-frame deletion on the flagellin encoding gene (flaA) was performed in L. monocytogenes EGD-e to compare its adhesion ability with the parental strain, after cultivation at various pH values and temperatures. The pH, as well as the temperature, affected the adhesion of L. monocytogenes EGD-e. In addition, the adhesion of L. monocytogenes EGD-e was reduced in energy-depressed cells. Conversely, the physicochemical bacterial surface characteristics affected by growth history did not influence the adhesion. Adhesion variations observed among environmental and clinica…
Resource or waste? A perspective of plastics degradation in soil with a focus on end-of-life options.
2018
‘Capable-of-being-shaped’ synthetic compounds are prevailing today over horn, bone, leather, wood, stone, metal, glass, or ceramic in products that were previously left to natural materials. Plastic is, in fact, economical, simple, adaptable, and waterproof. Also, it is durable and resilient to natural degradation (although microbial species capable of degrading plastics do exist). In becoming a waste, plastic accumulation adversely affects ecosystems. The majority of plastic debris pollutes waters, accumulating in oceans. And, the behaviour and the quantity of plastic, which has become waste, are rather well documented in the water, in fact. This review collects existing information on pla…
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).