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Free-radical Initiator (free-radical + initiator)
Selected AbstractsPrediction of Chain Length Distribution of Polystyrene Made in Batch Reactors with Bifunctional Free-Radical Initiators Using Dynamic Monte Carlo SimulationMACROMOLECULAR REACTION ENGINEERING, Issue 3 2007Ibrahim M. Maafa Abstract The objective of this paper is to present a dynamic Monte Carlo model that is able to simulate the polymerization of styrene with bifunctional free-radical initiators in a batch reactor. The model can predict the dynamic evolution of the chain length distribution of polystyrene in the reactor. The model includes all relevant polymerization mechanistic steps, including chemical and thermal radical generation, and diffusion-controlled termination. The model was applied to styrene polymerization and the Monte Carlo estimates for chain length averages were compared to those obtained with the method of moments. Excellent agreement was obtained between the two methods. Although styrene polymerization was used as a case study, the proposed methodology can be easily extended to any other polymer type made by free-radical polymerization. [source] A High-Yield, Liquid-Phase Approach for the Partial Oxidation of Methane to Methanol using SO3 as the OxidantADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2005Sudip Mukhopadhyay Abstract A direct approach for producing methanol from methane in a three-step, liquid phase process is reported. In the first step, methane is reacted with SO3 to form methanesulfonic acid (MSA) at 75,°C using a free-radical initiator and MSA as the solvent. Urea-H2O2 in combination with RhCl3 is found to be the most effective initiator (57% conversion of SO3; 7.2% conversion of CH4). MSA is then oxidized by SO3 at 160,°C in a second step to produce a mixture containing methyl bisulfate and some methyl methanesulfonate (87% conversion of MSA). In the third step, the mixture of methyl bisulfate and methyl methanesulfonate is hydrolyzed in the presence of an organic solvent, to produce an organic phase containing methanol and an aqueous phase containing sulfuric acid and some MSA (63% conversion of methyl bisulfate; 72% conversion of methyl methanesulfonate). Overall, 58% of the MSA (of which 23% is derived from methane) is converted to methanol. [source] Synthesis of polymeric core,shell particles using surface-initiated living free-radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2007Sarav B. Jhaveri Abstract An easy and novel approach to the synthesis of functionalized nanostructured polymeric particles is reported. The surfactant-free emulsion polymerization of methyl methacrylate in the presence of the crosslinking reagent 2-ethyl-2-(hydroxy methyl)-1,3-propanediol trimethacrylate was used to in situ crosslink colloid micelles to produce stable, crosslinked polymeric particles (diameter size , 100,300 nm). A functionalized methacrylate monomer, 2-methacryloxyethyl-2,-bromoisobutyrate, containing a dormant atom transfer radical polymerization (ATRP) living free-radical initiator, which is termed an inimer (initiator/monomer), was added to the solution during the polymerization to functionalize the surface of the particles with ATRP initiator groups. The surface-initiated ATRP of different monomers was then carried out to produce core,shell-type polymeric nanostructures. This versatile technique can be easily employed for the design of a wide variety of polymeric shells surrounding a crosslinked core while keeping good control over the sizes of the nanostructures. The particles were characterized with scanning electron microscopy, transmission electron microscopy, optical microscopy, dynamic light scattering, and Raman spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1575,1584, 2007 [source] Novel amorphous perfluorocopolymeric system: Copolymers of perfluoro-2-methylene-1,3-dioxolane derivativesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2006Yu Yang Abstract Perfluorotetrahydro-2-methylene-furo[3,4- d][1,3]dioxole (monomer I) and perfluoro-2-methylene-4-methoxymethyl-1,3-dioxolane (monomer II) are soluble in perfluorinated or partially fluorinated solvents and readily polymerize in solution or in bulk when initiated by a free-radical initiator, perfluorodibenzoyl peroxide. The copolymerization parameters have been determined with in situ19F NMR measurements. The copolymerization reactivity ratios are rI = 1.80 and rII = 0.80 in 1,1,2-trichlorotrifluoroethane at 41 °C and rI = 0.97 and rII = 0.85 for the bulk polymerization. These data show that this copolymerization pair has a good copolymerization tendency and yields nearly ideal random copolymers. The copolymers have only one glass-transition temperature from 101 to 168 °C, depending on the copolymer compositions. Melting endotherms have not been observed in their differential scanning calorimetry traces, and this indicates that all the copolymers with different compositions are completely amorphous. These copolymers are thermally stable (the initial decomposition temperatures are higher than 350 °C under an N2 atmosphere) and have low refractive indices and high optical transparency from UV to near-infrared. Copolymer films prepared by casting were flexible and tough. These properties make the copolymers ideal candidates as optical and electrical materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1613,1618, 2006 [source] Photoinitiated polymerization of styrene from self-assembled monolayers on gold.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2002Abstract Ultrathin films of polystyrene (PS) were grown from self-assembled monolayers by the "grafting-from" technique. The initiating system consisted of a dithiol azobisisobutyronitrile-type free-radical initiator that was activated by irradiation at 300 nm. The thickness of the PS films ranged from 7 to 190 nm and could be controlled by varying the reaction time or the monomer concentration. The films were characterized by ellipsometry and Fourier transform-reflection absorption infrared spectroscopy after Soxhlet extraction of residual physisorbed polymer. These films were unstable above 60 °C, and a water-jacketed Soxhlet extractor was designed to maintain solvent temperatures below 45 °C during extraction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3284,3291, 2002 [source] Preparation and HPLC applications of rigid macroporous organic polymer monolithsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10-11 2004Frantisek Svec Abstract Rigid porous polymer monoliths are a new class of materials that emerged in the early 1990s. These monolithic materials are typically prepared using a simple molding process carried out within the confines of a closed mold. For example, polymerization of a mixture comprising monomers, free-radical initiator, and porogenic solvent affords macroporous materials with large through-pores that enable applications in a rapid flow-through mode. The versatility of the preparation technique is demonstrated by its use with hydrophobic, hydrophilic, ionizable, and zwitterionic monomers. Several system variables can be used to control the porous properties of the monolith over a broad range and to mediate the hydrodynamic properties of the monolithic devices. A variety of methods such as direct copolymerization of functional monomers, chemical modification of reactive groups, and grafting of pore surface with selected polymer chains is available for the control of surface chemistry. Since all the mobile phase must flow through the monolith, the convection considerably accelerates mass transport within the molded material, and the monolithic devices perform well, even at very high flow rates. The applications of polymeric monolithic materials are demonstrated mostly on the separations in the HPLC mode, although CEC, gas chromatography, enzyme immobilization, molecular recognition, advanced detection systems, and microfluidic devices are also mentioned. [source] Polymacromonomers with polyolefin branches synthesized by free-radical homopolymerization of polyolefin macromonomer with a methacryloyl end groupMACROMOLECULAR SYMPOSIA, Issue 1 2004Hideyuki Kaneko Abstract Polymacromonomers with polyolefin branches were successfully synthesized by free-radical homopolymerization of polyolefin macromonomer with a methacryloyl end group. Propylene-ethylene random copolymer (PER) with a vinylidene end group was prepared by polymerization using a metallocene catalyst. Then, the unsaturated end group was converted to a hydroxy end group via hydroalumination and oxidation. The PER with the hydroxy end group was easily reacted with methacryloyl chloride to produce methacryloyl-terminated PER (PER macromonomer; PERM). The free-radical polymerization of thus-obtained PERM was done using 2,2,-azobis(isobutyronitorile) (AIBN) as a free-radical initiator. From NMR analyses, the obtained polymers were identified as poly(PERM). Based on gel permeation chromatography (GPC), the estimated degree of polymerization (Dp) of these polymers were about 30. Thus, new class of polymacromonomers with polyolefin branches was synthesized. [source] Prediction of Chain Length Distribution of Polystyrene Made in Batch Reactors with Bifunctional Free-Radical Initiators Using Dynamic Monte Carlo SimulationMACROMOLECULAR REACTION ENGINEERING, Issue 3 2007Ibrahim M. Maafa Abstract The objective of this paper is to present a dynamic Monte Carlo model that is able to simulate the polymerization of styrene with bifunctional free-radical initiators in a batch reactor. The model can predict the dynamic evolution of the chain length distribution of polystyrene in the reactor. The model includes all relevant polymerization mechanistic steps, including chemical and thermal radical generation, and diffusion-controlled termination. The model was applied to styrene polymerization and the Monte Carlo estimates for chain length averages were compared to those obtained with the method of moments. Excellent agreement was obtained between the two methods. Although styrene polymerization was used as a case study, the proposed methodology can be easily extended to any other polymer type made by free-radical polymerization. [source] | |||||||||||||