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Initiator Efficiency (initiator + efficiency)
Selected AbstractsKinetic study of the free-radical polymerization of vinyl acetate in the presence of deuterated chloroform by 1H-NMR spectroscopyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Mohammad Ali Semsarzadeh Abstract The free-radical polymerization of vinyl acetate was performed in the presence of deuterated chloroform (CDCl3) as a chain-transfer agent (telogen) and 2,2,-azobisisobutyronitrile as an initiator. The effects of the initiator and solvent concentrations (or equivalent monomer concentration) and the reaction temperature on the reaction kinetics were studied by real-time 1H-NMR spectroscopy. Data obtained from analysis of the 1H-NMR spectra were used to calculate some kinetic parameters, such as the initiator decomposition rate constant (kd), kp(f/kt)1/2 ratio (where kp is the average rate constant for propagation, f is the initiator efficiency, and kt is the average rate constant for termination), and transfer constant to CDCl3 (C). The results show that kd and kp(f/kt)1/2 changed significantly with the solvent concentration and reaction temperature, whereas they remained almost constant with the initiator concentration. C changed only with the reaction temperature. Attempts were made to explain the dependence of kp(f/kt)1/2 on the solvent concentration. We concluded from the solvent-independent C values that the solvent did not have any significant effect on the kp values. As a result, changes in the kp(f/kt)1/2 values with solvent concentration were attributed to the solvent effect on the f and/or kt values. Individual values of f and kt were estimated, and we observed that both the f and kt values were dependent on the solvent (or equivalent monomer) concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Synthesis of poly(4-vinylpyridine) by reverse atom transfer radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2007Gregory T. Lewis Abstract Controlled radical polymerization of 4-vinylpyridine (4VP) was achieved in a 50 vol % 1-methyl-2-pyrrolidone/water solvent mixture using a 2,2,-azobis(2,4-dimethylpentanitrile) initiator and a CuCl2/2,2,-bipyridine catalyst,ligand complex, for an initial monomer concentration of [M]0 = 2.32,3.24 M and a temperature range of 70,80 °C. Radical polymerization control was achieved at catalyst to initiator molar ratios in the range of 1.3:1 to 1.6:1. First-order kinetics of the rate of polymerization (with respect to the monomer), linear increase of the number,average degree of polymerization with monomer conversion, and a polydispersity index in the range of 1.29,1.35 were indicative of controlled radical polymerization. The highest number,average degree of polymerization of 247 (number,average molecular weight = 26,000 g/mol) was achieved at a temperature of 70 °C, [M]0 = 3.24 M and a catalyst to initiator molar ratio of 1.6:1. Over the temperature range studied (70,80 °C), the initiator efficiency increased from 50 to 64% whereas the apparent polymerization rate constant increased by about 60%. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5748,5758, 2007 [source] High-Temperature Propagation and Termination Kinetics of Styrene to High Conversion Investigated by Electron Paramagnetic Resonance SpectroscopyMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2004Per B. Zetterlund Abstract Summary: The free radical bulk polymerization of styrene at 120,°C has been investigated over almost the entire conversion range using electron paramagnetic resonance spectroscopy, Fourier-transform near-infrared spectroscopy and gel permeation chromatography. The free radical concentration went through a sharp maximum that coincided with the peak in the rate of polymerization during the gel effect, and shifted to higher conversion with increasing initiator concentration. The termination rate coefficient (kt), decoupled from the initiator efficiency (f) by use of the instantaneous degree of polymerization, remained close to constant up to as high as approximately 80% conversion, at which a dramatic decrease occurred. Both the propagation rate coefficient (kp) and f fell orders of magnitude near 80% conversion in spite of the temperature being above the glass transition temperature of the system. The value of kp increased with the initiator concentration at a given conversion in the highest (diffusion-controlled) conversion range. Termination rate coefficient (kt) versus conversion for bulk free radical polymerization of St initiated by TBP at 120,°C. [TBP],=,0.15 (,), 0.10 (,) and 0.05 M (). [source] Free Radical Bulk Polymerization of Styrene: Simulation of Molecular Weight Distributions to High Conversion Using Experimentally Obtained Rate CoefficientsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 6 2003Per B. Zetterlund Abstract Previously obtained experimental conversion-dependences of the propagation rate coefficient (kp), the termination rate coefficient (kt) and the initiator efficiency (f) for the free-radical bulk polymerization of styrene at 70,°C have been used to simulate the full molecular weight distributions (MWD) to high conversion using the software package PREDICI, providing a robust test of the kinetic model adopted. Satisfactory agreement with the experimental MWD's (GPC) was obtained up to approximately 70% conversion. Beyond 70% conversion, the high MW shoulder that appears was correctly predicted, although the amount of such polymer was somewhat underestimated. This discrepancy is believed to probably have its origin in experimental error in the conversion-dependences of kp, kt and f, in particular kt, that were employed in the simulations, rather than indicate a more fundamental short-coming of the model employed. [source] Engineering analysis of crosslinking polymerization of diallyl lsophthalatePOLYMER ENGINEERING & SCIENCE, Issue 3 2000Bogdan Znoj A kinetic model for crosslinking free radical polymerization of DAIM (monomer diallyl isophthalate) with initiator CHPC (dicyclohexyl peroxydicarbonate) is developed. An improved version of Batch and Macosko's model was used to describe the initiator efficiency (f) and the active radical fraction (Fact). The experimental data of allyl and carbonyl group consumption are used for the optimization of the model and calculating of f and Fact. From the developed kinetic model and experimental results, obtained by FT-IR measurements of monomer conversion, the introduction of the Fact was proved. Application of this model may be of use in process modeling of DAIM and other crosslinking polymerizations with CHPC as initiator. [source] | ||||||||||