Home About us Contact
|
Home About us Contact | ||
|
|
||
Polymerization System (polymerization + system)
Selected AbstractsA Novel Synthetic Procedure for Stereoblock Poly(propylene) with a Living Polymerization System,MACROMOLECULAR RAPID COMMUNICATIONS, Issue 10 2004Kei Nishii Abstract Summary: Propylene polymerization was conducted at 0,°C in heptane or chlorobenzene (CB) by an ansa -fluorenylamidodimethyltitanium complex combined with dried, modified methylaluminoxane that had been treated by dilution with heptane and successively repeatedly vacuum dried to remove any free trialkylaluminiums. The post-polymerizations testified that the living polymerization proceeded irrespective of the solvent used. The heptane system gave the syndiotactic poly(propylene)s (PPs), whereas the CB system gave almost atactic PPs. After the first polymerization in heptane had been completed, the same amounts of propylene and CB were added for the second polymerization. This procedure gave the syndiotactic-atactic stereoblock PP with narrow molecular-weight distributions. Structure of the ansa -fluorenylamidodimethyltitanium complex and its application to the synthesis of syndiotactic-atactic stereoblock poly(propylene)s reported here. [source] Binary Neodymium Alkoxide/Dialkylmagnesium Polymerization Systems: Studies on the Nature of the Reaction Intermediates and Active SpeciesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2004Jérôme Gromada Abstract Attempts to identify the intermediates and/or active species generated from binary combinations of a lanthanide alk(aryl)oxide with a dialkylmagnesium reagent, which behave as efficient olefin polymerization systems, are reported. The well-defined trinuclear complex [Nd3(,3 -OtBu)2(,2 -OtBu)3(,-OtBu)4(THF)2] (1) and the monomeric precursor [Nd(OC6H2tBu2 -2,6-Me-4)3(THF)] (2) were used in association with [Mg(CH2SiMe3)2(Et2O)] (3). The new heterodimetallic complex [(THF)Nd(,3 -OtBu)2(,2 -OtBu)2(OtBu)Mg2(CH2TMS)2] (4) and the alkyllanthanide complex [Nd(OC6H2tBu2 -2,6-Me-4)2(CH2SiMe3)(THF)2] (5) have been isolated and characterized in the solid state and in solution. Complex 4 is proposed to be a reaction intermediate in the active species formation, while complex 5 is the first alkyllanthanide species isolated from an "Ln(OR)3"/MgR2 mixture, consistent with the observed behavior of these combinations in olefin polymerization. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Emulsion polymerization of styrene with amphiphilic random copolymer as surfactant: Predominant droplet nucleationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009Li Liu Abstract Amphiphilic random copolymer consisting of monomeric units of poly (butyl acrylate) and poly (maleic acid salt) was synthesized and characterized. The emulsion polymerization kinetics of styrene stabilized by this copolymer was investigated. The influencing factors, including polymeric surfactant concentration, initiator concentration and polymerization temperature, were systematically studied. The kinetic data show that the polymerization rate (RP) increased with the increase of the polymeric surfactant concentration ([S]) and polymerization temperature (T). At the higher [S], droplets nucleation and micelle nucleation coexisted in the polymerization system; at the lower [S], only the droplets nucleation process existed. The polymerization did not follow Smith-Ewart Case II kinetics. Dynamic light scatter and transmission electron microscope were utilized to measure the sizes and shapes of the particles, respectively. It would be speculated that a kind of large heterogeneous particles with multiple-active-sites was formed in the polymerization system. The increasing of RP with increasing initiator concentration ([KPS]) was rapid at a medium [KPS], but the slowly increasing was observed at a lower or higher [KPS]. It was attributed to the barrier effect of the polymeric surfactant around the monomer droplets. The polymerization activation energy was 60.29 kJ/mol. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Modeling and predictive control using fuzzy logic: Application for a polymerization systemAICHE JOURNAL, Issue 4 2010Nádson M. N. Lima Abstract In this study, a predictive control system based on type Takagi-Sugeno fuzzy models was developed for a polymerization process. Such processes typically have a highly nonlinear dynamic behavior causing the performance of controllers based on conventional internal models to be poor or to require considerable effort in controller tuning. The copolymerization of methyl methacrylate with vinyl acetate was considered for analysis of the performance of the proposed control system. A nonlinear mathematical model which describes the reaction plant was used for data generation and implementation of the controller. The modeling using the fuzzy approach showed an excellent capacity for output prediction as a function of dynamic data input. The performance of the projected control system and dynamic matrix control for regulatory and servo problems were compared and the obtained results showed that the control system design is robust, of simple implementation and provides a better response than conventional predictive control. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Synthesis and kinetic analysis of DPE controlled radical polymerization of MMAJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2009Ying-Da Luo Abstract The 1,1-diphenylethene (DPE) controlled radical polymerization of methyl methacrylate was performed at 80 °C by using AIBN as an initiator and DPE as a control agent. It was found that the molecular weight of polymer remained constant with monomer conversion throughout the polymerization regardless of the amounts of DPE and initiator in formulation. To understand the result of constant molecular weight of living polymers in DPE controlled radical polymerization, a living kinetic model was established in this research to evaluate all the rate constants involved in the DPE mechanism. The rate constant k2, corresponding to the reactivation reaction of the DPE capped dormant chains, was found to be very small at 80 °C (1 × 10,5 s,1), that accounted for the result of constant molecular weight of polymers throughout the polymerization, analogous to a traditional free radical polymerization system that polymer chains were terminated by chain transfer. The polydispersity index (PDI) of living polymers was well controlled <1.5. The low PDI of obtained living polymers was due to the fact that the rate of growing chains capped by DPE was comparable with the rate of propagation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009 [source] Artificial polymerases and molecular chaperonesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2009Akira Harada Abstract Cyclodextrins (CDs) were found to initiate polymerization of lactone to give polyesters with a CD ring at the end of the polymer chain in high yields only by mixing and heating with monomer without cocatalysts or solvents. CD-tethered polyester propagates with the formation of poly-pseudorotaxane, which is necessary to initiate further polymerization. CDs threaded onto the polymer chain are also essential for maintaining the propagating state of the polyester. By polymerizing with CD, switching the activity of the polymerization by photoisomerization was demonstrated. This polymerization system showed specific substrate recognition, releasing the products from the active site. By using the above polymerization system, ,-CD nanospheres which initiates the oligomerization of lactone were constructed. It was found that the formation of poly-pseudorotaxane on the nanosphere enabled further polymerization activity for lactone. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4469,4481, 2009 [source] Synthesis of PMMA- b -PBA block copolymer in homogeneous and miniemulsion systems by DPE controlled radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2009Ying-Da Luo Abstract In this research, poly(methyl methacrylate)- b -poly(butyl acrylate) (PMMA- b -PBA) block copolymers were prepared by 1,1-diphenylethene (DPE) controlled radical polymerization in homogeneous and miniemulsion systems. First, monomer methyl methacrylate (MMA), initiator 2,2,-azobisisobutyronitrile (AIBN) and a control agent DPE were bulk polymerized to form the DPE-containing PMMA macroinitiator. Then the DPE-containing PMMA was heated in the presence of a second monomer BA, the block copolymer was synthesized successfully. The effects of solvent and polymerization methods (homogeneous polymerization or miniemulsion polymerization) on the reaction rate, controlled living character, molecular weight (Mn) and molecular weight distribution (PDI) of polymers throughout the polymerization were studied and discussed. The results showed that, increasing the amounts of solvent reduced the reaction rate and viscosity of the polymerization system. It allowed more activation,deactivation cycles to occur at a given conversion thus better controlled living character and narrower molecular weight distribution of polymers were demonstrated throughout the polymerization. Furthermore, the polymerization carried out in miniemulsion system exhibited higher reaction rate and better controlled living character than those in homogeneous system. It was attributed to the compartmentalization of growing radicals and the enhanced deactivation reaction of DPE controlled radical polymerization in miniemulsified droplets. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4435,4445, 2009 [source] Confined space regulated polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2008Ye-Zi You Abstract The confined space produced during the polymerization has access for all small organic molecules or oligomers with small size to enter this confined space; however, it can prevent the macromolecules with big size from entering. Therefore, the reaction between two branched macromolecules is excluded in A2+B3 polymerization system, resulting uncrosslinked branched polymers, and there was no gel point observed throughout the polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1730,1737, 2008 [source] Preparation of single-walled carbon nanotubes-induced poly(p -oxybenzoyl) crystalsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2008Kazufumi Kobashi Abstract Crystallization of oligomers was applied for the preparation of single-walled carbon nanotubes (SWNTs)/poly(p -oxybenzoyl) (POB) crystals using SWNTs as a nucleating agent. Polymerization conditions were investigated to induce the crystallization of POB oligomers through SWNTs. SWNTs/POB plate-like or lozenge-shaped crystals were successfully prepared by direct polymerization of p -hydroxybenzoic acid (HBA) in a mixed solvent of DMF/Py with TsCl in the presence of functionalized SWNTs. The size of the plate-like crystals were ,200 nm to 3 ,m. The crystals consisted of some layers, ,3 nm thick plates. Model reactions showed that esterification reactions proceed between functionalized SWNTs and HBA monomers in the polymerization system. The obtained crystals exhibited unique morphology and high crystallinity, producing a novel SWNT/POB hybrid. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1265,1277, 2008 [source] Copolymerizations of butyl methacrylate and fluorinated methacrylates via RAFT miniemulsion polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2007Tian-Ying Guo Abstract Copolymerizations of n -butyl methacrylate (BMA) and fluoro-methacrylates (including 2,2,3,4,4,4-hexafluorobutyl methacrylate, HFBMA and 2,2,2-trifluoroethyl methacrylate, TFEMA) were carried out via reversible addition-fragmentation chain transfer miniemulsion polymerization, using cumyl dithiobenzoate as a chain transfer agent. The experimental results show that the copolymerizations exhibit "living" fashion, with controlled molecular weights and narrow polydispersities. The reactivity ratios of BMA and fluoromethacrylate in this kind of polymerization system were investigated by size exclusion chromatography and nuclear magnetic resonance, from which the Q - and e -values of HFBMA and TFEMA were calculated. Compared with its corresponding non-fluoric methacrylate, fluorinated methacrylate exhibits higher resonance stability of the radical adducts. The Q -value of fluorinated methacrylate is higher (QBMA = 0.82 to QHFBMA = 1.70 and QEMA = 0.76 to QTFEMA = 1.01), and e -value is much larger (eBMA = 0.28 to eHFBMA = 1.24 to and eEMA = 0.17 to eTFEMA = 1.29) for its rather unique high electron-withdrawing inductive effect of the fluoroalkyl ester group. The thermal property and the wetting property of copolymers were also discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5067,5075, 2007 [source] Developing a hybrid emulsion polymerization system to synthesize Fe3O4/polystyrene latexes with narrow size distribution and high magnetite contentJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2007Longlan Cui Abstract A hybrid emulsion polymerization was formulated for synthesizing Fe3O4/polystyrene composite latex. This system, containing binary droplets that are magnetic (Mag)-droplets with a diameter of 100,200 nm and styrene (St)-droplets with a diameter of 3,4 ,m, was obtained by mixing Mag-miniemulsion and St-macroemulsion. With extremely low surfactants concentration (,critical micelle concentration, CMC), the nucleated loci are selectively controlled in the Mag-droplets, as the result of smaller droplet size and larger surface ratio. Both water-soluble potassium persulfate (KPS) and oil-soluble 2,2,-azobis(2-isobutyronitrile) was adopted to initiate the polymerization. In the presence of KPS, magnetic polystyrene latices with particles size of 60,200 nm, narrow size distribution, and high magnetite content (86 wt % measured by TGA) were attained successfully. The synthesized magnetic Fe3O4/polystyrene latices assembled into well-ordered hexagonal structure in the surface of a carbon supported copper grid. The influence of various parameters on various aspects of the as-synthesized Fe3O4/polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag-miniemulsion and St-macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5285,5295, 2007 [source] Deactivation reactions in the modeled 2,2,6,6-tetramethyl-1-piperidinyloxy-mediated free-radical polymerization of styrene: A comparative study with the 2,2,6,6-tetramethyl-1-piperidinyloxy/acrylonitrile systemJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2007Andrzej Kaim Abstract The competitiveness of the combination and disproportionation reactions between a 1-phenylpropyl radical, standing for a growing polystyryl macroradical, and a 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) radical in the nitroxide-mediated free-radical polymerization of styrene was quantitatively evaluated by the study of the transition geometry and the potential energy profiles for the competing reactions with the use of quantum-mechanical calculations at the density functional theory (DFT) UB3-LYP/6-311+G(3df, 2p)//(unrestricted) Austin Model 1 level of theory. The search for transition geometries resulted in six and two transition structures for the radical combination and disproportionation reactions, respectively. The former transition structures, mainly differing in the out-of-plane angle of the NO bond in the transition structure TEMPO molecule, were correlated with the activation energy, which was determined to be in the range of 8.4,19.4 kcal mol,1 from a single-point calculation at the DFT UB3-LYP/6-311+G(3df, 2p)//unrestricted Austin Model 1 level. The calculated activation energy for the disproportionation reaction was less favorable by a value of more than 30 kcal mol,1 in comparison with that for the combination reaction. The approximate barrier difference for the TEMPO addition and disproportionation reaction was slightly smaller for the styrene polymerization system than for the acrylonitrile polymerization system, thus indicating that a ,-proton abstraction through a TEMPO radical from the polymer backbone could diminish control over the radical polymerization of styrene with the nitroxide even more than in the latter system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 232,241, 2007 [source] Living cationic polymerization of azobenzene-containing vinyl ether and its photoresponsive behaviorJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2005Tomohide Yoshida Abstract The living cationic polymerization of 4-[2-(vinyloxy)ethoxy]azobenzene (AzoVE) was achieved with various Lewis acids in the presence of an ester as an added base. When Et1.5AlCl1.5 was used as a catalyst, the living polymerization system was controllable by UV irradiation as a result of cis and trans isomerization of the azobenzene side groups. Furthermore, an initiating system consisting of SnCl4 and EtAlCl2 realized fast living polymerization of AzoVE. The polymerization rate of this system was 3 orders of magnitude faster than that obtained with Et1.5AlCl1.5. Poly(4-[2-(vinyloxy)ethoxy]azobenzene) was soluble in a diethyl ether/hexane mixture at 25 °C but became insoluble upon irradiation with UV light. This phase-transition behavior was sensitive and reversible upon irradiation with UV or visible light and reflected the change in polarity occurring with cis and trans isomerization of the azobenzene side groups in the polymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5138,5146, 2005 [source] Synthesis and characterization of new alternating, amphiphilic, comblike copolymers of poly(ethylene oxide) macromonomer and N -phenylmaleimideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2005Luminita Cianga Abstract A surface-active p -vinyl benzyloxy-,-hydroxy-poly(ethylene oxide) macromonomer containing 22 pendant structural units of ethylene oxide (St,PEO22) was synthesized with an initiation method. Because of its solubility in a large variety of solvents, the free-radical copolymerization with electron-acceptor N -phenylmaleimide (NPMI) was performed at 60 °C in benzene and tetrahydrofuran (THF) as isotropic media and in a water,THF mixture or water as a heterogeneous medium. Oil-soluble 2,2,-azobisisobutyronitrile and water-soluble 4,4,-azobis(4-cyanovaleric acid) were used as the initiators at fixed concentrations. Two different St,PEO22/NPMI comonomer ratios (1/1 and 3/7) at a fixed total comonomer concentration in the polymerization system were used. The structures, compositions, and microstructure peculiarities of the obtained alternating, amphiphilic, comblike copolymers were determined by NMR analysis. For the copolymers synthesized in hydrophilic media, differential scanning calorimetry showed, near the endothermic peak attributed to the melting of the poly(ethylene oxide) side chains, the presence of a second peak due to the partially ordered phase that could exist between the crystalline state and the isotropic melt. Also, the thermal stability of the obtained copolymers was studied with thermogravimetric analysis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 479,492, 2005 [source] Hydrogen-bond-assisted stereocontrol in the radical polymerization of N -isopropylacrylamide with primary alkyl phosphate: The effect of the chain length of the straight ester groupJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2005Tomohiro Hirano Abstract The radical polymerizations of N -isopropylacrylamide (NIPAAm) were carried out in toluene at low temperatures in the presence of phosphoric acid esters such as trimethyl phosphate, triethyl phosphate (TEP), tri- n -propyl phosphate, and tri- n -butyl phosphate (TBP). Syndiotactically rich poly(NIPAAm)s were obtained from ,60 to 0 °C, and TEP provided the highest syndiotacticity (racemo dyad = 65%) at ,40 °C. On the other hand, lowering the temperature reversed the stereoselectivity of the propagation reaction so that isotactically rich poly(NIPAAm)s were obtained at ,80 °C. In particular, TBP exhibited the most isotactic specificity (meso dyad = 57%). Job's plots for NIPAAm,TBP mixtures revealed that NIPAAm and TBP formed a 1:1 complex at 0 °C and a predominantly 1:2 complex at ,80 °C through a hydrogen-bonding interaction. Therefore, the stereospecificity of NIPAAm polymerization should depend on the stoichiometry of the hydrogen-bond-assisted complex. Thus, the mechanism for this polymerization system was discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 50,62, 2005 [source] High-Speed Living Polymerization of Polar Vinyl Monomers by Self-Healing Silylium CatalystsCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2010Dr. Yuetao Zhang Abstract This contribution describes the development and demonstration of the ambient-temperature, high-speed living polymerization of polar vinyl monomers (M) with a low silylium catalyst loading (, 0.05,mol,% relative to M). The catalyst is generated in situ by protonation of a trialkylsilyl ketene acetal (RSKA) initiator (I) with a strong Brønsted acid. The living character of the polymerization system has been demonstrated by several key lines of evidence, including the observed linear growth of the chain length as a function of monomer conversion at a given [M]/[I] ratio, near-precise polymer number-average molecular weight (Mn, controlled by the [M]/[I] ratio) with narrow molecular weight distributions (MWD), absence of an induction period and chain-termination reactions (as revealed by kinetics), readily achievable chain extension, and the successful synthesis of well-defined block copolymers. Fundamental steps of activation, initiation, propagation, and catalyst "self-repair" involved in this living polymerization system have been elucidated, chiefly featuring a propagation "catalysis" cycle consisting of a rate-limiting CC bond formation step and fast release of the silylium catalyst to the incoming monomer. Effects of acid activator, catalyst and monomer structure, and reaction temperature on polymerization characteristics have also been examined. Among the three strong acids incorporating a weakly coordinating borate or a chiral disulfonimide anion, the oxonium acid [H(Et2O)2]+[B(C6F5)4], is the most effective activator, which spontaneously delivers the most active R3Si+, reaching a high catalyst turn-over frequency (TOF) of 6.0×103,h,1 for methyl methacrylate polymerization by Me3Si+ or an exceptionally high TOF of 2.4×105,h,1 for n -butyl acrylate polymerization by iBu3Si+, in addition to its high (>90,%) to quantitative efficiencies and a high degree of control over Mn and MWD (1.07,1.12). An intriguing catalyst "self-repair" feature has also been demonstrated for the current living polymerization system. [source] Binary Neodymium Alkoxide/Dialkylmagnesium Polymerization Systems: Studies on the Nature of the Reaction Intermediates and Active SpeciesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2004Jérôme Gromada Abstract Attempts to identify the intermediates and/or active species generated from binary combinations of a lanthanide alk(aryl)oxide with a dialkylmagnesium reagent, which behave as efficient olefin polymerization systems, are reported. The well-defined trinuclear complex [Nd3(,3 -OtBu)2(,2 -OtBu)3(,-OtBu)4(THF)2] (1) and the monomeric precursor [Nd(OC6H2tBu2 -2,6-Me-4)3(THF)] (2) were used in association with [Mg(CH2SiMe3)2(Et2O)] (3). The new heterodimetallic complex [(THF)Nd(,3 -OtBu)2(,2 -OtBu)2(OtBu)Mg2(CH2TMS)2] (4) and the alkyllanthanide complex [Nd(OC6H2tBu2 -2,6-Me-4)2(CH2SiMe3)(THF)2] (5) have been isolated and characterized in the solid state and in solution. Complex 4 is proposed to be a reaction intermediate in the active species formation, while complex 5 is the first alkyllanthanide species isolated from an "Ln(OR)3"/MgR2 mixture, consistent with the observed behavior of these combinations in olefin polymerization. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Multivariate monitoring of batch processes using batch-to-batch informationAICHE JOURNAL, Issue 6 2004Jesus Flores-Cerrillo Abstract Multiway principal component analysis (MPCA) and multiway partial-least squares (MPLS) are well-established methods for the analysis of historical data from batch processes, and for monitoring the progress of new batches. Direct measurements made on prior batches can also be incorporated into the analysis by monitoring with multiblock methods. An extension of the multiblock MPCA/MPLS approach is introduced to explicitly incorporate batch-to-batch trajectory information summarized by the scores of previous batches, while keeping all the advantages and monitoring statistics of the traditional MPCA/MPLS. However, it is shown that the advantages of using information on prior batches for analysis and monitoring are often small. Its main advantage is that it can be useful for detecting problems when monitoring new batches in the early stages of their operation., the approach and benefits are illustrated with condensation polymerization and emulsion polymerization systems, as examples. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1219,1228, 2004 [source] Sol MWD During Styrene, Vinyl Acetate, Methyl Methacrylate, and Butyl Acrylate Homopolymerization: A Numerical Study Using the NFT ApproachMACROMOLECULAR THEORY AND SIMULATIONS, Issue 3 2009Bibiana Alejandra Yáñez-Martínez Abstract Complete parameter sensitivity analyses using the numerical fractionation technique are presented for the cases of homopolymerization with chain transfer to polymer and termination by combination. Also, using reported values for the kinetic rate constants associated with the linear and non-linear homopolymerizations of styrene, vinyl acetate, methyl methacrylate and butyl acrylate, overall molecular weight distributions and averages of the MWD were calculated using the NFT. Good agreement with the expected behavior, with MMA and STY not gelling while BA and VAc do, was obtained. It is concluded that the NFT produces coherent and reliable performance for known polymerization systems, whether linear or non-linear. [source] Matrix Representation of Polymer Chain Size Distributions, 3 , Case Studies for Linear Polymerization Mechanisms at Transient ConditionsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 4-5 2008Heloísa L. Sanches Abstract The mass balance equations used to describe different polymerization systems are represented and analyzed with the help of a general matrix framework previously developed. Some of its properties were presented in previous works and are illustrated here in three examples. The first example regards the dynamics of a copolymerization reactor. It is shown that terminal and penultimate models may predict qualitatively different responses in batch reactions. The second example also regards the dynamics of copolymerization reactions. It is shown how manipulation of initial conditions and monomer feed rates can be used to keep copolymer composition constant throughout the batch. The third example concerns the existence of oscillating chain size distributions when there are multiple monomer insertion steps. [source] Kinetics of Stable Free Radical Mediated Polymerization inside Submicron ParticlesMACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2007Hidetaka Tobita Abstract Controlled/living radical polymerization systems in which the active period is extremely small, ,A,,,1, such as the cases of stable free radical mediated polymerization (or nitroxide mediated polymerization) and atom transfer radical polymerization, are considered theoretically. The polymerization rate, Rp, for such systems increases by lowering the trapping agent concentration [X]. When the polymerization is conducted inside small particles, Rp decreases with D below the diameter Dp,SMC at which a single molecule concentration (SMC) is equal to [X]bulk. On the other hand, when the average number of trapping agents in a particle is smaller than about 10, the fluctuation of nX among particles is significant, which leads to a larger Rp than in the cases where all particles contain the same nX. Because of the effects of SMC and fluctuation, Rp may show an acceleration window, Dp,SMC,<,Dp,<,Dp,Fluct where Rp is slightly larger than that in bulk. [source] Transient Behavior and Gelation of Free Radical Polymerizations in Continuous Stirred Tank ReactorsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 4 2005Rolando C. S. Dias Abstract Summary: Using the authors' previously developed method for the general kinetic analysis of non-linear irreversible polymerizations, the simulation of free radical homogeneous polymerization systems with terminal branching and chain transfer to polymer has been carried out for continuous stirred tank reactors. Its improved accuracy on the numerical evaluation of generating functions has been exploited in order to perform their numerical inversion and chain length distributions could also be estimated with or without the presence of gel. A comparison with alternative techniques emphasizing the effect of their simplifying assumptions on the accuracy of calculations is also presented. Predicted CLD before gelation (t,=,1 h), after gelation (t,=,15 h, steady state), and close to gel point for a free radical polymerization with transfer to polymer in a CSTR with ,,=,60 min. [source] The Quenched Instationary Polymerization Systems (QUIPS)MACROMOLECULAR THEORY AND SIMULATIONS, Issue 2-3 2003Irene Schnöll-Bitai Abstract The common element of quenched instationary polymerization systems is that at a given time all radicals present are deactivated by an efficient and fast quench reaction. Quenched instationary polymerizations can be carried out in a variety of ways distinguished by the way periods differing in their initiation characteristics are combined. The total chain length distribution of the resulting polymer is always the sum of the quenched radical and polymer chain length distribution. This distribution is either completely or at least partially dominated by the contribution of the quenched radical spectrum. Depending on the experimental conditions monomodal or multimodal distributions are obtained which can be characterized by their extrema (maximum, points of inflection) and peak widths (absolute, relative). The location of the extrema are related to the experimental parameters and can be used in an unambiguous way for the direct determination of the rate constant of propagation. Absolute peak widths (defined as the difference between two succeeding points of inflection) are invariant quantities with respect to the number, molar mass and hyper distribution which is only true for Poisson (and narrow Gauss) distributions. Relative peak widths are a valuable tool for the direct determination of axial dispersion which occurs in size exclusion chromatography. Comparison of experimental and ideal relative peak widths can be used for the direct determination of the axial dispersion. The influence of the type of termination and [R0] (termination by combination) on the total (number) chain length distribution for single , -pulse initiation. [source] | |||||||||||||