A kinetic study of the thermally initiated free radical reactions of styrene with octanedithiol as a model for the reactions of multifunctional thiols with divinylbenzene

The kinetics of chain reactions of octanedithiol with styrene, thermally initiated with TX29B50 (a 50:50 wt% solution of TX29 diperoxy initiator in a phthalate plasticizer), have been studied over a range of initiator concentrations, a range of mixture formulations and a range of temperatures. This system has been investigated as a model system for the reactions of polyfunctional thiols with divinyl benzene. The reactions have been shown to follow first-order kinetics for both the thiol and the ene species and to be characterized by a dependence on the initiator concentration to the power of one half. The kinetic rate parameters have been shown to adhere to Arrhenius behaviour. A kinetic model for the chain reactions for this system has been proposed. (C) 2003 Society of Chemical Industry.

Radiation-induced reactions in swollen polymers /

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Radiation-induced reactions in swollen polymers /

The content was printed on only one side of the paper.

Regioregular improvement on the oxidative polymerization of poly-3-octylthiophenes by slow addition of oxidant at low temperature

Many pathways can be used to synthesize polythiophenes derivatives. The polycondensation reactions performed with organometallics are preferred since they lead to regioregular polymers (with high content of heat-to-tail coupling) which have enhanced conductivity and luminescence. However, these pathways have several steps; the reactants are highly moisture sensitive and expensive. On the other hand, the oxidative polymerization using FeCl3 is a one-pot reaction that requires less moisture sensitive reactants with lower cost, although the most common reaction conditions lead to polymers with low regioregularity. Here, we report that by changing the reaction conditions, such as FeCl3 addition rate and reaction temperature, poly-3-octylthiophenes with different the regioregularities can be obtained, reaching about 80% of heat-to-tail coupling. Different molar mass distributions and polydispersivities were obtained. The preliminary results suggest that the oxidative polymerization process could be improved to yield polythiophenes with higher regioregularity degree and narrower molar mass distributions by just setting some reaction conditions. We also verified that it is possible to solvent extract part of the lower regioregular fraction of the polymer further improving the regioregularity degree. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Modeling the molecular weight distribution of block copolymer formation in a reversible addition-fragmentation chain transfer mediated living radical polymerization

Block copolymers have become an integral part of the preparation of complex architectures through self-assembly. The use of reversible addition-fragmentation chain transfer (RAFT) allows blocks ranging from functional to nonfunctional polymers to be made with predictable molecular weight distributions. This article models block formation by varying many of the kinetic parameters. The simulations provide insight into the overall polydispersities (PDIs) that will be obtained when the chain-transfer constants in the main equilibrium steps are varied from 100 to 0.5. When the first dormant block [polymer-S-C(Z)=S] has a PDI of 1 and the second propagating radical has a low reactivity to the RAFT moiety, the overall PDI will be greater than 1 and dependent on the weight fraction of each block. When the first block has a PDI of 2 and the second propagating radical has a low reactivity to the RAFT moiety, the PDI will decrease to around 1.5 because of random coupling of two broad distributions. It is also shown how we can in principle use only one RAFT agent to obtain block copolymers with any desired molecular weight distribution. We can accomplish this by maintaining the monomer concentration at a constant level in the reactor over the course of the reaction. (c) 2005 Wiley Periodicals, Inc.

Controlled Radical Polymerization of Styrene and Methyl Acrylate in the Presence of Reversible Addition-Fragmentation Chain Transfer Agents, Phenylethyl Phenyl Dithioacetate and Phenyldithioacetic Acid

The use of phenyldithioacetic acid (PDA) in homopolymerizations of styrene or methyl acrylate produced only a small fraction of chains with dithioester end groups. The polymerizations using 1-phenylentyl phenyldithioacetate (PEPDTA) and PDA in the same reaction showed that PDA had little or no influence on the rate or molecular weight distribution even when a 1:1 ratio is used. The mechanistic pathway for the polymerizations in the presence of PDA seemed to be different for each monomer. Styrene favors addition of styrene to PDA via a Markovnikov type addition to form a reactive RAFT agent. The polymer was shown by double detection SEC to contain dithioester end groups over the whole distribution. This polymer was then used in a chain extension experiment and the M-n was close to theory. A unique feature of this work was that PDA could be used to form a RAFT agent in situ by heating a mixture of styrene and PDA for 24 h at 70 degrees C and then polymerizing in the presence of AIBN to give a linear increase in Mn and low values of PDI (< 1.14). In the case of the polymerization of MA with PDA, the mechanism was proposed to be via degradative chain transfer. (c) 2005 Wiley Periodicals, Inc.

Design strategies for controlling the molecular weight and rate using reversible addition-fragmentation chain transfer mediated living radical polymerization

Living radical polymerization has allowed complex polymer architectures to be synthesized in bulk, solution, and water. The most versatile of these techniques is reversible addition-fragmentation chain transfer (RAFT), which allows a wide range of functional and nonfunctional polymers to be made with predictable molecular weight distributions (MWDs), ranging from very narrow to quite broad. The great complexity of the RAFT mechanism and how the kinetic parameters affect the rate of polymerization and MWD are not obvious. Therefore, the aim of this article is to provide useful insights into the important kinetic parameters that control the rate of polymerization and the evolution of the MWD with conversion. We discuss how a change in the chain-transfer constant can affect the evolution of the MWD. It is shown how we can, in principle, use only one RAFT agent to obtain a poly-mer with any MWD. Retardation and inhibition are discussed in terms of (1) the leaving R group reactivity and (2) the intermediate radical termination model versus the slow fragmentation model. (c) 2005 Wiley Periodicals, Inc.

Solution Polymerization of N-vinylcaprolactam in 1,4-dioxane. Kinetic Dependence on Temperature, Monomer, and Initiator Concentrations

The kinetics of the solution free radical polymerization of N-vinylcaprolactam, in 1,4-dioxane and under various polymerization conditions was studied. Azobisisobutyronitrile and 3-mercaptopropionic acid were used as initiator and as chain transfer agent (CTA), respectively. The influence of monomer and initiator concentrations and polymerization temperature on the rate of polymerizations (R(p)) was investigated. In general, high conversions were obtained. The order with respect to initiator was consistent with the classical kinetic rate equation, while the order with respect to the monomer was greater than unity. The overall activation energy of 53.6 kJ mol(-1) was obtained in the temperature range 60-80 degrees C. The decreasing of the absolute molecular weights when increasing the CIA concentration was confirmed by GPC/SEC/LALS analyses. It was confirmed by UV-visible analyses the effect of molecular weights on the lower critical solution temperature of the polymers. It was also verified that the addition of the CTA influenced the kinetic of the polymerizations. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 229-240, 2010

The Effect of the Mixtures of Photoinitiators in Polymerization Efficiencies

The photoinitiated polymerization of methyl methacrylate using the mixtures of camphorquinone (CQ) and acylphosphine oxides (monoacylphosphine oxide, MAPO or bisacylphosphine oxide,BAPO) was studied to determine the possible synergistic effects. The addition of the acylphosphines to CQ resulted in an increase of the polymerization rate compared with CQ alone. On the other hand, a significant decrease of the polymerization quantum yield is observed for the mixtures compared with the pure acylphosphines. Therefore, the increase in the polymerization efficiency of the two rnixtures studied, MAPO/CQ and BAPO/CQ (compared with CQ) can be traced to the larger light absorption range, rather than to the onset of new mechanisms. The presence of the coinitiator ethyl 4-dimethylaminobenzoate, EDB, always present in CQ formulations, has no effect at all on the rates of polymerization photoinitiated by the acylphosphine oxides. From the point of view of photopolymerization quantum yields, an antagonistic effect is observed because Of the energy transfer of the M more efficient initiator (MAPO or BAPO) to the less efficient one (CQ). (C) 2008 Wiley Periodicals, Inc. j Appl Polym Sci 112: 129-134, 2009

Influence of cerium (IV) ions on the mechanism of organosilane polymerization and on the improvement of its barrier properties

In this work, the effect of cerium (IV) ammonium nitrate (CAN) addition on the polymerization of bis-[triethoxysilyl]ethane (BTSE) film applied on carbon steel was studied. The electrochemical characterization of the films was carried out in 0.1 mol L(-1) NaCl solution by open-circuit potential measurements, anodic and cathodic polarization curves and electrochemical impedance spectroscopy (EIS). Morphological and chemical characterization were performed by atomic force microscopy (AFM), contact angle measurements, infrared-spectroscopy, nuclear magnetic resonance and thermogravimetric analysis. The results have clearly shown the improvement on the protective properties of the Ce(4+) modified film as a consequence of the formation of a more uniform and densely reticulated silane film. A mechanism is proposed to explain the accelerating role of Ce(4+) ions on the cross-linking of the silane layer. (C) 2008 Elsevier Ltd. All rights reserved.

Novel M(II) beta-diketiminate complexes for the polymerization of lactide

Des ligands diketimines porteurs de substituants N-benzyl, N-9-anthrylmethyl et N-mesitylmethyl (nacnacBnH, nacnacAnH, and nacnacMesH) ont été synthétisés par condensation d’une amine et d’acétyl acétone ou son monoacétal d’éthylène glycol. La chlorination de la position 3 a été effectuée à l’aide de N-chlorosuccinimide conduisant à la formation des ligands ClnacnacBnH et ClnacnacAnH. Cette même position 3 a également été substituée par un groupement succinimide par lithiation du nacnacBnH, suivi de la réaction avec le N-chlorosuccinimide (3-succinimido-nacnacBnH). Les ligands N-aryl nacnacippH et nacnacNaphH (ipp = 2-isopropylphenyl, Naph = 1-naphthyl) ont été préparés selon les procédures reportées dans la littérature. La réaction de ces ligands avec Zn(TMSA)2 (TMSA = N(SiMe3)2) conduit à la formation des complexes nacnacAnZn(TMSA) et ClnacnacBnZn(TMSA). La protonation avec l’isopropanol permet l’obtention des complexes nacnacAnZnOiPr et ClnacnacBnZnOiPr. La réaction avec Mg(TMSA)2 permet quant à elle la formation des complexes nacnacAnMg(TMSA), nacnacMesMg(TMSA), ClnacnacBnMg(TMSA) et ClnacnacAnMg(TMSA). La protonation subséquente à l’aide du tert-butanol permet l’obtention du nacnacMesMgOtBu et du ClnacnacBnMgOtBu, alors que l’on observe uniquement une décomposition avec les ligands possédant des substituants N-anthrylmethyl. La réaction de ces diketimines avec Cu(OiPr)2 conduit aux dimères hétéroleptiques [nacnacBnCu(μ-OiPr)]2 et [3-Cl-nacnacBnCu(μ-OiPr)]2 lors de l’usage des ligands stériquement peu encombrés. Lors de l’utilisation de ligands plus encombrés, la stabilisation du complexe hétéroleptique par dimérisation n’est plus possible, conduisant, par un échange de ligand, à la formation des complexes homoleptiques Cu(nacnacipp)2 et Cu(nacnacNaph)2. Les complexes homoleptiques Cu(nacnacBn)2 et Cu(3-succinimido-nacnacBn)2 ont été obtenus à partir des ligands N-benzyl. Les ligands encore plus encombrés tels que nacnacAnH, nacnacMesH ou ceux comportant des substituants N-methylbenzyl ne présentent alors plus de réactivité avec le Cu(OiPr)2. La plupart des complexes ont été caractérisés par Diffraction des Rayons X. Les complexes homoleptiques ainsi que ceux de TMSA sont monomériques, alors que ceux formés à partir d’alkoxides se présentent sous forme de dimères à l’état solide. Tous les complexes d’alkoxides ainsi que les nacnacAnMg(TMSA)/BnOH et ClnacnacAnMg(TMSA)/BnOH présentent une réactivité modérée à haute en matière de polymérisation du rac-lactide (90% de conversion en 30 secondes à 3 heures). Le nacnacAnZnOiPr permet la synthèse d’un polymère hautement hétérotactique (Pr = 0.90) quand le ClnacnacBnMgOtBu/BnOH génère un polymère isotactique à -30°C (Pr = 0.43). Tous les autres catalyseurs produisent des polymères atactiques avec une légère tendance hétérotactique (Pr = 0.48 – 0.55). Les complexes hétéroleptiques [nacnacBnCu(μ-OiPr)]2 et [3-Cl-nacnacBnCu(μ-OiPr)]2 se révèlent être de très bons catalyseurs pour la polymérisation du rac-lactide présentant une conversion complète du monomère à température ambiante, en solution, en 0,5 à 5 minutes. Le [nacnacBnCu(μ-OiPr)]2 est actif en présence ou absence d’isopropanol, agissant comme agent de transfert de chaine à haute activité (k2 = 32 M–1•s–1) dans le dichlorométhane. Dans l’acétonitrile, le THF, le dichloromethane et le toluène, [nacnacBnCu(μ-OiPr)]2 conduit à une étroite polydispersité, possédant respectivement des kobs = 2.4(1), 5.3(5), 3.6-4.4 and 10(1) min–1. Aucune réaction parasite, telle qu’une trans-esterification, une épimerisation ou une décomposition du catalyseur, n’a été observée. Les complexes homoleptiques en présence d’alcool libre semblent présenter un équilibre avec une petite quantité de leurs équivalents hétéroleptiques, permettant une polymérisation complète, en moins de 60 min, à température ambiante. Tous les catalyseurs de cuivre présentent un haut contrôle de la polymérisation avec une polydispersité égale ou inférieure à 1.1. Les polymères obtenus sont essentiellement atactiques, avec une légère tendance à l’hétérotacticité à température ambiante et -17°C. Le [nacnacBnCu(μ-OiPr)]2 polymérise également la -butyrolactone (BL), l’-caprolactone (CL) et la -valerolactone (VL) avec des constantes respectivement égales à kobs = 3.0(1)•10–2, 1.2–2.7•10–2, et 0.11(1) min–1. Les homopolymères présentent une étroite polydispersité d’approximativement 1.1. Les polymérisations par addition séquentielle ont mis en évidence une trans-estérification (non observée dans les homopolymérisations) si BL ou CL sont introduits après un bloc lactide.

Intermediate ion stability and regio selectivity polymerization using neutral salicyladiminato in propene nickel(II) and palladium(II) complexes as catalysts

The mechanism of the Heck reaction has been studied with regard to transition metal catalysis of the addition of propene and the formation of unsaturated polymers. The reactivity of nickel and palladium complexes with five different bidentate ligands with O,N donor atoms has been investigated by computational methods involving density functional theory. Hence, it is possible to understand the electronic and steric factors affecting the reaction and their relative importance in determining the products formed in regard of their control of the regiochemistry of the products. Our results show that whether the initial addition of propene is trans to O or to N of the bidentate ligand is of crucial importance to the subsequent reactions. Thus when the propene is trans to 0, 1,2-insertion is favoured, but when the propene is trans to N, then 2,1-insertion is favoured. This difference in the preferred insertion pathway can be related to the charge distribution engendered in the propene moiety when the complex is formed. Indeed charge effects are important for catalytic activity but also for regioselectivity. Steric effects are shown to be of lesser importance even when t-butyl is introduced into the bidentate ligand as a substituent. (C) 2007 Elsevier B.V. All rights reserved.

Spectroscopic study of the polymerization of intercalated anilinium ions in different montmorillonite clays

The polymerization of the intercalated aniline ions was studied in three different clays, Swy2-montmorillonite (MMT), synthetic mica-montmorillonite (Synl) and pillarized Swy2-montmorillonite (PILC). PANI is formed between the MMT and Syn1 clay layers, being confirmed by the shift of d(001) peak in the X-ray pattern. X-ray Absorption near to Si K edge (Si K XANES) data show that the structures of clays are preserved after the polymerization process and in addition to the SEM images show that morphologies of the clays are maintained after polymerization, indicating no polymerization in their external surface. UV-vis-NIR and resonance Raman data display that the PANI formed in Syn1 galleries has higher amount of phenazinic rings than observed for PANI intercalated in montmorillonite (MMT) clay. No polymer formation was detected in the PILC. N K XANES and EPR spectroscopies show the presence of azo and radical nitrogen in intercalated PAN! chains. Hence, the results are rationalized considering the structural differences between the clays for understanding the role of the anilinium polymerization within the clays galleries. (C) 2011 Elsevier B.V. All rights reserved.

Effect of addition of pigments and opacifier on the hardness, absorption, solubility and surface degradation of facial silicone after artificial ageing

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)