Poly(<Emphasis Type="Italic">n</Emphasis>-octyl methacrylate) viscosity index improver: Kinetic study via on-line <Superscript>1</Superscript>H-NMR technique

The free radical solution polymerization of n-octyl methacrylate has been studied in benzene-d ₆ in the presence of 2,2′-azobisisobutyronitrile as thermal initiator. An on-line nuclear magnetic resonance spectroscopy was applied to record the reaction data and to determine the monomer conversion at different times during the polymerization reaction. Effect of monomer and initiator concentration as well as reaction temperature on polymerization rate was studied. The order of the reaction with respect to initiator (0.45) was consistent with the classical kinetic rate equation, while the order of reaction with respect to monomer (1.87) was much greater than unity. An overall activation energy (E _a = 53.8 kJ/mol) was obtained over the temperature range 328?338 K. Also, the efficiency of the synthesized poly(n-octyl methacrylate) for improving the viscosity index of the lube oil was investigated.     

Kinetic modeling of two-step RAFT process for the production of novel fluorosilicone triblock copolymers

Well-defined poly(dimethylsiloxane)-b-poly(2,2,3,3,4,4,4-heptafluorobutylmethacryl-ate-b-poly(styrene) (PDMS-b-PHFBMA-b-PS) triblock copolymers were prepared by two-step reversible addition-fragmentation chain transfer (RAFT) polymerization. A comprehensive mathematical model for the two-step RAFT polymerization in a batch reactor was presented using the method of moments. The model described molecular weight, monomer conversion and polydispersity index as a function of polymerization time. Good agreements in the polymerization kinetics were achieved for fitting the kinetic profiles with the suggested model. In addition, the model was used to predict the effects of initiator concentration, chain transfer agent concentration and monomer concentration on the two-step RAFT polymerization kinetics. The simulated results showed that for the two-step RAFT polymerizations, the effects initiator concentration, chain transfer agent concentration and monomer concentration are identical and the influence degrees are different yet.     

Synthesis characterizations and properties of a new fluoro-maleimide polymer

Novel 4-(4-trifluoromethyl)phenoxy N-phenyl-maleimide (FPMI) was synthesized. The free radical-initiated polymerization of FPMI was carried out in 1,4-dioxane solution using azobisisobutyronitrile as initiator. The monomer was investigated by FTIR, ¹H NMR, ¹³C NMR and elemental analysis, while the polymer was investigated by FTIR, ¹H NMR and ¹³C NMR. The effect of the monomer concentration, initiator concentration and temperature on the rate of polymerization (R_p) was studied. The activation energy of the polymerization was calculated (ΔE = 48.94 kJ/mol). The molecular weight of PFPMI and polydispersity index of the polymer were determined by gel permeation chromatography and were equal to 73,500, 16,700 and 2.27, respectively. The properties of PFPMI, including thermal behavior, thermal stability, the glass transition temperature (T_g = 236 °C), photo-stability, solubility and solution viscosity were studied.     

On the inverse miniemulsion copolymerization and terpolymerization of acrylamide, <Emphasis Type="Italic">N,N′</Emphasis>-methylenebis(acrylamide) and methacrylic acid

The kinetics of free-radical copolymerization and terpolymerization of acrylamide (AAm), N, N′-methylenebis(acrylamide) (MBA) and methacrylic acid (MA) in the inverse water/monomer/cyclohexane/Tween 85 miniemulsion was investigated. Polymerizable sterically-stable miniemulsions were formulated in cyclohexane as a continuous medium. Polymerizations are very fast and reach the final conversion within several minutes. The dependence of the polymerization rate vs. conversion is described by a curve with two nonstationary rate intervals. The maximum rate of polymerization slightly increases with increasing concentration of crosslinking monomer (MBA) and strongly decreases by the addition of MA. The rate of polymerization is inversely proportional to the 0.9 ^th and 1.8 ^th power of the particle concentration without and with MA, respectively. The number of polymer particles is inversely proportional to the 0.18 ^th and 0.13 ^th power of MBA concentration. The kinetic and colloidal parameters of the miniemulsion polymerization are discussed in terms of microemulsion polymerization model.     

Kinetics of photopolymerization of acrylamide initiated by copper (II)–bis(amino acid) chelates in aqueous solution. II

The kinetics of photopolymerization reactions of acrylamide initiated by copper (II)–bis(amino acid) chelates with amino acids glutamic acid, serine, or valine were studied at 30°C. The extent of monomer conversion increases with increased initiator concentration and falls off after reaching a maximum. Analysis of the results shows that for lower concentrations of the initiator, the rate of monomer disappearance is proportional to light absorption fraction f[monomer] and the square root of the intensity. At higher concentrations of the initiator, the rate of monomer disappearance is proportional to F_ε/[initiator]^1/2; the monomer exponent is 1.5 and the intensity exponent 0.5. Mutual termination of the radicals is proposed at lower concentrations of the initiator; at higher concentrations of the initiator termination of the initiator radical by the copper (II) complex along with mutual termination occurs. The initiator radical species is identified from flash photolysis studies of these complexes as the Cu(I)-coordinated radical. The effect of pH on the monomer conversion is explained. The data indicate a free-radical mechanism of polymerization and a reaction scheme is proposed for the polymerization reactions.     

Influence of polymerization conditions on the molecular weight and polydispersity of polyepichlorohydrin

The influence of the relevant reaction conditions on the molecular weight and polydispersity during the cationic ring-opening polymerization of epichlorohydrin has been studied using an experimental design. The polymerization was conducted in the presence of an alcohol (diol and triol), a Lewis acid at two temperatures (5 °C and 25 °C), and with two monomer addition rates. FT-IR spectra were used for the chemical characterization of the polymer, and MALDI-TOF mass spectrometry was used to determine the oligomeric composition and the masses of the initiator or transfer agent. The FT-IR showed the characteristic peaks of polyepichlorohydrin, and the mass spectra indicate that the alcohol was incorporated in the polymer structure. The MW and polydispersity were determined using gel permeation chromatography. We observed that the two most significant parameters that affected MW were the monomer addition rate and the reaction temperature, whereas polydispersity was most strongly affected by the monomer addition rate.     

Radical polymerization of N-vinylcaprolactam in benzene solutions in a wide conversion range

The kinetics of radical polymerization of N-vinylcaprolactam initiated by the thermal decomposition of AIBN at 60°C in monomer solutions in benzene has been studied in a wide range of conversions. The heat of polymerization of N-vinylcaprolactam is 76.0 ± 0.9 kJ/mol; at initial conversions, the polymerization of N-vinylcaprolactam is of the first order with respect to the monomer and of the 0.5th order with respect to the initiator. The ratio of chain propagation and chain termination rate constants k _p/k _ter ^0.5 is 0.578 l^0.5/(mol s)^0.5, thus suggesting a high propagation rate constant k _p > 10³ l/(mol s). At a high initial concentration of the monomer, the kinetic curves demonstrate a weakly pronounced gel effect, and, in the gel permeation chromatography curves of the polymers, the second high-molecular-mass mode emerges, whose intensity grows with conversion. The observed kinetic features are interpreted in terms of the diffusion control of the gel effect.     

Polymerization of hex-1-ene initiated by diimine complexes of nickel and palladium

The effect of monomer concentration, reaction temperature and initiator structure on the activity, molar mass, branching and thermal properties of poly(hex-1-ene)s was investigated for the polymerization of hex-1-ene initiated by four α-diimine complexes of nickel and palladium. Hex-1-ene polymerization exhibits an apparent negative kinetic order with respect to monomer concentration. Polymerization of hex-1-ene initiated by MAO activated 1,4-bis(2,6-diisopropylphenyl)acenaphtenediiminenickel(II) dibromide (1a/MAO) proceeds in living-like fashion not only at sub-zero temperatures but even at 20 °C. However, molar masses of the polymers are higher than predicted values in agreement with an initiator efficiency lower than one.     

The influence of small additives of arenes on low-temperature isobutylene polymerization in an aliphatic solvent

Isobutylene polymerization in hexane at –78 °C initiated by the methanol—aluminum bromide and tert-butyl chloride—aluminum bromide systems in the presence of minor additives (to 10 mmol L^–1) of arenes (benzene, chlorobenzene, toluene, and mesitylene) was studied. The addition of the arenes to a monomer solution has virtually no effect on the polymer yield, whereas the preliminary interaction of a concentrated solution of the Lewis acid with benzene and chlorobenzene sharply increases the monomer conversion and initiation efficiency. The results are interpreteted within a mechanism involving the participation of arene - and -complexes in initiation. The concentration of the complexes is determined by the order of arene addition, and the activity and stability are related to their nature. In these experiments, hexafluorobenzene unexpectedly exhibited a pronounced inhibiting ability.     

Mechanism of the polymerization of trifluoroacetaldehyde initiated by azobisisobutyronitrile

The polymerization of fluoral initiated by the photolyzed decomposition of azobisisobutyronitrile at low temperature has been studied. Up to 2% conversion, the effect of radical scavengers and the order with respect to initiator and light intensity indicate that the reaction occurs by a conventional radical polymerization mechanism. At about 2% conversion autoacceleration sets in and the rates become irreproducible. This is explained by typical occlusion phenomena. Tracer studies show that polymer prepared at high conversion contains initiator fragments indicating that primary propagation is by monomer addition to radicals. The reaction mechanism is discussed.     

Direct and inverse neural network modeling in free radical polymerization

The first part of this paper reviews of the most important aspects regarding the use of neural networks in the polymerization reaction engineering. Then, direct and inverse neural network modeling of the batch, bulk free radical polymerization of methyl methacrylate is performed. To obtain monomer conversion, number and weight average molecular weights, and mass reaction viscosity, separate neural networks and, a network with multiple outputs were built (direct neural network modeling). The inverse neural network modeling gives the reaction conditions (temperature and initial initiator concentration) that assure certain values of conversion and polymerization degree at the end of the reaction. Each network is a multi-layer perceptron with one or two hidden layers and a different number of hidden neurons. The best topology correlates with the smallest error at the end of the training phase. The possibility of obtaining accurate results is demonstrated with a relatively simple architecture of the networks. Two types of neural network modeling, direct and inverse, represent possible alternatives to classical procedures of modeling and optimization, each producing accurate results and having simple methodologies.     

Ring-opening polymerization of ε-caprolactone initiated by diphenylzinc

In the present work the polymerization of ε-caprolactone (ε-CL) using Ph₂Zn as initiator is reported. The effects of reaction temperature, molar ratio of monomer/initiator and reaction time on the yield and the molecular weight are investigated. The temperature is varied between 20 and 120 °C and the molar ratio of monomer to initiator between 200 and 800 mol/mol. The results indicate that the Ph₂Zn induces the polymerization of ε-CL to high conversion and produces polymer with high molecular weight at temperatures around 40-60 °C.     

Mathematical Modeling of Atom‐Transfer Radical Polymerization Using Bifunctional Initiators

Summary: Bifunctional initiators can produce polymers with higher molecular weight at higher initiator concentrations than monofunctional initiators. In this study, we developed a mathematical model for ATRP with bifunctional initiators. The most important reactions in ATRP were included in the model. The method of moments was used to predict monomer conversion, average molecular weights and polydispersity index as a function of polymerization time in batch reactors. The model was used to understand the mechanism of ATRP and to quantify how polymerization conditions affect monomer conversion and polymer properties by examining the effect of several rate constants (activation, deactivation, propagation and chain termination) and of catalyst and initiator concentration on polymerization kinetics and polymer properties. When compared to monofunctional initiators, bifunctional initiators not only produce polymers with higher molecular weight averages at higher polymerization rates, but also control their molecular weight distributions more effectively.

Effect of initial catalyst concentration on polydispersity index as a function of time.     

Investigation of the Gel Effect in Reactive Extrusion Processes for Free Radical Polymerization

The gel effect in the reactive extrusion process for free radical polymerization in a closely intermeshing co‐rotating twin screw extruder was investigated. First the reaction kinetic model was constructed mainly on the basis of entanglement theory. Next, numerical calculation expressions for the initiator and monomer concentrations, monomer conversion, average molecular weight and apparent viscosity were deduced. Finally, the evolution of the above variables were shown and discussed for the example of butyl methacrylate. The simulated results of the monomer conversion are in good agreement with experimental results.

     

Emulsion polymerization of styrene. I. Review of experimental data and digital simulation

Isothermal emulsion polymerization at 60°C of styrene in a batch reactor were studied by using sodium lauryl sulfate as surfactant and potassium persulfate as initiator source. The concentrations of surfactant and initiator were varied during the runs. The polymerization evolution was followed as samples were taken at regular intervals. These emulsion samples were analyzed for monomer conversion, rate of polymerization, as well as for the size and the size distribution of the particles. The molecular weight and molecular weight distribution were obtained by gel permeation chromatography. Our study showed that fresh nucleation takes place even at high conversion, causing a continuous shifting toward broadening of particle size distribution. Contrary to the theory of Smith and Ewart, which assumes a constant number of particles during interval II of the polymerization reaction, our digital simulation of the reaction presents better experimental results with a variable number of particles, and indicates that the Hui–Hamielec model for termination constant k_t as function of conversion is not applicable under our working conditions.     

丁基锂引发的活性宽分布聚双烯烃的合成

<正> 用烷基锂引发的丁二烯“活性”聚合,通常只能得到分子量分布较窄的聚合物。这类聚合物的门尼粘度较高,不易加工,且易冷流。为了解决这些问题,一般是合成分子量分布较宽且有一定支化的聚合物。但在以往的合成宽分布聚合物的方法中,大多只能得到非“活性”聚双烯烃,因而无法进行“活性”高分子的一些典型反应,如嵌段、接枝及偶     

Free Radical Ring-Opening Polymerization of 4-n-Hexyl- and 4-n-Decyl-2-methylene-1,3-dioxolanes

Two alkyl-substituted cyclic ketene acetals, 4-n-hexyl-2-methylene-1,3-dioxolane (4) and 4-n-decyl-2-methylene-1,3-dioxolane (6), were shown to undergo free radical ring-opening polymerization with the introduction of an ester group into the backbone of an addition polymer. The spontaneous polymerization of 4 (presumable by an ionic mechanism) produced a polymer containing no ring-opened units; furthermore 4 and 6 could be stabilized with respect to spontaneous polymerization by the addition of small amounts of pyridine. On the other hand, the polymerization of 4 in a 50% (by weight) benzene solution at 110°C with di-tertbutyl peroxide as the catalyst gave quantitative ring opening to give a polyester containing both possible isomeric ring-opened units. Bulk polymerization of 4 at 60°C at 53% conversion gave 50% ring opening which was divided 31% to 19% between cleavage to give the intermediate secondary free radical and the intermediate primary radical. Copolymerization of 4 with equimolar quantities of styrene at 110°C gave at 56% conversion a copolymer consisting of 67% styrene units, 22% ester-containing units resulting from cleavage to form a secondary radical, 7% of the isomeric ester-containing units, and 4% nonring-opened units. Polymerization studies with monomer 6 gave results very similar to those obtained with 4.     

Synthesis and utilization of alternative chain transfer agent in cobalt catalyzed 1,3-butadiene polymerization reaction to produce cis-polybutadiene rubber

The cyclodimerization of 1,3-butadiene was performed to synthesize 1,5-cyclooctadiene by using nickel-phosphite based catalyst system. The optimization of cyclodimerization reaction was done to achieve up to 80% selectivity towards 1,5-cyclooctadiene. 1,5-Cyclooctadiene, thus synthesized, was subsequently employed as a chain transfer agent (CTA) for controlling the molecular weight (M.W.) of cis-polybutadiene rubber (BR) in cobalt-complex catalyzed 1,3-butadiene polymerization reaction. The M.W. of BR was reduced from 6.7 to 1.88 × 10⁵ g/mol by escalating the concentration of 1,5-cyclooctadiene from 0% to 0.5% with respect to 1,3-butadiene (monomer) concentration. Similar reducing trend was observed for the Mooney viscosity and gel content of BR with increasing 1,5-cyclooctadiene concentration. The efficacy of 1,5-cyclooctadiene as a CTA for 1,3-butadiene polymerization reaction was further explored by conducting polymerization reaction in various solvents and at higher monomer conversion (∼70%). The effect of 4-vinyl cyclohexene, which was a dominant byproduct during cyclodimerization of 1,3-butadiene, was also investigated. The presence of 4-vinyl cyclohexene has shown adverse effect in the polymerization reaction and was not functioning as a chain transfer agent. Finally, a feasibility of replacement of commercially used gaseous CTA, 1,2-butadiene, by in-house synthesized liquid CTA, 1,5-cyclooctadiene, was also investigated.     

Atom transfer radical polymerization of N‐vinyl carbazole: Optimization to characterization

The homopolymerization of N‐vinylcarbazole was performed with atom transfer radical polymerization (ATRP) with Cu(I)/Cu(II)/2,2′‐bipyridine (bpy) as the catalyst system at 90 °C in toluene. N‐2‐Bromoethyl carbazole was used as the initiator, and the optimized ratio of Cu(I) to Cu(II) was found to be 1/0.3. The resulting homopolymer, poly(N‐vinylcarbazole) (PVK), was formed after a monomer conversion of 76% in 20 h. The molecular weight as well as the polydispersity index (PDI) showed a linear relation with the conversion, which showed control over the polymerization. A semilogarithmic plot of the monomer conversion with time was linear, indicating the presence of constant active species throughout the polymerization. The initiator efficiency and the effect of the variation of the initiator concentration on the polymerization were studied. The effects of the addition of CuBr₂, the variation of the catalyst concentration with respect to the initiator, and CuX (X = Br or Cl) on the kinetics of homopolymerization were determined. With Cu(0)/CuBr₂/bpy as the catalyst, faster polymerization was observed. For a chain‐extension experiments, PVK (number‐average molecular weight = 1900; PDI = 1.24) was used as a macroinitiator for the ATRP of methyl methacrylate, and this resulted in the formation of a block copolymer that gave a monomodal curve in gel permeation chromatography. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1745–1757, 2006     

Controlled Radical Polymerization of Furfuryl Methacrylate

Atom transfer radical polymerization provides a new method of controlled radical polymerization. The most important advantage of ATRP is that it is tolerant to the different functional groups present in the initiator as well as in the monomer. Furfuryl Methacrylate (FMA) is a specialty monomer, which has applications in coatings, adhesives and in biomedicals. Conventional radical polymerization of FMA leads to excessive gel formation, which limits its applications. In this investigation homo and co-polymerization of FMA has been carried out via ATRP. ATRP of FMA was carried out using CuBr as catalyst and 1, 1, 4, 7, 10, 10 hexamethyltriethylenetetramine (HMTETA) as ligand. There was no gel formation during the polymerization. ATRP of FMA was well controlled with a linear increase of molecular weight (Mn) with monomer conversion. The polymers were characterized by using ¹HNMR, FT-IR and GPC analysis. Interestingly, it was observed that the furfuryl ring was not affected during polymerization.