Radiation-induced emulsion polymerization of ethylene. III. Emulsion polymerization with ammonium perfluorooctanoate as the emulsifier

Radiation-induced emulsion polymerization of ethylene with ammonium perfluoro-octanoate as an emulsifier was studied in order to elucidate the effect of the number of polymer particles. Owing to the stable structure of the emulsifier from a radical attack, no C? F bond was detected in the polyethylene as expected. The polyethylene produced was mostly gel containing a small amount of low molecular weight polyethylene. This may be attributable to chain transfer to the polyethylene. The effects of dose rate and of concentration of the emulsifier were determined without considering the chain-transfer reaction to the emulsifier. By considering the escape of the radical which is produced by chain transfer to the monomer from the polymer particle to the aqueous phase at the steady state, the following equation is derived: The experimental results could be explained by this equation, and the apparent rate constants were obtained.     

Stoichiometric formation of methyl methacrylate oligomer by triethylaluminum in the presence of azobisisobutyronitrile

The yield of methyl methacrylate (MMA) polymerization as a function of triethylaluminum (TEA) concentration for a constant azobisisobutyronitrile (AIBN) concentration at 50°C has been measured. The polymerization yield does not differ markedly from that with AIBN alone as long as the initial TEA concentration is held smaller than four times the initial AIBN concentration. A sudden decrease in yield and molecular weight is observed at TEA/AIBN concentration ratios between 4 and 5. A plot of M?_w^?1 vs. TEA gives a rate-transfer constant of 89 1./mole-sec. If the reaction mixture is vacuum-evaporated with a previous addition of water, instead of precipitating the polymer, the formation of a considerable amount of MMA oligomer is detected for TEA/AIBN concentration ratios larger than 4. On the average, each TEA molecule in excess of four times the initial amount of AIBN yields one oligomer molecule. The data are consistent with a radical polymerization mechanism for the high molecular weight polymer and with a nonradical one for the oligomer formation.     

Free-radical polymerization of methyl methacrylate in the presence of dithiobenzoates as reversible addition-fragmentation chain transfer agents

The pseudoliving radical polymerization of methyl methacrylate in bulk mediated by dithiobenzoates with various leaving groups as reversible addition-fragmentation chain-transfer agents has been studied. It has been shown that polymerization proceeds under conditions of the low steady-state concentration of radical intermediates; as a result, the steady-state of the process is rapidly achieved even at low conversions. Retardation of polymerization observed at high concentrations of reversible addition-fragmentation chain-transfer agents is apparently associated with the occurrence of chain termination reactions involving intermediates, as evidenced by the model reaction. The autoacceleration of polymerization is suppressed with an increase in the concentration of reversible addition-fragmentation chain-transfer agents. An efficient approach to the synthesis of a narrow-dispersed PMMA with the controlled molecular mass has been suggested.     

Vinyl monomer polymerization mechanism in the presence of trialkylboranes

The polymerization of methyl methacrylate in the presence and in the absence of triethylborane and different inhibitors was carried out. An ethyl radical displacement reaction between the inhibitor radical (produced through the reaction between a radical chain and the inhibitor) and the triethylborane is postulated. This new chain-transfer reaction explains the large excess of inhibitor which must be added in the presence of triethylborane in order to suppress the production of high molecular weight polymer. The results are in agreement with a typical free-radical mechanism.     

Effect of formaldehyde on the cationic polymerization of styrene

Polymerization of styrene has been carried out in the presence of formaldehyde at 30°C in benzene solution by using boron trifluoride etherate as a catalyst. The rate of polymerization in the initial stage was accelerated with addition of formaldehyde, while the steady-state rate of polymerization was retarded in the presence of formaldehyde. The acceleration for the rate of polymerization was found only in a short time from the beginning. The steady-state rate of polymerization followed the equation: where [C]₀ and [F]₀ are initial concentrations of catalyst and formaldehyde, [M] is the monomer concentration, and k₁, k₂, and k₃ are constants. It has been assumed that the chain-transfer reaction does not involve formaldehyde itself but rather the reaction products of formaldehyde, such as polystyrene having ethoxy or hydroxymethyl ends. The apparent chain-transfer constant for the added formaldehyde has been determined to be 1.63.     

Kinetic study of the alternating copolymerization of butadiene and methyl methacrylate

A kinetic investigation of the alternating copolymerization of butadiene and methyl methacrylate with the use of a system of ethylaluminum dichloride and vanadyl chloride as a catalyst was undertaken. The relation between the polymer yield and the molar fraction of methyl methacrylate in the feed was examined by continuous variation of butadiene and methyl methacrylate, the concentrations of total monomer, ethylaluminum dichloride, and vanadyl chloride being kept constant. This continuous variation method revealed that the polymer yield attains its maximum value with a monomer feed containing less than the 0.5 molar fraction of methyl methacrylate. This value of the molar fraction of methyl methacrylate affording the maximum polymer yield decreased on increasing the total monomer concentration but was not changed on varying the concentration of ethylaluminum dichloride. The number of active species estimated from the relation between yield and molecular weight of the polymer was almost constant, regardless of the molar fraction of methyl methacrylate in the feed. Consequently, it can be said that the maximum polymer yield depends mainly on the propagation reaction, not on the initiation reaction or the termination reaction. Three types of the mechanism have been discussed for this alternating copolymerization: polymerization via alternating addition of butadiene and methyl methacrylate complexed with ethylaluminum dichloride by the Lewis-Mayo scheme; polymerization via the ternary intermediate of butadiene, methyl methacrylate, and ethylaluminum dichloride; polymerization via the complex formation of butadiene and methyl methacrylate complexed with ethylaluminum dichloride occurring only at the growing polymer radical. From the kinetic results obtained, it was shown that the first and third schemes are excluded, and polymerization by way of the ternary intermediate is compatible with the data.     

Controlled synthesis of oligomeric poly(acrylic acid) and its behavior in aqueous solutions

The controlled synthesis of oligomeric poly(acrylic acid) via the pseudoliving radical reversible addition-fragmentation chain-transfer polymerization of acrylic acid in bulk is developed. It is shown that, at high concentrations of reversible addition-fragmentation chain-transfer agents, the polymerization of acrylic acid in bulk occurs via the pseudoliving mechanism, as evidenced by a linear increase in the numberaverage molecular mass of oligomers with conversion and a narrow molecular-mass distribution of the reaction products. The surfactant properties and behavior of the oligomers in aqueous solutions are studied.     

Gas-phase polymerization of propylene: Reaction kinetics and molecular weight distribution

Gas-phase polymerizations have been executed at different temperatures, pressures, and hydrogen concentrations using Me₂Si[Ind]₂ZrCl₂ / methylaluminoxane / SiO₂(Pennsylvania Quarts) as a catalyst. The reaction rate curves have been described by a kinetic model, which takes into account the initially increasing polymerization rate. The monomer concentration in the polymer has been calculated with the Flory–Huggins equation. The kinetic parameters have been determined by fitting the reaction rate curves with the model. At high temperatures, pressures, and hydrogen concentrations a runaway on particle scale may occur leading to reduced polymer yields. The molecular weight and molecular weight distribution of the polymer samples could be described by a “two-site model.” At constant temperature the chain-transfer probability of sites 1 and 2 depends only on the hydrogen concentration divided by the monomer concentration. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 500–513, 2001     

Hybrid atom transfer radical polymerization system for balanced polymerization rate and polymer molecular weight control

A hybrid polymerization system that combines the fast reaction kinetics of conventional free radical polymerization and the control of molecular weight and distribution afforded by ATRP has been developed. High‐free radical initiator concentrations in the range of 0.1–0.2 M were used in combination with a low concentration of ATRP catalyst. Conversions higher than 90% were achieved with ATRP catalyst concentrations of less than 20 ppm within 2 h for the hybrid ATRP system as compared with ATRPs where achieving such conversions would take up to 24 h. These reaction conditions lead to living polymerizations where polymer molecular weight increases linearly with monomer conversion. As in living polymerization and despite the fast rates and low ATRP catalyst concentrations, the polydispersity of the produced polymer remained below 1.30. Chain extension experiments from a synthesized macroinitiator were successful, which demonstrate the living characteristics of the hybrid ATRP process. Catalyst concentrations as low as 16 ppm were found to effectively mediate the growth of over 100 polymer chains per catalytic center, whereas at the same time negating the need for post polymerization purification given the low‐catalyst concentration. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2294–2301, 2010     

Cationic polymerization of formaldehyde in liquid carbon dioxide. Part I

A cationic polymerization of formaldehyde which gave a high molecular weight polymer was studied in liquid carbon dioxide at 20–50°C. In the polymerization without any catalyst both the rate of polymerization and the molecular weight of the resulting polymer increased rapidly with a decrease in the loading density of the monomer solution to the reaction vessel, and also increased with an increase in the initial monomer concentration. From these results it was concluded that the initiating species could be ascribed to an impurity contained in the monomer solution. Both the rate of polymerization and the degree of polymerization of the polymer also increased with rising temperature. The carboxylic acid added acted as a catalyst in the polymerization because of increase in the polymer yield, the molecular weight of polymer formed, and the number of moles of polymer chain with increasing dissociation constant of acid used. It was concluded that the polymerization in liquid carbon dioxide proceeded by a cationic mechanism. Methyl formate had no influence on the polymerization, but methanol and water acted as a chain-transfer agent.     

Controlled radical polymerization of styrene and <Emphasis Type="Italic">n</Emphasis>-butyl acrylate mediated by trithiocarbonates

The free-radical bulk homopolymerization of styrene and n-butyl acrylate at 80°C mediated by dibenzyl trithiocarbonate, poly(styryl) trithiocarbonate, or poly(n-butyl acrylate) trithiocarbonate as reversible addition-fragmentation chain-transfer agents has been studied. It has been shown that the use of low-and high-molecular-mass reversible addition-fragmentation chain-transfer agents makes it possible to efficiently control the molecular-mass characteristics of polymers. In the case of styrene, the rate of polymerization slightly depends on the concentration of the addition-fragmentation chain-transfer agent. In contrast, for the polymerization of n-butyl acrylate, the rate significantly decreases with the concentration of the chain-transfer agent. Formation of radical intermediates during the polymerization of styrene and n-butyl acrylate mediated by trithiocarbonates has been studied by ESR spectroscopy. It has been demonstrated that the polymeric chain-transfer agents are efficient for the synthesis of block copolymers with the controlled block length.     

Electroinitiated polymerization of acrylamide in acetonitrile medium

The electroinitiated polymerization of acrylamide (AA) has been studied in acetonitrile medium using tetrabutylammonium perchlorate (TBAP) as the electrolyte. Split-cell experiments showed that the polymer formation takes place both in the anode and the cathode compartments. The polymer yield depends on several factors such as the magnitude of the current flow, the duration of the electrolysis, the monomer concentration, the electrolyte concentration, the temperature of the solution, presence or absence of air, and finally whether or not the cell content was stirred. The current exponent of the polymerization was 0.28 with a reaction rate constant of 1.06 reaction % per hour. The IR and NMR spectra of the polymers suggest that the anodic polymer is polyacrylamide and the cathodic polymer is poly-β-alanine (? CH₂? CH₂? CO? NH? ). Based on the experimental results, a radical mechanism for the anodic polymerization and an anionic mechanism for the cathodic polymerization have been proposed.     

Kinetics of two-phase bulk polymerization. II. The influence of dissolved polymer

The effect of dissolved polybutadiene on the initial rate of polymerization of styrene was investigated by using high-precision dilatometric techniques. The dissolved polymer reduced the rate of polymerization by amounts greater than can be accounted for by a reduction in monomer concentration. Rate reductions increased with the amount of dissolved polybutadiene and with its molecular weight and were greater for benzoyl peroxide initiator than for equal concentrations of azobisisobutyronitrile. Surprisingly, analogous rate reductions were observed when polystyrene were substituted for the polybutadienes, except that at high polystyrene concentrations, the expected autoacceleration was observed. These rate reductions showed no correlation with the viscosity of the reaction mass, nor did the dissolved polymer affect initiator efficiency. At a given level of a particular dissolved polybutadiene, rate reductions were diminished by increasing levels of each initiator, and by adding a chain-transfer agent. Good quantitative agreement was obtained with the number-average length of the growing polymer chains, whether varied by using different initiators, changing initiator level, or adding chain-transfer agent. These results are inconsistent with a chemical mechanism, but they are explained by a proposal originated by North and Reed whereby the dissolved polymer makes the reaction mass a “poorer” solvent for the growing polymer chains, reducing their overall coil dimensions and enhancing their rate of diffusion together for termination.     

Microemulsion polymerization of styrene in the presence of a cationic emulsifier

The principal subject discussed in the current paper is the radical polymerization of styrene in the three- and four component microemulsions stabilized by a cationic emulsifier. Polymerization in the o/w microemulsion is a new polymerization technique which allows to prepare the polymer latexes with the very high particle interface area and narrow particle size distribution. Polymers formed are very large with a very broad molecular weight distribution. In emulsion and microemulsion polymerizations, the reaction takes place in a large number of isolated loci dispersed in the continuous aqueous phase. However, in spite of the similarities between emulsion and microemulsion polymerization, there are large differences caused by the much larger amount of emulsifier in the latter process. In the emulsion polymerization there are three rate intervals. In the microemulsion polymerization only two reaction rate intervals are commonly detected: first, the polymerization rate increases rapidly with the reaction time and then decreases steadily. Essential features of microemulsion polymerization are as follows: (1) polymerization proceeds under non-stationary state conditions; (2) size and particle concentration increases throughout the course of polymerization; (3) chain-transfer to monomer/exit of transferred monomeric radical/radical re-entry events are operative; and (4) molecular weight is independent of conversion and distribution of resulting polymer is very broad. The number of microdroplets or monomer-starved micelles at higher conversion is high and they persist throughout the reaction. The high emulsifier/water ratio ensures that the emulsifier is undissociated and can penetrate into the microdroplets. The presence of a large amount of emulsifier strongly influences the reaction kinetics and the particle nucleation. The mixed mode particle nucleation is assumed to govern the polymerization process. At low emulsifier concentration the micellar nucleation is dominant while at a high emulsifier concentration the interaction-like homogeneous nucleation is operative. Furthermore, the paper is focused on the initiation and nucleation mechanisms, location of initiation locus, and growth and deactivation of latex particles. Furthermore, the relationship between kinetic and molecular weight parameters of the microemulsion polymerization process and colloidal (water/particle interface) parameters is discussed. In particular, we follow the effect of initiator and emulsifier type and concentration on the polymerization process. Besides, the effects of monomer concentration and additives are also evaluated.     

Controlled free-radical polymerization of methyl acrylate in the presence of a cyclic trithiocarbonate under γ-ray irradiation at low temperature

Controlled radical polymerization of MA has been achieved in the presence of a cyclic trithiocarbonate, 1,5-dihydro-2,4-benzodiehiepine-3-thione, under γ-ray irradiation (60 Gy/min) at low temperature. The narrow molecular weight distributions and the linear kinetics curve indicate that the polymerization is a controlled free-radical process at low temperature (especially at −76 °C). The structures of resultant polymers were characterized by matrix assisted laser desorption/ionization time-of-flight mass spectrometry, and the results show that cyclic polymers can be formed at −76 °C, which may result from the reduced diffusion rate and the suppressed chain-transfer reaction at the lower temperature. It is further evidenced that the good control of the polymerization at the lower temperature may be associated with the suppressed chain-transfer reaction, not like reversible addition-fragmentation transfer polymerization. The linear polymers probably result from the polymer chain radicals reacting with the radicals produced by the interaction of the irradiation and the monomer.     

Construction of a polymer skeleton that is cut in half by ionizing radiation

Polystyrene with a benzyl ester of carboxylic acid at the center of a polymer skeleton was synthesized by living radical polymerization. The initiator used had two functional groups for 2,2,6,6‐tetramethylpiperidinoxyl (TEMPO)‐mediated living radical polymerization on the benzyl and the carboxylic sides of the benzyl ester. Introduction of the benzyl ester changed the polystyrene from a crosslink type to a scission type polymer on γ‐irradiation. Irradiation of the polymer resulted in a binary change of the molecular weight because of the dissociative capture of secondary electrons by the benzyl ester, as: The binary change of the molecular weight suggests that the polymer can be used as a new type of radiation resist with high sensitivity and spatial resolution to ionizing and high resistivity to plasma etching. The number of scissions per 100 eV radiation energy absorbed was 0.29, which was about one fourth of the yield of secondary electrons. The low efficiency was because of the recombination of polymer radicals generated by the dissociative electron attachment. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1068–1075, 2005     

Controlled synthesis of acrylic homo- and copolymers in the presence of trithiocarbonates as reversible addition-fragmentation chain transfer agents

Formation of homo- and copolymers of various structures (random and block) based on tert-butyl acrylate and n-butyl acrylate via polymerization mediated by trithiocarbonates as reversible addition-fragmentation chain-transfer agents has been studied. The process is found to proceed according to a three-stage mechanism. As a result, it is possible to synthesize symmetric triblock copolymers with the use of polymer trithiocarbonates; the polymer reversible addition-fragmentation chain transfer agent predetermines the composition and molecular mass of end blocks, the composition of the monomer mixture determines the structure of the central block, and the concentration of the agent and the conversion of the monomers define its molecular-mass characteristics. The modification of polymerization products gives rise to amphiphilic copolymers.     

Copper‐mediated initiators for continuous activator regeneration atom transfer radical polymerization of acrylonitrile

Initiators for continuous activator regeneration atom transfer radical polymerization technique was first accessed to acrylonitrile by using CuBr₂/2,2′‐bipyridine as the catalyst, ethyl 2‐bromoisobutyrate as the halogen initiator, and azobis(isobutyronitrile) as the free radical initiator. The key to success is ascribed to the facile achievement of the rapid equilibrium between active species and dormant species. Effects of ligand, catalyst concentration, free radical initiator concentration, and reaction temperature on the polymerization reaction and molecular weight (MW) as well as polydispersity index (PDI) were investigated in detail. The polymerization proceeded in a controlled/living fashion even though the concentration of copper catalyst decreased to 50 ppm, which is evident in pseudo first‐order kinetics of polymerization, linear increase of molecular weight, low PDI, and high chain‐end functionality of the generated polymer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Studies on addition polymerization in mixed solvent system. Part I. Chain transfer of water in polymerization of methyl methacrylate

The role of water as a chain-transfer agent in addition polymerization of methyl methacrylate and acrylamide in a mixed solvent system was studied. Water does not have any transfer with the growing polymer radical. The degree of polymerization is found to increase with increasing water concentration. This is probably due to a reduced termination rate resulting from coiling of the polymer chain in the presence of a nonsolvent like water.     

Copolymerization of acrylonitrile with itaconic acid in dimethylformamide: effect of triethylamine

The copolymerization of acrylonitrile (AN) in dimethylformamide (DMF) was retarded by the presence of itaconic acid (IA) comonomer. Addition of TEA helped overcome the retardation at enhanced concentrations of IA in the feed. The monomer reactivity ratios determined by both terminal and penultimate models revealed that the overall monomer reactivity’s are practically unaffected by the presence of TEA. The penultimate-unit effect for radicals terminated in AN was enhanced by the presence of TEA. Higher TEA concentrations helped regain the reactivities of AN and IA to AN-radical to the state in pure DMF. The penultimate model could explain the feed-copolymer composition profile for the whole range. Whereas IA systematically retarded the polymerization rate at all concentration regime in DMF, it increased the rate at higher IA concentration in DMF/TEA system. For a given IA concentration, the polymerization rate decreased as the solvent is enriched in TEA. The copolymers synthesized in the presence of TEA, manifested higher cyclization temperature and consequently lower char residue, attributed to the incorporation of TEA in the polymer by means of salt formation with IA moiety camouflaging the catalytic effect of the -COOH group in cyclization reaction. ¹³C-NMR studies confirmed the incorporation of the TEA molecules in the polymer chain.