Principles of Polymer Design and Synthesis pp Cite as.
New technology of Inhibition for Styrene Polymerization (TISP)
The polymerization of unsaturated monomers typically involves a chain reaction. In a chain polymerization, one act of initiation may lead to the polymerization of thousands of monomer molecules. High molecular weight molecule formed at the end of reaction, change with time. Polymer growth is terminated at some point by destruction of the reactive center by an appropriate reaction depending on the type of reactive center and the particular reaction conditions.
Some commercial chain-growth vinyl polymers prepared by free radical polymerization [ 12 ]. Open image in new window. Sheets, films, bottles, toys and house wares, wire and cable, coverings, shipping containers, insulation.
Carpeting, car and truck parts, packaging, toys, house wares, pipes, insulation. Packaging and containers Styrofoamtoys, appliance parts, disposable food containers and utensils, insulation. Plastic pipe and pipe fittings, films and sheets, floor tile, records, coatings, building materials, insulation.
The head-to-tail placement is predominant, since successive propagations by Eq. The propagating radical radical II formed by attachment of a radical at carbon 2 is the more stable one. The radical II can be stabilized by the resonance effects of the X and Y substituents.
The substituents cannot stabilize radical I, since they are not attached to the carbon bearing the unpaired electron. Furthermore, the attachment of a propagating radical at the unsubstituted carbon 2 of a monomer molecule is much less sterically hindered compared with the attachment at the substituted carbon 1.
A propagation proceeding with predominantly H—T placement is a regioselective process, that is, one orientation H—T is favored over another H—H.
The term isoregic has been used to indicate a polymer structure with exclusive head-to-tail placements. The terms syndioregic and aregic are used for polymer structures with alternating and random arrangements, respectively, of H—T and H—H placements. These theoretical predictions have been experimentally verified for a number of polymers. The extent of H—H replacement in fluoro polymers [ 3 ]. Reaction temperature effect on the extent of H—H replacement of polymer [ 3 ].
Ideally, the initiators should be relatively stable at room temperature but should decompose rapidly enough at polymer processing condition to ensure a practical reaction rate. A large number of free radical initiators are available [ 234 ]; they may be classified into three major types: 1 thermal initiators including peroxides and azo compounds, 2 redox initiatorsand 3 photoinitiatorscertain compounds that form radicals under influence of light.
Electrons can be used as initiating agent to generate radical ions for chain polymerization.These metrics are regularly updated to reflect usage leading up to the last few days. Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts. The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online.
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Cited By. This article is cited by 25 publications. Bockstaller, Krzysztof Matyjaszewski.
Macromolecules52 22 Bockstaller, and Krzysztof Matyjaszewski. Macromolecules47 16 Macromolecules35 7 Macromolecules29 12 Macromolecules, 28, Macromolecules29 15The first free radically synthesized polymers were produced between and by initiation with peroxy compounds.
In the s the systematic investigation of azo compounds as free radical initiators followed.
Compounds with labile C—C-bonds were investigated as initiators only in the period from the end of the s until the early s. At about the same time, iniferters with cleavable S—S-bonds were studied in detail.
In technical polymerization processes, peroxy compounds play since about years the most important role beside about 60 years old redox systems and the azo initiators. Since about 30 years, the modern possibilities to control free radical polymerization reactions especially by suppressing termination and transfer processes attract increasing attention and technical interest, even if their share in the total polymer production is still rather small.
In most textbooks and monographs on free radical polymerization, only very few if at all is said on the history of this part of macromolecular chemistry. Therefore, the following review deals mainly with the development of initiation of free radical polymerization processes and the most important initiator classes.
Due to the limitation to history of the initiating systems, the more recent developments in theory and details of the mechanisms and the kinetics of free radical polymerization processes will not be discussed. This term soon came in general use. So a chemical dictionary of the s offered the following, very modern sounding definition:.
He discussed three possibilities to initiate such reactions. As far back to the early days of the modern valence theory, organic chemists discussed the possible existence of free radical species and attempted to isolate them or at least their direct reaction products.
In the s, Charles Adolphe Wurtz proposed that the reaction of sodium with alkyl iodides RI produced compounds with empirical formulas corresponding to alkyl radicals :. But in his experiments the obtained gases did not contain the free radicals but their dimers, as was deduced from their vapour densities. In the following years with its success in explaining many of the known aspects of organic chemistry in terms of tetravalent carbon, little effort was made to isolate organic free radicals until the turn of the century.
Since this invention, the existence of free radicals soon became a part of organic chemistry. However, it lasted almost about forty years before the importance of free radicals as species with unpaired electrons and as short-living reaction intermediates began to be fully accepted. In a paper ofStaudinger et al. In Flory described the kinetics of the vinyl polymerization as a chain reaction with participation of free radicals and postulated that two active growing chains can be terminated only by bimolecular combination or disproportionation reactions [ 7 ].
In all these cases it is not clear to which extent the presence of molecular oxygen took part in these reactions.
Probably the earliest description of a polymerization process was given by Simon [ 9 ] in He isolated styrene from storax, a liquid product from a plane tree liquidamber orientalis and observed that the liquid during storing became more and more viscous and finally a glass-like solid. Blyth and Hofmann also observed that this metastyol was formed when styrene was exposed to sunlight, while it remained unchanged in the dark. According to Morawetz, [ 11 ] this is probably the first report on a light-induced polymerization.
Stobbe and Posnjak reported the first kinetic investigation of a vinyl polymerization in [ 13 ].A few experiments have also been carried out with ethyl trichloracetate as the halide component.
These systems are considerably more active than those involving nickel tetracarbonyl, and, unlike other carbonyl systems studied, do not inhibit at high concentrations. In benzene solution the rate-determining step of the initiation reaction is first order in monomer concentration. The primary process involves the S N 2 displacement of a comparatively labile triphenylphosphine ligand by a monomer molecule to form a complex Iwhich subsequently reacts with the organic halide giving a free radical capable of initiating polymerization.
Addition of triphenylphosphine to the reaction mixture reverses the primary step, thus reducing the rate of initiation. Carbon monoxide also causes inhibition by the deactivation of complex I.
The nature of the initiation process has been confirmed by experiments designed to measure the evolution of carbon monoxide under a variety of experimental conditions.
The activation energy for the primary step is Kinetic parameters have been evaluated from equations derived for steady-state relationships. If you are not the author of this article and you wish to reproduce material from it in a third party non-RSC publication you must formally request permission using Copyright Clearance Center. Go to our Instructions for using Copyright Clearance Center page for details. Authors contributing to RSC publications journal articles, books or book chapters do not need to formally request permission to reproduce material contained in this article provided that the correct acknowledgement is given with the reproduced material.
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Radical Chain Polymerization
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This may take some time to load. Jump to main content.TISP is a non-traditional technology applying Inhibitor, well soluble in hydrocarbons, not containing heavy metals, nitroaromatics and sulfur.
TISP is based on the new principles of Inhibition. TISP is used in the styrene and isoprene Industries. In order to avoid polymer formation since inhibitor has been used for the process of styrene distillation by ethylbenzene dehydrogenation and since for styrene distillation by methylphenylcarbinol dehydration or by ethylbenzene hydroperoxide. TISP means very low toxicity and easy handling. Tolling operations. Synthetic rubbers.
The TISP characteristics are as follows: High effectiveness for polymerization inhibition, which does not adversely affect the quality of styrene monomer product. TISP enables to reduce tar content in the product in comparison with any other conventional inhibitors. Tar can be used as a fuel or for anticorrosion coatings production. TISP does not cause any environmental pollution. Inhibitor of TISP can be injected continuously in a closed system. TISP components are low toxycal.
TISP inhibits polymerization in a vapor phase. Inhibitor solubility in aromatic solvents is very high.Solutions, Suspensions, and Colloids
Inhibitor is insoluble in water. TISP protects against equipment corrosion. Comparison of TISP process characteristics against other styrene inhibitors. Vapor can irritate nose and throat. Liquid may cause slight skin Irritation. Ingestion lead to the nausea, headache, vomiting, and dizziness. Affects metabolism, causes dermatitis, eczema, development of cataract, as well as common and local allergy.Polystyrene PS is one of the largest volume vinyl polymers, used in countless products from food-packing and plastic cutlery to house insulation.
The primary reasons for its great popularity are its low cost, high transparency, good mechanical properties and ease of coloring, foaming, and processing. Commercial polystyrene is mostly synthesized by bulk, suspension or solution polymerization of ethylbenzene styrene.
The most common method is free radical polymerization, using benzoyl peroxide as initiator. However, other initiators such as redox systems and azo compounds can be used as well to start the polymerization.
The reaction is exothermic, and thus the monomer-polymer mixture has to be cooled. In the case of bulk or mass polymerizationthe reaction exotherm is controlled by using a two-stage polymerization process.
In the first stage, the styrene is polymerized in a stirred tank reactor, the so-called pre-polymerizer. Only a low conversion is achieved. The mixture of dispersed polymer in monomer is then transferred to a tubular thin-film reactor. The pure molten polystyrene that emerges from the reactor is pumped through spinnerets or through an extruder to produce the desired finished granulate mm pellets. PS can also be prepared by solution and suspension techniques. Both processes can be carried out in batch or continuously.
In the case of solution polymerizationstyrene is dissolved in a suitable solvent such as ethylbenzene, which makes temperature control much easier. However, the presence of solvent reduces the molecular weight and lowers the transparency due to a higher degree of impurities. The suspension process is also very common, especially in the production of expandable polystyrene EPS and high impact polystyrene HIPS.
PS is one of the few vinyl monomers that can be polymerized at moderate temperatures without the addition of free radical initiators. The process is known as spontaneous thermal polymerization and has been extensively studied for more than half a century.
The first plausible mechanism was suggested by Flory. Another mechanism of self-initiation was suggested by Mayo. This mechanism was confirmed by Khuong et al. Styrene is one of the most versatile monomers. Besides thermal or radiation induced free radical polymerization, it can be polymerized by practically any other method of chain polymerization including cationic and anionic polymerization.
The relative ease of polymerization of styrene can be explained by resonance stabilization of the growing polystyrene in its transition state, that is the aromatic ring of the growth center delocalizes and stabilizes positive and negative charges as well as radicals as shown below. The styrene polymerization has been studied more extensively than any other mainly because of its relatively reproducible and simple kinetic.
The free radical mechanism for styrene is shown below. It involves a the formation of heat induced radicals followed by the radical's reaction with a styrene monomer Initiation 6b the progressive addition of monomers to the growing polymer chain propagationand c a termination step, which is the destruction of the growth active center by combination or coupling of two radicals. In the case of heat-induced initiation, the initiator concentration in the steady-state is second-order in styrene concentration:.
The rate of propagation is proportional to both the concentration of monomer and free radical initiator:.All the monomers from which addition polymers are made are alkenes or functionally substituted alkenes. The most common and thermodynamically favored chemical transformations of alkenes are addition reactions. Many of these addition reactions are known to proceed in a stepwise fashion by way of reactive intermediates, and this is the mechanism followed by most polymerizations.
A general diagram illustrating this assembly of linear macromolecules, which supports the name chain growth polymers, is presented here. Indeed, cases of explosively uncontrolled polymerizations have been reported. It is useful to distinguish four polymerization procedures fitting this general description. Virtually all of the monomers described above are subject to radical polymerization. Since this can be initiated by traces of oxygen or other minor impurities, pure samples of these compounds are often "stabilized" by small amounts of radical inhibitors to avoid unwanted reaction.
When radical polymerization is desired, it must be started by using a radical initiator, such as a peroxide or certain azo compounds. The formulas of some common initiators, and equations showing the formation of radical species from these initiators are presented below. By using small amounts of initiators, a wide variety of monomers can be polymerized.
One example of this radical polymerization is the conversion of styrene to polystyrene, shown in the following diagram. The first two equations illustrate the initiation process, and the last two equations are examples of chain propagation.
Each monomer unit adds to the growing chain in a manner that generates the most stable radical. Since carbon radicals are stabilized by substituents of many kinds, the preference for head-to-tail regioselectivity in most addition polymerizations is understandable. Because radicals are tolerant of many functional groups and solvents including waterradical polymerizations are widely used in the chemical industry.
In principle, once started a radical polymerization might be expected to continue unchecked, producing a few extremely long chain polymers. In practice, larger numbers of moderately sized chains are formed, indicating that chain-terminating reactions must be taking place.
The most common termination processes are Radical Combination and Disproportionation.
Origins and Development of Initiation of Free Radical Polymerization Processes
These reactions are illustrated by the following equations. The growing polymer chains are colored blue and red, and the hydrogen atom transferred in disproportionation is colored green. Note that in both types of termination two reactive radical sites are removed by simultaneous conversion to stable product s. Since the concentration of radical species in a polymerization reaction is small relative to other reactants e.
The relative importance of these terminations varies with the nature of the monomer undergoing polymerization. For acrylonitrile and styrene combination is the major process. However, methyl methacrylate and vinyl acetate are terminated chiefly by disproportionation.