Now let us look at an example for step growth polymerization for better understanding. Chain growth polymerization an overview sciencedirect topics. Free radical in slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Chaingrowth, or addition polymerization of vinyl monomers that contain an. Chaingrowth polymerization wikipedia republished wiki 2. This article is an overview of chaingrowth polymerization and a list of some of the. Bpo or aibn to yield a pair of free radicals r, and the second the addition of a monomer to the primary radical r to yield the chain radical, which is called the initiation. This mechanism is known as chain growth and is shown schematically in figure 36 a, where a monomer unit is activated by initiator i and forms a chain very quickly. The new species may initiate polymerization or may truncate it. Chain growth polymerisation involves a chain reaction. Differences between stepgrowth polymerization and chaingrowth polymerization.
Free radical polymerization is the most widely used process for polymer synthesis. There are four principal mechanisms of chain growth polymerization. Free radical polymerization is particularly suitable for polymerizing monomers containing carboncarbon double bonds. Polymerization is an important process in so many industries. In this chapter, we only discuss free radical chain polymerization. Chaingrowth polymerization is a process in which the high molecular weight. Well over 100 billion pounds of polymer are produced each year, and it is expected that this. Equivalent terms are either chain polymerization or chain. This has several attractive features from an industrial point of view but suffers several drawbacks as well, not the least of which is the difficulty of achieving high molecular weights. This process is similar to radical polymerization, as demonstrated by the following equations. Converting step growth polymerization to chain growth.
Converting step growth polymerization to chain growth free download as powerpoint presentation. Step growth polymerization is the formation of a polymer from bifunctional or multifunctional monomers. Polymerization kinetics step growth slow can use statistical methods as well as kinetics to describe mol. The principal steps in the chain growth mechanism are the. The polymerization of vac for pvoh production was, and still is, done by freeradical solution polymerization in methanol. It is the addition of monomers to an evergrowing chain. Following its generation, the initiating free radical adds nonradical monomer units, thereby growing the polymer chain. Chaingrowth polymerization is a process in which the high molecular weight polymer is formed early in the polymerization process and the polymer yield the percentage conversion of the monomer into the polymer gradually increases with time. On the other hand, in chain growth polymerization, the monomer consumed steadily but the degree of polymerization could be increased very quickly after chain initiation.
Chaingrowth polymerization or chain polymerization is a polymerization technique in which unsaturated monomer molecules add onto the active site of a growing polymer chain one at a time. Differences between stepgrowth polymerization and chaingrowth polymerization step growth chain growth growth throughout matrix rapid loss of monomer early in the reaction similar steps repeated throughout reaction process average molecular weight increases slowly at low conversion and high. Termination reactions unique to chain growth polymerization produce a material with flexibility, mechanical strength and biocompatibility. Chain transfer chain transfer is a chain breaking reaction leading to a decrease in the size of the propagating polymer chain. Kinetics of free radical addition polymerization youtube. Therefore it requires an initiator like organic peroxide to form free radical. Simple statistical arguments can be used to show how the distribution develops with extent of reaction. The other process, called stepgrowth polymerization, involves the buildup of molecular weight not in a chainlike fashion but in a stepwise fashion, by the random combination of monomer molecules containing reactive functional groups.
Chain growth polymerization is a process in which the high molecular weight polymer is formed early in the polymerization process and the polymer yield the percentage conversion of the monomer into the polymer gradually increases with time. Initiation of the active monomer, propagation or growth of the active chain by sequential addition of monomers, termination of the active chain to give the final polymer product. Polymer design and synthesis, reaction types and processes, introduction to step growth polymerization, types of monomers, kinetics and equilibrium considerations, polyaramids, polyimides, free radical chain polymerization, ionic polymerization, polymer functionalization and modification, less traditional approaches to. Differences between step growth polymerization and chain growth polymerization.
Free radicals can be formed by a number of different mechanisms, usually involving separate initiator molecules. Chainreaction polymerization, sometimes called addition polymerization, requires an initiator to start the growth of the reaction. Lecture notes mit opencourseware free online course materials. The number of moles of glycol available for step growth polymerization will be 1. Transformation of stepgrowth polymerization into living.
The main difference between chain growth polymerization and step growth polymerization is that the chain growth polymerization involves the growth a polymer chain at its ends whereas the step growth polymerization involves the combination of oligomers to form a polymer chain. On the other hand, in chaingrowth polymerization, the monomer consumed steadily but the degree of polymerization could be increased very quickly after chain initiation. In the polymerizations, the propagations are chain reactions. Chain growth polymerization has been successfully performed for many decades through conventional free radical, anionic, or cationic polymerization. Chain polymerizations require an initiator, which produces an initiator species with a reactive center. Pdf modeling of the penultimate unit effect in chain. Other articles where step growth polymerization is discussed. Chain growth polymerization an overview sciencedirect. The active site in chaingrowth polymerizations can be an ion instead of a freeradical. Here the addition polymer forms by addition of atoms with a free electron in its valence shells. Chain growth polymerization is basically a threestage process, involving initiation of active molecules, their propagation and termination of the active chain ends.
In contrast to chain growth reactions, where high molecular mass polymers are formed almost from the start of the reaction, a stepwise reaction results in the molecular mass of the polymer increasing slowly as the reaction progresses. Polymerization processes are categorized into two broad classes, according to their reaction mechanisms. In chaingrowth or chain polymerization, the only chainextension reaction step is the addition of a monomer to a growing chain with an active center such as a free radical or ion. Feb 16, 2016 chain growth polymerisation involves a chain reaction. Virtually all of the monomers described above are subject to radical polymerization. Schematic of reaction schemes for chaingrowth polymerization. Pdf reinvestigation of numerous ringopening polymerizations by means of malditof mass spectrometry has evidenced that. Polymerizations by a free radical mechanism are typical freeradical reactions. Chemistry of industrial polymers stepgrowth polymerization. Freeradical chaingrowth polymerization springerlink. Simultaneous chain growth and stepgrowth polymerizationa new route to cyclic polymers. Chaingrowth polymerization has been successfully performed for many decades through conventional free radical, anionic, or cationic polymerization.
A reaction initiated by an anion, cation, or radical in which a large number of monomer units are added rapidly a chain reaction until terminated by some mechanism, forming a highmolecularweight polymer in a very short time. Addition of each monomer unit regenerates the active site. That is to say, there is an initiation, when the radicals are formed, a propagation, when the products are developed, and a termination, when the radical reactions end. The mw and the mw distribution, referred to as polydispersity, are two fundamental factors that dictate the physical nature of polymeric materials. Pdf simultaneous chaingrowth and stepgrowth polymerization. Ammonia is an example of such a protic solvent and the reaction results in the formation of a negatively charged nh 2 ion, which can initiate the polymerization of a new chain. Stepgrowth polymerization typically takes place between monomers containing functional groups that react in high yield to form new functionalities. Freeradical polymerization frp is a method of polymerization by which a polymer forms by the successive addition of freeradical building blocks. Synthesis block copolymer by controlledliving radical polymerizationfree radical polymerization fabrication nanostructures by selfassembly toward biomedical applications, environmental trea. Stiile colorado state university, fort collins, co 80523 as illustrated in the articles on chain polymerization, a chaingrowth polymerization is one in which each polymer chain, after being started by a free radical initiator, a cationic catalyst or an anionic catalyst, grows rapidly, producing a high. It is much less sensitive to the effects of adventitious impurities than step growth polymerization and ionic chain growth polymerization. The ionic chain polymerization will be discussed in chap. The largest family of polymers 3, vinyl polymers, are produced by chain polymerization reactions.
In chaingrowth polymerizations, two propagation models are normally used to describe the polymerization. During propagation, only monomers react to the active site at the end of the growing chain. The most common example of chain growth polymerization is the conversion of ethylene. The other process, called step growth polymerization, involves the buildup of molecular weight not in a chainlike fashion but in a stepwise fashion, by the random combination of monomer molecules containing reactive functional groups.
Chemistry of industrial polymers chemistry of industrial polymers stepgrowth polymerization. Most chain growth polymers are formed from unsaturated hydrocarbons, with the unsaturation present as a double bond between carbon atoms table 1. Polymer chemistry university of south carolina upstate. The initiator free radical will react rapidly with the monomer to form a second.
The reactive center may be a free radical, cation, anion, or. Polymerizations by freeradical mechanism are typical freeradical reactions. Free radical polymerization is one type of chain polymerization. Stiile colorado state university, fort collins, co 80523 as illustrated in the articles on chain polymerization, a chaingrowth polymerization is one in which each polymer chain, after being started by a free radical initiator, a cationic catalyst or an anionic catalyst, grows rapidly, producing a high molecular weight polymer. Jul 15, 2011 equivalent terms are either chain polymerization or chain. These polymerization techniques generate many important commodity polymers where their broad range of molecular weight distribution gives rise to important physical properties. Once the growth of a chain is initiated by formation of an active center, chain propagation is usually rapid by addition of a sequence of monomers. A good example is the freeradical polymerization of styrene, which is initiated by a free radical r that reacts with styrene. As you work through this course you will need various resources to help you complete some of the activities. In chain growth polymerization, an activated species initiator or.
They join in a successive chain during free radical polymerization. Monomers are added one by one to the active site on the growing polymer. Differences between step growth polymerization and chain growth polymerization step growth chain growth growth throughout matrix rapid loss of monomer early in the reaction similar steps repeated throughout reaction process average molecular weight increases slowly at low conversion and high extents of reaction are. Chaingrowth polymerization article about chaingrowth.
Polymerization of isobutylene 2methylpropene by traces of strong acids is an example of cationic polymerization. In step growth polymerization, oligomers are formed at the beginning and are later combined together, forming the polymer chain. After 75 per cent of the monomer molecules have reacted in this case the degree of polymerization n 12. Chaingrowth polymerization forms polymers in such a manner that. A polymerization where a cation is formed causing a chain reaction.
Controlled radical polymerization guide sigmaaldrich. Chain grow and free radical polymerization introduction chain growth polymerization monomers for chain. Chain growth polymerization proceeds by the formation of an active center of growth 8,9. The chain growth polymers count more than 80 % total usage of polymers in our daily life. Synthesis block copolymer by controlledliving radical polymerization free radical polymerization fabrication nanostructures by selfassembly toward biomedical applications, environmental trea. Controlled stepgrowth polymerization ccs chemistry. The main difference between chain growth polymerization and step growth polymerization is that the chain growth polymerization involves the growth a polymer chain at its ends whereas. A variety of synthetic routes, including free radical 9,20e22.
Once the propagation reaction within a given polymer chain is stopped either by a termination or chaintransfer step, usually no further chain growth occurs. Simultaneous chaingrowth and stepgrowth polymerization of methoxystyrenes by rareearth catalysts. Nov 10, 2015 simultaneous chain growth and step growth polymerization of methoxystyrenes by rareearth catalysts. In chain growth or chain polymerization, the only chain extension reaction step is the addition of a monomer to a growing chain with an active center such as a free radical or ion. Compared to step growth polymerization, living chain growth polymerization shows low pdi, predictable molecular mass and controllable conformation. Molecule empire building by radical groups chaingrowth polymerization addition processes 1. Thus the process of chain initiation involves two steps. 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. Compared to stepgrowth polymerization, living chaingrowth polymerization shows low pdi, predictable molecular mass and controllable conformation. Two different approaches have been used to derive expressions for the rate of copolymerization basis on how the termination reactions are proceeded. Chain growth polymerization, by contrast, requires at least three distinctly different kinds of reactions to describe the mechanism. Other articles where stepgrowth polymerization is discussed. The active center is transferred from the growing chain to a different species chain transfer agent, initiator, monomer, or polymer.
This can induce chain branching through the terminal double bond propagation reaction. These three types of reactions will be discussed in the following sections in considerable detail. Examples of such functional groups are carboxylic acids, which react with alcohols to form esters and with amines to form amides. Pdf comparison of chaingrowth polymerization in solution versus.
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