Due to the nature of the polymerization mechanism, a high extent of reaction is required to achieve high molecular weight. Pdf reinvestigation of numerous ringopening polymerizations by means of malditof mass spectrometry has evidenced that cyclic polymers were formed. Monomers exist throughout the reaction, but large quantities of monomers are consumed early in. It is a chain reaction where free radicals or ionic groups are responsible for propagating the chain. Chain growth polymerization an overview sciencedirect topics. Polymerization kinetics step growth slow can use statistical methods as well as kinetics to describe mol. Most chain growth polymers are formed from unsaturated hydrocarbons, with the unsaturation present as a double bond between carbon atoms table 1.
Monomers are molecules having either unsaturated bonds or at least two functional groups per molecule. 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. Stepgrowth polymerization and stepgrowth polymers rro. Different steps operate at different stages of mechanism. In so doing we shall also have the opportunity to indicate some of the different types of chain growth systems. 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. 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. Controlled polymerizations the dong group at ut austin. Compared to step growth polymerization, living chain growth polymerization shows low pdi, predictable molecular mass and controllable conformation. Feb 28, 20 animation of the different steps of chain growth polymerisation, made for the class polymer chemistry at avans hogeschool. Sep 20, 2017 both step growth and chain growth approaches are widely followed in the synthesis of hb polymers. Polymers are giant molecules made of small units known as monomers. Thus at 75 per cent completion, the average degree of polymerization is one quarter of that for a chain growth reaction. Long and others published stepgrowth polymerization find, read and cite all the research you need on researchgate.
Animation of the different steps of chaingrowth polymerisation, made for the class polymer chemistry at avans hogeschool. In the following example, the same bisphenol a intermediate used as a monomer for lexan serves as a. Monomer does not react with monomer and the different sized species such as dimer, trimer, and nmer do not react with each other. Stepgrowth polymerscondensation polymers chemistry. All molecules present monomer, oligomer, polymer can react with any other molecule. Putting them together polymer science learning center. All doublebonded monomers, like the vinyls and dienes, polymerize in a chain growth mechanism whereas monomers with functional end groups react in a stepwise fashion, for example, terephthalic acid and ethylene glycol table 5 which form pet. As stated in chapter 1, chaingrowth polymerizations take place in discrete steps.
Generally, polycondensation proceeds in a step growth polymerization mode. Step growth polymerization, types of monomers, kinetics and equilibrium considerations, closed vs. It is used for most step growth polymers and many types of chain growth polymers. A stepgrowth polymerization is a stepwise reaction between bifunctional or multifunction. 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. Equivalent terms are either chain polymerization or chain.
Whereas chain growth approaches include radical copolymerization, surface grafting, and other controlled polymerization. The most common example of chain growth polymerization is the conversion of ethylene. There exist, exceptionally, some polymerizations that proceed via chain reactions that, according to the definition, are not chain polymerizations. The growth of the polymer chain is therefore referred to as chain growth. Step growth approaches mainly include ab x polycondensation and double monomer symmetricasymmetric pairs methodologies. In chapter 2 we saw that step growth polymerizations occur, one step at a time, through a series of relatively simple organic reactions. Now let us look at an example for step growth polymerization for better understanding. Welldefined aromatic polyamides, polyesters, and polyethers have been synthesized via substituent effectassisted chain growth condensation polymerization, in which the polymer propagating ends are more reactive than the monomers due to resonance or inductive effects between the functional groups of the. Polymerization reactions are divided into two groups known as step reactions also called condensation reactions and chain reactions also known as addition reactions. Main difference chain growth polymerization vs step growth polymerization. This mechanism is known as chain growth and is shown schematically in figure 36 a, where a. Stepgrowth polymerization forms polymers in a manner that is. Stepgrowth polymerization american chemical society.
The distinction between stepgrowth polymerization and chaingrowth polymerization was introduced by paul flory in 1953, and refers to the. The mechanism requires that at least two different monomers participate in the reaction. Chain growth polymerization an overview sciencedirect. These free radicals are added to another monomer forming another free radical. Step reactions require bifunctional or polyfunctional monomers, while chain reactions require the presence of an initiator. In a step growth reaction, the growing chains may react with each other to form even longer chains.
In other words, addition of each monomer unit regenerates the active site. Many naturally occurring and some synthetic polymers are produced by stepgrowth polymerization, e. 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. Other articles where step growth polymerization is discussed. Comparison of molecular weight vs conversion plot between stepgrowth and living chaingrowth polymerization. Monomers are added one by one to the active site on the growing polymer. In many other polymerizations a chain process is not involved, but many stable intermediates are formed along the way in. Controlled stepgrowth polymerization ccs chemistry.
Now the differences between a chain growth polymerization and a step growth. Stepgrowth polymerization an overview sciencedirect topics. Intro to polymer chemistry exam 2 flashcards quizlet. The polymerization reaction occurs between the functional groups of molecules. Jun 27, 2017 main difference chain growth polymerization vs step growth polymerization. It is the addition of monomers to an evergrowing chain.
Small molecules such as water are eliminated by the chemical reaction in step growth polymerization. All doublebonded monomers, like the vinyls and dienes, polymerize in a chain growth mechanism whereas monomers with functional end groups react in a stepwise fashion, for example, terephthalic acid and ethylene glycol. The products usually have a carbon backbone with pendant substituent groups ex. Step growth polymers are defined as polymers formed by the stepwise. I as stated in chapter 1, chain growth polymerizations take place in discreet steps. In a stepgrowth polymerization, the molecular weight of the polymer chain builds up slowly and there is only one re action mechanism for the. Pdf simultaneous chaingrowth and stepgrowth polymerization. The main difference between chain growth polymerization and step growth polymerization is that chain growth polymerization has a growth a polymer chain at its ends whereas step growth polymerization has a combination of oligomers to form a polymer chain. Difference between chain growth and step growth polymerization. Chain growth polymerization can be understood with the chemical equation. Feb 16, 2016 the process results in the formation of chain and ultimately a polymer is formed. Some researchers are working on the transformation of two polymerization methods. Here the covalent bonding occurs by an s n 2 reaction between a nucleophile, usually an amine, and a terminal epoxide. Pdf simultaneous stepgrowth and chaingrowth cationic.
During propagation, only monomers react to the active site at the end of the growing chain. 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. All of the polymerizations except for the zn method discussed thus far have been chain processes. Following a comparison of chain growth and step growth polymerization, focuses on the latter process by describing requirements for high molecular weight, step growth polymerization kinetics, synthesis and molecular weight distribution of some linear step growth polymers, and threedimensional network step growth polymers. The kinetics of stepgrowth polymerization can be derived from a. Chain addition polymerization also referred to as chaingrowth polymerization technique is a chain reaction in which the growth of a polymer chain proceeds exclusively by reactions between monomerss and active sites on the polymer chain with regeneration of the active sites at the end of each growth step. Step growth polymerization is also used for preparing a class of adhesives and amorphous solids called epoxy resins.
The distinct initiation, propagation, and termination steps of chaingrowth polymerization are meaningless in. Many naturally and synthetic polymers are produced by stepgrowth polymerization including polyesters, polyethers, urethanes, epoxies, and polyamides see table below. Once the propagation reaction within a given polymer chain is stopped either by a termination or chaintransfer step, usually no further chain growth occurs. Stepgrowth polymerization refers to a type of polymerization mechanism in which bifunctional. Chain growth polymerisation therefore it requires an initiator like organic peroxide to form free radical. Chain growth polymerization is basically a threestage process, involving initiation of active molecules, their propagation and termination of the active chain ends. Polymerization mechanism o stepgrowth polymerization o chaingrowth polymerization o stepgrowth vs. Chapter two, step growth polymerization, version of 1505 76 2. The first is to activate a small number of monomer units m which then successively consume other monomers.
Stepgrowth polymerization forms polymers in a manner that is quite different from chaingrowth polymerization. Stepgrowth polymerization refers to a type of polymerization mechanism in which bifunctional or multifunctional monomers react to form first dimers, then trimers, longer oligomers and eventually long chain polymers. Chain growth polymerization proceeds by the formation of an active center of growth 8,9. Many naturally occurring and some synthetic polymers are produced by step growth polymerization, e. Equilibrium step condensation polymerizations, interchange reactions.
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