Chain Growth
Chain Growth - Related Videos
01:17
Radical Chain-Growth Polymerization: Chain Branching
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2023
The skeletal structure of polymers synthesized via radical polymerization is always branched. For example, the polymerization of ethylene by radical polymerization results in a low-density grade of polyethylene with a heavily branched skeletal structure. Here, the radical site abstracts hydrogen from the growing chain, and the radical site shifts from the end (a primary carbon center) to anywhere within the growing chain (a secondary carbon center). Consequently, the part of the chain from the...
01:09
Radical Chain-Growth Polymerization: Mechanism
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2023
The radical chain-growth polymerization mechanism consists of three steps: initiation, propagation, and termination of polymerization. The polymerization initiates when a free radical generated from the radical initiator adds to the unsaturated bond in the monomer. The unpaired electron of the free radical and one π electron in the unsaturated bond creates a σ bond between the free radical and the monomer. As a result, the other π electron in the unsaturated bond converts this species into the...
01:20
Anionic Chain-Growth Polymerization: Overview
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2023
The polymerization process that involves carbanion as an intermediate is called anionic polymerization. It is also a type of addition or chain-growth polymerization. Anionic polymerization gets initiated by a strong nucleophile such as an organolithium or a Grignard reagent. The most commonly used initiator for anionic polymerization is butyl lithium. Monomers involved in anionic polymerization must possess a vinyl group bonded to one or two electron-withdrawing groups. For instance,...
01:04
Anionic Chain-Growth Polymerization: Mechanism
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2023
The mechanism for anionic chain-growth polymerization involves initiation, propagation, and termination steps. In the initiation step, a nucleophilic anion, such as butyl lithium, initiates the polymerization process by attacking the π bond of the vinylic monomer. As a result, a carbanion, stabilized by the electron‐withdrawing group, is generated. The resulting carbanion acts as a Michael donor in the propagation step and attacks the second vinylic monomer, which acts as a Michael acceptor.
00:57
Cationic Chain-Growth Polymerization: Mechanism
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2023
The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the generated carbocation,...
FAQs
The initiator creates the active site that starts polymer formation, and its chemical nature determines whether the growing chain carries a radical, cation, anion, or metal-bound species. This distinction matters because the active center remains associated with the chain during monomer addition, establishing the mechanistic basis for subsequent propagation and eventual deactivation.
Propagation depends on an active chain end adding one monomer molecule at a time while preserving its reactivity after each addition. Repeated transfer of activity to the new chain end allows a relatively small starting unit to develop into a long polymer chain. The persistence of this active site therefore controls how sequential growth proceeds.
Termination or another form of deactivation stops the active chain end from continuing to add monomers. This event ends the growth sequence for that chain and influences the resulting polymer population. Because chain growth depends on maintaining reactive centers, the balance between continued propagation and loss of activity is fundamental to the final material.
The sequence of monomer additions and the behavior of active chain ends determine important aspects of polymer architecture. By controlling how chains grow and how their active sites are maintained or deactivated, chemists can tailor molecular weight, branching, and composition. These structural features provide a route to adjusting the properties of the resulting polymer material.
A typical workflow begins with selecting the monomer and an initiator capable of generating the desired reactive center. The initiator starts a chain, monomer molecules add sequentially at the active end, and growth continues until termination or deactivation occurs. The resulting polymer is then considered in terms of its chain structure and composition.
Chain-growth methods support the production of plastics, elastomers, coatings, and specialty polymers. Their value extends beyond making long chains because the process can help researchers tailor molecular weight, branching, and composition. Those structural controls connect polymerization chemistry with the design of materials having different performance characteristics for research and practical applications.