What is chain transfer constant?

is called the chain transfer constant. It is the slope of the plot of log[S] against log[M]. In the equation above, we neglected reinitiation by radical transfer to polymer chains and assumed that the solvent radicals S· do not participate in termination reactions of the type: S· + Rr· → Pr+s· (ktx) S· + S· → Q· (kts)

What is chain transfer process?

Chain transfer is a polymerization reaction by which the activity of a growing polymer chain is transferred to another molecule. P• + XR’ → PX + R’• Chain transfer reactions reduce the average molecular weight of the final polymer.

What is the function of chain transfer agent?

Chain-transfer agents are often added to control the chain length during synthesis to achieve certain mechanical and processing properties. Very effective chain transfer agents are halogen compounds, some aromatic hydrocarbons, and thiols (mercaptans).

What is intermolecular chain transfer?

In an intramolecular chain transfer (backbiting) reaction, a secondary radical (live chain) abstracts a hydrogen atom from its backbone, producing a midchain radical. ( 11, 19-21) In an intermolecular chain transfer reaction, however, a live polymer chain abstracts a hydrogen atom from a dead polymer. (

What is the difference between chain growth and step growth?

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.

What is meant by group transfer polymerization?

Group transfer polymerization (GTP) is an effective method for the synthesis of poly(methyl methacrylate) (pMMA) with controlled molecular weights and narrow polydispersities. Silyl ketene acetals initiate the polymerization of methyl methacrylate in the presence of either nucleophilic or Lewis acid catalysts.

What is a transfer reaction?

Definition of transfer reaction : a chemical reaction (as a transamination) in which a group is transferred from one molecule to another.

In which polymerization initiator and CTA are dissolved in the monomer *?

suspension polymerization
In suspension polymerization, monomer droplets with dissolved initiator are commonly dispersed in water. As the polymerization progresses, the droplets are transformed into sticky, viscous monomer–polymer particles that finally become rigid, spherical polymer particles of size 50–500 μm.

What is the ionic chain?

Ionic polymerization is a chain-growth polymerization in which active centers are ions or ion pairs. It can be considered as an alternative to radical polymerization, and may refer to anionic polymerization or cationic polymerization.

What is chain growth mechanism?

In chain-growth polymerization, long macromolecules with high molecular weight are formed when only a small fraction of monomer has reacted. Monomers are consumed over the course of the whole reaction. The mechanism of step-growth reaction is based on their functional group.

What is difference between step-growth and chain growth polymerization?

What is the structure of polymers?

The four basic polymer structures are linear, branched, crosslinked, and networked. Diagrams of linear, branched, crosslinked, and networked polymer structures.

What are group transfer reactions in biochemistry?

In organic chemistry, a group transfer reaction is a pericyclic process where one or more groups of atoms is transferred from one molecule to another. They can sometimes be difficult to identify when separate reactant molecules combine into a single product molecule (like in the ene reaction).

What is a transfer of electrons called?

Redox, or electron transfer, reactions constitute one of the broadest and most important classes of reactions in chemistry. All reactions that involve molecular oxygen, such as combustion and corrosion, are electron transfer reactions.

What is the function of the initiator catalyst for chain polymerization?

initiator, a source of any chemical species that reacts with a monomer (single molecule that can form chemical bonds) to form an intermediate compound capable of linking successively with a large number of other monomers into a polymeric compound.

What is the difference between an initiator and a catalyst?

Initiators trigger chemical reactions. They are not true catalysts, as they become an integral part of the end product; because of this they are instead considered to be co-reactants. Reaction accelerators are catalysts which quicken the progress of a chemical reaction.

What is ring opening reaction?

Ring-opening polymerization is a reaction in which one polymer chain has a reactive center on its terminal end that reacts with another cyclic monomer, hence opening its ring system to form a longer polymer chain. The reactive center on the terminal end of the polymer chain can be ionic, cationic, or radical.

What is cationic and anionic polymerization?

Anionic Polymerization: Anionic polymerization takes place with monomers having electron-withdrawing groups such as nitrile, carboxyl, phenyl, and vinyl. Cationic Polymerization: Alkenes having alkoxy, phenyl, vinyl and 1,1-dialkyl substituents are some examples of monomers used in the cationic polymerization.

What is chain-growth polymerisation explain with an example?

Polycondensation is a kind of polymerization whose chain growth is based on condensation reaction between two molecules with various degree of polymerization. The typical example are polyesters, polyamides and polyethers. It is sometimes confused by condensation previous definition of condensation polymerization.

What is meant by chain growth polymerization?

Chain Growth Polymerization In chain-growth polymerization, the molecules of the monomers are added together to form a large chain. The monomers adding maybe the same type or different. Generally, alkenes, alkadienes and their derivatives are used.

Why is it called chain transfer?

He coined the term “chain transfer” to explain observations that, during polymerization, average polymer chain lengths were usually lower than predicted by rate considerations alone. The first widespread use of chain transfer agents came during World War II in the US Rubber Reserve Company.

What is a chain transfer reaction?

Chain transferis a termination reaction by which the free-radical site of a growing polymer chain is transferred to another molecule. The amount of chain transfer to monomers is usually low because this reaction requires breaking strong carbon-hydrogen bonds.

What is chain transfer in polymerization?

Chain transfer (in a chain polymerization ): Chemical reaction occurring during a chain polymerization in which an active center is transferred from a growing macromolecule or oligomer molecule to another molecule or to another site on the same molecule.

What is meant by chain transfer to monomer?

Chain transfer to monomer may take place in which the growing polymer chain abstracts an atom from unreacted monomer existing in the reaction medium.