What are the differences between anionic and cationic polymerization?

Question

Accepted Answer

Anionic polymerization and cationic polymerization are two types of chain growth polymerization reactions that are used for synthesizing different types of polymers. Although both reactions have the same mechanism, there are several differences between the two.

Basis of differentiation

Anionic polymerization

Cationic polymerization

Definition

Anionic polymerization refers to a type of polymerization process that is dependent on the reactivity of anions to initiate and propagate the polymerization reaction.

Cationic polymerization refers to a type of chain growth polymerization mechanism in which the formation of a carbocation intermediate initiates the polymerization reaction.

Initiation mechanism

The process is initiated by the removal of a proton from a monomer by a strong base or organometallic compound.

The process is initiated by the reaction of the cation with a monomer, resulting in the formation of a reactive carbocation.

Examples of initiators

Initiators include nucleophiles such as hydroxide, cyanide, alkoxide, cyanide or a carbanion.

Initiators include electrophilic agents such as HCl, H2SO4, HBr, HClO4.

Monomer reactivity

Anionic polymerization involves monomers that are electron-deficient and are capable of stabilizing the negative charge of the carbanion.

Cationic polymerization involves monomers that are electron-rich and are capable of stabilizing the positive charge of the carbocation.

Reaction Rate

Anionic polymerization reactions proceed at a relatively slower speed because the negative charge on the anionic initiator can be stabilized by several other factors. The ions become less reactive when they are stable.

Cationic polymerization reactions proceed at a relatively faster speed because the cationic initiator is very reactive and is difficult to control and stabilize.

Yield

These reactions typically yield more regular polymers with less branching, narrow molecular weight distribution and more controlled tacticity. If necessary, end groups can be tailored for further reactivity.

The high reactivity of these reactions often result in undesirable side reactions, such as chain transfer and chain termination, which, in turn, lead to high branching, lower molecular weight and broader molecular weight distribution.

Uses

Because anionic polymerizations are difficult to carry out, they are limited to being used only on an industrial scale when polymers with regular structure and narrow molecular weight distribution are required.

Because cationic polymerizations are difficult to control and are limited to olefinic monomers, their main commercial use is to manufacture butyle rubber and polyisobutylene.

Basis of differentiation	Anionic polymerization	Cationic polymerization
Definition	Anionic polymerization refers to a type of polymerization process that is dependent on the reactivity of anions to initiate and propagate the polymerization reaction.	Cationic polymerization refers to a type of chain growth polymerization mechanism in which the formation of a carbocation intermediate initiates the polymerization reaction.
Initiation mechanism	The process is initiated by the removal of a proton from a monomer by a strong base or organometallic compound.	The process is initiated by the reaction of the cation with a monomer, resulting in the formation of a reactive carbocation.
Examples of initiators	Initiators include nucleophiles such as hydroxide, cyanide, alkoxide, cyanide or a carbanion.	Initiators include electrophilic agents such as HCl, H2SO4, HBr, HClO4.
Monomer reactivity	Anionic polymerization involves monomers that are electron-deficient and are capable of stabilizing the negative charge of the carbanion.	Cationic polymerization involves monomers that are electron-rich and are capable of stabilizing the positive charge of the carbocation.
Reaction Rate	Anionic polymerization reactions proceed at a relatively slower speed because the negative charge on the anionic initiator can be stabilized by several other factors. The ions become less reactive when they are stable.	Cationic polymerization reactions proceed at a relatively faster speed because the cationic initiator is very reactive and is difficult to control and stabilize.
Yield	These reactions typically yield more regular polymers with less branching, narrow molecular weight distribution and more controlled tacticity. If necessary, end groups can be tailored for further reactivity.	The high reactivity of these reactions often result in undesirable side reactions, such as chain transfer and chain termination, which, in turn, lead to high branching, lower molecular weight and broader molecular weight distribution.
Uses	Because anionic polymerizations are difficult to carry out, they are limited to being used only on an industrial scale when polymers with regular structure and narrow molecular weight distribution are required.	Because cationic polymerizations are difficult to control and are limited to olefinic monomers, their main commercial use is to manufacture butyle rubber and polyisobutylene.

What are the differences between anionic and cationic polymerization?

Posted July 10, 2023