Contents
- 1 What is cationic and anionic polymerization?
- 2 Which catalyst is used for cationic polymerization?
- 3 Which of the following initiators is used in cationic polymerization?
- 4 Which initiators are used in anionic polymerization?
- 5 How are photo cationic initiators used in polymerization?
- 6 Which is an example of a cationic center?
What is cationic and anionic polymerization?
Cationic polymerization reactions are sensitive to temperature. Both the reaction rate and molecular weight rapidly decrease with increasing temperature. Anionic polymerization reactions typically yield more regular polymers with less branching, more controlled tacticity and narrow molecular weight (MW) distribution.
Which catalyst is used for cationic polymerization?
Lewis acid catalyst
A Lewis acid catalyst is generally used to initiate the cationic polymerization reaction by activation of the oxetane ring oxygen, allowing nucleophilic attack from the ring oxygen atom of a second oxetane molecule and ring opening.
Is anionic a polymer?
Anionic polymerization is a form of chain-growth polymerization that encompasses the polymerization of vinyl monomers with strong electronegative groups. This type of polymerization is often employed to produce synthetic polydiene rubbers, solution styrene-butadiene rubbers (SBR), and thermoplastic styrenic elastomers.
Why does styrene undergo cationic polymerization?
Cationic Addition Polymerization : In the case of vinylic monomers containing electron donating groups, electron density on double bonded carbon will be more and it can easily be attacked by H+ so as to undergo cationic polymerization. Cations are stabilised by electron donating groups.
What is anionic and cationic?
Cations are positively-charged ions (atoms or groups of atoms that have more protons than electrons due to having lost one or more electrons). Anions are negatively-charged ions (meaning they have more electrons than protons due to having gained one or more electrons).
What do you mean by cationic polymerization?
In chemistry, cationic polymerization is a type of chain growth polymerization in which a cationic initiator transfers charge to a monomer which then becomes reactive. This reactive monomer goes on to react similarly with other monomers to form a polymer.
Which of the following initiators is used in cationic polymerization?
Lewis acids are the most common compounds used for initiation of cationic polymerization. The more popular Lewis acids are SnCl4, AlCl3, BF3, and TiCl4.
Which initiators are used in anionic polymerization?
Initiation by strong anions Nucleophilic initiators include covalent or ionic metal amides, alkoxides, hydroxides, cyanides, phosphines, amines and organometallic compounds (alkyllithium compounds and Grignard reagents).
What is an anionic mechanism?
Mechanism of Anionic Polymerization Anionic polymerization is a type of chain growth polymerization in which an anionic initiator transfers a charge to a vinyl monomer which then becomes reactive. Each reactive monomer goes on to react with other monomers to form a linear polymer.
What is anionic reaction?
Anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of monomers initiated with anions. The type of reaction has many manifestations, but traditionally vinyl monomers are used.
Which type of monomer is used in cationic polymerization?
Monomers. Monomer scope for cationic polymerization is limited to two main types: alkene and heterocyclic monomers. Cationic polymerization of both types of monomers occurs only if the overall reaction is thermally favorable.
What type of alkenes prefer under cationic polymerization?
Alkenes that give rise to delocalized cations are also good candidates for cationic polymerizaton. Styrene, PhCH=CH2, as well as butadiene, CH2=CHCH=CH2, and the related natural product isoprene, CH2=C(CH3)CH=CH2, can all be polymerized using cationic methods.
How are photo cationic initiators used in polymerization?
Photo cationic initiators (WPI series) Photo cationic initiator is a compound generating acid by UV-irradiation. Since it generates different types of acid derived from anionic sites, it is used for various polymerization reactions such as epoxy cure.
Which is an example of a cationic center?
Cationic active centers are created by reaction of the monomer with an electrophile. Examples of good initiators are H 2 SO 4 or HClO 4; BF 3, AlCl 3, SnCl 3 with ‘co-catalyst’ (water or organic halide, makes for more stable counter ion). The general steps of initiation are shown in Figure 6.3.
Are there any cationic initiators of iodonium salt?
There are cationic initiators of iodonium type which have substituents such as long chain alkyl group in our lineup. The initiators have high compatibility with resin, and have low toxicity because of low-volatile benzene by-produced after photolysis. Iodonium salt has high photolytic property.
How are monomer units in cationic ring opening polymerization?
Cationic ring-opening polymerization follows the same mechanistic steps of initiation, propagation, and termination. However, in this polymerization reaction, the monomer units are cyclic in comparison to the resulting polymer chains which are linear.