What are Initiators in 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.
Which of the following monomer Cannot be polymerised by radical polymerisation?
Which of the following monomer cannot be polymerised by radical polymerisation? Explanation: Isobutylene monomer can be polymerised by cationic polymerisation. Butadiene, vinyl chloride and acrylates can be polymerised by radical polymerization.
What are the limitations of radical polymerization?
Some disadvantages related to the mechanism of free radical polymerization is the poor control of the molecular weight and the molecular weight distribution, and the difficulty (or even impossibility) of preparing well-defined copolymers or polymers with a predetermined functionality.
How do chain transfer agents work?
Chain transfer is a polymerization reaction by which the activity of a growing polymer chain is transferred to another molecule. Chain-transfer agent: Substance able to react with a chain carrier by a reaction in which the original chain carrier is deactivated and a new chain carrier is generated.
Why are peroxides good radical initiators?
Although there are several other initiators with a high decomposition temperature, such as aliphatic dialkyl peroxides, DTBP is often preferred because it is easier to handle due to its lower explosion hazard. It can also be easily purified. DTBP undergoes symmetrical fission (homolysis), forming two t-butoxy radicals.
How can we stop radical polymerization?
Reversible deactivation radical polymerization Because these polymerizations stop only when there is no more monomer, polymerization can continue upon the addition of more monomer. Block copolymers can be made this way. RDRP allows for control of molecular weight and dispersity.
Which of the following is initiator in free radical polymerization?
1. Which of the following is an initiator molecule in the free radical polymerisation? Explanation: The whole process of free radical polymerisation starts off with a molecule called an initiator. This is a molecule like benzoyl peroxide.
Which is the range of tensile strength exhibited by Fibre?
Thus, under dry condition the fibre behaves like an elastic–brittle material with a high average tensile strength (~62.2 MPa) and average elastic modulus (~5.8 GPa).
What is the last step in free radical polymerization?
Termination. Chain termination is inevitable in radical polymerization due to the high reactivity of radicals. Termination can occur by several different mechanisms. If longer chains are desired, the initiator concentration should be kept low; otherwise, many shorter chains will result.
Which is the initiator of free radical polymerization?
Free radical polymerization can be iniitated by thermal, chemical or photolytic decomposition of initiator molecules. The initiator molecule splits homolytically into two radicals and each radical adds to a monomer, converting it into a new radical that propagates. Two very common initiators are benzoyl peroxide and 2,2′-azo-bis-isobutyrylnitrile.
How are thermal polymerization initiators used in chain growth?
Polymerization Initiators Initiators are often used in chain-growth polymerization such as radical polymerization to regulate initiation by heat or light. Thermal polymerization initiators are compounds that generate radicals or cations upon exposure to heat.
Why is chain termination inevitable in radical polymerization?
The mechanism of chain propagation is as follows: Figure 13: Propagation of polystyrene with a phenyl radical initiator. Chain termination is inevitable in radical polymerization due to the high reactivity of radicals. Termination can occur by several different mechanisms.
How are radicals transferred from the initiator to the monomer?
In the second step, radicals are transferred from the initiator molecules to the monomer units present. Several choices are available for these initiators. The initiator is heated until a bond is homolytically cleaved, producing two radicals (Figure 1). This method is used most often with organic peroxides or azo compounds.