Is free radical polymerization reversible?
Is free radical polymerization reversible?
A living radical polymerization that does not end on its own, but continues to synthesize long polymeric chains with controlled molecular weights is known as reversible addition fragmentation chain transfer (RAFT).
Is polymerisation reversible?
Reversible polymerization typically involves two steps, including (i) forward polymerization, which converts small monomers into macromolecule; and (ii) depolymerization, which is capable of regenerating original monomers. Furthermore, recycled monomers can be repolymerized into new polymers.
How can we stop radical polymerization?
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 catalyst is used in free radical polymerization?
When radical polymerization is desired, it must be started by using a radical initiator, such as a peroxide or certain azo compounds.
What are polymers Byjus?
A polymer is a large molecule or a macromolecule which essentially is a combination of many subunits. The term polymer in Greek means ‘many parts’. Polymers can be found all around us. Polymers may be naturally found in plants and animals (natural polymers) or may be man-made (synthetic polymers).
What occurs during polymerization?
polymerization, any process in which relatively small molecules, called monomers, combine chemically to produce a very large chainlike or network molecule, called a polymer. The monomer molecules may be all alike, or they may represent two, three, or more different compounds.
What makes a polymerization reaction irreversible?
A polymerization reaction is made irreversible by: creation of a phosphodiester bond: hydrolysis of a pyrophosphate group. the entry of a free nucleotide into an RNA polymerase hybridization of a free nucleotide to a template.
How does raft polymerisation work?
RAFT is a type of living polymerization involving a conventional radical polymerization which is mediated by a RAFT agent. Monomers must be capable of radical polymerization. There are a number of steps in a RAFT polymerization: initiation, pre-equilibrium, re-initiation, main equilibrium, propagation and termination.
What is the termination step in radical mediated addition polymerization?
The termination step involves disproportionation and/or combination reactions between two propagating radicals (Fig. 5). Although termination in St polymerization proceeds mainly by combination, disproportionation predominates during MMA polymerization.
What is nitnitroxide-mediated polymerization?
Nitroxide-mediated polymerization (NMP) is a controlled/living radical polymerization (CLRP) technique that enables the design of well-defined, functional and complex macromolecular architectures. This comprehensive review covers all aspects, features and achievements of NMP, from its discovery to 2012.
What is the polydispersity of glycopolymers in NMP reactions?
The polymerizations afforded glycopolymers of narrow polydispersity (1.1) in high conversions (up to 90%). However, the reactions required high temperatures and the protection of the hydroxyl groups of the sugars prior to the polymerizations. 14 Another largely popular nitroxide complex used in NMP is 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO).
Which polymers can be synthesized using NMP?
Polymers that have been successfuly synthesized using NMP include polystyrene, polyacrylates, polymethacrylates, and polyvinylpyridine. 4-7
What is NMRP polymerization?
NMRP is based on sterically hindered alkoxyamines having a thermally labile alkoxyamine bond (C-ON) to control the addition of vinyl monomers to the growing polymer chains. Several vinyl monomers with polar side groups such as methacrylates, acrylates and styrene have been succesfully polymerized using NMRP polymerization techniques.