I faced with this structure, when I studied about PE-g-MAH for tie layers application.
Polymer synthesis can be done by several methods. I think you are familiar with most common two techniques
1. Addition Polymerization (Free radicals are involved)
2. Condensation polymerization (Step growth polymerization)
Condensation Polymerization: molecules are joined by the elimination of a small molecule. Slow building up of chains in a step-wise fashion – e.g., polyester – Some small side product substances are brought up in the polymerization (water, alcohol etc.) The functional groups of the monomer react. The size of molecule grows steadily but slowly. Functionality is defined as the number of sites, at which the new molecule can be attached to the - mer. bi-functional monomer – linear polymer chains can be formed. Tri-functional monomer stronger 3 dimensional network molecules can be formed. Poly-functional – several potential points of contact – 3 dimensional network molecules can be formed.
In addition to these other methods are also there, viz.,
3. Cationic Polymerization
4. Anionic Polymerization
5. Coordination Polymerization
General features of ionic polymerization:
Initiation: most common initiators are butyl-lithium isomers (n-, sec-, tert-) – these are soluble in hydrocarbon solvents (alkanes, aromatics) but are unstable in air.
Propagation: just as with radical polymerization – simple chain growth polymerization
Termination: NONE; if exclude groups which will react with alkyl-lithium; “living polymerization”
Sometimes it is difficult to obtain kinetic data or even reproducible data, The mechanisms of these are less thoroughly understood than that of radical polymerization for several reasons. Heterogeneous catalysts, Rate of reaction is very high, Very high molecular weight polymers, Polarity of the monomer, Acid-base strength of the ion-pair
Basis of selection:-
Electron donating group - Cationic Polymerization
Electron withdrawing group - Anionic Polymerization
Moderate electron withdrawing and bond conjugation in the free radical polymerization
Initiation involves the transfer of an ion to or from the monomer with the formation of an ion pair of the monomer. Unsaturated monomers are involved. In Anionic polymerization of the active site is a carbanion. In cationic polymerization: aprotonic acids [Lewis acids], bronsted acids. All are strong electron acceptors. Reaction is initiated by the ionization of the added initiator.
it means polymerization again starts when you put monomer to medium
Hi Bahattin AYDINLI,
Many thanks for the quarry.
It might; but generally when the length of polymer increases the rate of migration of the molecules become slower. Here it is needed to supply the correct reaction conditions to let the reaction to initiate.
Generally at the first stage of polymerization reaction it is necessary to perform the termination reactions after adding retarders or special additives. By doing so it is possible to electrically neutral lengthy polymer molecule.
Best regards,
Asoka Panamgama
I think the living free radical techniques must be mentioned, including ATRP, NMP and RAFT. Those are often associated with the second grafting step.
Living indicates that termination reactions are limited to
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