7. ⢠âIt requires presence of an initiating molecule that can
be used to attach a monomer molecule at the start of
polymerization.â
⢠There are 3 types of it
1. Free-radical chain growth polymerization
2. Anionic chain growth polymerization
3. Cationic chain growth polymerization
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8. Free Radical
⢠It is an atom, ion or molecule having unpaired valence
electrons.
⢠These unpaired electrons make free radical highly
chemically reactive toward other substances.
⢠A notable example of free radical is hydroxyl radical(HOâ˘),
a molecule that has one unpaired electron on the oxygen
atom.
⢠In contrast, the hydroxyl anion (HOâ) is not a radical,
since the unpaired electron is resolved by the addition of
an electron.
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9. Free Radical
⢠Free radicals may be created in a number of ways,
including synthesis with very dilute or reactions at very
low temperatures, or breakup of larger molecules.
⢠Free radicals play an important role in combustion,
polymerization, plasma chemistry, biochemistry, and many
other chemical processes.
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14. Termination of Radical Polymerization
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⢠The termination steps of free radical polymerization steps are of
two types: recombination and dis-proportionation.
⢠In a recombination step, two growing chain radicals form a
covalent bond in a single stable molecule. For the example of a
vinyl polymer,
⢠-------CH2âC°HR + -------CH2âC°HX â -------CH2âCH2XâCH2Xâ
CH2------- Termination by recombination increases the chain
length and therefore the molecular weight of the final polymer.[2]
⢠In a disproportionation step, one radical transfers a hydrogen
atom to the other to form two stable molecules:
⢠-------CH2âC°HX + -------CH2âC°HX â -------CH2âCH2X + -------
CH=CHX
15. Termination of Radical Polymerization
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⢠In a disproportionation step, one radical transfers a hydrogen
atom to the other to form two stable molecules:
⢠----CH2âC°HX + ----CH2âC°HX â ---CH2âCH2X + ---CH=CHX
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Discussion about termination process of Anionic Polymerization
⢠Termination process in anionic polymerization is however not usually
spontaneous process.
⢠And unless some impurities are present or some strongly ionic substances are
added deliberately.
⢠Thus if polymerization is carried out under controlled condition and impurities
are avoided. The reaction proceeds till all the monomer is consumed.
⢠Studies have shown that polymerization may be restarted even after weeks by
adding fresh monomer.
⢠It is as if the polymer is living entity and called living polymer.
⢠Block co polymer can be prepared by this technique.
32. TYPES
⢠Polymerization usually proceeds by the
reactions between two different functional
groups, for example, hydroxyl and carboxyl
groups, or isocyanate and hydroxyl groups.
⢠All step polymerizations fall into two groups
1. Two different bifunctional and/or polyfunctional
monomers in which each monomer possesses
only one type of functional group.
2. The second involves a single monomer
containing both types of functional groups.
1 32
40. EXAMPLES
⢠The synthesis of polyamides illustrates both groups of
polymerization reactions. Thus polyamides can be
obtained from the reaction of diamines with diacids
⢠or from the reaction of amino acids with themselves:
1 40
41. GENERAL DESCRIPTION
⢠The two groups of reactions can be represented in a
general manner by the equations
⢠where A and B are the two different types of functional
groups.
1 41
In organic chemistry, a saturated compound is a chemical compound that has a chain of carbon atoms linked together by single bonds. Alkanes as. An unsaturated compound is a chemical compound that contains carbon-carbon double bonds or triple bonds, such as those found in alkenes or alkynes, respectively. Saturated and unsaturated compounds need not consist only of a carbon atom chain. They can form straight chain, branched chain, or ring arrangements. They can have functional groups, as well. It is in this sense that fatty acids are classified as saturated or unsaturated.
Termination by coupling,Termination by disproportionation, termination by chain transfer
Termination by coupling
Termination by coupling
Termination by coupling
BF3 is lewis acid generally called catalyst in the presence of small amount of water as a co catalyst
,Termination by disproportionation: H from one growing chain is abstracted by other growing chain and utilized by lone electron for getting stablized.while the chain which has denoted the H get stablized byformation of double bond.in this case formation of two polymer molecules of shorter chain length
Termination process in anionic polymerization is however not usually spontaneous process, and unless some impurities are present or some strongly ionic substances are added deliberatley.thus if polymerization is carried out under controlled condition and impurities are avoided.the reaction proceeds till all the monomer is consumed.studies have shown that polymerization may be restarted even after weeks by adding fresh monmer.it is as if the polymer is living entity and called living polymer.block co polymer can be prepared by this technique.
Termination process in anionic polymerization is however not usually spontaneous process, and unless some impurities are present or some strongly ionic substances are added deliberatley.thus if polymerization is carried out under controlled condition and impurities are avoided.the reaction proceeds till all the monomer is consumed.studies have shown that polymerization may be restarted even after weeks by adding fresh monmer.it is as if the polymer is living entity and called living polymer.block co polymer can be prepared by this technique.
Middle group of metals in periodic table. mostly acts as catalyst. add in sytem to start reaction but attermination step they are recovered
Polymers having an orderd arrangement of pendant groups along the chain is known as stereoregular arrangement. Stereoregular polymers are usually high-strength materials because the uniform structure leads to close packing of the polymer chains and a high degree of crystallinity..
Compounds that contain a metal-carbon bond, R-M, are known as "organometallic" compounds. Organometallic compounds of Li, Mg (Grignard reagents) are amongst some of the most important organic reagents.