![Termination of Radical Polymerization
10/31/2019 14
• 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,
• -------CH2–C°HR + -------CH2–C°HX → -------CH2–CH2X–CH2X–
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:
• -------CH2–C°HX + -------CH2–C°HX → -------CH2–CH2X + -------
CH=CHX](https://image.slidesharecdn.com/typesofpolymerization-191031183850/75/Types-of-polymerization-14-2048.jpg)
Uploaded byFarhan ullah baig
Types of polymerization
This document discusses different types of polymerization, including addition/chain growth polymerization and step polymerization. It focuses on addition/chain growth polymerization, describing the three types: free-radical chain growth polymerization, anionic chain growth polymerization, and cationic chain growth polymerization. Free-radical polymerization uses initiating molecules to start the polymerization reaction and grow polymer chains through a chain reaction mechanism. Anionic and cationic polymerizations also use initiating molecules and chain growth, but differ in whether an anion or cation is used to start and propagate the reaction. Termination of radical polymerization occurs through recombination or disproportionation of polymer chains.
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Types of polymerization
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- 3. 10/31/2019 3 Addition/Chain GrowthPolymerization
- 4. 10/31/2019 4 Addition/Chain GrowthPolymerization
- 5. 10/31/2019 5 Addition/Chain GrowthPolymerization
- 6. 10/31/2019 6 General CharacteristicsofAddition/Chain Growth Polymerization
- 7. • ‘It requirespresence of an initiating molecule that can be used to attach a monomer molecule at the start of polymerization.” • There are 3 types of it 1. Free-radical chain growth polymerization 2. Anionic chain growth polymerization 3. Cationic chain growth polymerization 10/31/2019 7
- 8. Free Radical • Itis 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(HO•), a molecule that has one unpaired electron on the oxygen atom. • In contrast, the hydroxyl anion (HO−) is not a radical, since the unpaired electron is resolved by the addition of an electron. 10/31/2019 8
- 9. Free Radical • Freeradicals 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. 10/31/2019 9
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- 14. Termination of RadicalPolymerization 10/31/2019 14 • 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, • -------CH2–C°HR + -------CH2–C°HX → -------CH2–CH2X–CH2X– 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: • -------CH2–C°HX + -------CH2–C°HX → -------CH2–CH2X + ------- CH=CHX
- 15. Termination of RadicalPolymerization 10/31/2019 15 • In a disproportionation step, one radical transfers a hydrogen atom to the other to form two stable molecules: • ----CH2–C°HX + ----CH2–C°HX → ---CH2–CH2X + ---CH=CHX
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- 24. 10/31/2019 24 Discussion abouttermination 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.
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- 32. TYPES • Polymerization usuallyproceeds 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
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- 40. EXAMPLES • The synthesisof 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 • Thetwo 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
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Editor's Notes
- #4 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.
- #6 Termination by coupling,Termination by disproportionation, termination by chain transfer
- #14 Termination by coupling
- #15 Termination by coupling
- #16 Termination by coupling
- #19 BF3 is lewis acid generally called catalyst in the presence of small amount of water as a co catalyst
- #21 ,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
- #23 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.
- #24 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.
- #26 Middle group of metals in periodic table. mostly acts as catalyst. add in sytem to start reaction but attermination step they are recovered
- #27 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..
- #28 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.