Polymer Science
Submitted By…
1st
Year 2nd
Semester
Group: C1
Roll: 151-175
Polymerisation
 The process by which the monomer molecules are linked
to form a big polymer molecule is called Polymerisa...
Polymerisation Mechanism 152
Functionality of Monomers
1. The number of reactive functional Group Represent in a monomer.
CH3 – COOH ; Functionality = ...
Examplesof functionality of monomer 153,
154
Cont…
153,
154
155,
156Functionality effects on line structure of
polymer
- In order to form a polymer, the monomer must be at least bi f...
155,
156
For example,
Consider the polymerisation of phthalic anhydride with glycerol where
functionality of monomer is 3 .
155,
156
So,
FUNCTIONALITY of MONOMER = 2 LINEAR CHAIN POLYMER
FUNCTIONALITY of MONOMER > 2 BRANCHED CHAIN POLYMER
Characteristics of chain-growth
polymerisation
 Growth by addition of monomer only at one end or both ends of
chain
 Som...
157,
158
Examplesof monomers, capableof undergoing chain polymerisation
FreeRadical Polymerisation
This Polymerisation is divided into 3 parts.
 Initiation
 Propagation
 Termination.
161-
165
Initiation
The first step in chain polymerization, Initiation involves the formation of a free
radical.
This free radicals...
161-
165
Initiator: A relatively unstablemoleculethat decomposesinto afree
radical. Used to initiateapolymer growth reacti...
161-
165
List of free-radical initiators:
161-
165Cont…
161-
165Cont…
161-
165
Cont…
161-
165
Cont…
161-
165Cont…
Propagation
It is the middle step in chain polymerization where successive monomers are
attached to the growing chain. In...
Modesof Propagation
1. Head to Tail
2. Head to Head
3. Tail to Head
4. Tail to Tail
166,
168
Termination
 Termination of reaction is nothing but stop the further propagation of chain.
 In theory, the propagation r...
171,
172
2. Disproportionation: It halts the propagation
reaction when a free radical strips a hydrogen atom from
an activ...
Chain Transfer Reaction
It is another method of termination, which takes place by transfer reaction.
In termination reacti...
Telomerisation
A solvent of high chain transfer ability and having a chemical structure similar to
that of a monomer to fo...
Thank you for your time…
of 27

Polymerisation Mechanism ( chain growth )

This slides contain brief description of polymerisation mechanism, specially chain growth mechanism.
Published on: Mar 4, 2016
Published in: Science      
Source: www.slideshare.net


Transcripts - Polymerisation Mechanism ( chain growth )

  • 1. Polymer Science Submitted By… 1st Year 2nd Semester Group: C1 Roll: 151-175
  • 2. Polymerisation  The process by which the monomer molecules are linked to form a big polymer molecule is called Polymerisation.  Polymerisation is a process of bonding monomer, or “single units” together through a variety of reaction mechanisms to form longer chains named Polymer  As important as polymers are, they exist with monomers, which are small, single molecules such as hydrocarbons and amino acids. 151
  • 3. Polymerisation Mechanism 152
  • 4. Functionality of Monomers 1. The number of reactive functional Group Represent in a monomer. CH3 – COOH ; Functionality = 1 HO – CH2 -- CH2 – OH ; Functionality = 2 1. The number of Hydrogenation that can be added to a monomer. CH2 = CH2 ----------------> CH3 – CH3 ; Functionality = 2 CH ≡ CH -------> CH2 = CH2 ------> CH3 – CH3 ; Functionality = 4 1. The number of replaceable atom present in a monomer. 153, 154
  • 5. Examplesof functionality of monomer 153, 154
  • 6. Cont… 153, 154
  • 7. 155, 156Functionality effects on line structure of polymer - In order to form a polymer, the monomer must be at least bi functional. When it is bi functional monomer, polymer chain is always linear. - Branched polymer contains molecules having a linear backbone with branches emanating randomly from it. In order to form this class of material, the monomer must have a capability of growing in more than two directions, which implies that the starting monomer must have a functionality greater than 2 .
  • 8. 155, 156 For example, Consider the polymerisation of phthalic anhydride with glycerol where functionality of monomer is 3 .
  • 9. 155, 156 So, FUNCTIONALITY of MONOMER = 2 LINEAR CHAIN POLYMER FUNCTIONALITY of MONOMER > 2 BRANCHED CHAIN POLYMER
  • 10. Characteristics of chain-growth polymerisation  Growth by addition of monomer only at one end or both ends of chain  Some monomer remains even at long reaction times  Different steps operate at different stages of mechanism (i.e. Initiation, propagation, termination, and chain transfer)  Molar mass of backbone chain increases rapidly at early stage and remains approximately the same throughout the polymerisation  Chains not active after termination  Initiator required 157, 158
  • 11. 157, 158 Examplesof monomers, capableof undergoing chain polymerisation
  • 12. FreeRadical Polymerisation This Polymerisation is divided into 3 parts.  Initiation  Propagation  Termination. 161- 165
  • 13. Initiation The first step in chain polymerization, Initiation involves the formation of a free radical. This free radicals are produced by the decomposition of initiators. 161- 165
  • 14. 161- 165 Initiator: A relatively unstablemoleculethat decomposesinto afree radical. Used to initiateapolymer growth reaction Freeradicals: An especially reactiveatom or group of atomsthat has oneor moreunpaired electrons
  • 15. 161- 165 List of free-radical initiators:
  • 16. 161- 165Cont…
  • 17. 161- 165Cont…
  • 18. 161- 165 Cont…
  • 19. 161- 165 Cont…
  • 20. 161- 165Cont…
  • 21. Propagation It is the middle step in chain polymerization where successive monomers are attached to the growing chain. In the propagation stage, the process of electron transfer and consequent motion of the active center down the chain proceeds. In following reaction(chain), refers to a chain of connected monomers, and X refers to a substituent group (a molecular fragment) specific to the monomer. For example, if X were a methyl group, the monomer would be propylene and the polymer, polypropylene. 166, 168
  • 22. Modesof Propagation 1. Head to Tail 2. Head to Head 3. Tail to Head 4. Tail to Tail 166, 168
  • 23. Termination  Termination of reaction is nothing but stop the further propagation of chain.  In theory, the propagation reaction could continue until the supply of monomers is exhausted. Most often the growth of a polymer chain is halted by the termination reaction. Termination typically occurs in two ways: 1. Combination: It occurs when the polymer's growth is stopped by free electrons from two growing chains that join and form a single chain. The following diagram depicts combination, with the symbol (R) representing the rest of the chain 171, 172
  • 24. 171, 172 2. Disproportionation: It halts the propagation reaction when a free radical strips a hydrogen atom from an active chain. A carbon-carbon double bond takes the place of the missing hydrogen. - Disproportionation can also occur when the radical reacts with an impurity. This is why it is so important that polymerization be carried out under very clean conditions.
  • 25. Chain Transfer Reaction It is another method of termination, which takes place by transfer reaction. In termination reaction, products form dead of non reactive due to coupling or disproportionation. However in chain transfer reaction, one polymer chain is stopped forming a dead polymer, there is a simultaneous generation of a new free radical capable of initiating a fresh polymer chain growth. 173
  • 26. Telomerisation A solvent of high chain transfer ability and having a chemical structure similar to that of a monomer to form polymer is known as telomerisation. The solvent used in such cases is known as telogen. 175
  • 27. Thank you for your time…

Related Documents