Polymerization Reaction
“a chemical reaction in which two or more molecules
combine to form larger molecules that contain
repeating structural units”
Addition
Polymerization
Condensation
Polymerization
Addition (Chain Reaction) Polymerization
• A chemical reaction in which monomers are added to each other
to form long-chain molecules without by-products.
• can only occur when the monomer molecule is unsaturated
Addition (Chain Reaction) Polymerization
- initiator is a radical
Radical
Polymerization - propagating site is a carbon radical
- initiator is an acid
Cationic
Polymerization - propagating site is a carbocation
- initiator is a nucleophile
Anionic
Polymerization - propagating site is a carbanion
Coordination - initiator is a transition metal complex
Catalytic - propagating site is a terminal
Polymerization catalytic complex
Addition (Chain Reaction) Polymerization
• most common type is radical polymerization
Initiation
Propagation
Termination
The molecules of the monomer join together to form a
polymeric product in which the molecular formula of the
repeating unit is identical with that of the monomer
Addition Polymerization
Examples:
Addition Polymerization
o Radical Polymerization Mechanism
1
Initiation
2
Propagation
3
Termination
4
Chain Transfer
Radical Polymerization Mechanism
Initiation
1
- Initiator decomposes into free radicals in the presence of monomers
Initiator
• Thermosensitive: Benzoyl peroxide , H2O2, Azobisisobutyronitrile (AIBN)
• Photosensitive:
• Redox-system:
Radical Polymerization Mechanism
Initiator
Radical Polymerization Mechanism
Initiation
1
- free radical initiators attack db of monomer and form new reactive
radical or “activated monomer”
In general,
I
R* + M
2R*
RM1*
Radical Polymerization Mechanism
Propagation
2
- the newly-formed activated monomer attacks and attaches to the
double bond of another monomer molecules
In general,
M 1* + M
M2*
M2* + M
M 3*
Mx* + M
Mx+1*
Radical Polymerization Mechanism
2
Propagation
Radical Polymerization Mechanism
Termination
3
- typically occurs in two ways: combination and disproportionation
Combination
two radical species react with each
other forming a single molecule
Mx* + M y*
Mx+y
Disproportionation
two radicals meet & exchange proton,
which gives two terminated chains
Mx* + M y*
Mx + M y
Radical Polymerization Mechanism
4
Chain Transfer
• free radical is transferred from the polymer chain to another by
> an intermolecular hydrogen atom transfer or
> intramolecular hydrogen atom transfer
• polymerization process (the propagation step) is stopped
• molecular weight gained from a polymerization reaction is reduced
Radical Polymerization Mechanism
4
Chain Transfer
Radical Polymerization Mechanism
4
Chain Transfer
usually categorized as
transfer to monomer
Transfer to dead polymer
Intramolecular transfer (back-biting)
transfer to added transfer agent (used to control the molecular
weight to overcome the processing problems)
Inhibitors
- react with the radicals as soon
as they are produced
- prevents self-polymerization in
the storage of pure monomers
Retarders
-like less-reactive inhibitors,
- can reduce the rate and degree
of polymerization
Condensation (Step) Polymerization
• A chemical reaction which involves interaction of two
similar or different monomers and generally liberate liquid or
gaseous by products (such as water, hydrochloric acid or
nitrogen gas)
• Types of condensation polymers include polyamides,
polyacetals and polyesters.
Condensation Polymerization
Condensation Polymerization
Condensation Polymerization
Phenol formaldehyde
Condensation Polymerization
Urea formaldehyde
Addition vs. Condensation
Addition
Condensation
Vinyl monomer
มอนอเมอร์ที่มห
ี มูฟ
่ งั ก์ชนั ต่างกัน
ได้ผลิตภัณฑ์ และมักเกิด
ปฏิกริ ยิ าสังเคราะห์ต้องใช้ intiator
สารโมเลกุลเล็ก
Repeating unit มีจานวนอะตอมเท่ากับ Repeating unit มีจานวนอะตอมน้อย
จานวนอะตอมโดยรวมของ
กว่าจานวนอะตอมโดยรวมของ
มอนอเมอร์เริ่มต้น
มอนอเมอร์เริ่มต้น
น้าหนักโมเลกุลเฉลีย่ ของพอลิเมอร์
น้าหนักโมเลกุลเฉลีย่ ของผลิตภัณฑ์
ไม่ขึ้นกับเวลาที่ใช้ในการสังเคราะห์
เพิ่มขึน้ ตามเวลาที่ใช้ในการสังเคราะห์
Addition vs. Condensation
Addition Polymerization
Condensation Polymerization