Polymer Synthesis
CHEM 421
• Odian Book
2-12
Common Engineering Thermosets
(Not elastomers)
Polymer Synthesis
CHEM 421
• Bismaleimides
Step & Chain Growth
• Epoxies
Step & Chain Growth
• Phenol / Formaldehyde
Step Growth
• Sheet Molding Compound
Chain Growth
• Polyurethanes**
**Also thermoplastics
Step Growth
Epoxy Systems
Polymer Synthesis
CHEM 421
f = 2 “Tube A”
f = 4 “Tube B”
Mechanism
Network
Epoxy Systems
• Advantageous Properties of epoxies
– High chemical and solvent resistance
– Outstanding adhesion to many substrates
– Good impact resistance
– Good electrical properties
Polymer Synthesis
CHEM 421
Epoxy Systems
Polymer Synthesis
CHEM 421
f = 2 “Tube A”
f = 4 “Tube B”
Network
Epoxy Systems
Polymer Synthesis
CHEM 421
Diglycidal Ether of Bisphenol-A (DGEBA)
Epichlorohydrin:
Background
Chlorine intensive
- 4 atoms of chlorine/epi
Yields:
- chlorination: 82%
- HOCl and closure: 92%
Byproducts:
- chlorinated organics
Hydraulic load:
- 47 lbs water/lb of epi
Polymer Synthesis
CHEM 421
Epoxy Systems
<Mn> ≈ 15,000 – 20,000 g/mol
Viscous liquid to solid
Polymer Synthesis
CHEM 421
Polyurethanes and Polyureas
• Thermoplastics
• Thermosets
Polymer Synthesis
CHEM 421
Important Starting Materials
for Polyurethanes
Polymer Synthesis
CHEM 421
• Diisocyantes
• Polymeric Glycols (aka polyols)
–MW < 3,000 g/mol
• Chain extenders
• Catalysts
–Trialkyl tin acetate
–Dialkyl tin diacetate
Relative rates
30,000x
Diisocyanates
• Diphenylmethane diisocyanate (MDI)
• Toluene diisocyanate (TDI)
• Dicyclohexylmethane diisocyanate (H-MDI)
• Hexamethylene diisocyanate (HDI)
• Cycloaliphatics
Polymer Synthesis
CHEM 421
Diisocyanates
Polymer Synthesis
CHEM 421
• Phosgenation
O
H
N
C
Cl
N
C
O
+
HCl
Chain Extenders
• For urethanes
• For ureas
Polymer Synthesis
CHEM 421
Polyurethane Fibers
Polymer Synthesis
CHEM 421
Excess
Pre-polymer
Chain extenders
Sheet Molding Compound
Polymer Synthesis
CHEM 421
Sheet Molding Compound
Polymer Synthesis
CHEM 421
Phenol Formaldehyde Resins
Polymer Synthesis
CHEM 421
• 1872 – Invented by Bayer
• 1907 – First patent and commercial
process by Baekeland
• Success: First wholly synthetic
polymer used commercially
Phenol Formaldehyde Resins
• Excellent thermal stability
• High char yield
• Low smoke generation
• Low smoke toxicity
Polymer Synthesis
CHEM 421
Base-Catalyzed PhenolFormaldehyde Resins (Resols)
• Base catalyzed
• Excess formaldehyde
• Resols cure with heat alone
Polymer Synthesis
CHEM 421
Base-Catalyzed PhenolFormaldehyde Resins (Resols)
Polymer Synthesis
CHEM 421
Base-Catalyzed PhenolFormaldehyde Resins (Resols)
• Excess formaldehyde
• Resols cure with heat alone
Polymer Synthesis
CHEM 421
Polymer Synthesis
CHEM 421
Base-Catalyzed PhenolFormaldehyde Resins (Resols)
• Cure of resole prepolymer proceeds
under neutral or acidic conditions
and at elevated temperature.
• Crosslinking occurs via the
continued formation of methylene
links and the formation of dibenzyl
ether linkages.
• Higher temperatures favor the
formation of methylene bridges
• Both are condensation reactions
and produce water
Polymer Synthesis
CHEM 421
Acid-Catalyzed PhenolFormaldehyde Resins (Novolacs)
Polymer Synthesis
CHEM 421
Acid-Catalyzed PhenolFormaldehyde Resins (Novolacs)
•
•
•
•
•
•
Acid Catalyzed
Excess phenol
No hydroxy methyl groups
Tg = 40 C
MW = 1 – 3000 g/mol
Require second additive for cure
– Hexamethylene tetraamine
Polymer Synthesis
CHEM 421