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Polymer SynthesisCHEM 421
• Odian Book
2-12
Polymer SynthesisCHEM 421
Common Engineering Thermosets(Not elastomers)
• Bismaleimides
• Epoxies
• Phenol / Formaldehyde
• Sheet Molding Compound
• Polyurethanes**
**Also thermoplastics
Chain GrowthChain Growth
Step GrowthStep Growth
Step GrowthStep Growth
Step & Chain GrowthStep & Chain Growth
Step & Chain GrowthStep & Chain Growth
Polymer SynthesisCHEM 421
Epoxy Systems
H2C CH
O
CH CH2
O
H2N NH2
+
R
N NR
H2C
H2C
CH2
CH2
CH
CHCH
CH CH2
OH
OH
CH2
CH2
OH
CH2
OH
f = 2 “Tube A”
f = 4 “Tube B”
Network
Mechanism
Polymer SynthesisCHEM 421
Epoxy Systems
• Advantageous Properties of epoxies
– High chemical and solvent resistance
– Outstanding adhesion to many substrates
– Good impact resistance
– Good electrical properties
H2C CH
O
CH CH2
O
H2N NH2
+ Network
Polymer SynthesisCHEM 421
Epoxy Systems
H2C CH
O
CH CH2
O
+
H2N CH2 NH2
N N
H2C
H2C
CH2
CH2
CH
CHCH
CH CH2
OH
OH
CH2
CH2
OH
CH2
OH
CH2
f = 2 “Tube A”
f = 4 “Tube B”
Network
Polymer SynthesisCHEM 421
Epoxy Systems
CHOCH3
CH3
OHH2C C
H
O
CH2 Cl
Bisphenol-A Epichlorohydrin
COCH3
CH3
O CH2 CH
O
CH2CH2CHH2C
O
Diglycidal Ether of Bisphenol-A (DGEBA)
Polymer SynthesisCHEM 421
Epichlorohydrin: Background
ClCl2
H2C CH
O
CH2 Cl
ClHOCl
Hypochlorous acid
Cl
OH
ClHO
Cl
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
Caustic
Polymer SynthesisCHEM 421
Epoxy Systems
CHOCH3
CH3
OHCOCH3
CH3
O CH2 CH
O
CH2CH2CHH2C
O
<Mn> ≈ 15,000 – 20,000 g/mol
Viscous liquid to solid
COCH3
CH3
O CH2 CH
OH
CH2CH2CHH2C
O
R CH CH2
O
n
Polymer SynthesisCHEM 421
Polyurethanes and Polyureas
• Thermoplastics
• Thermosets
R N C
O
NC
O
R' O
polyurethane
O
H H
n
R N C ONCO
Diisocyanate
R' OHHO
Diol
+
R N C ONCO
Diisocyanate
R' NH2H2N
Diamine
+ R N C
O
NC
O
R' N
polyurea
N
H H
n
H H
Polymer SynthesisCHEM 421
Important Starting Materials for Polyurethanes
• Diisocyantes
• Polymeric Glycols (aka polyols)–MW < 3,000 g/mol
• Chain extenders
• Catalysts–Trialkyl tin acetate
–Dialkyl tin diacetateRelative rates 30,000x
Polymer SynthesisCHEM 421
Diisocyanates
• Diphenylmethane diisocyanate (MDI)
• Toluene diisocyanate (TDI)
• Dicyclohexylmethane diisocyanate (H-MDI)
• Hexamethylene diisocyanate (HDI)
• Cycloaliphatics
CH2OCN NCO
CH2OCN NCO
CH3
NCO
NCO
CH3
NCOOCN
CH2CH2CH2CH2CH2CH2OCN NCO
CH2NCO
CH2NCOH3C
H3C
H3C
Polymer SynthesisCHEM 421
Diisocyanates
• Phosgenation
NH2
Cl C Cl
O
HN C
O
Cl + HCl
HN C
O
Cl + HClN C O
Polymer SynthesisCHEM 421
Chain Extenders
• For urethanes
• For ureas
O CH2CH2CH2CH2 O HH
HO CH2CH2 O H
HO CH2 CH O
CH3
H
CH
CH2
CH2 OH
OH
OH
H2N CH2CH2 NH2
H2N CH2CH2CH2CH2 NH2
Polymer SynthesisCHEM 421
Polyurethane Fibers
HO CH2CH2CH2CH2 O H
OCN R NCO
+
OCN R R NCO Prepolymer
OCN R NCO + H2N R' NH2
Excess
Pre-polymer
Chain extenders
Polymer SynthesisCHEM 421
Sheet Molding Compound
O OO O OO HO CH2 CH
CH3
OH++
Maleic Anhydride Phthalic Anhydride Propylene Glycol
Esterification
O C
O
CH CH C
O
O CH2 CH
O
CH3
C C O
OO
Soluble, Processible "Pre-polymer" 5,000 - 10,000 g/mol
Polymer SynthesisCHEM 421
Sheet Molding Compound
StyreneFiberglassMgOInitiator"Low Profile Additives"
Mix on a conveyor belt...mold...cure!
O C
O
CH CH C
O
O CH2 CH
O
CH3
C C O
OO
Soluble, Processible "Pre-polymer" 5,000 - 10,000 g/mol
Polymer SynthesisCHEM 421Phenol Formaldehyde Resins
• 1872 – Invented by Bayer
• 1907 – First patent and commercial process by Baekeland
• Success: First wholly synthetic polymer used commercially
Polymer SynthesisCHEM 421Phenol Formaldehyde Resins
• Excellent thermal stability
• High char yield
• Low smoke generation
• Low smoke toxicity
Polymer SynthesisCHEM 421
Base-Catalyzed Phenol-Formaldehyde Resins (Resols)
• Base catalyzed
• Excess formaldehyde
• Resols cure with heat alone
Polymer SynthesisCHEM 421
Base-Catalyzed Phenol-Formaldehyde Resins (Resols)
Polymer SynthesisCHEM 421
Base-Catalyzed Phenol-Formaldehyde Resins (Resols)
• Excess formaldehyde
• Resols cure with heat alone
Polymer SynthesisCHEM 421
Polymer SynthesisCHEM 421
Base-Catalyzed Phenol-Formaldehyde 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 SynthesisCHEM 421
Acid-Catalyzed Phenol-Formaldehyde Resins (Novolacs)
Polymer SynthesisCHEM 421
Acid-Catalyzed Phenol-Formaldehyde 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
NN
N
NO
HH6 + NH3
