Aromatic Polyamides
“Aramids”
Beth Neilson
CH 392N
February 19, 2009
Outline
•
•
•
•
•
Definition / Invention
Preparation
Physical properties
Fiber spinning
Applications
Aramids
• Federal Trade Commission definition for
aramid fiber: A manufactured fiber in which the fiberforming substance is a long-chain synthetic polyamide
in which at least 85% of the amide (-CO-NH-) linkages
are attached directly between two aromatic rings
O
O
C
H2N
*
Ar
H
N
C
Ar
R
Amide
Aromatic
Aromatic polyamide
• Invention
– DuPont – Morgan, Kwolek et. al.
– Japan, Netherlands
*
n
Chemical Structure
O
*
Ar
H
N
C
Ar
*
n
• Homopolymer repeat units:
O
H
N
Ar
H
N
1
C
O
Ar
C
O
H
N
2
• AB homopolymers – Type 3
• AABB homopolymers – Types 1 and 2
• Copolymers
Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989.
Ar
3
C
Chemical Structure
• Aromatic units
Backbone:
Pendent Groups:
X
X= Alkyl, Aryl, Halogen,
Alkoxy, Cyano, Acetyl, Nitro
Bridging Units:
N
N
H
N
O
X
N
N
X
Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989.
X = ether, sulfide, sulfone, ketone, amine,
isopropylidine, ethylene, fumaryl, azo
H
N
Preparation
• AB Homopolymers
O
n H2N
Ar
O
C
X
H
N
*
Ar
C
A
n
* + HX
B
• AABB Homopolymers
O
O
HX +diamines
– Polycondensation of diacid halides with
n H2N
Ar
NH2 +
n X
C
Ar
C
X
• Solution polycondensation
*
• Interfacial polycondensation
O
H
N
Ar
A
• Melt or vapor phase polymerization
Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177.
H
N
C
A
B
O
Ar
C
B
*
n
Solution Polycondensation
O
n H2N
NH2 + n Cl
Ar
O
C
Ar
HCl +
C
Cl
O
*
H
N
Ar
A
H
N
C
A
B
• Diamine and diacid chloride – DuPont
– Low temperature
– Monomer purity and concentration
– Amide solvent (NMP, HMPA, DMA)
O
O
H3C
N
N
H3C
P
N
H3C
N-methylpyrrolidone
O
CH3
N
N
CH3
CH3
Hexamethylphosphoramide
Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177.
H3C
CH3
CH3
Dimethylacetamide
O
Ar
C
B
*
n
Solution Polycondensation
• Poly(m-phenylene isophthalamide) Nomex®
O
H2N
O
NH2
Cl
Cl
Amide Solvent
+
*
H
N
H
N
O
O
C
C
*
n
• Kwolek, S. L.; Morgan, P. W.; Sorenson, R. W. U.S.
Patent 1 199 458, November 13, 1962.
• DuPont, 1967
Solution Polycondensation
• Poly(p-phenylene terephthalamide) (PPTA) Kevlar®
O
H2N
NH2
Cl HMPA/NMP
2:1
-15o C
O LiCl or CaCl2
+
Cl
*
H
N
H
N
O
O
C
C
• DuPont – Bair, Blades, Morgan, Kwolek
• AKZO – Leo Vollbracht, Twaron®
Kwolek, S. L. U.S. Patent 3 819 587, 1974.
Blades, H. U.S. Patent 3 869 429, 1975.
Bair, T. I.; Morgan, P. W. U.S. Patent 3 673 143, 1972.
n
*
Solution Polycondensation
• Higashi synthesis - phosphorus-containing
activating agent
OAr'
OAr'
O
O
HO
C
Ar
C
OH
N
NMP/LiCl
O
N
P(OPh)3 /
H
P
O
Ar'O
O
C
Ar
C O
OAr'
H2N
O
*
C
H
OAr'
Ar'
NH2
O
Ar
+
Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177.
Odian, G. Principles of Polymerization, 4th Ed. Wiley: New York, 2004.
P
Ar'O
Advantages:
• Eliminates acid chloride
starting material
• Can tune reactivity by
changing Ar’
N
C
H
N
Ar'
2 Ar'OH + 2 HO
H
N
n*
P(OAr')2
Solution Polycondensation
• Silylated diamine with diacid chloride
H
H2N
Ar
NH2
Me3SiCl
SiMe3
N
Ar
Me3Si
Me3SiCl
Ar'(COCl)2
N
O
H
*
H
N
Ar
H
N
C
•Increases reactivity of aromatic diamine
•Faster reaction
•Elimination of Me3SiCl rather than HCl
•Higher molecular weight
Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177.
+
O
Ar'
C
n
*
Solution Polycondensation
• Copolymers
– Copolymerization of three or more aromatic diamines
and diacid halides.
– Improved solubility, thermal properties, fiber
properties
– Technora®
*
H
N
H
N
H
N
m
O
H
N
n
O
O
C
C
*
Solution Polycondensation Summary
• Preparation of AABB homopolymers, copolymers
• Aromatic diamine with diacid halide
• High molecular weight
– Low temperature
– Monomer stoichiometry, purity, concentration
– Solvent
– Salt concentration
– Monomer structure (silylated amines)
– Reagents (triarylphosphites, pyridine)
Physical Properties
•
•
•
•
High thermal stability (Td ≥ 400°C)
High tenacity (tensile strength)
Chemical resistance
Unique solution properties
– Low solubility
– Liquid crystallinity in p-aramids due to chain rigidity
• Structure dependent
– Meta vs. para linkages
– Structure of aromatic backbone
Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989.
Hearle, J. S. High Performance Fibers, Woodhead Publishing Limited: Cambridge, 2001.
Liquid Crystallinity
• Liquid crystal – substance that has properties
of both a solid and a liquid
– Thermotropic – phase transition occurs with
temperature change
– Lyotropic
• Liquid crystallinity occurs only in solution
• Varies as a function of polymer concentration and
temperature
Odian, G. Principles of Polymerization, 4th Ed. Wiley: New York, 2004.
Liquid Crystallinity of p-Aramids
• In solution of proper concentration, liquid crystalline
domains form, in which there is a high degree of
order of the solute molecules.
– Para linkages result in rod-like extended chain structure.
– Hydrogen bonding
• Crystallization from liquid crystal solutions results in
polymers with highly ordered extended-chain
morphology
• Gives rise to polymers with higher strength and
modulus
Odian, G. Principles of Polymerization, 4th Ed. Wiley: New York, 2004.
Aramid Fiber Spinning
Dry-jet Wet Spinning
• Spinning Solution
– 10-20 wt% polymer
– 100% H2SO4 (H2O free)
• Elongation aligns
crystalline domains
• Precipitates out of
coagulation bath
• Crystallinity of solution is
translated to fiber
Hearle, J. S. High Performance Fibers, Woodhead Publishing Limited: Cambridge, 2001.
Properties of Aramid Fibers
• Tenacity and Modulus
– Spinning and drawing conditions
• Wet vs. dry
• Heat treatment
– Polymer composition
– Molecular weight
Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989.
Applications of Aramids
Kevlar®
*
H
N
http://en.wikipedia.org/wiki/Aramid#Major_industrial_uses
H
N
O
O
C
C
n
*
Applications of Aramids
Nomex®
H
N
*
Technora®
*
H
N
C
C
O
O
*
n
H
N
H
N
H
N
m
O
H
N
n
O
O
C
C
*
Applications of Aramids
Hearle, J. S. High Performance Fibers, Woodhead Publishing Limited: Cambridge, 2001.