Aromatic Polyamides “Aramids” Beth Neilson CH 392N February 19, 2009.

Aromatic Polyamides“Aramids”

Beth NeilsonCH 392N

February 19, 2009

Outline

• Definition / Invention

• Preparation

• Physical properties

• Fiber spinning

• Applications

• Federal Trade Commission definition for aramid fiber: A manufactured fiber in which the fiber-forming 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

• Invention– DuPont – Morgan, Kwolek et. al.– Japan, Netherlands

ArHN C

O

Ar* *n

Aramids

C

O

H2N R

Amide Aromatic Aromatic polyamide

• Homopolymer repeat units:

• AB homopolymers – Type 3

• AABB homopolymers – Types 1 and 2

• Copolymers

HN Ar

HN Ar CC

O

HN Ar C

1 2 3

O O

Chemical Structure

Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989.

ArHN C Ar* *

n

O

• Aromatic units

NN

O N

X

N

Chemical Structure

Backbone:X

X= Alkyl, Aryl, Halogen,Alkoxy, Cyano, Acetyl, Nitro

HN X

HN

X = ether, sulfide, sulfone, ketone, amine,isopropylidine, ethylene, fumaryl, azo

Pendent Groups:

Bridging Units:


• AB Homopolymers

Ar C

O

XCX

O

H2N Arn NH2 + n

HN Ar

HN C* Ar C *

O O

nA A B B

HX +

• AABB Homopolymers

– Polycondensation of diacid halides with diamines

• Solution polycondensation

• Interfacial polycondensation

• Melt or vapor phase polymerization

Preparation

Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177.

H2N Ar C

O

Xn *HN Ar C

O

*n

+ HX

A B

Ar C ClCCl

O

H2N Arn NH2 + n

HN Ar

HN C* Ar C *

O O

nA A B B

HCl +O

• Diamine and diacid chloride – DuPont– Low temperature

– Monomer purity and concentration

– Amide solvent (NMP, HMPA, DMA)

N CH3

O

DimethylacetamideN-methylpyrrolidone Hexamethylphosphoramide

N

O

P

O

N

N

NCH3

CH3

CH3H3C

H3C

H3C

H3C

CH3

Solution Polycondensation


• Poly(m-phenylene isophthalamide) Nomex®

• Kwolek, S. L.; Morgan, P. W.; Sorenson, R. W. U.S. Patent 1 199 458, November 13, 1962.

• DuPont, 1967

HN

HN C C **

O O

n

+

H2N NH2

Cl Cl

O O

Amide Solvent


• Poly(p-phenylene terephthalamide) (PPTA) Kevlar®

• 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.

NH2H2N +

HN

HN* C

O

C

O

*n

HMPA/NMP2:1

-15o CLiCl or CaCl2

Cl

Cl

O

O

• Higashi synthesis - phosphorus-containing activating agent

Ar CP(OPh)3 /

N

NMP/LiClO Ar CP

N

Ar'O OAr'

H P H

N

OAr'Ar'O

OAr'

H2N Ar' NH2

C Ar*

O

CHN

O

Ar'HN *n

+ HO P(OAr')222 Ar'OH +

OAr'

C OHHO

O O

C

O

O

O

Advantages:• Eliminates acid chloride

starting material• Can tune reactivity by

changing Ar’


Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177.Odian, G. Principles of Polymerization, 4th Ed. Wiley: New York, 2004.

• Silylated diamine with diacid chloride

H2N Ar NH2

Me3SiClAr NN

Ar'(COCl)2

HN Ar*

HN C

O

Ar' C *

O

n

H SiMe3

HMe3Si

Me3SiCl +

•Increases reactivity of aromatic diamine•Faster reaction

•Elimination of Me3SiCl rather than HCl

•Higher molecular weight



• Copolymers– Copolymerization of three or more aromatic diamines

and diacid halides.

– Improved solubility, thermal properties, fiber properties

– Technora®


HN

HN* C

O

C

O

*HN O

HN

m n

• 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)

Solution Polycondensation Summary

• 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

Physical Properties

Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989.Hearle, J. S. High Performance Fibers, Woodhead Publishing Limited: Cambridge, 2001.

• 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

Liquid Crystallinity

Odian, G. Principles of Polymerization, 4th Ed. Wiley: New York, 2004.

• 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

Liquid Crystallinity of p-Aramids

Odian, G. Principles of Polymerization, 4th Ed. Wiley: New York, 2004.

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

Aramid Fiber Spinning

Hearle, J. S. High Performance Fibers, Woodhead Publishing Limited: Cambridge, 2001.

• Tenacity and Modulus

– Spinning and drawing conditions

• Wet vs. dry

• Heat treatment

– Polymer composition

– Molecular weight

Properties of Aramid Fibers


Kevlar®HN

HN* C

O

C

O

*n

http://en.wikipedia.org/wiki/Aramid#Major_industrial_uses

Applications of Aramids

HN

C

O

C*

HN

O

* n

Nomex® Technora®

HN

HN* C

O

C

O

*HN O

HN

m n



Hearle, J. S. High Performance Fibers, Woodhead Publishing Limited: Cambridge, 2001.

Aromatic Polyamides “Aramids” Beth Neilson CH 392N February 19, 2009.

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Transcript of Aromatic Polyamides “Aramids” Beth Neilson CH 392N February 19, 2009.