synthesis and properties of cross-linked polyamide …...national aeronautics and space...

National Aeronautics and Space Administration

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Synthesis and properties of cross-linked

polyamide aerogels

Jarrod Williams

Mary Ann Meador

Linda McCorkle

NASA Glenn Research Center21000 Brookpark Rd, Cleveland, OH 44135

https://ntrs.nasa.gov/search.jsp?R=20150023054 2020-03-01T19:40:26+00:00Z


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Overview

• Aerogel Basics/Applications

• Relevant prior work involving polyamides and polyimides

• Hurdles– The first step growth polyamide aerogel

• Optimization of completely aromatic systems

• Results– Density

– Porosity

– Surface area

– Compressive strength

– Dielectric measurements

• Conclusions/Acknowledgements


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Typical monolithic silica aerogels

What are aerogels?

• Highly porous solids made by drying a wet gel

without shrinking

• Pore sizes extremely small (typically 10-40

nm)—makes for very good insulation

• 2-4 times better insulator than fiberglass under

ambient pressure, 10-15 times better in light

vacuum

• Invented in 1930’s by Prof. Samuel Kistler of

the College of the Pacific

Sol Gel Aerogel


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Potential applications

Optically transparent antennae for use

with solar components

Flexible Insulation

for spacesuits

Low dielectric antenna substrates

Durable/Fire

resistant

structural

insulation

Insulation for crucial

mechanical components


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Basic polymer aerogel processing

Cross-linker

Syringe Mold

Solvent

Exchange

(acetone or

Ethanol)

Supercritical

CO2 drying

Polymer

solution Cross-

linked gel

Solvent

exchanging

in ethanol

Solvent

removed/

Aerogel

4 STEPS1. Polymer solution prepared

2. Cross-linking agent is added and the

mixture is poured into a mold

3. The resulting gel is solvent exchanged

with a SCF compatible solvent such as

ethanol

4. The solvent is then removed using an

SCF such as carbon dioxide


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Polymer Aerogels vs. Silica Aerogels

6

Recently developed polyurea

and polyimide aerogels have

Young’s moduli that are

orders of magnitude larger

than traditional silica aerogel.

The motivation behind

investigating stepgrowth

polyamide aerogels is to see

if we can obtain species that

are even stronger.


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Early literature involving polyamide aerogels

+

Desmodur RE (TIPM) Trimesic acid (TMA)

90°C, anh. DMF

(-CO2)

TIPM

TMA

TIPMTIPM

• Made via non-conventional

amide forming methodology

• No control over chain length

• Glove box conditions

• Long reaction times

• High temperature

• Attempts at polymer chain

formation lead to precipitation

Leventis et. al. J. Mater. Chem., 2011, 21, 11981

X

90°C, anh DMF

(-CO2)

.........

Precipitate

......... X

X,Y=Aromatic

Y

X Y YX


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Polyimides as a Model for Polyamide Aerogels

Comparable to polyimide aerogel

processes.

Similarities include:

1. Analogous polymerization between

diamines and diacid chlorides

2. Crosslinking through the use of a

trifunctional monomer (higher

degrees of functionality are also

possible)

3. Quick reaction times

4. No glove box required

5. Low temperature reaction conditions

6. Polymer chains that stay in solution


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Cross-linked Polyamides (general)

Polymer 41 (2000) 8487-8500

Niesten et. al.

Aromatic amines do not

require a catalyst

Aliphatic amines do require a

catalyst (Et3N)

0°C, NMP

n=20-30

0°C, NMP

X

X=Aromatic

Y=Aromatic or

Aliphatic

Y

X Y YX


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Potential features of polyamide aerogels

• Wide range of properties

– From flexible/soft to rigid/strong

– Hydrophobic/Hydrophilic

– Colorless (maybe translucent/clear)

– Low cost (monomers, cross-linker)


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Completely aromatic systems

Advantages: 1. No catalyst required (NMP

complexes with HCl)

2. Amine end caps make mixture

stable to moisture indefinitely.

3. Reaction mixtures remain

homogenous

4. Reactions undergo reliable

gelation (more user friendly than

acid chloride endcaps)

5. Control over rigidity

One problem

remained……….

DMBZ

Isophthaloyl chloride

[

]n

NMP, Room temperature

NMP, 0°C

Cross-linked PolyamideNetwork


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Optimized vs. Non-optimized Systems

Left two figures:

Polyamide

aerogels before

procedure

optimization.

Right two figures:

Three different

polyamide

aerogels (and

SEMs) made via

and optimized

procedure.


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Optimization of Polyamide Aerogels

• To minimize distortion, the following reaction

parameters were examined and optimized

– Reaction and Cross-linking temperature

– Stirring time/Stirring speed

– Concentration of solutions

– Cross-link density

– Order and manner of addition of the reactants

– Monomer species


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Samples From Optimized Procedure

Isophthaloyl chloride, terephthaloyl chloride, m-phenylene

diamine, 0.10g/cm3, 93% porous, 192 m2/g.

Terephthaloyl chloride, 0.33g/cm3, 77% porous, 384

m2/g.


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Monomers

1,3,5-Benzenetricarbonyl

trichloride (1,3,5-BTC)

Isophthaloyl chloride

(IPC)Terephthaloyl chloride

(TPC)m-phenylenediamine

(mPDA)


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Aerogel Synthesis

16


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5.0

7.5

10.0

0

50

100

2030

40

Solid

concentr

ation, %

p-A

cid c

hlo

ride, %

Repeat units, n

Experimental design study

• Face-centered

central composite

design

• 15 different data

points to model full

quadratic equation

• 4 repeats of the

center point to

assess error


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Results: Density

• Density increases as

the fraction of the para

substituted acid

chloride increases.

• Density increases as

the concentration of

solids in the gel

increases.

• n-value or length of the

polymer chains, is not

a significant factor for

density

• Standard

deviation=0.016

• R2=0.98

0.0

0.1

0.2

0.3

0.4

0

20

406080100

5678910

Density,

g/c

m3

TP

C c

onc.

, %

Polymer conc., w/w %

n = 20

n = 40


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Results: Porosity

• Porosity decreases as

the fraction of the para

substituted acid

chloride increases.

• Porosity decreases as

the concentration of

solids in the gel

increases.

• n-value of the polymer

chains is not a

significant factor for

porosity.

• SD=1.26

• R2=0.98

70

75

80

85

90

95

100

105

020

4060

80100

67

89

10

Poro

sity,

%

TPC conc., %

Polymer conc., wt%

n = 20

n = 40


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Surface area

• All three variables

significant

• Data was log

transformed before

fitting to normalize

data

• S.D. = 36.64

• R2=0.88

20

0

100

200

300

400

500

0

25

50

75

100

56

78

9

Surf

ace

are

a, m

2/g

TPC c

onc.

, %

Polymer conc., %

3D Graph 1

n=20

n=40


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Dielectric and Loss Tangent

21

1.2

1.4

1.6

020

4060

80100

56

78

910R

ela

tive d

iele

ctric

const

ant

TPC conc., %Polymer conc., %

3D Graph 1

0.000

0.005

0.010

0.015

0.020

0.025

0

20

40

6080

100

56

78

9

Loss

tangent

TPC c

onc.

, %

Polymer conc., %

3D Graph 1

n = 20

n = 40

2D Graph 1

Density, g/cm3

0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36

Rela

tive d

iele

ctr

ic c

onsta

nt

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

2D Graph 1

Density, g/cm3

0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36

Loss t

ang

en

t

0.000

0.005

0.010

0.015

0.020

0.025

0.030

SD=0.042, R2=0.92SD=0.0017, R2=0.93


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Compressive Strength

22

0

1

2

3

4

5

6

0

20

4060

80100

56

78

910

Str

ess a

t 10%

str

ain

, M

Pa

TPC

con

c., %

Polymer conc., %

3D Graph 2

2D Graph 2

Density, g/cm3

0.05 0.06 0.070.080.09 0.2 0.3 0.40.1

Str

ess

at 1

0% s

trai

n, M

Pa

0.1

1

10

SD=0.16, R2=0.90

2D Graph 2

Strain, %

0 10 20 30 40 50 60 70 80

Str

ess

, M

Pa

0

2

4

6

8

10

12

14

16

18100% TPC

50% IPC/50% TPC

100% IPC

2D Graph 1


4 5 6 7 8 9 10 11

Str

ess a

t 1

0%

str

ain

, M

Pa

0.1

1

10

100 % IPC

50 % IPC/50% TPC

100% TPC


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Young’s Modulus

23

2D Graph 1


4 5 6 7 8 9 10 11

Mo

dulu

s,

MP

a

1

10

100

1000

100 % IPC

50 % IPC/50% TPC

100% TPC

(log standard deviation=0.25, R2=0.79)1. Guo et. al. ACS. Appl. Mater. Interfaces, 2011, 3,

546-552.

2. Leventis et. al. J. Mater. Chem. 2011, 21, 11981-

11986.

3. Fricke et. al. J. Non-Cryst. Solids, 1988, 100

169-173.


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Conclusions/Summary

• A simple procedure for the fabrication of polyamide

aerogels has been developed and optimized

• A series of polyamide aerogels were produced that

having densities ranging from 0.06g/cm3 to 0.3g/cm3,

high porosities (77-93% porous), and surface areas

as high as 426m2/g

• Diverse properties arise through controlling monomer

types, stoichiometry and weight percent solids

• Remaining work

– Examine new monomer species

– Experiment with different crosslinking methodologies

– N-alkylate for hydrophobicity


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Acknowledgements

NASA Glenn

1. Dr. Mary Ann Meador

2. Stephanie Vivod

3. Baochau Nguyen

4. Heidi Guo

5. Linda McCorkle

6. Dan Haas

7. Dan Scheiman

The NASA Postdoc Program and Oak

Ridge associated Universities (ORAU)

NASA Glenn Center Director’s Special

Project Fund

synthesis and properties of cross-linked polyamide …...national aeronautics and space...

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