Curing of Diglycidyl Ether of Bisphenol with Nitro Derivatives of Amine CompoundsYanxi Zhang and Sergey Vyazovkin

Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL 35294

IntroductionIntroduction

Cured epoxy resins are one of the most important thermosetting polymers, which are extensively used as composite materials and adhesives. If liquid crystalline (LC) structures are introduced into epoxy networks, their performance application can be improved. Recently studies have been initiated on a new type of epoxy resin, DGEBP due to the interest on liquid crystal materials. Another application area is nonlinear optical materials. The latter can be produced by curing of epoxy with nitro derivatives of amino compounds.

Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), polarized light microscope (PLM), isoconversional kinetic analysis were used to study the cure reaction of DGEBP with three aromatic amines. Quantum mechanical calculations complement the experimental findings.

Main reaction of epoxy-amine cureMain reaction of epoxy-amine cure

H2C CH + RNH2 RNHCH2CH(OH)O

H2C CHO

+ RNHCH2CH(OH) RN(CH2CH(OH) )2

Primary amine addition

Secondary amine addition

Materials and methodsMaterials and methods

O CH2 CH CH2CH2 CH CH2

O

O

O

Diglycidyl Ether of Bisphenol P (DGEBP)

N

N

N O

H2

H2

2 N

N

NH

O

H2

2

2

NH2

NO2

NO2

3-Nitro-1,2-phenylenediamine(3-NPDA)

4-Nitro-1,2-phenylenediamine(4-NPDA)

2,4-Dinitroaniline(2,4-DNA)

Advanced isoconversional kinetic analysisAdvanced isoconversional kinetic analysis

n

i

n

ij j

i

tTEJtTEJE

1 ,

,

dttRT

Et

ttTEJ

ii

exp,where

TGA DMA DSCPLMResults DiscussionResults Discussion

exo

DGEBP/4-NPDA

T /oC

Heat

Flo

w /m

W

Mas

s Fr

actio

n /%

70

80

90

100

0 50 100150200250300350-4

-2

0

2

4

DGEBP

65

70

75

80

85

90

95

100

Mas

s Fr

actio

n /%

T /oC

DGEBP

0 50 100150200250300350-4

-2

0

2

4 DGEBP/3-NPDA

exo

Heat

Flo

w /m

W

DSC and TGA curves at 2C min-1

0.05

0.10

0.15

0.20

0.25 tan

Tan

T /oC0 100 200 300 400

0

1x107

2x107

3x107

4x107

5x107

6x107

G'

Mod

ulus

/Pa

0.00

0.05

0.10

0.15

0.20

0.25 tan

0 100 200 300 4000.0

5.0x107

1.0x108

1.5x108

2.0x108

2.5x108

G'

Tan

Mod

ulus

/Pa

T /oC

DMA curves for DGEBP/4-NPDA DMA curves for DGEBP/3-NPDA

ConclusionConclusion

Cure reaction of DGEBP with 4-NPDA occurs in one step and cure reaction of DGEBP with 3-NPDA involves two steps, which are assigned to the cure of DGEBP with –NH2 in position 1 and in position 2 respectively.

DGEBP/4-NPDA system shows the formation of a liquid crystalline phase that can be converted to another mesophase on cooling if the system is not completely cured. The transition becomes irreversible on further heating.

Presence of –NO2 group makes neighboring –NH2 group highly congested and hindered from nucleophilic effects by electrostatic repulsion of the –NO2 group, which leads to a significant increase (from 50 to 100kJ mol-1) in the activation energy of cure reaction .

H Electrostatic Charge

O Electrostatic Charge

N N-H bond angle

H2 0.467 O1 -0.542 N1 110 H8 0.444 O2 -0.547 N2 109.78 H1 0.449 H7 0.482

H Electrostatic Charge

O Electrostatic Charge

N N-H bond angle

H8 0.492 O1 -0.600 N2 113.91 H2 0.443 O2 -0.519 N3 109.72 H9 0.488 H3 0.445

H Electrostatic Charge

O Electrostatic Charge

N N-H bond angle

H1 0.485 O1 -0.585 N1 116.77 H7 0.436 O2 -0.512

100 120 140 160 180-30-24-18-12-6-20246

exo

3'

3

2'

2

1'

1

Heat

Flo

w /m

W

T /oC

DSC curves for repetitive heating and cooling of

DGEBP/4-NPDA system at 2C min-1

Micrograph of the cured DGEBP/4-NPDA under crossed polarizers

(50x)

158C 170C 181C

191C

191C

Micrographs of DGEBP/4-NPDA system from a PLM with hot stage at 2C min-1

212C

0 100 200 300 400

-8

-4

0

4

8dc

c

cb

b

b

a

a

a

exo

DGEBP/3-NPDA DGEBP/4-NPDA DGEBP/2,4-DNA

Heat

Flo

w /m

W

T /oC

0.0 0.2 0.4 0.6 0.8 1.040

60

80

100

120

140 DGEBP/2,4-DNA DGEBP/3-NPDA DGEBP/4-NPDA

E k

J m

ol-1

ReferenceReferenceYanxi Zhang, Sergey Vyazovkin, Macromolecular Chemistry and Physics, 2005, 206, 342; 2005, 206, 1084; 2005, 206, 1840

212C

DSC curves at 2C min-1

Variation of activation energy with conversion

0 50 100 150 200 250

-3

-2

-1

0

exo

172oC

142oC

135oC

8 h

6 h

0 h

Hea

t Flo

w /m

W

T /oC

DSC curves for Tg of DGEBP/3-NPDA at 20C min-1

DSC and TGA curves at 2C min-1

0 50 100150200250300350

DGEBP

Heat

Flo

w /m

W

-4

-2

0

2

4

6 DGEBP/2,4-DNA

70

80

90

100 exo

Mas

s Fr

actio

n /%

T /oC

DSC and TGA curves at 2C min-1