Binding Interaction Between Dantocol and RDX

Chris Williams

Supervised by Dr Stephen ClarkeCo-Supervised Dr Simon Mathew

& Dr Ian Lochert (DSTO)

Introduction

• Components of polymer bonded explosives (PBX)

• Function of bonding agents

• Analysis of interaction between Dantocol and RDX

– Scanning electron microscope– Raman spectroscopy– Diffuse reflectance infrared spectroscopy– Attenuated total reflectance infrared spectroscopy– Nuclear magnetic resonance

• Conclusion

• Future work

Polymer Bonded Explosives

• Nitramine explosive material suspended in a polymer matrix

• Desire for increased safety in handling explosives

• Possess favourable mechanical properties

• Various constituents added to improve properties

– Decrease likelihood of detonation due to external stimuli– Maintain a precise shape under severe stress– High explosive energy

• Commonly used in military application

PBXN-109

• Investigating components of PBXN-109

• Forerunner in PBX formulation developed in 1980’s

• Provide maximum explosive force and minimal sensitivity

Metal fuel

Cure catalyst

Plasticiser

Antioxidant

Bonding agent

Binder

Curing agent

Energetic Filler

Function

20.0

0.02

7.34

0.10

0.26

7.34

0.95

64.0

Nominal Weight %

Aluminium

Triphenylbismuth

Dioctyl adiapate

2,2’-methylenebis(6-tert-butyl)-4-methylphenol

N,N’-di(2-hydroxyethyl) dimethylhydantoin (Dantocol)

Hydroxyl-terminated polybutadiene

Isophorone diisocyanate

RDX

PBXN-109 Components

Bonding Agents

• Bonding agents utilised to overcome problem of dewetting

• Improve bonding through filler reinforcement

• Upon inclusion to a PBX formulation:

– Adsorbs onto RDX crystals– Enables effective crosslinking reaction with binder

• Prevents formation of voids improved mechanical properties

• Dantocol example of a commercial bonding agent

N N

CH3

H3C

O

O

OHHO

N,N’-di(2-hydroxyethyl) dimethylhydantoin

Dewetting

• Nitramine-polymer composites suffer dewetting

• Caused by due to weak adhesion between nitramine crystals and binders

– surface of nitramine crystal

– Isocyanate side reaction with moisture:

• Bonds fail under stress, allowing binder to break free or “dewet”

nitramine

– Puts neighbouring particles under stress

– Void propagates until reaching the filler-binder interface

R N C O H2O R NH2 CO2

R N C O R NH2 R NH CO NH R

• Filler-binder adhesion decreases overtime

– causing mechanical properties to deteriorate

– Increasing sensitivity of the PBX to that of a pure nitramine.

• Voids act as initiation sites for detonation

• Propellant Systems

– Causes an uneven burn Motor failure

Problems Associated

Experimental Aim

• Analyse interaction between RDX and Dantocol

– Coating RDX crystals– Reporting spectral shifts observed upon coating of Dantocol

• Determine functional groups responsible for spectral shifts

• Investigate the strength of the interaction

• Enabling synthesis of improved bonding agents

Coating Technique

• Heat RDX at 60oC under vacuum to remove impurities

• Determine suitable solvent systems to dissolve Dantocol

• Weigh out samples of RDX and Dantocol

– 50%, 10%, 8%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% (w/w)

• Tumble in centrifuge tube for 3hours

• Centrifuge at 3500rpm for 45mins

• Place sample under high vacuum

• Investigate the coating of bonding agent on RDX crystals

• XL30 Philips-XL30 FEGSEM w EDAX EDS

• Smooth crystalline surface

Scanning Electron Microscope

10% Dantocol Coating

• High level of RDX coverage

• Good adhesion to the surface

4% Dantocol Coating

• Less coverage observed

• Dantocol forms thick, malleable coating

• DRIFT-IR to examine interactions via bond shifts

• Advantageous for analysing solid samples

• Coated RDX samples mixed with KBr

• Ground and analysed in sample tray

Infrared Spectroscopy

DRIFT-IR Spectrum

1537

.70

1570

.45

1590

.15

0.00 0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

0.14

0.15

0.16

0.17

0.18

0.19

KM 1500 1520 1540 1560 1580 1600 1620 1640 1660

Wavenumbers (cm-1)

NO2 Asymmetrical stretching vibration

784, 7541039, 1019 , 946, 924

1351, 1312, 1268, 1234, 12191459, 14341593, 1573, 1532Peaks (cm-1)

(NO2)Ring StretchingVs (NO2) + V (N-N)CH2Vas (NO2)Vibrational Bands

-0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

0.14

KM

1000 1500 2000 2500 3000 Wavenumbers (cm-1)

RDX

• Samples pre-ground with KBr

• Excess grinding removed coating

Sample Grinding

RDX 1st Grinding

0.0

0.1

0.2

KM

RDX 2nd Grinding

0.0

0.2

KM

RDX 3rd Grinding

0.0

0.2

0.4

KM

RDX 4th Grinding

0.0

0.1

KM

RDX 5th Grinding

0

1

KM

1000 1500 2000 2500 3000

Wavenumbers (cm-1)

Peak Shifts

0.000.050.100.150.200.25

0.300.350.400.450.50

60011001600210026003100

Wavenumber (cm-1)

Kub

elka

-Mun

k

RDX + 10% Dantocol

1513.05 cm-1

RDX1537.70 cm-1

5.360.430.171.771.871.236.080.98∆V

911.76945.541018.541036.401221.251235.631258.901319.75RDX + 10% Dantacol

917.12945.111018.711038.171219.381234.401264.981318.77RDX

Ring StretchingVs NO2 + V (N-N)Sample

cm-1

0.033.101.520.781.1424.652.220.93∆V

753.42788.041360.071432.741460.121513.051568.231589.22RDX + 10% Dantacol

753.45784.941361.591433.521458.981537.701570.451590.15RDX

RingCH3Vas (NO2)Sample

Peak Shifts

--50% Dantocol

24.651513.0510% Dantocol

24.471513.238.0% Dantocol

20.871516.836.0% Dantocol

19.791517.915.0% Dantocol

18.331519.374.0% Dantocol

15.191522.513.0% Dantocol

11.31526.402.0% Dantocol

14.261523.441.0% Dantocol

8.361529.340.5% Dantocol

∆Vas (cm-1)Vas NO2 (cm-1)RDX & Dantocol

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

149615161536155615761596

Wavef unct ion (cm-1)

RDX + 10% Dantocol

• Attenuated total reflection infrared spectroscopy

• Several advantages over DRIFT-IR

– Overcomes problem of grinding

– Less preparation

– Fewer scans required (256scans – 64scans)

– Reproducible spectra

ATR-IR

ATR-IR Spectra

• Sharp Peaks with low noise interference

• RDX peaks consistent with DRIFT-IR

45

50

55

60

65

70

75

80

85

90

95

100

%T

1000 1500 2000 2500 3000 3500 4000 Wavenumbers (cm-1)

RDX

1537.70 cm-1

RDX and Dantocol IR

20

40

60

80

%T

20

40

60

80

%T

20

40

60

80

%T

1000 1500 2000 2500 3000 3500 Wavenumbers (cm-1)

RDX

1537.70 cm-1

Dantocol

RDX + 50% Dantocol

1518.162 cm-1

Raman Spectroscopy

• Raman used to compare vibration spectra specifically nitro group

• Small spectral shifts observed

• Behaviour consistent with literature

• Nitro shifts coincide with FTIR data

RDX

Raman Peak Shifts

5.38.2409.6

2.00.9456.8Ring Deformation

14.314.0599.6

0.20.2664.0V NO2

0.11.8844.5

0.60.4879.6

1.61.4940.0

1.72.31028.3Ring Stretch

0.50.61213.4

0.50.61270.6

0.80.41306.8

3.85.31383.5Vs NO2

1.60.31428.0CH Deformation

0.20.21592.1Vas NO2

RDX + 3% Dantocol∆V(cm-1)

RDX + 4% Dantocol∆V(cm-1)

RDXV(cm-1)Vibration Band

NMR Complexation

N

N NNO2

NO2

O2N

• Investigate peak shifts upon increasing equivalency Dantocol

• Mole ratio RDX : Dantocol

– 1 : 0, 1 : 0.5, 1 : 2, 1 : 3

• 1H NMR, 300MHz, CD3C

RDX

CH2

6.16ppm

NMR TitrationRDX : Dantocol RDX : Dantocol

1 : 0.5 1 : 1

6.17ppm 6.17ppm3.112ppm 3.127ppm2.843ppm 2.999ppm

RDX : Dantocol RDX : Dantocol1 : 2 1 : 3

6.19ppm 6.19ppm3.135ppm 3.190ppm2.999ppm 3.061ppm

NMR Complexation

6.166.166.17

6.176.186.186.19

6.196.20

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50Dantocol Equivanents

Chem

ical

Shi

ft (p

pm)

RDX CH2 Peak Shift

Hydrogen Bonding

• Data indicates hydrogen bonding responsible for bonding

• Between nitro of RDX and hydroxyl functional group of Dantocol

RDX Dantocol

N N

H3C

H3C

O

O

O OHH

N N

N

N

NO

O

O O

N

O

O

Synthesis of Bonding Agents

• Alternate bonding agents derived from Dantocol

• Used to determine if hydrogen bonding is responsible for interaction

• 1st compound substituted hydroxyl group for strong proton donating

carbamate

• 2nd compound functioned to block the hydroxyl groups

Bond Promoting Carbamate

• Dantocol reacted with phenyl isocyanate under reflux conditions

• Product separated by column chromatography

• Characterised by NMR and Mass Spectroscopy

10ml TolueneHeated 24hrs

N,N’-di(2-ethyl phenylcarbamate) dimethylhydantoin

N N

H3C

H3C

O

O

O OC

O

NH

CNH

O

N N

H3C

H3C

O

O

HO OH

N C O2

Product Interaction

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

%T

1000 1500 2000 2500 3000 3500 4000 Wavenumbers (cm-1)

• SEM to determine adequate coating

• DRIFT spectroscopy and ATR consistent with peak change at 1537.7cm-1

RDX + 10% Bonding Agent

• 1529.4cm-1

Tert-butyldimethylsilyl Chloride Protection

• Dantocol reacted with tert-butyldimethylsilyl Chloride

• Product separated by column chromatography

• Characterised by NMR and Mass Spectroscopy

Methlene chloride, ImidazoleHeated 24hrs

N,N’-(tert-butyldimethylsilyl) dimethylhydantoin

Si

CH3

CH3

CH3

CH3

CH2ClN N

H3C

H3C

O

O

HO OH

N N

H3C

H3C

O

O

O OSi

CH3

CH3

CH3

CH3

CH3SiH3C

CH3

CH3

CH3

CH3

Tert-butyldimethylsilyl Chloride Protection

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

KM

1000 1500 2000 2500 3000 3500 4000 Wavenumbers (cm-1)

• SEM to determine adequate coating

• DRIFT spectroscopy and ATR produce similar spectra to uncoated RDX

• Conclusive evidence of hydrogen bonding at the interface

RDX + 10% Bonding Agent

1533.85cm-1

Conclusion

• RDX coated with Dantacol was analysed using ATR, DRIFTs, Raman, NMR

• Peak shifts indicate the nitro group interacts with hydroxyl group to form a

stable complex

• This was confirmed by synthesis of Dantocol derivatives

• Prevention of hydrogen bonding by reaction with hydroxyl group

• Promoted hydrogen bonding by formation of proton donating carbomate

Future Developments

• Further characterisation by analytical methods (NMR,

spectrophotometry, DSC, TGA)

• Informatively design and synthesise second generation bonding agents

• Exploit the understanding the molecular interactions to design highly

sensitive explosive detection devices

1. Hamshere, B.L., Lochert, I.J., Dexter, R.M., Evaluation of PBXN-109 : the explosive fill for the

Penguin Anti-Ship Missile Warhead, W.S. Division, Editor. 2003, Defence Science & Technology

Organisation: Edinburgh. p. 30.

2. J. M. Bellerby, C.K., Explosive-Binder Adhesion and Dewetting in nitramine-filled energetic

materials. Propellants, Explosives, Pyrotechnics, 1989. 14(2): p. 82-85.

3. Bailey, A., et al., The identification of bonding agents for TATB HTPB polymer bonded explosives.

Philosophical Transactions of the Royal Society of London Series a-Mathematical Physical and

Engineering Sciences, 1992. 339(1654): p. 321-333.

4. C. Sue Kim, H.Y.P.N.N.A.G., Developement of neutral polymeric bonding agents for propellants with

polar composites filled with organic nitramine crystals. Propellants, Explosives, Pyrotechnics, 1992.

17(1): p. 38-42.

5. Guy Perrault, R.L., Jean-Francois Drolet, High-energy explosive or propellant composition. 1981, Her

Majesty the Queen in right of Canada, as represented by the Minister of National Defence: United

States. p. 9.

Reference