CRANFIELD UNIVERSITY ALESSANDRO E. CONTINI CALORIMETRIC INVESTIGATIONS OF A SERIES OF ENERGETIC POLYPHOSPHAZENES DEFENCE ACADEMY OF THE UNITED KINGDOM PhD THESIS CRANFIELD UNIVERSITY DEFENCE ACADEMY OF THE UNITED KINGDOM DEPARTMENT OF ENVIRONMENTAL AND ORDNANCE SYSTEMS PhD THESIS Academic Year 2004-2005 Alessandro E. Contini Calorimetric Investigations of a Series of Energetic Polyphosphazenes Supervisor: Dr A.J. Bellamy September 2005 © Cranfield University 2005. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright owner. Abstract ABSTRACT Energetic, fluorinated, linear polyphosphazenes are currently under investigation as potential, high-density binders for new, polymer bonded explosive compositions. A series of such polymers was synthesised and the enthalpy of combustion of each member of the series was measured by static bomb calorimetry. This was performed after combusting appropriate secondary thermochemical standards to model the combustion stoichiometry of the hetero- atoms nitrogen, fluorine and phosphorus. The water-soluble combustion products were identified and quantified using 19F NMR spectroscopy and Ion Chromatography. Since some of the combustion products are hydrolytically unstable, it was found necessary to stabilise the initial combustion product mixtures by using a buffer solution instead of pure water in the bomb, and then to determine the composition of the stabilised product mixtures in order to obtain meaningful values for the enthalpies of combustion and thence enthalpies of formation. The thermochemical measurements themselves were made with pure water in the bomb. The composition and structures of the various polyphosphazenes were correlated with their energies of combustion and enthalpies of formation. The latter were calculated using the latest CODATA values of enthalpy of formation of the combustion products. The ‘combustion’ of the polyphosphazenes under a nitrogen atmosphere was also investigated with the view to calculating the enthalpies of detonation of each member of the series. Three conference papers which include the results of this work have been published and are included in Appendices C-E. KEY WORDS Energetic polyphosphazenes, heat of combustion, heat of formation, heat of detonation. ii Acknowledgements ACKNOWLEDGEMENTS I would like to thank first of all my supervisor, Dr Tony Bellamy, for his help, encouragement, guidance and great patience. He has done well to ‘put up’ with my general stubbornness and eccentric ‘Italianness’ for three whole years! Financial sponsoring of this project by AWE Aldermaston is also greatfully acknowledged. My gratitude is also extended to Dr Peter Golding, Dr Steve Trussell and other members of the AWE Polymer Synthesis Group, for their general advice, and to Dr Hugh Davies, Thermochemical Modelling Team, NPL Teddington, for his valuable criticism and suggestions. Special thanks go to Dr Alistair MacCuish and Dr Matt Andrews for all of their contributions and for literally bringing me, from feather-quill and ink-bottle, into the world of 21st century word-processing. Other people in the department to whom I am indebted include Roger Cox, for the PC interfacing of the digital thermometer unit, Jenny Lovell, Marjorie Saunders and Maggie Harris for their great help with consumables, and for always providing me with just the right ‘bit’ at the right time, Dr Phil Gill and Anjum Agha for the recording of mass spectra; Richard Hall, for mending my broken glassware and Dr Mike Williams for his sense of humour. I am also indebted to my landlady, Anne Ward, for her friendship, to her Terrier dog, Poppy, for constantly reminding me of the most fundamental principles in life i.e. eating and sleeping, and, last but not least, to my uncle and aunt in Derby, John and Maureen Hadway, for the many Sunday roasts and Chinese dinners consumed together. Finally, a special thank you goes to my parents for everything they have done to get me to this point. iii Acknowledgements To Mum and Dad iv Favourite Quote FAVOURITE QUOTE Play It by Ear… v Glossary GLOSSARY A Ampere AWE Atomic Weapons Establishment COSY Correlation Spectroscopy Cp Heat capacity at constant pressure Da Dalton DEPT Distortionless Enhancement by Polarisation Transfer DFPA Difluorophosphoric acid DSC Differential Scanning Calorimetry DC Direct current EGDN Ethyleneglycol dinitrate ES% Energetic Substituent Percentage eV Electronvolt GAP Glycidyl Azide Polymer GC-MS Gas Chromatography- Mass Spectrometry GPC Gel Permeation Chromatography H Enthalpy HCTP Hexachlorocyclotriphosphazene HE High Explosive HFPA Hexafluorophosphoric acid HMX 1,3,5,7-Tetranitro-1,3,5,7-tetraazacyclooctane HNS 2,2’,4,4’,6,6’-Hexanitrostilbene HPLC High Pressure Liquid Chromatography HTPB Hydroxy-terminated polybutadiene IC Ion Chromatography ICTAC International Confederation for Thermal Analysis and Calorimetry IM Insensitive Munitions IUPAC International Union of Pure and Applied Chemistry IR Infra Red J (1) Coupling constant vi Glossary J (2) Joule K Kelvin K-W Kistiakowsky-Wilson MFPA Monofluorophosphoric acid Mod K-W Modified Kistiakowsky-Wilson Mn Number average molecular weight Mw Weight average molecular weight NENA Nitratoethylnitramines NIST National Institute for Standards Testing NG Nitroglycerine NMR Nuclear Magnetic Resonance NPL National Physical Laboratory NTO 3-Nitro-1,2,4-triazol-5-one OB Oxygen balance PETN Pentaerytritol tetranitrate PolyAMMO Poly(3-azidomethyl-3-methyloxetane) PolyBAMO Poly(3,3-bisazidomethyloxetane) PBX Polymer Bonded Explosive PDI Polydispersity Index Perspex Trademark for poly(methyl methacrylate) in sheet form PolyGLYN Poly(glycidylnitrate) PolyNIMMO Poly(3-nitratomethyl-3-methyloxetane) polyNEO Poly(2-nitratoethyloxirane) PTFE Polytetrafluoroethylene Polymer 1 Random linear poly[P-2-nitratoethoxy/P-2,2,2-trifluoro- ethoxyphosphazene] Polymer 2 Random linear poly[P-2,3-dinitratoprop-1-oxy/P-2,2,2- trifluoroethoxyphosphazene Polymer 3 Random linear poly[P-3,4-dinitratobut-1-oxy/P-2,2,2- trifluoroethoxyphosphazene] Polymer 4 Random linear poly[P-4,5-dinitratopent-1-oxy/P-2,2,2- trifluoroethoxyphosphazene] vii Glossary Polymer 5 Random linear poly[P-5,6-dinitratohex-1-oxy/P-2,2,2- trifluoroethoxyphosphazene] RDX 1,3,5-Trinitro-1,3,5-triazacyclohexane RM Reference materials RT Room temperature SI International System of Units S-R Springhall-Roberts STP Standard Temperature and Pressure TATB 1,3,5-Triamino-2,4,6-trinitrobenzene THF Tetrahydrofuran Tg Glass transition temperature TNT 1,3,5-Trinitrotoluene TMS Tetramethylsilane TrMS Trimethylsilyl SYMBOLS ∆ Difference ∆Uc Internal energy of combustion ∆Hc Enthalpy of combustion ∆Hd Enthalpy of detonation ∆Hf Enthalpy of formation δ Chemical shift ε Heat equivalent of the calorimeter Ω Oxygen balance or OB viii List of Contents LIST OF CONTENTS Abstract............................................................................................................................ii Key Words .......................................................................................................................ii Acknowledgements.........................................................................................................iii Favourite Quote...............................................................................................................v Glossary...........................................................................................................................vi Symbols .........................................................................................................................viii List of Contents ..............................................................................................................ix List of Figures.................................................................................................................xi List of Tables ..............................................................................................................xxiii 1 Introduction..........................................................................................................1 1.1 Polymer bonded explosives ...................................................................................1 1.2 Polyphosphazenes..................................................................................................2 1.3 Standard enthalpy of formation ...........................................................................13 1.4 Relation between internal energy of combustion and enthalpy of combustion...........................................................................................................14 1.5 Standard enthalpy of combustion: measurement versus calculation ...................16 1.6 Hess’s law............................................................................................................17 1.7 Calorimetry..........................................................................................................19 1.8 Oxygen bomb calorimetry ...................................................................................21 1.9 Overall aim of work and specific objectives .......................................................28 2 Results and Discussion ......................................................................................29 2.1 Synthesis and characterisation of the energetic polymers 1-5.............................29 2.2 Calorimetry..........................................................................................................52