PHYSICO-CHEMICAL PROPERTIES OF POLYPROPYLENE GLYCOLS BY SALONI GUPTA [B.Sc. (Hons)] A thesis submitted in partial fulfilment of the requirements of the University of Greenwich for the Degree of Doctor of Philosophy January, 2015 Department of Chemical, Pharmaceutical & Environmental Sciences Faculty of Engineering & Science, University of Greenwich (Medway Campus), Chatham Maritime, Kent ME4 4TB, UK I DECLARATION I certify that this work has not been accepted in substance for any degree, and is not concurrently being submitted for any degree other than that of Doctor of Philosophy being studied at the University of Greenwich. I also declare that the work is the result of my own investigations except where otherwise identified by references and that I have not plagiarised the work of others. Saloni Gupta (Candidate): ………………................................................................................................................................. PhD Supervisors Dr A. P. Mendham: Prof. S. A. Leharne: Prof. B. Z. Chowdhry: Date: January 15th, 2015 II ACKNOWLEDGEMENTS I would like to express my sincere thanks to Prof. Stephen A. Leharne, Prof. Babur Z. Chowdhry and Dr Andrew P. Mendham for the invaluable guidance, support and encouragement they have given me as my supervisors throughout my PhD journey. They have always believed in me and encouraged me to do better. I am indebted to everyone who has assisted and encouraged me in the course of my studies, particularly Prof. Peter Griffiths, Dr Samuel Owusu-Ware, Dr Milan Antonijevic, Dr Beatrice Cattoz and Dr Joanna Thorne. The technical support I have received from staff members, particularly, Devyani, Atiya, Mark Allen, Steve Williams and the Link laboratory technicians has been invaluable. Most importantly thank you to my wonderful parents, my sisters (Sanya and Mannat) and my brother (Yatharth) for their love and encouragement. My parents are the two most hard- working people I know and they have been my inspiration and the driving force to complete this doctoral thesis. None of this would have been possible without them. My little sister Sanya has always set an example for me to never give up no matter what the circumstances are. I cannot thank my husband Sunny Goyal enough for his love, support and patience. He has always pushed me to perform better. I am grateful to all my friends and family who have supported me emotionally throughout this process. I also believe that having the opportunity to undertake and complete this PhD has been a complete blessing from God. God has constantly blessed me with miracles when I thought I could not do it. III ABSTRACT Physico-chemical properties of polypropylene glycols Poly(propylene glycol) (PPG) samples of different molecular mass were characterized using differential scanning calorimetry, modulated differential scanning calorimetry, thermogravimetry and thermally stimulated current (TSC) spectroscopy. It was shown, by TSC, that the glass transition temperature and the degree of molecular mobility increased with increasing molecular mass of PPG. Additional experiments showed that PPGs of molecular mass 425, 1000 and 2000 Da undergo one global relaxation process; however, PPG 2700 (Da) undergoes an additional relaxation process after the glass transition which has been attributed either to the release of the excess charge delocalised in the polymer structure or a liquid-liquid transition. Thermally induced phase separation in aqueous solutions of PPG has been examined using a variety of techniques including high sensitivity scanning calorimetry (HSDSC), hot stage microscopy, small angle neutron scattering, and turbidity measurements. The data suggest that phase separation is a consequence of PPG aggregation (droplets); the aggregates grow in size, as the temperature is raised further. It is postulated that phase separation occurs via nucleation and growth, which is corroborated by model fitting the calorimetric data using a mass action aggregation model. It is concluded that phase separation of PPG occurs as a result of the disruption of a hydrogen bonded network between water and PPG. The effect of five sugars (mannitol, maltose, raffinose, sucrose and trehalose) on the Tm (transition temperature) of aqueous PPG 1000 solutions was studied by HSDSC and turbidity measurements. All the sugars decreased the phase separation temperature of the PPG solutions, with trehalose and maltose showing the greatest effect. A series of experiments, using HPLC, showed that phase separated PPG (1000 Da) increased the apparent aqueous solubility of naphthalene. SALONI GUPTA [B.Sc. (Hons)] IV OVERVIEW Chapter 1 provides a brief background to the subject area of the research reported in the thesis and the project objectives. Chapter 2 gives a general introduction to polymers, in particular PPG, and the phase-separation behaviour of PPG is discussed. Chapter 3 provides the theory and the principles underlying the experimental techniques used in the research reported herein. In Chapter 4 the experimental thermal properties of five different molecular weight PPG samples obtained using different techniques are discussed. In Chapter 5 the experimental phase-separation behaviour of aqueous samples of PPG 1000, using different techniques, as a function of concentration, is reported and discussed. In Chapter 6 the effect of the presence of five sugars, at different concentrations, on the phase- separation behaviour of aqueous PPG solutions is reported. In Chapter 7 the use of aqueous PPG solutions as a solubilizing medium using a model hydrophobic compound, naphthalene, is reported. V CONTENTS DECLARATION..................................................................................................................... II ACKNOWLEDGEMENTS ................................................................................................. III ABSTRACT ........................................................................................................................... IV OVERVIEW ............................................................................................................................ V FIGURES ............................................................................................................................... IX TABLES ........................................................................................................................... XVIII ABBREVIATIONS AND SYMBOLS ................................................................................ XX CONFERENCE/SEMINAR PRESENTATIONS AND PUBLICATIONS ................ XXVI Chapter 1 : Project Overview ..................................................................................................... 1 1.1 Project Background .......................................................................................................... 1 1.2 Project Objectives ............................................................................................................ 5 Chapter 2 : Polymers and their Phase-Separation in Aqueous Solutions .................................. 8 2.1 Polymers ........................................................................................................................... 8 2.1.1 Classification of Polymers ......................................................................................... 8 2.1.2 Polymer Architecture ............................................................................................... 10 2.1.3 Molar Mass of Polymers .......................................................................................... 15 2.2 Glass-Transition and Melting: Important Polymer Properties ....................................... 16 2.3 Poly(Propylene Glycol) (PPG) ....................................................................................... 19 2.3.1 Properties ................................................................................................................. 21 2.3.2 Applications ............................................................................................................. 21 2.3.3 PPG as a Thermosensitive/Thermoresponsive Polymer .......................................... 22 2.4 Thermodynamics of Phase-Separation in Polymer Solutions ........................................ 22 2.4.1 Phase Diagrams ....................................................................................................... 27 Chapter 3 : Principal Experimental Techniques: Theory, Instrumentation and Applications . 43 3.1 Introduction .................................................................................................................... 43 3.2 Calorimetric Analysis ..................................................................................................... 43 3.2.1 Definition of Calorimetry ........................................................................................ 43 3.2.2 Classification of Calorimeters ................................................................................. 44 3.2.3 Differential Scanning Calorimetry .......................................................................... 44 3.2.4 High Sensitivity Differential Scanning Calorimetry (HSDSC) ............................... 46 3.3 Thermogravimetric Analysis (TGA) .............................................................................. 53 3.4 Hot Stage Microscopy (HSM)........................................................................................ 55 VI 3.5 Thermally Stimulated Current (TSC)