Anionic Polymerization of Ethylene Oxide And
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ANIONIC POLYMERIZATION OF ETHYLENE OXIDE AND PROPYLENE OXIDE by HRIRE MIRZAKHAN-GHARAPETIAN, B.Sc.,M.Sc. A thesis submitted for the degree of Doctor of Philosophy in the University of London Physical Chemistry Laboratories Department of Chemistry Imperial College of Science and Technology London SIR 2AY June 1974 2 ACKNOWLEDGEMENTS I am deeply indebted to my supervisor, Dr Maurice George, who patiently guided and encouraged me throughout the entire course of this work. I would also like to express my sincere gratitude to the Calouste Gulbenkian Foundation, Lisbon, Portugal, for the award of a Scholarship which enabled me to perform this work. Grateful acknowledgement is made to Dr J.A. Barrie for allowing me to use some of the apparatus in the Polymer Characterization Laboratory. I am grateful to Dr J.M. Evans, Rubber and Plastics Research Association, Shawbury, for performing gel permeaton chromatography analysis on polymer samples, and to Mr G.C. Goode, Atomic Weapons Research Establishment, Aldermaston, for carrying out neutron activation analysis. Thanks are due to the technical staff of the Chemistry Department of Imperial College. I should like to thank Andrew J. Tinker, David C. Evans and Ronald N. Sheppard for many helpful and interesting discussions. Finally, I wish to thank Mrs U.O. Fowler for typing the manuscript, HRIRE M, GHARAPETIAN 3 1. ABSTRACT Kinetic studies of ethylene oxide and propylene oxide were performed dilatometrically using cumyl potassium and tetrahydrofuran as initiator and solvent, respectively. Ethylene oxide polymerizations were carried out usually at 40°C. Due to the gradual change in the density of growing short-length living a polyethylene oxide chains, the rate of decrease in the volume of polymeriz- ing solutions was initially slow. The rate of decrease in volume gradually increased until it reached a constant value. The order of the reaction rate with respect to monomer and initiator concentration was 0.935 + 0.15 and 1.00 + 0.27, respectively. The second order rate constant, k , was (6.61 + 0.42) x 10 2 dm3 mol-1 s-1 at 40°C. p Rates of ethylene oxide polymerization using cumyl potassium/THF-dioxane were measured for different THF-dioxane compositions at 40°C. No significant variation in the reaction rates were observed for different solvent mixtures. Propylene oxide polymerizations were performed usually at 50°C. The initial increase in the rate of change of volume for propylene oxide was much less pronounced than that for ethylene oxide. This was due to the slower change in the density of the growing polypropylene oxide chains and the occurrence of transfer to monomer. The order of the reaction rate with respect to the monomer and initiator concentration was 0.91 + 0.26 and 1.01 + 0.21, respectively. The k value was -3 3 -1 -1 (1.62 + 0.10) x 10 dm mol s at 50°C. The transfer constant to monomer, a, was (2.04 + 0.22) x 10-2. The end group unsaturation was in the range of (5.42 - 9.33) x 10-5 equivalents g-1. -1 The overall activation energies were 3.94 + 0.37 kJ mol and -1 4.3 + 0.81 kJ mol for ethylene oxide and propylene oxide polymerizations, respectively. 4 The homopolymers prepared by polymerization of ethylene oxide and propylene oxide were isolated and their molecular weights were measured by vapour pressure osmometry. The higher molecular weight polyethylene oxides and some polypropylene oxides were analysed by gel permiation chromatography. The molecular weights of some samples were also measured by viscometry. *. A monodisperse sample of polystyrene was prepared using cumyl potassium in tetrahydrofuran. Monodisperse polystyrene samples were chloromethylated and attempts were made to prepare graft copolymers of styrene and ethylene oxide by anionic coupling technique. .5 CONTENTS D292. 1. Abstract 3 PART ONE LITERATURE SURVEY 2. Anionic Polymerization of Alkenes 11 2.1. The kinetics of Anionic Polymerization of Alkenes 11 2.2. Molecular Weight and Molecular Weight Distribution in Anionic Polymerizations 13 3. Anionic Polymerization of Epoxides 15 3.A. Initiation by Alkali Metal Hydroxides, Alkyls and Alkoxides 15 3.B. Initiation by Alkali Metal-Aromatic Hydrocarbons 15 3.C. The Kinetics of Anionic Polymerization of Epoxides 15 3.D. The nature of Propagating Species 16 3.D.1. The Effect of Solvent on the Nature of the Propagating Species 17 3.E. The Association Phenomena 17 3.E.1. Associations in Alkali Metal Alkoxides 18 3.1. Anionic Polymerization of EpoXides Initiated with Hydroxides, Alkoxides and Alkyls of Alkali Metals 19 3.1.A. Anionic Polymerization of Ethylene Oxide with Sodium Methoxide 3.1.A.1. The Proton Exchange Reactions 19 3.1.B. Propylene Oxide Polymerization with Hydroxides and Alkoxides of Alkali Metals 20 3.1.C. Polymerization of Epoxides with Potassium t-Butoxide in Dimethyl Sulphoxide (LUSO) 21 3.1.C.1. Polymerization of Ethylene Oxide with Potassium t-Butoxide in Dimethyl Sulphoxide (DMSO) 22 b Page 3.1.C.2. Polymerization of Propylene Oxide with Potassium t-Butoxide in Dimethyl Sulphoxide (DMSO) 23 3.1.C.3. Polymerization of Propylene Oxide with Potassium t-Butoxide in DMSO and THF Mixtures 23 3.1.C.4. Polymerization of neo-Pentylethylene Oxide Initiated with Potassium t-Butoxide 24 3.1.C.5. Polymerization of 1,2 Butylene Oxide in DMS0 and DMSO and THF Mixtures 24 3.2. Anionic Polymerization of Epoxides with Alkali Metal- Aromatic Hydrocarbon Initiators 25 3.2.A. Polymerization of Ethylene Oxide with Alkali Metal Naphthalene Initiators in THF 27 3.2.B. Polymerization of Propylene Oxide with Sodium Naphthalene in DMSO and THF Mixtures 28 3.3. Transfer Reactions in Alkyl Substituted Ethylene Oxide Polymerizations 28 3.3.A. Transfer Reactions to Monomer 28 3.3.B. Transfer to Solvent 30 3.3.C. The Unsaturation Content 30 3.3.D. The Effect of Transfer Reactions on Molecular Weights in Alkyl Substituted Ethylene Oxide Polymerizations 31 4. Preparation of Monodisperse Polystyrene by Anionic Polymerization 32 4.A. The Stability of Alkali Metal Initiators and Living Polymers in THF 35 5. Graft Copolymers 37 5.1. Preparation of Graft Copolymers by Anionic Methods 37 7 Page 5.1.A. Preparation of Graft Copolymers by Growing Chains from Active Centres on the Polymer Backbone 37 5.1.B. Preparation of Graft Copolymers by Deactivation 44 PART TWO MATERIALS 6. Purification and Storage of Materials 50 6.1. Purification Techniques 50 6.1.A. Preparation of Sodium Mirror 50 6.1.B. Preparation of Sodium Potassium Alloy 50 6.2. Solvents 51 6.2.A. Tetrahydrofuran (THF) 51 6.2.B. Dioxane 51 6.3. Monomers 51 6.3.A. Ethylene Oxide 51 6.3.B. Propylene Oxide 52 6.3.c. Styrene 52 6.4. n-Butyl Bromide 52 6.5. Chloromethylation Catalysts 53 6.5.A. Stannic Chloride 53 6.5.B. Zinc Chloride 53 6.6. Chloromethyl Methyl Ether 53 6.7. Initiators 54 6.7.A. The Solution of n-Butyl Lithium in Hexane 54 6.7.B. Solutions of Cumyl Potassium in THF 51+ 6.7.B.1. Determination of Cumyl Potassium in Cumyl Potassium-THF Solutions 54 8 PART THREE EXPERIMENTAL Page 7. Apparatus 56 7 .1. The High Vacuum Inert Gas System 56 7.2. The Thermostatted Bath 57 7.3. The Use of the "Sovirel" Taps and Joints 57 7.4. The Use of the Splash Head in the Purifications 58 7.5. The Containers used for Liquid Storage in Argon Gas Atmosphere 59 7.6. The Syringes and Needles 59 8. Kinetic Studies of Ethylene Oxide and Propylene Oxide Polymerizations 60 8.1. The Dilatometric Measurements 60 • 8.1.A. Filling the Dilatometers 60 8.2. Determination of the Unsaturation Content in Propylene Oxide 61 8.3. Measurement of Molecular Weights by Vapour Phase Osmometry 61 8.4. The Automatic Viscometer and Viscosity Measurements 62 8.5. The Calculation of Rates of Polymerization 63 8.6. Calculation of Activation Energies of Polymerizations 64 9. Preparation of Monodisperse Polystyrene Initiated by Cumyl Potassium in THE 65 10. Attempted Preparation of Graft Copolymers of Styrene and Ethylene Oxide 67 10.1. Determination of Chlorine in Chloromethylated Polystyrene by Neutron Activation Analysis 70 9 PART FOUR PROPERTIES OF ETHYLENE OXIDE PROPYLENE OXIDE AND THEIR HOMOPOLYMERS Page 11. Epoxides 78 11.1. The Structure of Epoxides 78 II.I.A. The Physical Properties of Ethylene Oxide 79 11.1.B. The Physical Properties of Propylene Oxide 79 11.2.A. The Physical Properties of Polyethylene Oxide 79 11.2.B. The Physical Properties of Polypropylene Oxide 80 PART FIVE RESULTS AND DISCUSSION 12. The Kinetics of Ethylene Oxide Polymerization with. Cumyl Potassium,in THE and THF-Dioxane Mixtures 82 12.1. The Kinetics of Ethylene Oxide Polymerization with Cumyl Potassium in THF 82 12.1.A. Initiation 82 12.1.B. Propagation 83 12.1.C. The Dependence of the Rate of Polymerization, Rp , on Monomer Concentration 88 12.1.D. The Dependence of the Rate of Polymerization, R p, on Initiator Concentration 90 12.1.E. The Effects of Counter Ion on the Polymerization Rates of Ethylene Oxide 92 12.I.F. The activation Energies of Polymerization of Ethylene Oxide 93 12.2. The Ethylene Oxide Polymerizations in THF-Dioxane Mixtures 94 12.3. Molecular Weights and Molecular Weight Distributions in Ethylene Oxide Polymerizations 96 12.4. Kinetics of Ethylene Oxide Polymerization Initiated with n-Butyl Lithium in THF 96 10 Page 13. The Kinetics of Propylene Oxide Polymerization with Cumyl Potassium in THE 106 13.A. Initiation 106 13.B. Propagation 106 13.C. The Dependence of the Rate of Polymerization, R , on Monomer Concentration 107 13.D.