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Synthesis of Functional Stimulus Responsive Oligovinyl Ethers and Towards Highly Branched Polymers Using Ab Initio Cationic Polymerisation

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Synthesis of functional stimulus responsive oligovinyl ethers and towards highly branched polymers using ab initio cationic polymerisation By Rami Obaid Department of Chemistry The University of Sheffield Submitted to the University of Sheffield In fulfilment of the requirements for the award of Doctor of Philosophy October 2015 I Declaration This thesis is submitted to the University of Sheffield for the degree of Doctor of Philosophy, having not been submitted to any other University for any degree. I declare that all work contained herein is my own work, except where referenced and acknowledged accordingly. .................................. Rami Obaid October 2015 II Acknowledgements First of all I would like to thank Allah (God) and sincerely thanks are addressed to my parents and also, my sisters and brother: without their constant support and encouragement, I would certainly never have been able to reach the point where I am now and would not be who I am. I would like to thank King Abdullah Scholarship Program (KASP) for funding this PhD. Professor Stephen Rimmer is thanked for his supervision and giving me the opportunity to work in his group without whom I could not have done this project. I am grateful to Mr. Simon Thorpe who has been very considerate and helpful on MALDI-TOF MS analysis during the whole project. Many thanks are addressed to my great teacher Dr. Mouslim Messali who has always been ready to help me a lot during my BSc, MSc and PhD degrees. I also want to thank my friends in Sheffield; it was a great pleasure to live with all of you. Finally, I would like to thank the Rimmer group for their warm welcome and help during the whole project. It was a beautiful and very rewarding for me and I liked very much to work in this laboratory on an exciting topic. III Abstract Oligo(vinyl ethers) with functionalised end groups were produced through the alkylation of silyl enol ethers in ab initio cationic polymerisations. In order to obtain high degrees of chain end functionality a great deal of care was taken in choosing the monomer concentration, the reaction temperature, Lewis acids and the concentration of silyl enol ether. The experiment also required the use of highly nucleophilic species such as silyl ketene acetal, which react with carbocations at similar rates to vinyl ethers. Rapid elimination of the primary adduct produced the ester end-groups. MALDI-TOF mass spectrometry was used to analyse the oligomers obtained and to assess the side reactions and chain end functionalisation processes. Oligo(methyl vinyl ether)s were synthesised in cationic polymerisations using the HCl-isobutyl vinyl ether/SnCl4 initiating system within the polymerisation temperature range -26 °C to -78 °C, and in the absence of an end-capping agent. It was observed that the use of a lower temperature yielded well-defined oligomers. Furthermore, during the polymerisation the silyl enol ether reactivity suppressed the termination rate and oligomethyl vinyl ether with increased levels of ester end groups were then produced. In addition, a size exclusion chromatograph was calibrated using MALDI-TOF MS to obtain molecular weights of narrow fractions (SEC-MALDI TOF). The Kuhn-Mark- Houwink relation for oligo(methyl vinyl ether) was then established. In the light of the above, it was possible to infer that the solution coil conformation is dependent on the end group structure. Oligo(isobutyl vinyl ethers) were also prepared successfully at different temperatures (-26 and -78 °C) in the presence of a silyl enol ether using HCl- iBVE/TiCl4 as the initiating system. At a lower temperature, and with a high concentration of silyl enol ether, the normal termination reactions were suppressed and oligo(isobutyl vinyl ethers) with a high ester group chain end functionality were produced. This phenomenon can be attributed to the fact that, at lower reaction temperatures, the rate of propagation relative to the rate of termination and the control of polymerisation was observed. Another means by which oligo(isobutyl vinyl ethers) were prepared in this experiment with ester end groups was by using continuous reaction processes. These IV processes are commonly applied in many industrial applications as they allow for the production of large quantities of polymer in a short period of time. These particular polymerisations were applied by using HCl-iBVE as an initiating system with SnCl4 and TiCl4 as Lewis acids at -15 °C. The production of oligomers with a high degree of ester group functionality was carried out by the use of SnCl4 with a high concentration of silyl enol ether at a slow flow rate. It was also possible to produce highly branched functional polymers by using continuous processes. In this instance, isobutyl vinyl ether was used as a first monomer with diethyl divinyl ether (DEDVE) and divinyl benzene (DVBz) being used as second monomers in the presence of silyl enol ether at a temperature of -15 °C. Many different Lewis acids were used in these polymerisation reactions It was observed that the polymerisation of iBVE with DEDVE was only successful by using Sc(OTf)3 as a Lewis acid. Highly branched polymers with ester group functionality were detected at a monomer ratio of 9:1 with a low concentration of silyl enol ether at a high feed rate. In the polymerisation of iBVE with DVBz, only two Lewis acids successfully aided these reactions (ZnI2/HI and Sc(OTf)3). In ZnI2/HI, a low concentration of silyl enol ether with a high flow time was found to form highly branched polymers with the chain end group. In using Sc(OTf)3, a high concentration of SEE with a low feed rate was shown to produce highly branched functional polymers. By analysing the aforementioned information it was possible to deduce that the feed rate and the concentration of silyl enol ether had a substantial effect on the chain end attained. V Table of Contents Chapter 1 .......................................................................................................................... 1 1.1 Cationic polymerisation when silyl enol ether is present ............................... 1 1.1.1 Introduction ............................................................................................... 1 1.1.2 Ionic polymerisation .................................................................................. 2 1.1.3 Cationic polymerisation ............................................................................ 2 1.1.4 Telechelic oligomers ............................................................................... 15 1.1.5 Living cationic polymerisation ............................................................... 16 1.1.6 Alkylation reactions of silyl enol ethers and the aldol reaction .............. 17 1.1.7 Ab initio end capping by silyl enol ethers ................................................ 22 1.2 Synthesis of highly branched functional polymers ........................................ 26 1.2.1 Stimuli responsive polymers ...................................................................... 26 1.2.3 pH responsive polymers ............................................................................. 27 1.2.4 Temperature responsive polymers ............................................................. 27 1.2.5 Hyperbranched polymer synthesis ............................................................. 28 1.2.6 Branching and gelation theory ................................................................... 31 1.3 Mass spectrometric analysis of oligomers/ polymers .................................... 32 1.4 Aim of this project ............................................................................................ 37 Chapter 2 ........................................................................................................................ 41 2. Ab initio cationic polymerisation of MVE and iBVE using batch system .... 41 2.1 Introduction ................................................................................................. 41 2.2 Experimental ............................................................................................... 43 2.3 Organic and polymer characterisation ........................................................ 46 2.4 Results and discussion ................................................................................ 49 2.5 Conclusions ................................................................................................. 86 Chapter 3 ........................................................................................................................ 88 3. Polymerisation of isobutyl vinyl ether using continuous processes .............. 88 3.1 Introduction ................................................................................................. 88 3.2 Experimental ............................................................................................... 90 3.3 Results and discussion ................................................................................ 92 3.4 Conclusions ................................................................................................... 126 Chapter 4 ...................................................................................................................... 128 4. Synthesis of difunctional chain end capping agent ........................................ 128 4.1 Introduction ............................................................................................... 128 4.2 Experimental ............................................................................................
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