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Title: New initiating systems for the polymerisation of isobutene
Author: Joly, Laurence
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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The work described in this thesis has been concerned with the preparation of high vinylidene end-group polyisobutene using new initiating systems such as alkoxydifluoroboranes (ROBF2) and alkyldifluoroboranes (RBF2), and their adducts with ethanol and Brønsted acids (water, sulfuric acid, trifluorosulfonic acid, acetic acid and trifluoroacetic acid). In all cases, comparison is made with the currently used initiating system of a 1 : 1 complex of boron trifluoride with ethanol (BF3.EtOH). From nuclear magnetic resonance (NMR) spectroscopic studies, n-pentoxydifluoroborane (C5H11OBF2) and methoxydifluoroborane (CH3OBF2) were found to have a trimeric structure in deuteriochloroform, whilst both pentafluorophenoxydifluoroborane (C6F5OBF2) and phenoxydifluoroborane (C6H5OBF2) existed as mixtures of trialkoxyborane [(RO)3B] and boron trifluoride. In most cases, the addition of ethanol or Brønsted acids to alkoxydifluoroboranes led to decomposition of the latter and to the formation of complex mixtures of boron compounds, viz. monofluoroboranes [(RO)2BF], trialkoxyboranes and boron trifluoride. By comparison, acetic acid and trifluoroacetic acid did not decompose methoxydifluoroborane. Both n-butyldifluoroborane (C4H9BF2) and n-pentydifluoroborane (C5H11BF2) showed the same stability when their adducts with ethanol and trifluoroacetic acid were formed. These boron trifluoride derivatives and their adducts were evaluated as initiating systems for the carbocationic polymerisation of isobutene at low temperature with particular reference to their influence on the extent of conversion, molecular weight (Mn) and more importantly, vinylidene content of the resulting polyisobutene. From experimental results, it is evident that BF3.EtOH is a much more reactive initiating system than the adducts of ethanol with alkoxydifluoroboranes, which initiated the polymerisation of isobutene, but only when used in high concentrations, to produce polymers with a high vinylidene content (ca. 88%). Alkyldifluoroboranes, whether used with ethanol or trifluoroacetic acid as an initiator, proved to be inactive co-initiators for the polymerisation of isobutene. Of all the Brønsted acids used as initiators, trifluoroacetic acid produced polyisobutene in high yield when methoxydifluoroborane was used as the co-initiator. The molecular weight of the resulting polymer was found to be within the desired range (Mn 1000-1500) with a concomitant vinylidene end-group content of up to 75% being achieved.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available