Chapter 10
Synthesis and Characterization of α-Hydroxyl-ωMethoxycarbonyl and α-Hydroxyl-ω-Carboxyl Asymmetric Telechelic Polyisobutylenes
Downloaded by MONASH UNIV on June 18, 2013 | http://pubs.acs.org Publication Date: May 8, 1998 | doi: 10.1021/bk-1998-0704.ch010
Balint Koroskenyi and Rudolf Faust Polymer Science Program, Chemistry Department, University of Massachusetts at Lowell, One University Avenue, Lowell, MA 01854 The convenient synthesis of α-hydroxyl-ω-methoxycarbonyl asymmetric telechelic PIBs has been achieved by the combination of two recently discovered techniques, haloboration-initiation and end capping with 1,1-diphenylethylene followed by end quenching with silyl ketene acetals, 1-methoxy-1-trimethylsiloxy-2-methyl-propene (MTSMP), 1-methoxy-1-trimethylsiloxy-propene (MTSP), and 1 -methoxy-1-trimethylsiloxy-ethene (MTSE). Nearly quantitative chain end functionalization has been proved by H N M R , quantitative C N M R , and FT-IR spectroscopy. The methoxycarbonyl end arising by quenching with MTSMP could not be hydrolyzed under either basic or acidic conditions. These methods also failed to yield the acid when the corresponding diisobutylene derivative was used. The sterically less hindered esters, however, readily underwent hydrolysis resulting in the formation of α-hydroxyl-ω-carboxyl asymmetric telechelic PIBs. 1
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Hydroxyl and carboxyl functional groups are very valuable in the chemistry of polymers due to the wide variety of reactions that can be carried out through these intermediates, such as transformations into other useful functional groups or block and graft copolymer synthesis. Thus, there have been many attempts to synthesize PIBs with such end groups, mostly by rather cumbersome methods [1-4]. Most of these methods involve the polymerization of isobutylene (IB) with a difunctional initiator, such as dicumyl chloride, followed by chain end functionalization resulting in symmetric telechelic PIBs with either hydroxyl or carboxyl end groups. The synthesis of asymmetric telechelic polymers is more difficult and usually carried out via a multistep process. A most useful synthetic strategy would involve the living polymerization of IB by an initiator with a protected functional group or a precursor, and functionalization of the living chain end. We recently reported that BX3 (X=C1, Br) alone can initiate the living polymerization of IB using polar solvents in the presence of a proton trap to prevent ©1998 American Chemical Society In Functional Polymers; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.
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136 initiation by protic impurities [5-7] (Scheme 1). The products are asymmetric telechelic polyisobutylenes (PIBs) with controlled molecular weight and narrow molecular weight distribution, carrying X 2 B - head groups andter/.-haloend groups. Upon quenching with methanol, the X 2 B - head groups are converted into alkylboronic esters. These materials are valuable intermediates to obtain asymmetric telechelic polymers carrying different functionalities that are difficult to obtain by conventional methods. One of the most important transformations of the head group to primary, HO- upon oxidation by alkaline hydrogen peroxide at room temperature, was shown to be rapid (
