Title:
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Studies of the cationic polymerisation of vinylic and energetic cyclic ether monomers
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The cationic polymerisation of various monomers, including cyclic ethers bearing
energetic nitrate ester (-ON02) groups, substituted styrenes and isobutylene has been
investigated. The main reaction studied has been the ring-opening polymerisation of 3-
(nitratomethyl)-3-methyl oxetane (NIMMO) using the alcohol/BF3.0Et2 binary initiator
system. A series of di-, tri- and tetrafunctional telechelic polymers has been
synthesised. In order to optimise the system, achieve controlled molecular weight
polymers and understand the mechanism of polymerisation the effects of certain
parameters on the molecular weight distribution, as determined by Size Exclusion
Chromatography, have been examined. This shows the molecular weight achieved
depends on a combination of factors including -OH concentration, addition rate of
monomer and, most importantly, temperature. A lower temperature and OH
concentration tends to produce higher molecular weight, whereas, slower addition rates
of monomer, either have no significant effect or produce a lower molecular weight
polymer. These factors were used to increase the formation of a cyclic oligomer, by a
side reaction, and suggest, that the polymerisation of NIMMO is complicated with endbiting
and back biting reactions, along with other transfer/termination processes. These
observations appear to fit the model of an active-chain end mechanism. Another cyclic
monomer, glycidyl nitrate (GL YN), has been polymerised by the activated monomer
mechanism. Various other monomers have been used to end-cap the polymer chains to
produce hydroxy ends which are expected to form more stable urethane links, than the
glycidyl nitrate ends, when cured with isocyanates. A novel monomer, butadiene oxide
dinitrate (BODN), has been prepared and its homopolymerisation and copolymerisation
with GL YN studied.
In concurrent work the carbocationic polymerisations of isobutylene or substituted
styrenes have been studied. Materials with narrow molecular weight distributions have
been prepared using the diphenyl phosphate/BC13 initiator.
These systems and monomers are expected to be used in the synthesis of thermoplastic
elastomers.
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