Self-Assembly of Synthetic and Biological Polymeric Systems of ...

where Em represents a growing chain, the active centre is an ion pair, and the rapid
equilibration ensures that all chains are equally likely to grow. This ideal scheme would
produce polymers with Mn= (mass of E polymerised)/(moles of initiator used) and a Poisson
distribution of chain lengths. In practice, the chain length distribution can be widened by a
slow initiation. In the absence of termination, the system is living and is ideal for preparation
of block copolymers. The same scheme applies to styrene oxide.
It is known that block poly(oxyalkylene) copolymers with hydrophobic blocks formed by
propylene oxide or butylene oxide (either diblock or triblock architectures) have a
spontaneous formation of spherical and cylindrical micelles in dilute aqueous solution. On the
other hand, formation of vesicular structures for poly(oxyalkylene) block copolymers needs
oftenly an energy supply via mechanical, sonochemical or electrical methods (85)(86).
Nevertheless, it has been previously reported the spontaneous formation of vesicles (87)(88),
where these types of structures are likely to form because of relatively large volume to length
ratios of the hydrophobic block and the relative lengths of the poly(oxyethylene) blocks. In the
case of block copolymers containing poly(oxystyrene) blocks as the hydrophobic block, the
formation of elongated micelles has been unusual, whereas vesicle formation has not been yet
reported.
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