Crystallisation-driven self-assembly of poly(2-isopropyl-2- oxazoline)-block-poly(2-methyl-2-oxazoline) above the LCST

The solution behaviour in water of a polyoxazoline-type block copolymer, namely poly(2-
isopropyl-2-oxazoline)-block-poly(2-methyl-2-oxazoline), denoted as P(iPrOx-b-MeOx),
above the lower critical solution temperature (LCST) of the PiPrOx block was exploited to
induce a temporary or permanent self-assembly. Spherical micelles were first obtained and
could be disassembled in a reversible manner when kept for a short period of time (i.e. t <
1h30) above the LCST, and cooled down to room temperature. In contrast, annealing the
copolymer solution for more than 1h30 at 65 °C induced the crystallisation of the PiPrOx
block, as evidenced by wide angle X-ray scattering (WAXS) experiments. This crystallisationdriven
self-assembly phenomenon resulted in different morphologies, including spherical and
distorted crystallised micelles and micron-size fibers, their relative proportion varying with
annealing time. Formation of micron-size range fiber-like structures might be explained by a
re-organization of parent crystallised micelles. The crystal structure, as determined by WAXS,
appeared to be identical to that of the PiPrOx homopolymer.