We have investigated the heat-induced self-association of block copolymers poly(2-isopropyl-2-oxazoline)-b-poly(2-ethyl-2-oxazoline) (PIPOZ-b-PEOZ) in water and poly(2-isopropyl-2-oxazoline)-b-poly(N-isopropylacrylamide) (PIPOZ-b-PNIPAM) in water-methanol (MeOH) mixtures using differential scanning caloriemetry, light scattering and small-angle X-ray scattering (SAXS) together with visual observation. The dehydration temperatures of the PIPOZ and PEOZ blocks in water are 43 and 54 �C, respectively. When heated abruptly to 50 �C where PIPOZ-b-PEOZ is amphiphilic, the copolymer first forms star micelles that further aggregate to form large concentrated phase droplets, and finally the droplets coalesce into a bulk liquid phase. When heated abruptly to 70 �C, where both blocks are hydrophobic, the copolymer solution also separates into two liquid phases, consisting of phase-separated polymer-rich droplets dispersed in a polymer-poor phase, but the droplets do not coalesce into a liquid bulk phase.Although the difference in the phase-separation temperature between solutions of the PIPOZ and PNIPAM homopolymers is enlarged with increasing the MeOH content, the dehydration occurs almost simultaneously on both block copolymer chains in most solvent conditions, and the solutions undergo a liquid-liquid phase separation. The copolymer chain in the coexisting dilute phase was mostly molecularly dispersed, having more compact conformation with increasing temperature, without forming micelles. Although PIPOZ-b-PNIPAM behaved like a homopolymer in water and water-MeOH mixtures, the amphiphilicity of the block copolymer affects the colloidal stability of concentrated-phase droplets in the phase separating solutions in a complex manner.

Dehydration and phase-separation behaviors of poly(2-oxazoline) containing block copolymers in solution

248th National Meeting (2014)

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