Abstract
We have investigated the collapse transition of aqueous solutions of gradient copolymers from poly(iso-propyl-2-oxazoline)s (PiPrOx), which contain few hydrophobic moieties (n-nonyl-2-oxazoline (NOx) monomers). We extend our previous investigations (Salzinger et al., Colloid Polym Sci 290:385–400, 2012), where, for the gradient copolymers, an intermediate regime right above the cloud point was identified where small aggregates are predominant. Large aggregates are present in significant numbers only at higher temperatures. To investigate the stability of the intermediate regime, we performed time-resolved small-angle neutron scattering (SANS) experiments during temperature jumps starting below the cloud point and ending in the intermediate regime or in the high-temperature regime. We found that the intermediate regime is stable during the time investigated (∼1 h). Moreover, the collapse of the small aggregates and the surface structure of the large aggregates are related to the number of hydrophobic moieties and the quench depth. The present results elucidate the structural evolution of these polymers and relate them to their final state as well as to their macroscopic behavior.
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Notes
Due to restricted rotation of the methylene group, the signal is generally split into two signals (cis/trans position). Here, the signal at 2.97 ppm is overlapped by the multiplet of the 2-iso-propyl-2-oxazoline signal.
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Acknowledgments
The authors gratefully acknowledge financial support by the DFG (Pa771/6-2 and Jo287/4-3). The authors thank ILL for allocating beamtime and providing excellent equipment and Robert Luxenhofer for MALDI-ToF measurements.
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Jaksch, S., Schulz, A., Kyriakos, K. et al. The collapse and aggregation of thermoresponsive poly(2-oxazoline) gradient copolymers: a time-resolved SANS study. Colloid Polym Sci 292, 2413–2425 (2014). https://doi.org/10.1007/s00396-014-3333-6
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DOI: https://doi.org/10.1007/s00396-014-3333-6