How Structure-Related Collapse Mechanisms Determine Nanoscale Inhomogeneities in Thermoresponsive Polymers

Continuous wave electron paramagnetic resonance (CW EPR) spectroscopy on the amphiphilic spin probe TEMPO in solutions of selectively chosen functional, thermoresponsive poly(propylene oxide) (PPO)- and poly(ethylene oxide) (PEO)-based copolymers of both linear and branched structure is used to elucidate their host guest interactions and inverse phase transitions. Three different fundamental types of host guest interactions between probes and polymers could be correlated to the phase transition mechanisms (supported by MD simulations), evidencing that these proceed via nanoscale inhomogeneities of the polymers. Because of their ability to host small amphiphilic guest molecules, thermoresponsive copolymers are promising candidates for molecular transport applications. The host guest interaction principles derived from our small amphiphilic spin probes may also aid in finding the appropriate design for the desired release property of a specific thermoresponsive polymer-based host guest systems.