Investigation of the LCST-Thermoresponsive Behavior of Novel Oligo(Ethylene Glycol)-Modified Pentafluorostyrene Homopolymers

Featured Application The combined use of light scattering, turbidimetry, and differential scanning calorimetry highlighted the thermoresponsive self-assembling behavior in water of the oligo(ethylene glycol)-modified pentafluorostyrene homopolymers. The potential applications of such novel smart materials are open to study in advanced fields, including nano-medicine, nano-catalysis and bottom-up nanotechnology at large. Amphiphilic tetrafluorostyrene monomers (EFS8) carrying in the para position an oligoethylene glycol chain containing 8 oxyethylenic units on average were synthesized and used for preparation via activator regenerated by electron transfer atom transfer radical polymerization (ARGET-ATRP) of the corresponding amphiphilic homopolymers (pEFS8-x) with different degrees of polymerization (x = 26 and 46). Combining light transmittance and nano-differential scanning calorimetry (n-DSC) measurements revealed that pEFS8-x homopolymers displayed a lower critical solution temperature (LCST) thermoresponsive behavior in water solutions. Moreover, n-DSC measurements revealed the presence in heating scans of a broad endothermic peak ascribable to the dehydration process of the polymer single chains (unimers) and their collapse into aggregates. Consistently, dynamic light scattering (DLS) measurements showed below the LCST the presence of small nanostructures with a hydrodynamic diameter size D-h of 6-7 nm, which collapsed into concentration-dependent larger multichain aggregates (D-h = 300-3000 nm) above LCST. Interestingly, n-DSC data showed that the unimer-aggregate transition was reversible up to a specific temperature (T-rev) of each homopolymer, which in any case was higher than T-max. When heating above T-rev the transition was no longer reversible, causing the shift of T-onset and T-max at lower values, thus suggesting an increase in hydrophobicity of the polymer systems associated with a temperature-dependent dehydration process.

Automated summary

The study reveals a novel smart material with self-assembling behavior in water and identifies its thermoresponsive properties at the nanoscale level.