Investigation of the internal structure of thermoresponsive diblock poly(2-methyl-2-oxazoline)-b-poly[N-(2,2-difluoroethyl)acrylamide] copolymer nanoparticles

The poly(2-methyl-2-oxazoline)-b-poly[N-(2,2-difluoroethyl)acrylamide] self-assembled nanoparticles show great potential in biological applications as, e.g., 19F MRI tumour diagnostic agents. As such their internal structure needs to be thoroughly investigated while the results also help to understand temperature-dependent self-assembly behaviour of copolymers comprised of the hydrophilic and thermoresponsive blocks in general. In this paper, we elucidate internal structure of the nanoparticles formed by temperature-driven self-assembly of the abovementioned diblock copolymer by various methods. The majority of our polymers form micelle-like structures above the cloud point temperature (CPT). However, the presence of thermoresponsive homopolymer chains even in amounts below standard detection limits as well as strong hydrogen bonding causes the formation of larger aggregates interconnected by hydrophobic networks and hydrogen bonds, which contain large amounts of solvent. In the case of our particles, we also observe a strong influence of solvent on CPT, particle formation and overall sample behaviour. The ability of nanoparticles to provide usable 19F NMR signal was also confirmed.