A molecular brush with thermoresponsive poly(2-ethyl-2-oxazoline) side chains: a structural investigation

The thermoresponsive behavior of a poly(2-oxazoline)-based molecular brush is investigated in aqueous solution. The molecular brush under study, P i POx 100 - g -PEtOx 17 , has a poly(2-isopropenyl-2-oxazoline) (P i POx) backbone grafted with thermoresponsive poly(2-ethyl-2-oxazoline) (PEtOx) side chains. Since the backbone degree of polymerization is only a factor of ~ 6 higher than the ones of the side chains, it features an architecture between a star-like polymer and a comb-like polymer. Its aqueous solution exhibits lower critical solution temperature (LCST) behavior with a cloud point temperature T cp = 40.5 °C at 30 g L −1 . The temperature-dependent structural evolution is disclosed using dynamic light scattering (DLS) and small-angle neutron scattering (SANS). An increase of the molecular brush size is found upon heating from room temperature to T cp , which is attributed to the extension of the backbone resulting from the dehydration and collapse of the side chains. Above T cp , the size decreases again, which indicates the collapse of the whole molecular brush. Large aggregates are found to be present in the solution in the temperature range 25–50 °C. These become more compact, as the temperature is increased across T cp . Graphical abstract Transmission and scattering intensity in relation to temperature and momentum transfer, respectively