Synthesis of poly(2-oxazoline)-based hydrogels with tailor-made swelling degrees capable of stimuli-triggered...

A 32-membered library of poly(2-oxazoline)-based hydrogels of the composition pEtOx(m) -pPhOx(n) -pPBO(q) (m/n = 150/0, 100/50, 50/100, and 0/150; q = 1.5-30) was prepared from 2-ethyl- (EtOx), 2-phenyl-2-oxazoline (PhOx), and phenylene-1,3-bis-(2-oxazoline) (PBO). The polymerizations were performed from ground monomer mixtures at 140 °C in a single-mode microwave reactor in reaction times as short as 1 h. Purified hydrogels, containing no residual monomers, were obtained in yields of 95% or higher. Acid-mediated hydrolysis rates as well as swelling degrees of the hydrogels were adjustable over a broad range; swelling degrees in water/ethanol/dichloromethane ranged from 0 to 13.8/11.7/20.0. The hydrogels could incorporate organic molecules according to in situ or post-synthetic routines. Post-synthetic routines enabled for the preparation of hydrogels from which the incorporated compounds were only released through diffusion processes if the solvent was changed or through hydrogel degradation if the pH was lowered.