Thermally responsive core–shell microparticles and cross-linked networks based on nitrone chemistry

Abstract

Complex cross-linked soluble architectures with molecular weights ranging from 25 000 to 71 000 g mol⁻¹ and polydispersities (PDIs) ranging from 2.5 to 8.1 are generated using nitrone mediated chemistry. These cross-linked architectures are subsequently cleaved into their constituting fragments, i.e. linear chains with molecular weights ranging from 36 000 to 40 000 g mol⁻¹ and a PDI of 2.0 or network fragments with molecular weights ranging from 28 000 to 30 000 g mol⁻¹ and PDIs from 2.5 to 3.7, respectively. The cleavage into linear chains or network fragments depends on the pathway of network formation. Nitrone mediated reactions are also applied for the synthesis of microspheres. Conventional distillation precipitation polymerization was performed in the presence of a nitrone, leading to uniform microspheres with diameters ranging from 2.2 to 2.4 μm. These microspheres feature alkoxyamine functionalities throughout their interior and on their surface. The alkoxyamine functionality on the surface is employed in a subsequent nitroxide mediated polymerization (NMP) with N-isopropylacrylamide (NiPAAm) in a ‘grafting from’ approach to generate pNiPAAm on the surface of the microspheres. The resulting stimuli-responsive core–shell microspheres are characterized via SEM, XPS, elemental analysis as well as turbidity measurements. The characterization methods confirm the presence of a stimuli-responsive layer of pNiPAAm on the microspheres' surface.