Synthesis and multi-responsiveness of poly(N-vinylcaprolactam-co-acrylic acid) core–shell microgels via miniemulsion polymerization

This paper reported a facile strategy to the large scale synthesis of multi-responsive core–shell microgels via seed miniemulsion copolymerization of N-vinylcaprolactam (NVCL) and acrylonitrile (AN) using 2,2′-azobis(2-methylpropionitrile) (AIBN) and divinylbenzene (DVB) as the initiator and the cross-linker, respectively. The core–shell microspheres were initially prepared via miniemulsion polymerization with polyacrylonitrile (PAN) as the core and poly(N-vinylcaprolactam) (PNVCL) as the shell. Then P(NVCL-co-AA) microgels were obtained by hydrolysis of the PAN core under base conditions. The sizes, morphologies and swelling behavior of the as-obtained microparticles were systematically investigated by transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analyses (TGA). The results showed that the obtained microgels were spherical in shape with an average size of about 100 nm. P(NVCL-co-AA) microgels had a core–shell morphology with PAA as the core and PNVCL as the shell. The contents of NVCL and DVB had an effect on the structure of microgels and hydrodynamic diameters, respectively. The resultant microgels can reversibly swell and shrink in response to pH and temperature variation, demonstrating great promise for potential applications in drug delivery and bio-sensors.