Carboxyl-functionalized dual pH/temperature-responsive poly(N-vinylcaprolactam) microgels based on isogenous comonomers for smart window applications.

Stimuli-responsive poly(N-vinylcaprolactam) (PVCL)-based microgels, which could response to small external environmental changes, have attracted great interests in the fields of biomedicine and nanotechnology. However, the preparation of such microgels meets severe challenge due to their low incorporation efficiency and thermoresponsivity passivation. To address these issues, we select 3-(tert-butoxycarbonyl)-N-vinylcaprolactam (TBVCL), a carboxyl-functionalized VCL derivative, as a comonomer to develop pH/temperature dual-responsive microgels. TBVCL, with a structure similar to VCL, enhances incorporation efficiency and colloidal stability, while reducing thermoresponsivity passivation. The volume phase transition temperature (VPTT) of the microgels can be adjusted over a broad range (19.0-49.5 °C). Notably, the radial swelling ratios of the microgels can be modulated by pH, achieving a maximum swelling ratio of 3. The distinct changes in dissolution-precipitation behavior under different temperatures or pH conditions make these microgels suitable for applications such as smart windows and sensors. Furthermore, this novel approach for fabricating microgels with pH-tunable phase-transition temperatures demonstrates significant potential for the controlled release of nanoparticles (e.g., drugs, catalysts, and quantum dots) and the development of smart nanocrystal-polymer composite sensors.