Novel N-isopropylacrylamide based polymer architecture for faster LCST transition kinetics

Temperature-responsive p(N-isopropylacrylamide-co-ethylene glycol dimethacrylate) (p(NIPAAm-co-EGDMA) films, graded in composition to provide a NIPAAm-rich surface, were synthesized successfully via initiated chemical vapor deposition (iCVD). Their dynamic response to temperature changes as monitored using quartz crystal microbalance with dissipation monitoring (QCM-D) was clearly distinguishable from the response of control iCVD-prepared films of homogeneous composition. The lower critical solution temperature (LCST) of the homogeneous copolymer (15 °C) was less than that reported for pure NIPAAM (32 °C) due to the hydrophobicity of the comonomer, EGDMA. The graded films displayed a broader transition over the range from 16 to 28 °C. The time constants associated with the response to small step changes in temperature around the LCST transition were significantly smaller in the graded (<143 s) than in the homogeneous films (1000-8000 s). The novel graded film architecture is promising for facilitating fast switching in applications requiring responsiveness to temperature swings.