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 degrees C) was less than that reported for pure NIPAAM (32 degrees C) due to the hydrophobicity of the comonomer, EGDMA. The graded films displayed a broader transition over the range from 16 to 28 degrees 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. (C) 2011 Elsevier Ltd. All rights reserved.