Characteristics of acrylic acid and N-isopropylacrylamide binary monomers - Grafted polyethylene film synthesized by photografting

Method for introducing grafted chains consisting of two types of monomer components, acrylic acid (AA) and N-isopropylacrylamide (NIPAAm), into low-density polyethylene (PE) film (thickness = 25 mu m) was investigated by two photografting technique using xanthone photoinitiator at 60 degrees C. In the first method (one-step method), AA and NIPAAm binary monomers were graftcopolymerized onto PE film. In the second method (two-step method), AA was first photografted onto PE film and then NIPAAm was further introduced into the AA-grafted PE film by a second-step photografting. Water absorbencies of the grafted films (one-and two-step samples) prepared by the one-and two-step methods, respectively, decreased in the order of AA-grafted film > one-step sample > two-step sample > NIPAAm-grafted film. The water absorbency steeply decreased at 20 to 40 degrees C with increasing temperature when immersed in water at the temperatures (5-60 degrees C) for 24 h. Thermosensitivity, which was defined as the ratio of water absorbencies of the grafted samples at 5 and 60 degrees C, was higher for the one-step sample than the two-step one. The different extent of the water absorbency and the thermosensitivity between both samples is discussed in terms of location of grafted chains in the film substrate, which was determined by electron probe microanalysis and attenuated total reflection-infrared measurements, and monomer sequence distribution of the grafted chains. (C) 1998 John Wiley & Sons, Inc.