THE EFFECT OF PREPARATION TEMPERATURE ON SOME PROPERTIES OF A TEMPERATURE-SENSITIVE HYDROGEL

The physical and chemical characteristics of temperature-sensitive hyd rogel, poly(N-isopropylacrylamide), were strongly dependent upon the p reparation temperature and the kind of accelerator used for free radic al polymerization. N,N,N',N'-tetramethyl-ethylenediamine (TEMED) was a better accelerator for consistent gelation near room temperatures (17 -24 degrees C) compared with sodium metabisulfite. Using TEMED, gelati on time was 3.6 min at 18 degrees C, but decreased to 1.8 min at 23 de grees C. When the gel was prepared in a glass cylinder of 37 mm ID and 191 mm height at temperatures of 18 degrees C and below, it was compl etely transparent. The gel became more opaque starring from the core p art of the gel cylinder, when prepared at higher temperatures. The gel became totally opaque at preparation temperatures of 23 degrees C and above. The transparent gel had better physical strength as determined by Instron, and higher transition temperature for volume change (lowe r critical solution temperature) as determined by differential scannin g calorimetry. The transparent gel also had a better volume change cap acity when the gel underwent temperature swings between 28 degrees C a nd 37 degrees C.