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

The physical and chemical characteristics of temperature-sensitive hydrogel, poly(N-isopropylacrylamide), were strongly dependent upon the preparation temperature and the kind of accelerator used for free radical 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, gelation time was 3.6 min at 18 degrees C, but decreased to 1.8 min at 23 degrees 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 completely transparent. The gel became more opaque starring from the core part 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 (lower critical solution temperature) as determined by differential scanning calorimetry. The transparent gel also had a better volume change capacity when the gel underwent temperature swings between 28 degrees C and 37 degrees C.