부산대학교 도서관

Hydrogel (also called Aquagel) becomes a popular research field in recent years thanks to its unique properties like significant water content, biological compatibility,and environmental sensitivity. Actually it is a network of polymer chains with some special groups responding to different environmental stimulants. This class ofpolymers usually has two reversible and transformable states, swollen state and collapsed state which is separated by lower critical solution temperature (LCST). Inswollen state, water content of hydrogels is considerable (even up to 99%). While in collapsed state, hydrogel shrinks acutely, so that it has to release most of water frominside. Generally speaking, this phase transition is a controllable and continuous process with different external stimulants such as temperature, pH-value, solventcomposition, ions, light, redox, electric field, and magnetic field. As a result of that, hydrogel has a wide potential range of applications, like drug delivery system, sensor,mesh replication, dispersion control, permeability control, nano film, microgel and separation.Of all hydrogels, poly (N-iso-propylacrylamide) (PNIPAM) is paid much more attention because its LCST is around 32°C experimentally, close to body temperature.It has an advantage in applications for biological field and medical science. Normally, to synthesize hydrogel in radical polymerization, crosslinker is necessary inpreparation which plays an important role to hydrogel properties. Conventionally N, N’-methylenebisacrylamide (BIS) is used as crosslinker which forms a fully organichydrogel that shows some limitations like low mechanical strength in high temperature or their relatively long response time. Thus it is tending to improve hydrogel properties via using different crosslinker these years.In Chapter 2, octa vinyldimethylsiloxysilsesquioxane (OVSS) is synthesized and characterized with the help of octa dimethylsiloxysilsesquioxane (OSS) and octaallyldimethylsiloxysilsesquioxane (OASS). It is a new organic and inorganic hybrid nanocomposite; this class of materials is under hot study as a result of novel properties. It possesses eight organic branches appended to the vertexes of the cube via -O-SiMe2- linkages, its core size is physically large with respect to polymer dimensions, about 0.53nm. But the influence of silicon-oxygen core can be ignored when polymer chains are long enough. OVSS has eight function groups (double bond);while BIS has two, which results in polymers with completely different space configuration. By using OVSS as crosslinker, it’s effective to change inner structureof PNIPAM hydrogel from conventional network structures to new three dimensional structures, which improves the mechanical properties and helps to make out thebehavior of hydrogels.In Chapter 3, PNIPAMs were prepared under same reaction conditions by two crosslinkers, BIS and OVSS. After further treatments of products, the swelling ratios in equilibrium were recorded and calculated under different temperatures. The interpretation of swelling behavior is addressed in this chapter. Additionally the compression tests were taken to investigate the difference of two hydrogels.