DIRECT OBSERVATION OF POLYMER NETWORK STRUCTURE IN MACROPOROUS N-ISOPROPYLACRYLAMIDE GEL BY RAMAN MICROSCOPY

The Raman microscopy technique is used to characterize the temperature -induced evolution of the pore structures of a macroporous N-isopropyl acrylamide (NIPA). The gel is synthesized using a suspension of 45 wt % toluene and 55 wt % pregel NIPA solution. The intensity of the band due to the CH2 bending vibration, centered at 1445 cm(-1), is used to monitor the distribution of the polymer chain density in the lateral p lane. It is found that the macroporous gel consists of water-rich area s, which can be interpreted as the pores, and polymer-rich areas. At r oom temperature, the average sizes of the pores and the width of polym er-rich areas are 75 mu m and 20 mu m, respectively. Both the pores an d their surrounding polymer-rich areas have random geometry, as demons trated by the Raman microimaging. With increased temperature the size of the pores decreases. This process is accompanied by a narrowing of the polymer-rich areas. At higher temperatures polymer chains bunch to gether and this process accelerates rapidly near the volume phase tran sition temperature (34 degrees C). Above 36 degrees C, the pore sizes become too small to be resolved using Raman microscopy.