POLYMER BULLETIN, vol.60, pp.169-180, 2008 (SCI-Expanded)
The copolymerization reactions of acrylamide and N,N'-methylenebis(acrylamide) were carried out in DMSO/water mixture (1:1 by volume) at various temperatures T(prep) between -18 and 22 degrees C. Scanning electron microscopy analysis of the networks revealed the presence of porous morphologies. All the network samples formed at or below 0 degrees C have relatively small pores with sizes about 10 degrees mu m. In this range of T(prep), the pore size only slightly increases with the temperature. As the temperature is increased above 0 degrees C, both the average pore size and the degree of polydispersity of the pores rapidly increase. Between T(prep)=0 and 13 degrees C, the microstructure gradually changes from networks having relatively small pores to those exhibiting regular assembly of polyhedral large pores of about 10(1) mu m in sizes. The formation of the porous structure at or below 0 degrees C is as a result of the cooling-induced phase separation mechanism, while the large polyhedral pores in the networks prepared at higher temperatures form during the freeze-dry process of the hydrogels after preparation.