Preparation of macroporous poly(acrylamide) hydrogels in DMSO/water mixture at subzero temperatures

Abstract

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 °C. Scanning electron microscopy analysis of the networks revealed the presence of porous morphologies. All the network samples formed at or below 0 °C have relatively small pores with sizes about 10⁰ µm. In this range of T_prep, the pore size only slightly increases with the temperature. As the temperature is increased above 0 °C, both the average pore size and the degree of polydispersity of the pores rapidly increase. Between T_prep=0 and 13 °C, the microstructure gradually changes from networks having relatively small pores to those exhibiting regular assembly of polyhedral large pores of about 10¹ µm in sizes. The formation of the porous structure at or below 0 °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.