Macroporous gels were prepared by solution crosslinking of butyl rubber (PIB) in frozen benzene solutions using sulfur monochloride (S2Cl2) as a crosslinking agent. The effect of different preparation conditions, including the crosslinker concentration and the gel preparation temperature, on the gel properties was investigated. S2Cl2 was found to be an efficient crosslinking agent even at very low reaction temperatures up to -22 degrees C and at crosslinker ratios down to about 0.9 mol S2Cl2/mol internal vinyl group on PIB. The gels prepared from frozen solutions of PIB contain about 97% organic liquid, and they are very tough; they can be compressed up to about 100% strain with out any crack development, during which the total liquid inside the gel is removed. Further, the compressed gel immediately swells in contact with good solvents to recover its original shape. The low-temperature gels have a porous structure with irregular large pores of 10(1)-10(2) mu m in diameter, separated by pore walls of about 10 mu m in width with a high polymer concentration, which provide structural support to the material. The gels also exhibit completely reversible swelling-deswelling cycles in toluene and methanol, respectively, i.e., they return to their original shape and original mass after a short reswelling period. The results suggest that both phase separation of PIB chains at low temperatures and the presence of frozen benzene templates are responsible for the porosity formation in PIB gels.