Degradation and crosslinking of dextran in aqueous solutions by gamma-radiolysis: The effect of hydrogen ions

The conditions under which crosslinking or degradation of dextran macromole cules (P-W = 930) is a predominant process upon gamma-irradiation of acidic aqueous dextran solutions in the dose range 0-0.32 MGy were found using vi scometry and gel chromatography. It was found that initial acidification of dextran solutions increased the role of crosslinking of macromolecules in the formation of the molecular-weight distribution of this polymer, whereas further acidification, in contrast, enhanced the degradation. The former i s due to the transformation of hydrated electrons into hydrogen atoms, and the latter results from the catalytic effect of protons on the unimolecular decomposition of primary macroradicals accompanied by the rupture of gluco sidic bonds. It was also found that radical centers can be transferred via macroradical-macromolecule reactions as the concentration of dextran increa sed. As a result of this, a macroradical capable of unimolecular decomposit ion, which results in degradation, is converted into a macroradical incapab le of this transformation.