We have studied the thermal decomposition of 1,3-benzenedisulfonyl azide (1,3-BDSA), and verified that sulfonyl nitrenes formed are able to cross-link polyolefins, including PP. The decomposition was studied with DSC, TGA, and the GC-MS analysis of gaseous products. Both the decomposition of pure 1,3-BDSA and 1,3-BDSA dissolved in a polyolefin were studied. Decomposition occurs by loss of nitrogen giving sulfonyl nitrenes. In the polyolefin nitrenes cross-links the carbon chains by C-H insertion. Cross-linking of PP was verified with SEC. SEC showed no signs of decomposition of PP. Decomposition in the polyolefin was a first order reaction with a half-life of 25.7 s at 200 degrees C. Hence, 1,3-BDSA is suited for processing with polyolefins. Decomposition of pure 1,3-BDSA is more complicated with unwanted products such as SO2 and benzene being formed, thereby emphasising the need for good blending when used in polyolefins. (c) 2005 Elsevier Ltd. All rights reserved.