Molecular structure and shear rheology of long chain branched polypropylene formed by light cross-linking of a linear precursor with 1,3-benzenedisulfonyl azide

Linear isotactic metallocene based polypropylene (Mw = 125,000 g/mol, Mn = 61,000 g/mol) was lightly crosslinked by small amounts of 1,3‐benzenedisulfonyl azide to form long chain branches (LCB). Crosslinking was carried out by reactive extrusion at 200°C in a small scale extruder. At the processing temperature, the two azide groups decompose to nitrenes that work as crosslinkers for PP. The crosslinking reaction occurs primarily by insertion of singlet nitrenes into CH bonds. 1,3‐benzenedisulfonyl azide concentrations of, respectively, 518, 806, 1029, and 2038 ppm were used. SEC revealed formation of a high molecular weight LCB fraction. No degradation was observed by SEC. The introduction of LCB gave rise to rheological behavior typical of LCB as increased zero shear viscosity, accompanied by increased shear thinning, increased flow activation energy and a phase angle plateau. However, the rheological impact and crosslinking efficiency observed were limited compared to earlier studies on PE. Possible reasons for this are discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007