IN-SITU, TIME-RESOLVED X-RAY-DIFFRACTION STUDY OF THE SOLID-STATE POLYMERIZATION OF DISULFUR DINITRIDE TO POLY(SULFUR NITRIDE)

Products and kinetic and mechanistic aspects of the title reaction wer e investigated by time-resolved X-ray powder diffraction combined with Rietveld refinement. The polymerization of S2N2 at 40 degrees C was m onitored with a time resolution better than one diffraction pattern pe r minute until completion. The reaction product comprised a mixture of monoclinic beta-(SN)(x) (90%) and an additional orthorhombic phase, i dentified as alpha-(SN)(x) (about 10%). The inversely proportional con version/formation vs time curves for educt and products indicate that the reaction involves only crystalline phases. The cell parameters of polymerizing S2N2 varied noticeably with progressing conversion, where as the cell volume remained unchanged up to a monomer conversion of 50 %, Refinement of atomic coordinates for S and N indicated retention of the reactant geometry, It is concluded that the polymerization of S2N 2 to (SN)(x) is of nondiffusive nature and involves a martensitic tran sition.