Due to the poor solubility of these polymers, many common solution-based characterization techniques such as gel permeation chromatography or solution-based NMR were not possible. Therefore, a cross-polarization, magic angle spinning carbon-13 NMR spectrum was obtained for three polymers: 50-poly(S-r-CPD) made using the gas phase method; 67-poly(S-r-CPD) using the reflux method; and 50-poly(S-r-DCPD) for comparison. While the peaks are broad, the copolymer made from sulfur and DCPD shows a clear peak for unreacted alkenes at 132 ppm (Fig. ). This peak is absent or significantly reduced in both polymers made by the direct reaction of sulfur and CPD. These results suggest that there is high alkene conversion in the polymerization. Reduction of the polymers with sodium borohydride, followed by GC-MS analysis, resulted in the detection of the tetrathiol product shown in Figure , which is consistent with the proposed repeating unit. Combustion analysis indicated 66 wt% sulfur in the polymer, which was consistent with the feed ratio of the polymerization.