Mechanochemistry Enabled Inverse Vulcanization of Norbornadiene for Optical Polymers and Elastomeric Materials

Abstract

The emergence of polymeric materials derived from elemental sulfur through inverse vulcanization has recently provoked great interest. Particularly, norbornadiene derived sulfur polymers are predicted to have high transmittance in the long-wave infrared region that can be an excellent candidate for polymeric IR optics. Moreover, owing to the unique cyclic structures of the norbornadiene moiety, it tends to form elastic material upon copolymerization with soft segments which has not been attained for elemental sulfur derived polymers. However, because of the volatility of norbornadiene (NBD) (boiling point is 89 °C), the chemicals could not bear the thermally induced inverse vulcanization process (T > 110 °C). Hence, in this work, for the first time, NBD is subjected to ball milling with elemental sulfur via solid mechanochemical induced inverse vulcanization, which successively affords poly(Sn-r-NBD) with a wide spectrum of sulfur content from 40 to 80 wt %. The synthesis is a green process that is solvent free and releases a traceless side product of H2S without heating. More importantly, the as-fabricated poly(Sn-r-NBD) displays superior transmittance (T > 40%) within the long-wave infrared region, which is obviously better than the most investigated poly(Sn-r-DIB). Furthermore, poly(Sn-r-NBD) derived polymeric material exhibits good elasticity. The present work not only demonstrates a facile and green methodology in fabricating norbornadiene derived sulfur polymers but also promotes the application of the sulfur polymer in high-performance IR optics and elastomeric materials.