Synthesis and Characterization of Disiloxane Cross-Linked Polysulfides

The discovery of inverse vulcanization has resulted in the formation of stable polysulfide materials synthesized from cheap and abundant elemental sulfur. To stabilize the sulfur chains, carbon-based cross-linkers containing alkene moieties have been the focus of the field so far. This research explores the two most basic siloxane dienes, 1,3-diallyl-tetramethyldisiloxane and 1,1,3,3-tetramethyl-1,3-divinyldisiloxane, as cross-linkers. Both cross-linkers successfully underwent inverse vulcanization with different weight percentages of sulfur (wt % S); the traditional method was used for 1,3-diallyl-tetramethyldisiloxane, while the catalytic method was used for 1,1,3,3-tetramethyl-1,3-divinyldisiloxane. Two series of polysulfides, X-poly-(S-r-allyldisiloxane) and X-poly-(S-r-vinyldisiloxane) (X = wt % S), were synthesized. For poly-(S-r-allyldisiloxane), 33 wt % S was the minimum sulfur content required to form a solid material, while for poly-(S-r-vinyldisiloxane), it was 30 wt % S. Both series at and above those wt % S showed great resistance to common laboratory solvents and have thermal stabilities to about 200 °C. Glass transition temperature (T_g) for poly-(S-r-allyldisiloxane) showed an increasing trend with an increase in wt % S, and a maximum T_g at 70 wt % S poly-(S-r-vinyldisiloxane) was measured at 26.4 °C. Elemental analysis and XPS showed inconsistent results due to the presence of unreacted sulfur on the material’s surface, as observed by microscopy. In most cases, excess sulfur could be removed using CS₂. The research reported herein provides a direct comparison of the synthesis and characterization of two series of disiloxane cross-linked polysulfides and will stimulate further studies into their applications as well as into future polysulfide materials formed using siloxane or other main-group cross-linkers.