posted on 2022-03-03, 15:12authored byKun Woo Park, Zoran Zujovic, Erin M. Leitao
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 (Tg) for poly-(S-r-allyldisiloxane) showed an increasing
trend with an increase in wt % S, and a maximum Tg 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.