Carbasulfanes as Crosslinker for Dienerubber — A Model Compound Study

Abstract

Abstract Model compound vulcanization in combination with reversed-phase high-performance liquid chromatography (RP-HPLC), NMR spectroscopy, and mass spectrometry was used to study the properties of the polysulfide polymers [Sx(CH2)y]p (x=2,3,4, y=1,2,3,6) as crosslinking agent in the vulcanization process. It was found that the tetrasulfidic polymers [S4(CH2)y]p are capable of forming hybrid bridges of general constitution Sn-[(CH2)y-Sm]k. Besides, they react as sulfur donors producing ordinary sulfur bridges. The yield of hybrid bridges strongly increased when the alkanediyl unit ((CH2)y) of the polymer was changed from methanediyl (y =1) to ethanediyl (y =2) and remained nearly constant for longer alkanediyl segments (y =3, 6). In general, the repeating unit k also increased with increasing length of the alkanediyl segment. The only exception was observed for poly(tetrathiopropanediyl) [S4(CH2)3]p. Compared to [S4(CH2)2]p it gave a slightly lower portion of hybrid bridges and also the maximum value of k appeared to be somewhat reduced. When the number of sulfur atoms in the poly(polythioethanediyl) polymers [Sx(CH2)2]p(x=2–4 was reduced from 4 to 3 the yield of bridged molecules diminished slightly. But in the case of the disulfidic polymer nearly no crosslinked products were observed. The disulfidic polymer could be activated by the addition of sulfur into the vulcanization mixture. Hybrid bridges Sn-[(CH2)6-Sm]k of low k-values were obtained when 1,6-bis-(N,N-dibenzyl-thiocarbamoyldisulfido) hexane was used as curing agent. In addition to RP-HPLC, we also used gel permeation chromatography (GPC) in the characterization of the vulcanizates. In contrast to RP-HPLC, where the number of sulfur atoms has the strongest influence on the retention time, GPC separates the vulcanization products according to the number k of alkanediyl units present in the hybrid bridge.