Chemistry Reference
In-Depth Information
Cramer et al.
25
investigated the kinetics of the thiol-ene reaction for the
synthesis of non-bio-based polymers. Their work focused mostly on highly
active double bonds: acrylates, vinyl esters and related species. The data was
modeled with k
1
/k
d
ratios of 13 : 1 to 0.2 : 1, while Chatgilialoglu et al.
16,19
reported ratios of 0.02 : 1 (see Table 4.2). Chatgilialoglu et al.'s results
indicate the thiyl attack on the double bond is much slower than the sub-
sequent chain-transfer abstraction of hydrogen by the carbon-centered
radical. Cramer et al.'s result showed a faster or slightly slower rate of thiyl
attack. This discrepancy can be attributed to the fact that Cramer et al.
25
used a simplified model which neglected the reversibility of Step 1. Other
observations can be attributed to the fact that Chatgilialoglu et al.
16,19
worked with small molecules with large diffusion coecients, while
Cramer et al.
25
investigated polymeric systems with more restricted dif-
fusion. The termination steps of these reactions can be diffusion controlled
and influence the overall reaction rates.
4.4 Bio-based Materials made with the Thiol-ene
Reaction
4.4.1 Low-molecular-weight Materials
Obtaining polymeric products with the thiol-ene reaction requires the
coupling of compounds with at least two thiol groups to compounds with at
least two ene groups. Otherwise, low-molecular-weight compounds will be
obtained. This reaction scheme is utilized in the synthesis of low-molecular-
weight compounds for lubricants.
The products of reacting of oleic acid, undecanoic acid and docosenoic
acid with mercaptoacetic and 3-mercaptopropionic acids were patented as
lubricating base oils by Gadd et al.
35
They used a thermo-initiator (lauroyl
peroxide) for the reaction. They reported the kinematic viscosity at 100 1Cas
being between 3.14 and 7.28 mm
2
s
1
, the viscosity index as being between
123 and 183, and the Pour Point as being below
9 1C for some compounds
and below
60 1C for others. The oxidative stability, measured as an onset
temperature to exothermic oxidative peak in a pressurized differential
scanning calorimetry (DSC) experiment, was substantially higher compared
to the corresponding polyol ester and synthetic hydrocarbon compounds.
Bantchev et al.
32
added butanethiol to corn and canola oils and evaluated
the products as lubricants and lubricating additives (see Scheme 4.5). The
resulting oils had better cold flow properties (Cloud Point and Pour Point)
than the starting vegetable oils; however, weak effects were observed when
the materials were used as additives. The sulfide-modified corn oil showed
improved oxidative stability and good anti-oxidative properties as an
additive.
36,37
In a very recent report by the same group, both sulfide-modified corn oil
and canola oil were also shown to effectively remove heavy metals from water
(see Scheme 4.6). The extraction of Ag
1
from a water solution was used as a
