Chemistry Reference
In-Depth Information
resulted in a high-molecular-weight poly soybean oil, ranging from 21 842 to
118 300 g mol
1
. This high-molecular-weight product is probably formed by
both polymerization and an intermolecular Diels-Alder reaction. Addition-
ally, the scCO
2
serves as a green reaction medium, making it a promising
method for the polymerization of renewable starting materials.
In addition to reactions with its double bonds, soybean oil can undergo
reactions with other functional groups. Wu et al.
14
generated thiol-functio-
nalized oligomers via a thermal free-radical-initiated thiol-ene reaction be-
tween the soybean oil double bonds and the thiol functional groups. It was
found that long reaction times and the use of a nitrogen reaction atmos-
phere were favorable for fast consumption of the soybean oil, and the re-
action produced high-molecular-weight products. The synthesized soy-thiol
oligomers can be used for renewable thiol-ene UV-curable materials and
thioureathane thermal-cure materials.
Soybean oil fatty acids are not only monomers for the synthesis of poly-
meric materials, but also building blocks for the synthesis of more sophis-
ticated monomers.
3
Recently, Chernykh et al.
15
synthesized a novel vinyl
ether monomer from soybean oil by a base-catalyzed transesterification of
2-(vinyloxy) ethanol with soybean oil. The cationic polymerization of this
monomer resulted in a polymer with a very low T
g
value of
90 1C, with the
expectation for the production of thermoplastic elastomers.
Co-polymerization of soybean oil with monomers containing heteroatoms
such as silicon, boron and phosphorous would result in polymers with
additional useful properties such as flame retarding. Sacrist´n et al.
16
prepared a co-polymer from soybean oil, styrene, divinylbenzene and
p-trimethylsilylstyrene by cationic polymerization using BF
3
OEt
2
as an ini-
tiator. The obtained thermosets had limited oxygen index (LOI) values from
22.6 to 29.7, with T
g
values ranging from 50 to 62 1C. This result indicated that
these materials are useful alternatives for current non-renewable-based ther-
mosets and that the flame-retardant properties of soybean-oil-based thermo-
sets can be improved by adding covalently bonded silicon to the polymer. They
also synthesized a boron-containing soybean-oil-based co-polymer with the
same strategy,
17
where 4-vinylphenyl boronic acid was used to introduce the
boron to the polymer. The LOI of the thermosets was in the range of 23.7 to
25.6, which is similar to those of their silicon counterparts. Ronda et al.,
18
on
the other hand, synthesized a phosphorus-containing soybean oil co-polymer
from dimethyl-p-vinylbenzylphosphonate. The resulting thermosets with
just 1% of phosphorus had an LOI of about 24.0, indicating an improvement
in the flame-retardant properties of the soybean-oil-based co-polymers.
5.2.2 Use of Soybean Oil after Chemical Modification for
Polymer Synthesis
The double bonds on the fatty acid chains in soybean oil possess low activity,
which drives people to perform modifications of soybean oil in order to
