Chemistry Reference
In-Depth Information
petroleum-based counterparts. Many reviews have been published in this
area covering the use of plant oils for the synthesis of polymeric materials,
focusing on various topics, such as different polymerization strategies
1-3
including radical polymerization, cationic polymerization, condensation
polymerization and olefin metathesis and so on, or different polymeric
materials
1,4,5
including polyester, polyamide, polyurethane, and bio-com-
posites, or different applications
6,7
such as paints, coatings, plasticizers and
adhesives as well as bio-medical applications. In this chapter, we will focus
on the synthesis of polymeric materials based on different types of plant oils
including soybean oil, castor oil, tung oils, linseed oil, and canola oil. Special
attention will be paid to the first three plant oils. Their applications in
coatings, adhesives, plasticizers and modifiers will also be reviewed.
5.2
Soybean Oil: Polymer Synthesis and Application
5.2.1 Use of Soybean Oil Directly for Polymer Synthesis
Soybean oil has an average number of double bond of 4.6 per triglyceride,
8
which makes it a semi-drying oil. The structure of a soybean oil triglyceride
is shown in Figure 5.1, which illustrates that it mainly contains two kinds of
fatty acids, oleic acid and linoleic acid. The unsaturation in the fatty acid
chains makes them ideal monomers for polymerization. However, due to the
relatively high molecular weights of the multiple-chain structures of soybean
oil and the non-conjugated double bonds in the fatty acid chains, its re-
activity is rather low.
9,10
For example, Acar et al.
11
exposed soybean oil to air
under daylight at room temperature to get oxidized soybean oil via an auto-
oxidation process. A cold-water-soluble soybean oil polymer was then ob-
tained by reaction with diethanol amine, the resulting hydroxylated soybean
oil polymer had a molecular weight of only 3800 to 5900 g mol
1
.
Therefore, homopolymerization of soybean oil and other semi-drying oils
is not favored due to steric hindrance of the bulky oil moieties, co-monomers
such as styrene or divinyl benzene are necessary for the preparation of
polymers from soybean oil directly.
12
However, recently, Liu et al.
10,13
re-
ported that cationic polymerization in supercritical carbon dioxide (scCO
2
)
media using boron trifluoride diethyl etherate (BF
3
OEt
2
) as an initiator
O
O
O
O
O
O
Soybean oil
Figure 5.1
Structure of a soybean oil triglyceride.
