Chemistry Reference
In-Depth Information
Figure 1.20
2-Mercaptoethanol photo-addition onto fatty compounds bearing one
double bond per chain.
98
conditions, requiring neither solvent nor photo-initiator. The crude product
could also be purified by an easy procedure. This one-step route to produce
fatty polyols represents a significant advance compared to the traditional
epoxidation approach (that occurs in two steps) and further evidence of the
synthetic usefulness of thiol addition in materials chemistry. Indeed, this
synthetic method can readily incorporate different reactive functionalities
onto vegetable oils and their derivatives, thus leading to functional pre-
cursors suitable for polymer synthesis. Through a similarly ecient coupling
procedure, Meier
99
described the syntheses of materials derived from plant
oils. By coupling both transesterification and thiol-ene addition, the Caillol
group
100
synthesized a pseudo-telechelic diol from vegetable oil.
Many works focusing on UV-curable systems based on monomers derived
from vegetable oils have been reported,
93-95,101
but UV-curable systems
based on maleates, fumarates and acrylates have not been widely studied.
Rawlins' group
101
reported the synthesis of thiol-ene UV-curable coatings
based on vinyl ether, allyl, acrylate and derivatives of castor oil together with
a multifunctional thiol. The films exhibited high solvent resistance and
hardness as well as excellent adhesion and flexibility. Samuelsson et al.
showed that coatings could be made by photo-induced thiol-ene polymer-
ization using the internal double bonds of fatty esters (methyl oleate and
methyl linoleate) and multifunctional thiols. The structure of both the un-
saturated fatty derivatives and the thiol reagents affects the reactivity.
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diz et al.
103
described polymer networks based on a kind of maleated
soybean oil glyceride which was photo-polymerized with multifunctional
thiols under very mild conditions (Figure 1.21). The mechanical properties of
the polymer networks produced, resemble those of elastomeric materials.
The materials exhibited a flexural modulus in the 240-340 MPa range
and glass-transition temperatures below room temperature. Increasing the
thiol functionality does not increase the rigidity of the materials due to
structural factors. Bexell et al. reported the eciency of a photo-induced
reaction for coating aluminum surfaces with vegetable-oil-based films. In this
case, linseed oil reacted with the thiol groups of mercaptosilane-treated
aluminum.
104,105
