Chemistry Reference
In-Depth Information
propagate the cycle. Apparently, the zwitterions played a very important role
for the curing of ESO with MHHPA by different catalysts.
In addition to MHHPA, ESO can be cured with other anhydrides such as
maleic anhydride (MA).
30
However, MA is a solid at room temperature, thus
heating to a moderate temperature is necessary in order to obtain a homo-
genous mixture with ESO. For this reason, liquid cyclic anhydrides like
MHHPA or nadic methyl anhydride (NMA) are more favorable.
31
NMA can be
used as a cross-linking agent for the curing of ESO, and the cured product
has improved mechanical and thermal properties with the addition of
protein-based fillers such as ovalbumin.
31
With only 15 wt% of ovalbumin,
the flexural modulus improved more than 150% compared with the unfilled
material.
Because of its excellent performance in the synthesis of epoxy resins, ESO
can be used to partially replace the synthetic epoxy pre-polymer based on the
diglycidyl ether of bisphenol A (DGEBA). Ruseckaite et al.
32
combined
DGEBA with 40 wt% of ESO in a resin using methyltetrahydrophthalic
anhydride as a cross-linking agent and 1-methyl imidazole as an initiator.
The product had an optimum set of properties; the Young's modulus in the
glassy state was 93% of that of the neat DGEBA resin, the T
g
value decreased
by only about 11 1C and the impact strength increased by about 38% without
loss of transparency. Another interesting strategy for using ESO in the syn-
thesis of epoxy resins is to get free epoxidized fatty acids by hydrolysis of
ESO.
33
The glycidyl esters of epoxidized fatty acids derived from soybean oil
have a higher oxirane content, more reactivity and lower viscosity than ESO,
thus leading to higher T
g
values.
ESO-based elastomers are another interesting type of polymer because of
their bio-degradability and bio-compatibility. Considering the structure,
toxicity and operability, the design for an ideal cross-linked elastomer
should meet the following principles:
34
(1) the raw materials are of low
toxicity and can be metabolized in vivo; (2) no toxic additives are used, in-
cluding the initiator, catalyst and solvent; (3) the cross-linked backbone used
is bio-degradable; and (4) the preparation is easy with good repeatability.
Based on these rules, Altuna et al.
35
synthesized a cross-linked smart ma-
terial capable of stress relaxation and self-healing without the addition of
any extrinsic catalyst from ESO with an aqueous citric acid without addition
of any other catalyst or solvent. This was achieved by molecular rearrange-
ments produced by the thermally activated transesterification reaction of
b-hydroxyester groups generated in the polymerization reaction. Wang
et al.
36
synthesized a new series of soybean-oil-based elastomers poly(ESO-
co-decamethylene diamie) (PESD) by the ROP of ESO with decamethylene
diamine (DDA). The glycerol center of ESO was broken by ammonolysis
which resulted in uncross-linked elastomers with low T
g
values ranging from
30 to
17 1C. And a cross-linked bio-elastomer was obtained from PESD
cross-linked with succinic anhydride. The final bio-elastomer possessed
good damping properties, low water absorption and a low degradation rate
in phosphate-buffered solution. In this process, ESO was employed to react
