Chemistry Reference
In-Depth Information
n-butanol in 3 h at 115 1C. Miao et al.,
48
on the other hand, synthesized a new
polyol by reaction of ESO with isopropanolamine through simultaneous
ring-opening and amidation reactions between both ester groups and epoxy
groups in ESO with the amino group of isopropanolamine. The polyol has a
high hydroxyl number of 317.0 mg KOH g
1
.
Another interesting strategy is to get polyols directly from soybean oil in
a single-step reaction. Desroches et al.
49
established a method involving a
single thiol-ene coupling reaction. E
cient thiol addition onto vegetable
oils leads to bio-based polyols. The most important feature of this reaction
is probably the number of double bonds per chain in the vegetable oil,
which strongly influences the thiol grafting yield. This one-step route to
produce fatty polyols represents a significant advance compared to the
traditional epoxidation approach whichoccursintwosteps.Sunet al.
50
also developed a single-step reaction for the synthesis of polyols from
soybean oil. The use of OsO
4
as the catalyst and 4-methylmorpholine-N-
oxide as the oxidant resulted in polyols with excellent yields with hydroxyl
numbersofupto467.7mgKOHg
1
. Advantages of this scheme include
that two hydroxyl groups can be readily added to one double bond in a
single step, and a wide range of hydroxyl numbers can be obtained by
changing the concentration of the catalyst, and the reaction can be per-
formed at room temperature.
PUs are one of the most interesting classes of copolymers with properties
varying from rubbery materials to glassy thermoplastics and from linear
polymers to thermosetting plastics. Recently, Lu et al.
51
synthesized novel
surfactant-free core-shell hybrid latexes by seeded emulsion polymerization
of 10-60 wt% vinyl monomers in the presence of a soybean-oil-based
waterborne PU dispersions as seed particles. The soybean-oil-based water-
borne PU, synthesized by reacting isophorone diisocyanate with methoxy-
lated soybean oil polyols and dimethylol propionic acid, formed the latex
shell and served as a polymeric high-molecular-weight emulsifier, whilst the
vinyl polymers formed the core. The core-shell hybrid latex films showed a
significant increase in thermal stability and mechanical properties when
compared with the pure PU films, and exhibited a change in mechanical
behavior from elastomeric polymers to tough and hard plastics, due to
grafting and cross-linking in the hybrid latexes. The T
g
values as well as the
Young's moduli and tensile strengths were enhanced significantly by an
increase in the cross-link density of both the shell and the core. Apparently,
the cross-link density is one of the most important factors that affect the
properties of the PU, and it is clearly related to the number of hydroxyl group
in the polyols. Wang et al.
52
prepared novel polyurethane acrylates (PUAs) by
the reaction of soybean polyols with isophorone diisocyanate and hydro-
xyethylacrylate. The cross-link density of PU and PUAs correlated with the
hydroxyl number of the polyols. The T
g
and initial decomposition tempera-
ture of the PU or PUAs were higher with larger hydroxyl numbers. Acrylation
of PU to PUAs improved its thermal stability and damping properties. The
tensile strengths of PUAs decreased with increasing hydroxyl number.
