Chemistry Reference
In-Depth Information
fascias for buildings and reinforcements for bridges. In addition to these applications,
vinyl ester resins are also being used in coatings, adhesives, moulding compounds,
structural laminates, electrical applications and for military and aerospace applications
[38-42]. Although vinyl ester resins have been used in industry for more than 30 years,
they are generally categorised together with the unsaturated polyester family. There
is much less research cited in the literature on vinyl ester resins compared to studies
on unsaturated polyesters and unsaturated polyester resins, especially with regard to
the studies on the formation and structure-property relationships of vinyl ester resins.
Commercial vinyl ester resins consist of a mixture of styrene with a methacrylated
epoxy compound based on bisphenol A. Using rosin offers the possibility of a lower
cost source for the latter component. Vinyl ester resins are usually produced by the
reaction of epoxy resins with unsaturated monocarboxylic acids. This reaction is
usually catalysed by tertiary amines, phosphites, and alkalis or ammonium salts.
Triphenyl phosphite is a more effective catalyst as than the others. Vinyl ester resins
can also be prepared by the reaction of glycidyl methacrylate with a multifunctional
phenol [43]. Atta and co-workers [44, 45 ] prepared vinyl ester resin from rosin acid.
Vinyl ester resins based on rosin were prepared from rosin adducts using rosin acid
as the diene and MA or AA as the dienophile. The adducts produced, MPA and APA,
were used to prepare vinyl ester resins. MPA and APA were reacted with ethylene
glycol (EG) followed by reaction with EC in the presence of sodium hydroxide as a
catalyst to produce epoxy resins. The terminal epoxy groups were reacted with AA
and methacrylic acid in the presence of triphenyl phosphite as a catalyst to produce
divinyl ester resins [44]. Schulze and co-workers [46] have reported the modification of
unsaturated polyesters by polyethylene glycol (PEG) end groups in order to influence
the solution behaviour in styrene and to modify the mechanical properties of the cured
resin. The synthesis of the block copolymer was carried out by reacting a carboxyl-
terminated unsaturated polyester with various polyethylene glycol monomethyl ethers
of molecular weights from 350 to 2000 g/mol. The block copolymers could be easily
diluted in styrene to create curable resins. The conversion of the typical polar end
groups to PEG end groups should improve the flexibility of the cured material. The
intermolecular chain interactions will also change considerably. Instead of hydrogen
bonds, which are responsible for aggregation and the high viscosity of the resin in
styrene, van der Waals interactions are dominant. Accordingly, we presumed that the
incorporation of EG into the structure of the vinyl esters enhances their solubility in
styrene monomer. Vinyl ester resins are produced by the reaction between glycidyl
ether coded as EMPAE (diglycidyl ether of ethoxyhydroxy maleopimaric acid-maleic
anhydride adduct) and acrylic or methacrylic acids. The resulting vinyl esters of
EMPAE with acrylic and methacrylic acid are referred to as AEMPAE (diacyloyl
ester of ethoxyhydroxy maleopimaric acid-maleic anhydride adduct) and MEMPAE
(dimethacyloyl ester of ethoxyhydroxy maleopimaric acid-maleic anhydride adduct),
respectively. The reaction scheme is illustrated in
Scheme 2.5
. EMPA in
Scheme 2.5
