Plant-oil-based Polymeric Materials and their Applications - Green Materials from Plant Oils - page 113

polymer networks by UV photo-polymerization with PEG diacrylate or PCL
diacrylate as the cross-linking agent. Recently, a simple, low-environmental-
impact procedure for preparing ACO was developed by Dillman et al. 102
using a hybrid acrylate isocyanate monomer, 2-acryloyloxyethyl isocyanate.
The photo-polymerization of neat ACO and the co-polymerization of ACO
with common low-molecular-weight acrylate monomers were rapid and
reached high conversions. The resulting co-polymers ranged from highly
flexible, low-glass-transition materials to rigid, high-glass-transition ma-
terials depending on the functionality and secondary functional groups of
the commercial monomers used. The ACO oligomer was compatible with a
variety of acrylate monomers and produced transparent films regardless
of the co-monomer used. ACO-based materials provide a promising route
to introducing renewable materials into many acrylate-based coating
applications.
Similar to that of soybean oil, epoxidation of double bonds in the fatty acid
chains of castor oil resulted in epoxidized castor oil (ECO). Bechi et al. 103
synthesized two series of organic-inorganic hybrid films from ECO and the
inorganic precursor titanium(IV) isopropoxide (TIP), combined with silicon
precursors, either 3-aminopropyltriethoxysilane or tetraethoxysilane with
different organic-to-inorganic proportions. The hardness and tensile
strength of the films increased with increased concentration of inorganic
precursor. The combination of the silicon-rich inorganic precursors with TIP
substantially improved the mechanical strength of the films. All of the films
exhibited good adhesion to an aluminum surface.
Xia et al. 104 synthesized two castor-oil-based monomers. Norbornenyl-
functionalized castor oil (NCO), which had about 0.8 norbornene rings per
fatty acid chain, and norbornenyl-functionalized castor oil alcohol (NCA),
which had about 1.8 norbornene rings per fatty acid chain. These two
monomers can be used to conduct a ring-opening metathesis polymer-
ization (ROMP) using a 2 nd generation Grubbs catalyst, resulting in
rubbery-to-rigid plastics with different cross-link densities. Higher cross-
link densities gave better thermal properties, including increasing the T g
from 17.1 to þ 65.4 1C, and increasing the room temperature storage
modulus, from 2.4 to 831.9 MPa, as well as enhanced mechanical prop-
erties, with a Young's modulus of 407 MPa and a tensile strength of 18 MPa
at high cross-link densities.
Allauddin et al. 105 developed an alkoxysilane-functionalized castor oil
(ASCO) for the synthesis of functional polyurethane-urea (PUU) coating
films. Hydrolyzable Si-OCH 3 groups were introduced into the castor oil
backbone and were used subsequently for the development of polyurethane-
urea silica hybrid coatings. The ASCO was reacted with different ratios of
IPDI to get an isocyanate-terminated hybrid PU pre-polymer which was cured
under atmospheric moisture to get the desired coating films. The T g values
of the hybrid networks were found to be in the range 29 to 70 1C. The alkoxy
silane-modified castor-oil-based coatings showed better mechanical and
viscoelastic properties compared with the unmodified castor oil coatings.