Abstract
Silylation of epoxidized soybean oil (ESBO) was carried out by epoxy ring opening reaction of methoxy and ethoxy silane compounds. $^{1}$H NMR and FTIR spectra confirmed that two novel bio-based polyols, PSiTh and PSiAm, were obtained through the ring opening of epoxy by the mercapto and amino moieties of MPTMS and APTES, respectively. Polyurethanes of these polyols were prepared using 4,4'- methylene-bis(phenyl isocyanate) (MDI) to incorporate silanol groups into polymer network and were labeled as PUSiTh and PUSiAm, respectively. To see the impact of silanol and phosphorous groups on flame retardant properties, the chain extended polyurethanes, PUSiThCE and PUSiAmCE were also prepared with bisphenol-A bis (hydroxy phenyl phosphonate) (BABHPP). Polyurethanes bearing thio-ether bonds besides alkoxy silane groups were characterized using FTIR spectroscopy. Prepared foams exhibited significant thermal stability and flame retardant properties with a limiting oxygen index (LOI) of 22-24%. Chain extended polyurethanes had 11-13% higher LOI value than the corresponding non-chain extended polyurethanes.
Highlights
Functional trialkoxysilanes (RSi(OR) 3) are used as coupling agents in some applications to improve adhesion between polymeric matrices and inorganic substrates [1,4]
The proposed reaction route for silylation of epoxidized soybean oil (ESBO) with 3-mercaptopropyltrimethoxysilane (MPTMS), 3Aminopropyltriethoxysilane (APTES), prepolymers of PUSiTh, PUSiAm and the structures of chain extended polyurethanes were presented in Figure 1, Figure 2, Figure 3 and Figure 4
Disappearance of epoxy peak at 830 cm −1 and appearance of new hydroxyl peaks at 3450cm −1 suggest that silylation of ESBO took place over the ring opening reaction
Summary
Functional trialkoxysilanes (RSi(OR) 3) are used as coupling agents in some applications to improve adhesion between polymeric matrices and inorganic substrates [1,4]. RSi(OR) 3 s have two types of reactive functionality, on one side alkoxy groups (OR) can hydrolyse to silanol containing species and form hydrogen bonds/covalent bonds with substrates bearing OH groups, on the other side organic functional groups (R’) such as amine, thiol, vinyl or phenyl react with other organic matrices or inorganic substrates [5,7]. Polyurethanes made up of hard and soft segments, find a variety of applications such as surface coatings, biomedical devices, foams, elastomers, composites and adhesives, due to the presence of hard and soft segments that give good elastic and reasonable mechanical strength [15,16,17,18,19,20].
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