Dwindling fossil resources and climate change caused by increasing atmospheric CO2 have spurred technological developments worldwide. Some help address this problem while producing another. One example is the overproduction of glycerol from a still growing biodiesel industry. This research investigates the production and properties of a novel polymer that could help address all three aforementioned issues.Through the use of a ring opening reaction involving CO2 inclusion, epoxides can be used to produce polycarbonates. In 2015, researchers from Ohio State’s department of food, agricultural, and biological engineering successfully produced glycidyl epoxides from soybean oil and epichlorohydrin (from glycerol). They also demonstrated that these monomers could be used to produce polycarbonates. Unfortunately, these fatty acid based (FAB) monomers were low yielding, at 31.7% polycarbonate yield (Chang, Qin, Luo, & Li, 2017). It was thought that yield could be increased through the use of propylene oxide (PO); whose high yielding nature is already well established. To assess PO’s effect on FAB polycarbonate’s yield and properties, polycarbonates were made from glycidyl oleate (GO) or glycidyl linoleate (GL), with or without the addition of PO at two FAB monomer to PO volume ratios.
Yield was evaluated using FT-IR and proton ratios calculated from relevant. ¹H-NMR resonance integrals. FT-IR spectra indicated that, while all samples showed good conversion, only terpolymer samples showed evidence of high yield. 1H-NMR results corroborated these findings. All samples showed monomer conversion in excess of 98%, and it was found that calculated yield could be increased roughly four times over using only 20% PO by volume, reaching nearly 97% at its highest. There was not a significant difference in the yields of GO and GL based polycarbonates and it did not appear that FAB monomer or PO were preferentially polymerized, as calculated polymer composition was in agreement with the relative quantities of monomer used. The polycarbonates’ molecular weights were measured using GPC. Molecular weight showed bimodal distribution and low dispersity (1.28±0.09). It was found that increasing relative quantities of PO increased molecular weight and that GO samples were consistently higher molecular weight than GL samples. Though, it remains uncertain as to whether FAB monomer type was responsible the differences.
After purifying the polycarbonates, they were applied to PTFE coated aluminum substrates and left to cure in an open air environment for two weeks. Changes in the polycarbonates’ FT-IR spectra showed good evidence of curing. Peaks associated with double bonds were either eliminated or significantly reduced, indicating crosslinking between polymer chains. Moreover, the appearance or intensification of other peaks was associated with a number of products formed through chain scission and free radical reactions known to occur during oxidative curing. There was also evidence to suggest that trace residual catalyst inadvertently served as a drying agent. DSC revealed that increasing relative quantities of PO significantly increased glass transition temperature and that GL based samples had a sigficantly higher glass transition temperature than GO based samples. This also is evidence of superior crosslinking among GL based polymers. All samples had a glass temperature below 25ºC. Also, all sample thermograms showed an exotherm around 150 ºC attributable to film degradation, as was made evident by the significant drop in glass transition temperature seen in a subsequent heating cycle. TGA corroborated that degradation occurred around 150 ºC, as there was a peak in the TGA curves around 145 ºC. Entirely FAB samples showed five distinct peaks in total. They were associated with various curing byproducts and cyclic carbonates produced during polymer degradation. Samples made with PO were very similar, but showed intensification and conflation of two adjacent peaks seen in entirely FAB sample curves.Tensile Tests showed that both tensile strength and percent elongation to break of GL based samples increased with increasing relative quantities of PO. Unfortunately, adhesion to the PTFE substrate prevented the testing of GO based samples. Tensile strength of GL based films ranged from 12.5 MPa to 18.0 MPa, and percent elongation to break ranged from 86.5% to 209.1%. These property values are similar to film grade linear low density polyethylene (LLDPE), a popular material for making plastic wraps. However, unlike LLDPE, the films’ stress-strain curves were more characteristic of natural rubber. By leveraging PO’s polymerizability, these efficiently produced FAB polymers showed potential to substitute for popular petrochemical derived products.