| dc.description.abstract | Solvents are most often the major component of chemical reactions. Indeed, global solvent demand and cost are growing exponentially every year. Thus, solvent waste and efficient solvent recycling are big environmental issues.
This work discusses solvent systems based on oligomeric hydrocarbons, poly(α-olefin)s (PAOs), whose low toxicity, low vapor pressure, low flammability, and simple gravity-based separations and recyclability make them promising as green alternative solvent systems. However, while PAOs can serve useful as solvents in stoichiometric and catalytic reaction, they are still alkanes with low polarity that sometimes are poor solvents for polar substrates. Here two strategies for introducing polar moieties into nonpolar media like PAOs will be discussed: hydrogen bond assisted solubilization of poly(N-isopropylacrylamide) (PNIPAM) and end-group modification of polyisobutylene (PIB) with hexamethylphosphoramide (HMPA).
The first case will illustrate how a polar polymer can be dissolved in heptane using H-bonding cosolvents. This study further shows that this chemistry can be sued with polymeric Rh(I) hydrogenation catalysts and that it is a feasible way to recycle catalysts using a gravity-based liquid/solid separation. Second, an organocatalyst, a PIB-bound HMPA was used to catalyze allylation of different aromatic aldehydes and reduction of α, β-unsaturated carbonyl compounds in PAOs. In this case, the catalyst and solvent are easily isolated from the organic products by liquid/liquid separation.
In addition, we also examined several polymerizations to form polar block onto PIB to form hydrocarbon soluble polar polymers. With several failed radical and controlled radical polymerization, we enabled to optimize the RAFT chemistry to build up a hydrocarbon soluble PMMA, PEMA, PNIPAM and PDMAA. Finally, we have shown that the polarity of PAO and a substrate can be markedly affected by even small amounts of cosolvent. Studies using solvatochromatic dyes show that 0.2- 2.0 M cosolvent creates microheterogeneity in otherwise miscible solvent mixtures. A polymer ester compound was synthesized and applied in the solvatchromic dyes’ polarity studies. The fluorescence behavior affected by the polymer ester compound is similar to the one with a low molecular weight polar cosolvent. The kinetic studies further show that this microheterogeneity translates into large rate changes in reactions. | en |
