Synthesis of Biorenewable Starch-Farnesene Amphiphilic Conjugates via Transesterification of Terpene-Derived Diels-Alder Adducts

Herein we describe a new class of terpene-starch esters synthesized from biorenewable building blocks. Although our work is specific to starch, we believe the synthetic methodology can be extended to a wide range of polysaccharide substrates. In our approach, an ester functionality is first introduced to the farnesene backbone via high yielding, solvent-free Diels-Alder chemistry. The farnesene esters are subsequently transesterified with starch to produce a range of starch-farnesene amphiphilic biopolymers. The key transesterification reaction between farnesene and starch employs 1,5,6-triazabicyclo[4.4.0]dec-5-ene (TBD) as a guanidine base organocatalyst and is capable of producing materials with a high degree of substitution (DS). The DS can be modulated by altering the starch/farnesene feed ratio. Low DS starch-farnesene esters show surfactant-like properties while the higher DS materials were successfully solvent-cast into standalone films. Thermal and mechanical tests reveal starch-farnesene esters to be robust under both solution and thermal processing conditions. Given the versatility of the synthetic method, the biorenewability of the components, and the biodegradability of the ester linkage joining the subunits, the newly produced polymer amphiphiles appear to be a promising class of new green materials.