Investigating the effect of α-pinene on the ROMP of δ-pinene

Poly(δ-pinene), PδP, is a promising new material derived from naturally abundant α-pinene. One of the persistent by-products in the synthesis of δ-pinene is α-pinene which required intensive and non-sustainable isocyanate chemistry to fully remove. This work presents an in-depth study on the effects that varying quantities of α-pinene has on the ring opening metathesis polymerization (ROMP) of δ-pinene using Grubbs 3rd generation catalyst (G3). It is determined that G3 is tolerant of low quantities of α-pinene (∼40 equivalents) in the reaction mixture and results in high conversions of δ-pinene and well controlled ROMP. Increasingly higher quantities of α-pinene have an inhibitory effect on conversion and loss of control. 1H NMR experiments revealed complex signals within the Ru-alkylidene and, surprisingly, the ruthenacyclobutane regions of the spectrum as a result of δ-pinene oligomerization. However, no identifiable signals were produced or lost upon interaction with α-pinene suggesting it does not inhibit ROMP through a productive metathesis event.