Coordinative Chain Transfer Polymerization of Sustainable Terpene Monomers Using a Neodymium-Based Catalyst System

Abstract

The present investigation involves the coordinative chain transfer polymerization (CCTP) of biobased terpenes in order to obtain sustainable polymers from myrcene (My) and farnesene (Fa), using the ternary Ziegler-Natta catalyst system comprising [NdV₃]/[Al(i-Bu)₂H]/[Me₂SiCl₂] and Al(i-Bu)₂H, which acts as cocatalyst and chain transfer agent (CTA). The polymers were produced with a yield above 85% according to the monomeric consumption at the end of the reaction, and the kinetic examination revealed that the catalyst system proceeded with a reversible chain transfer mechanism in the presence of 15-30 equiv. of CTA. The resulting polyterpenes showed narrow molecular weight distributions (M_w/M_n = 1.4-2.5) and a high percent of 1,4-cis microstructure in the presence of 1 equiv. of Me₂SiCl₂, having control of the molecular weight distribution in Ziegler-Natta catalytic systems that maintain a high generation of 1,4-cis microstructure.

Keywords: biobased monomer; coordinative chain transfer polymerization; farnesene; myrcene.

Figure 1

Reversible coordinative chain transfer polymerization mechanism applied for 1,3-diene initiated by an NdV₃/Al(i-Bu)₂H/Me₂SiCl₂ catalyst system. Adapted from references [29,30,42,43].

Figure 2

Conversion evolution as a function of time using different [Al]/[Nd] ratios for (a) Ip: entries Ip-3 to Ip-6; (b) My: entries My-3 to My-6; (c) Fa: entries Fa-3 to Fa-6, polymerizations initiated by NdV₃/Al(i-Bu)₂H/Me₂SiCl₂ in cyclohexane at 60 °C.

Figure 3

¹H NMR spectra using CDCl₃ as solvent on (a) Ip: entry Ip-11, (b) My: entry My-11, and (c) Fa: entry Fa-15.

Figure 4

¹³C NMR spectra using CDCl₃ as a solvent on (a) Ip: entry Ip-11, (b) My: entry My-11, and (c) Fa: entry Fa-15.

Figure 5

Effect of temperature on the reaction rate for (a) Ip: entries Ip-5 and Ip9, (b) My: entries My-5 and My-9 and (c) Fa: entries Fa-12 and Fa-13 polymerizations initiated by NdV₃/Al(i-Bu)₂H/Me₂SiCl₂ in cyclohexane.

Figure 6

Dependence of ${\overline{M}}_{\mathrm{n}}$ and dispersity against yield in (a) Ip: entry Ip-11, (b) My: entry My-11, and (c) Fa: entry Fa-15, polymerizations initiated by NdV₃/Al(i-Bu)₂H/Me₂SiCl₂ in cyclohexane at 70 °C.

Figure 7

Dependence of $N_{\mathrm{P}}$ against yield for isoprene, myrcene and farnesene polymerizations initiated by NdV₃/Al(i-Bu)₂H/Me₂SiCl₂ in cyclohexane at 70 °C.

Figure 8

${\overline{M}}_{\mathrm{n}}$, ${\overline{M}}_{\mathrm{ntheoretical}}$, and $N_{\mathrm{P}}$ as functions of [Al]/[Nd] ratios for (a) Ip: entries Ip-3 to Ip-6, (b) My: entries My-3 to My-6, and (c) Fa: entries Fa-3 to Fa-6, polymerizations initiated by NdV₃/Al(i-Bu)₂H/Me₂SiCl₂ in cyclohexane at 60 °C.