Ring-Opening Metathesis Polymerization of δ-Pinene: Well-Defined Polyolefins from Pine Sap

Abstract

Well-controlled ring-opening metathesis polymerization (ROMP) of δ-pinene is reported. The monomer is produced through a facile, metal-free, three-step synthesis from highly abundant and sustainable α-pinene. Using Grubbs third-generation catalyst, δ-pinene undergoes ROMP to high conversion (>95%) with molar mass up to 70 kg mol–1 and narrow dispersity (<1.2). A highly regioregular propagation mechanism was concluded by NMR spectroscopic analysis that revealed a head-to-tail (HT, >95%) microstructure and high trans content (>98%). Successful ROMP is corroborated with density functional theory calculations on δ-pinene’s ring strain energy (∼35 kJ mol–1). Poly­(δ-pinene) has a high glass transition temperature (∼104 °C) and a unique chiral microstructure bearing gem-dimethylcyclobutane rings. Controlled ROMP also allowed the synthesis of block copolymers containing segments of poly­(δ-pinene) and polynorbornene which are discussed. Finally, bulk polymerization of δ-pinene is possible, indicating a greener approach to these materials, albeit with some loss of control.

Monomers and Macromolecular Materials from Renewable Resources: State of the Art and Perspectives

“…The functionalization of monoterpenes is very promising to increase their potential as monomers. A metal-free conversion of α-pinene into δ-pinene was found to be useful to synthesize polyolefins via ring-opening metathesis polymerization using Grubbs 3rd generation catalyst [ 153 , 154 ]; α-pinene, β-pinene, and limonene were used to prepare terpene (meth)acrylate monomers, and the ensuing di- and multiblock copolymers were prepared by RAFT polymerization [ 155 ]; β-myrcene, an acrylic monoterpene, was submitted to anionic polymerization with D,L-limonene as a solvent, yielding polymyrcenes with narrow molecular weight distribution (Ð~1.06) [ 156 ]. The progress made in the field is indeed thanks to the exploitation of minor terpenes as platforms, and the conversion of limonene, limonene oxide, α-pinene oxide, borneol, camphor, menthol, carvone, as well as of β-pinene and other terpenes and their derivatives, into polyolefins, polycarbonates, polyesters, polyurethanes, and polyamides, was thoroughly reviewed [ 157 ].…”

Synthesis and properties of cyclic olefin polymers by ring-opening metathesis (co)polymerization of α-methyl-substituted norbornene lactones

“…The polymer should be amorphous, with high glass transition (T g ) temperatures ranging from 120 °C to 170 °C but with possible deformation processing for optical transparency material application. ROMP has an advantage over coordination polymerization in the applicability to various NB monomers; however, to synthesize high T g polymers, polycyclic NB monomers, such as dicyclopentadienes, [5][6][7][8][9] tetracyclododecenes, [10][11][12] and others, [13][14][15][16][17][18][19] should be employed. Optical properties, including refractive indexes and birefringence, are also important factors.…”

Polymers without Petrochemicals: Sustainable Routes to Conventional Monomers

“…710 An alternative route to make use of α-pinene is by converting it into δ-pinene, which has previously been realized in a 3-step process followed by a distillation step. 711 The resulting polymers in this case had M n values of 70 kg/mol and low dispersity values of around 1.2. Both of these methods highlight the potential for pinenes to act as bio-based precursors for monomer synthesis; however, the synthetic routes are far from sustainable.…”