Myrcenol-Based Monomer for Carbanionic Polymerization: Functional Copolymers with Myrcene and Bio-Based Graft Copolymers

Abstract

A bio-based hydroxyl group-containing diene monomer, silyl-protected β-myrcenol (MyrOSi), is introduced to the field of carbanionic polymerization. Polymerization in cyclohexane, using sec-butyllithium as an initiator, resulted in homopolymers with well-controlled molecular weights in the range of 7.9–31.3 kg mol–1 and dispersities between 1.10 and 1.27. The silyl protective groups can be removed quantitatively under mild conditions, using tetra-n-butylammonium fluoride (TBAF), resulting in well-defined polymyrcenol. The statistical copolymerization of MyrOSi with β-myrcene was also investigated. The monomer sequence distribution of the copolymers was evaluated by 1H NMR kinetic studies. Random copolymerization was observed for β-myrcene/MyrOSi copolymerization. Copolymers with varying MyrOH content, in the full range between 0 and 100 mol% MyrOH, were synthesized (Đ ≤ 1.11) and characterized with regard to their glass–transition temperatures and the polydiene microstructure. With an increasing MyrOH content in the polymer backbone, an increase in the number of 3,4-units was observed, resulting in an increase in Tg from −67 to −23 °C. The P(Myr-co-MyrOH) copolymers are valuable building blocks for the synthesis of more complex polymer architectures, such as graft copolymers. The P(Myr-co-MyrOH) copolymers were used for the synthesis of graft copolymers consisting of a flexible polymyrcene backbone and poly(l-lactide) side chains using the “grafting from” approach. The graft copolymers are promising candidates for bio-based thermoplastic elastomers.