β-Myrcene/isobornyl methacrylate SG1 nitroxide-mediated controlled radical polymerization: synthesis and characterization of gradient, diblock and triblock copolymers

Abstract

β-Myrcene (My), a natural 1,3-diene, and isobornyl methacrylate (IBOMA), from partially bio-based raw materials sources, were copolymerized by nitroxide-mediated polymerization (NMP) in bulk using the SG1-based BlocBuilder™ alkoxyamine functionalized with an N-succinimidyl ester group, NHS-BlocBuilder, at T = 100 °C with initial IBOMA molar feed compositions f_IBOMA,0 = 0.10–0.90. Copolymer reactivity ratios were r_My = 1.90–2.16 and r_IBOMA = 0.02–0.07 using Fineman–Ross, Kelen–Tudos and non-linear least-squares fitting to the Mayo–Lewis terminal model and indicated the possibility of gradient My/IBOMA copolymers. A linear increase in molecular weight versus conversion and a low dispersity (Đ ≤ 1.41) were exhibited by My/IBOMA copolymerization with f_IBOMA,0 ≤ 0.80. My-rich and IBOMA-rich copolymers were shown to have a high degree of chain-end fidelity by performing subsequent chain-extensions with IBOMA and/or My, and by ³¹P NMR analysis. The preparation by NMP of My/IBOMA thermoplastic elastomers (TPEs), mostly bio-sourced, was then attempted. IBOMA-My-IBOMA triblock copolymers containing a minor fraction of My or styrene (S) units in the outer hard segments (M_n = 51–95 kg mol⁻¹, Đ = 1.91–2.23 and F_IBOMA = 0.28–0.36) were synthesized using SG1-terminated poly(ethylene-stat-butylene) dialkoxyamine. The micro-phase separation was suggested by the detection of two distinct T_gs at about −60 °C and +180 °C and confirmed by atomic force microscopy (AFM). A plastic stress–strain behavior (stress at break σ_B = 3.90 ± 0.22 MPa, elongation at break ε_B = 490 ± 31%) associated to an upper service temperature of about 140 °C were also highlighted for these triblock polymers.