Thermoplastic Elastomers Derived from Menthide and Tulipalin A

Renewable ABA triblock copolymers were prepared by sequential polymerization of the plant-based monomers menthide and α-methylene-γ-butyrolactone (MBL or tulipalin A). Ring-opening transesterification polymerization of menthide using diethylene glycol as an initiator gave α,ω-dihydroxy poly­(menthide) (HO-PM-OH), which was converted to α,ω-dibromo end-functionalized poly­(menthide) (Br-PM-Br) by esterification with excess 2-bromoisobutyryl bromide. The resulting 100 kg mol^–1 Br-PM-Br macroinitiator was used for the atom transfer radical polymerization of MBL. Four poly­(α-methylene-γ-butyrolactone)-<i>b</i>-poly­(menthide)-<i>b</i>-poly­(α-methylene-γ-butyrolactone) (PMBL-PM-PMBL) triblock copolymers were prepared containing 6–20 wt % PMBL, as determined by NMR spectroscopy. Small-angle X-ray scattering, differential scanning calorimetry, and atomic force microscopy experiments supported microphase separation in the four samples. The mechanical behavior of the triblocks was investigated by tensile and elastic recovery experiments. The tensile properties at both ambient and elevated temperature show that these materials are useful candidates for high-performance and renewable thermoplastic elastomer materials