Positional Isomer of P3HB by Stereoselective Polymerization of Racemic α-Methyl-β-propiolactone Delivers...

Biobased and biodegradable poly(3-hydroxybutyrolactone) (P3HB) has long been considered as a more sustainable alternative to petroleum-based, nonbiodegradable polyolefins, but its properties are far off from its polyolefin (polyethylene, PE, and polypropylene, PP) counterpart's unique set of thermal (low T_g below -20 °C and high T_m > 100 °C) and mechanical (high ductility >350%) characteristics. Here, we report that a positional isomer of P3HB, poly(3-hydroxy-2-methylpropionate) (P3H2MP), synthesized by catalyst-controlled stereoselective polymerization of racemic α-methyl-β-propiolactone, can match that demanding set of thermomechanical properties of PE. In particular, isotactic-rich P3H2MP, readily synthesized under ambient conditions, reaches high M_n close to one million Da, T_g down to -25 °C, T_m up to 115 °C, tensile strength up to 64 MPa, and toughness up to 131 MJ m^-3, thus mechanically outperforming PE while maintaining a comparable low T_g and high T_m combination. A P3H2MP-based triblock copolymer further widens the low-high temperature window from T_g = -29 °C to T_m = 186 °C, resembling those of PP. These results show that P3H2MP exhibits the unique combination of thermomechanical properties matching those of high-performance polyolefins.