Sustainable Polyesters Derived from Glucose and Castor Oil: Building Block Structure Impacts Properties

Using the glucose derivatives isosorbide and glucarodilactone along with a castor oil derivative, 10-undecenoyl chloride, two monomers were synthesized: glucarodilactone undecenoate (GDLU) and isosorbide undecenoate (IU). These monomers were polymerized via acyclic diene metathesis (ADMET) polymerization to yield two homopolymers, P(GDLU) and P(IU), and two copolymers, P₁(GDLU-IU) and P₂(GDLU-IU), of similar number-averaged molecular weight and relative composition (51 and 61 kDa, Đ = 1.8 and 1.4, 46:54 and 52:48 mol percent). Comparison of the physical properties and degradation behavior of these polymers revealed divergent characteristics arising from differences in the nature of the carbohydrate building blocks. P(IU) is more thermally stable and has a lower glass transition temperature (T_d = 369 °C, T_g = -10 °C) than P(GDLU) (T_d = 206 °C, T_g = 32 °C) and P_1,2(GDLU-IU) (T_d = 210 and 203 °C, T_g = 1 and 7 °C). While all of the polymers were stable in acidic and neutral aqueous conditions, the two analogs containing GDLU hydrolytically degraded in the presence of base. Tensile testing of the systems revealed that both homopolymers are brittle materials while the P(GDLU-co-IU) is more tough. Notably, P_1,2(GDLU-IU) was found to be a rubbery material with a low Young's modulus (0.020 and 0.002 GPa, respectively), displaying an average elongation at break of 480 and 640%, and shape memory properties.