High Tg aliphatic polyesters by the polymerization of spirolactide derivatives

Abstract

A series of bicyclic and tricyclic lactide derivatives was prepared using L-lactide as the starting material. Exomethylene-lactide served as a platform for the Diels–Alder addition of various dienes to afford norbornene-, cyclohexadiene-, and isoprene-lactide derivatives. Norbornene-lactide (NL) was also hydrogenated to the saturated norbornane analog. These new lactide derivatives were subjected to ring-opening polymerization using 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as the catalyst. Homopolymers of poly(cyclohexadiene-lactide) (M_n = 6.4 kg mol⁻¹), poly(isoprene-lactide) (M_n = 15.3 kg mol⁻¹), and poly(norbornane-lactide) (M_n = 34.4 kg mol⁻¹) exhibited glass transition temperatures (T_g's) of 119 °C, 77 °C, and 107 °C, respectively. The decomposition temperature (T_d) of unsaturated PLA derivatives was ≤280 °C, whereas saturated poly(norbornane-lactide) has a T_d of 300 °C. Additionally, a series of poly(norbornene-lactide-s-L-lactide) (P(NL-s-L)) copolymers with varying ratios of NL and L-lactide were prepared. The T_g's of the P(NL-s-L) samples ranged from 61 to 100 °C, and the values were well-described by the Fox equation.