Thermodynamic Properties of Sustainable Long‐Spaced Aliphatic Polyesters and Polylactones

The thermodynamic properties of long‐spaced aliphatic polyesters (LSAPE) are important as they relate to the polyester's chain structure and crystal packing. We used DSC‐measured heats of fusion and corresponding levels of crystallinity by WAXD of two new series of LSAPE, PE‐X,18 and PE‐X,12 ( X = 2–18), to determine the thermodynamic heat of fusion of the pure crystals (Δ H °). These and literature values for PE‐2,Y and polylactones were analyzed as functions of methylene sequence length, total number of carbons in the repeat unit ( NC ), and ester mole fraction ( f e ). For all series, Δ H ° and Δ S ° increased linearly with NC , following Δ H ° = 4.2 NC − 6 (kJ mol −1 ) and Δ S ° = 10.8 NC − 6 (J mol −1 K −1 ), providing practical relationships for estimating thermodynamic parameters and levels of crystallinity in related aliphatic polyesters. The equilibrium melting temperature ( T m °) increased with decreasing ester content for X > 3–5 and exhibited the same even–odd alternation of the experimental melting points. Δ H ° and measured fusion enthalpies for PE‐X,18, PE‐X,12 with the same subcell packing showed little or no alternation. Alternation is found in polyesters with the shortest NC . Analysis of the thermodynamic data indicates that the even–odd alternation in T m ° is primarily enthalpic rather than entropic.