Structural Effects on the Vaporization of High Molecular Weight Esters

Article abstract of DOI:10.1021/j100367a077

To understand the effect of molecular weight and branching on the heats of vaporization (ΔH_v) and their flow behavior, ΔH_v and viscosity (η) were measured at different temperatures in the high molecular weight ester series: linear flexible di-n-alkyl sebacates and compact branched triglycerides with molecular weights ranging from 300 to 900. ΔH_v⁰ values (ΔH_v corrected to 298 K) have been obtained with experimental ΔH_v and also computed according to the group additivity method; a smaller -CH2- group value of 3.8 kJ mol^-1 compared to the normal value of 5.0 kJ mol^-1 is found to give good agreement with the experimental data (within 2-5percent error).Both ester series have the same ΔH_v⁰ irrespective of their molecular features, namely, shape, flexibility, and polarity, suggesting the coiling of the molecules during vaporization.The segmental motion of these ester series during their flow and its dependence on their molecular features unlike ΔH_v⁰ are demonstrated by the correlation of the enthalpie of activation for viscous flow (ΔH^*) and the ratio ΔE_v/ΔH^* = η (ΔE_v is the energy of vaporization) with molecular weight.