Alternating melting points,heats and entropies of fusion of linear aliphatic polyesters

Heats of fusion of polyethylene-adipate, pimelate, suberate and azelaate have been determined by two methods, viz. DTA and the pressure dependence of the melting point up to 6000 bar. Degrees of crystallization were measured dilatometrically. Entropies of fusion were divided into volume and conformational entropy terms, only the latter alternates. Alternation of melting points depends on enthalpy of fusion ΔH_m, entropy of fusion ΔS_m and volume change Δυ on melting; influence of the functions increases thus ΔV_m < ΔH_m < ΔS_m and ΔS_m is dominant. Entropy and heat of fusion alternation is explained by the conformational change on melting governed by the driving force of maximum H-bridge formation.