The effect of chemical composition on selected physical properties of linear polymers

A review of the data available in the literature and new data reported in this paper show that in any homologous series of condensation polymers there is a uniform change in the melting point as the hydrocarbon content of the polymer is increased. If all such series are treated as copolymers of the simplest modifying element and polyethylene and the composition expressed on a mole fraction basis, the data when presented graphically show that the melting points of any such series passes through a minimum at some intermediate composition. The position of the minimum as well as the depth of the minimum is dependent on the polarity of the modifying group. This survey has included aliphatic polyesters, aromatic polyesters, polysulfides, cellulose derivatives, and polyamides. Some of the series are complete enough to show a definite minimum with compositions on either side of the minimum with higher melting points. In some compositions based on the very highly polar groups, such as amides, the series is not complete enough to establish the complete shape of the curve, but the indications are strong that the minimum does exist.