Straightforward determination of equilibrium heat of fusion and interaction parameter for a Polymer-Diluent system

Melting point depression approach is a common method to determine equilibrium heat of fusion (& UDelta;H0m) and interaction parameter (& chi;) for a polymer-diluent system. Using melting temperatures of dried crystals with similar thickness prepared from a polymer with different degrees of dilution (dry melting temperature, DMT) rather than that for the undiluted polymer (normal melting temperature, NMT) substantially reduces the error arising from using non-equilibrium instead of equilibrium melting temperature (T0m). However, DMT measurement is a challenging process, because it needs selection of a diluent with particular features and doubles the number of experiments and material consumption. The results of this work for poly(3-hexylthiophene) (P3HT)-3-hexylthiophene (3HT) pair revealed NMT and DMT difference depended on the cooling rate (CR) of the crystallization process and showed a non-symmetrical bell-shape behavior. Nearly acceptable values of & UDelta;H0m and & chi; were obtained via performing crystallization at a low CR (1 degrees C min-1), regardless of using either DMT or NMT. A critical CR was introduced in which DMT equalled NMT. Performing crystallization at this CR guarantees obtaining correct values of & UDelta;H0m and & chi; with no need to use T0m s or DMT data. Finally, & chi; was predicted theoretically using Flory-Huggins and compressible regular solution models.

Automated summary

Melting point depression is a common method for determining equilibrium heat of fusion (& UDelta; H0m) and interaction parameter (& chi;) in polymer-diluent systems. Using melting temperatures of dried crystals from polymers with different dilution levels (dry melting temperature, DMT) helps to reduce errors caused by using non-equilibrium temperatures. However, DMT measurement is challenging as it requires specific diluents and increases the number of experiments. The study found that the difference between normal melting temperature (NMT) and DMT depended on the cooling rate (CR) during crystallization.