Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

Dissolution, crystallization and second dissolution traces of isotactic poly(propylene) have been obtained in a slow temperature ramp (3 K h^-1) with the C80 Setaram calorimeter. Traces of phase-change, in presence of solvent, are comparable to traces without solvent. The change of enthalpy on heating or cooling, ∆H_total, over the 40-170 °C temperature range, is the sum of two contributions, ∆H_DSC and ∆H_network. The change ∆H_DSC is the usual heat obtained in a fast temperature ramp and ∆H_network is associated with a physical network whose disordering is slow and subject to superheating due to strain. When dissolution is complete, ∆H_total is equal to ∆H₀, the heat of fusion of perfect crystals. The values of ∆H_tota for nascent and recrystallized samples are compared. Dissolution is the tool to evaluate the quality of the crystals. The repartition of ∆H_total, into the two endotherms, reflects the quality of crystals. The crystals grown more rapidly have a higher fraction of network crystals which are stable at high T in the solvents. A complete dissolution, i.e. a high temperature (170 °C or more) is necessary to obtain good crystals. The effect of concentration, polymer molecular weight and solvent quality on crystal growth is analyzed.