Crystallization of isotactic poly(propylene) in solution as followed by slow calorimetry

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, Delta H-total, over the 40-170 degrees C temperature range, is the sum of two contributions, Delta H-DSC and Delta H-network. The change Delta H-DSC is the usual heat obtained in a fast temperature ramp and network is associated with a physical network whose disordering is slow. and subject to superheating due to strain. When dissolution is complete, Delta H-total is equal to Delta H-0, the heat of fusion of perfect crystals, The values of Delta H-total for nascent and recrystallized samples are compared. Dissolution is the tool to evaluate the quality of the crystals. The repartition of Delta 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 Tin the solvents. A complete dissolution, i.e. a high temperature (170 degrees C or more) is necessary to obtain good crystals. The effect of concentration, polymer molecular weight and solvent quality on crystal growth is analyzed.