Analysis of calorimetric curves detected during the polymorphic transformation of isotactic polybutene-1

Multiple endotherms detected on heating melt-crystallized i-polybutene-1 (PBu-1) are associated to the polymorphic transformation from the tetragonal (Form II) to the hexagonal modification (Form I). During this transformation, a progressive increase of the intensity of the high temperature endotherm, at the expenses of that pertaining to the low temperature one, is observed in DSC heating curves. Depending on molecular characteristics of the constituent chains and crystallization conditions, the two endotherms may exhibit some extent of superposition. In these cases, a reliable procedure to analyze the whole thermal curve must be found and adopted in order to follow the progress of the transformation in quantitative terms. The same set of thermal curves, detected after various ageing times of melt-crystallized i-PBu-1, has been analyzed according to four different approaches. Comparison of the results shows that, with the exception of the analysis based on the 'partial area' routine, available to most instruments, all methods lead to equivalent results. The simplest approach, based on the mass balance during structural transformation, should be preferred whenever constant overall degree of crystallinity can be assumed throughout the whole process.