Influence of self-nucleation on phase transition in poly(1-butene)

The self-nucleation effect is often investigated to focus on kinetics and polymorphism of melt crystallization. In this work, the effect of self-nucleation on solid phase transition from the tetragonal phase into the thermody-namically most stable trigonal phase was studied with differential scanning calorimetry (DSC) for the isotactic poly(1-butene). With respect to the initial completely relaxed melt in Domain I, self-nucleation treatment of Domains II and III show the opposite influences on phase transition kinetics, where the former accelerates phase transition but the latter inhibits phase transition. Employing isothermal crystallization experiments, it is found that at the lowered self-nucleation temperature (Ts), the further accelerated phase transition was caused by the enlarged internal stress, which triggers nucleation of form I within form II. Interestingly, although cooling crystallization can be enhanced as Ts was cooled into Domain III, the corresponding phase transition of obtained crystallites was inhibited, even slower than that of relaxed melt in Domain I. As Ts was further lowered to 115 degrees C with the increased isothermal time, the initial crystallites not only survive but also thicken during the isothermal process at Ts. More interestingly, the annealed crystallites exhibited the most suppressed phase transition. The accelerated phase transition by Ts of Domain II was related to the increased internal stress, which drives the nucleation of transformed trigonal phase within the original tetragonal phase. Differently, the inhibited phase transition by self-nucleation of Domain III was associated with the reduced links between lamellae and amor-phous region, which facilitates the transfer of internal stress.