Transition of iPB-1 with low molecular weight crystallized from solutions

The dimension or entanglement of polymer chains is crucial to chain dynamics, and the polymer chains can be diluted and disentangled in a solution by reducing the interaction with each other. This letter addresses the role of solution concentration in the crystal transition of isotactic polybutene-1 (iPB-1) with low molecular weight crystallized from solution. It turned out that the transition of iPB-1 obtained from the higher concentration of the solution is faster than that obtained from the lower one. In addition, the disparity in the transition between the early stage and later stage for samples prepared from solutions with and without stirring was characterized. DSC and X-ray experiments revealed that initial temperatures for the solution-crystallized iPB-1 to melt and crystallize into form II dominated the transition. The role of entropy in the transition was proposed as a primary factor influencing the iPB-1 transition. Increasing the concentration of the solution or stirring during crystallization increases the supersaturation for iPB-1 to crystalize from the solution and form less stable crystals. The less stable iPB-1 crystals cause the formation of form II at lower temperatures during heating. Therefore, the lower entropy in amorphous regions resulted in an enhanced propensity for the helical conformation with a lower entropy and consequently accelerated the crystal transition.