Facilely assess the soluble behaviour of the β-nucleating agent by gradient temperature field for the construction of heterogeneous crystalline-frameworks in iPP

Nucleating agent (NA) species with solubility and self-assembly abilities can readily and effectively manipulate the crystalline morphology of semicrystalline polymers through the construction of heterogeneous frameworks prior to the primary crystallization of basal resins. However, the solubility of NA species is difficult to assess by the current traditional methods. In this study, gradient temperature field (g-T field) was utilized for the first time to ascertain the dissolution and self-assembly behaviors of β-NA in the melts of isotactic polypropylene (iPP). The g-T field technique can facilely assess the soluble behavior of β-NA by determining the transformation between several NA frameworks, namely the needle-, flower- and dendrite-like supramolecular structures. Clarifying the soluble behavior of β-NA is of great significance to guide the formation of various crystalline frameworks under the homo-temperature fields and control the resultant crystalline morphology of β-modified iPP. Some interesting findings are summarized as follows: (1) an in situ observation under the g-T field clearly indicates the sequential occurrence of various nucleation and crystallization events in the same observed window, and proves the migration of well molten β-NA, (2) the exact correlation between Tf and framework type reveals that an abrupt transformation (over the narrow temperature range of 1 °C) occurred between needle-like and dendrite-like frameworks, (3) the primary crystallization of iPP is strongly dependent on the construction mode of the β-NA framework.