Fundamental Understanding of the Seeded Heteroepitaxial Growth of Crystallizable Polymers from Crystallographic Data

Abstract

Creation of two-dimensional (2D) structures with low dispersity, controllable size, and spatially segmented compositions is of vital importance but still remains an enormous challenge. Living seeded heteroepitaxial growth of crystallizable block copolymers enables the formation of uniform 2D platelets with spatially defined and compositionally distinct cores. Therefore, revealing the general requirements such as lattice match criteria for the heteroepitaxial crystallization of one crystallizable polymer from the crystalline seeds of another polymer would lead to an expansion of the scope of the seeded heteroepitaxial growth. Herein, the melt polycondensation method has been utilized to synthesize a range of aliphatic polyesters that exhibit variable crystallographic data compared to a well-known polymer poly(ε-caprolactone) (PCL). The polyesters have been categorized into three groups that exhibit different lattice mismatches of d-spacing between two molecular stems for the contacted crystalline planes. Seeded growth experiments between two crystallizable polymers in different groups and crystallographic data analysis have confirmed that the distance between two neighboring stems of exposed crystal facets should be met for that of deposited crystals, which is due to a strong crystallographic interaction at the unit-cell level. Moreover, crystallization kinetics such as crystallization temperatures and polymer solubility are sufficient conditions for the occurrence of heteroepitaxial growth when the polymer pair meets the lattice match criteria. Therefore, detailed analysis of crystallographic data of the unit cell of each polymer would mostly predict the happening of heteroepitaxial crystallization of each crystallizable pair. On the basis of the result, we are able to predict the possibility of successful seeded heteroepitaxial growth between two polymers from the crystallographic data. This in-depth understanding of seeded heteroepitaxial growth from the crystallization perspective will further assist us in designing a wide range of 2D segmented polymer nanomaterials where the distinct core compositions and variable functionalities are spatially defined.