The Effects of Crystallizing Amphiphiles on the Self-Assembly of Block Copolymer Supramolecules

Complexation of block copolymers with amphiphilic small molecules widens their structural diversity to a greater extent. Such systems also provide synthetic versatility due to the nature of complexing through a secondary bond. This allows us to create a variety of supramolecular systems by making small changes to the nature of the small molecule. The small molecule geometry, the strength of the H-bond, and the ability of the small molecules to crystallize can greatly influence the self-assembly kinetics of the supramolecular complex. The crystallization kinetics further complicate the self-assembly by extending the dimensions of these multicomponent systems. Small mesogenic amphiphiles such as 3-pentadecylphenol are well-known to make self-assembled hierarchical structures when complexed with polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP(PDP)). Although the self-assembly of this system is well-studied, the influence of the small molecule crystallization on the self-assembly kinetics is largely unknown. This study focuses on understanding the role of small molecule crystallization in supramolecular BCP self-assembly based on PS-b-P4VP. We investigate the effects of small molecule loading by changing the complexing ratio ranging from r=0.5 to r=2.0 to investigate the existence of different crystallization regions depending on small molecule loading. By varying the respective chain lengths of PS and P4VP blocks while pertaining to constant parent volume fractions we present the idea that entropic penalty at the interface between the blocks can affect the crystallization, therefore, longer chains could impose better side chain crystallization due to smaller contribution from the interface. The differential scanning calorimetry (DSC) data implies that a change in molecular geometry can depress the melting point of the complex. This is proven when the BCP was complexed with a linear small molecule. Therefore, the steric effects brought by the molecular geometry will affect crystallization and thereby self-assembly kinetics. We employ small-angle X-ray scattering to verify the crystallization and crystal structures of these systems. This study reveals information on the crystallization behavior of amphiphilic block copolymer complexes which are complementary to the understanding of the kinetic pathways of self-assembly of such supramolecules.