Controllable Wet-Brush Blending of Linear Diblock Copolymers with Phenolic/DDSQ Hybrids toward Mesoporous Structure Phase Diagram

In recent decades, the microphase separation behavior of diblock copolymers has been extensively discussed, whereby their inherent thermodynamic tendencies enable the bottom-up establishment of various self-assembled nanostructures. In this study, we employed ring-opening polymerization (ROP) to synthesize three linear poly(ethylene oxide-b-caprolactone) (PEO-b-PCL) diblock copolymers with different degrees of polymerization but similar volume fractions and utilized phenolic resin modified with double-decker silsesquioxane (PDDSQ) for controllable wet-brush blending. FTIR analyses revealed a competitive hydrogen bonding phenomenon and confirmed that increasing the chain length led to self-coiling of the segments, weakening the extent of hydrogen bonding. Through the evaporation-induced phase separation (EISA) mechanism, the cross-linking of PDDSQ, we obtained the mesoporous hybrid materials after template removal. Remarkably, through temperature-dependent SAXS, we were able to reproduce the changes in surface energy and d-spacing during the curing process of PDDSQ, demonstrating the mechanism of reaction-induced microphase separation leading to order-order phase transition. The presence of DDSQ resulted in a relatively higher chi value for the system, allowing for the formation of mesoporous structures such as lamella, hexagonal-packing cylinder, double gyroid, sphere, and even the less common hexagonal-perforated layer (HPL) structure. Additionally, the degree of polymerizations of the three diblock copolymers resulted in different alpha values (alpha = M-n,M-h-A/M-n,M-b-A) for the blending system, whereby increasing the polymerization degree led to a decrease in the alpha value under the same blending weight fraction, prompting the system to form structures with higher interfacial curvature. TEM images and SAXS patterns served as evidence of this order-order phase transition. In summary, this study manipulated the polymerization degree of diblock copolymers to control the level of wet-brush blending in the system, presenting a mesoporous structure phase diagram for different weight fractions and template chain lengths, providing new insights and the opportunity to form desired self-assembled mesoporous structures at fixed volume fractions.