Mediated Competitive Hydrogen Bonding Form Mesoporous Phenolic Resins Templated by Poly(ethylene oxide‑<i>b</i>‑ε-caprolactone‑<i>b</i>‑l‑lactide) Triblock Copolymers

Abstract

A series of immiscible triple crystalline triblock copolymers, poly­(ethylene oxide-<i>b</i>-ε-caprolactone-<i>b</i>-l-lactide) (PEO-<i>b</i>-PCL-<i>b</i>-PLLA), synthesized through sequential ring-opening polymerization, have been blended with phenolic resin. FTIR spectra revealed that the ether groups of the PEO blocks were stronger hydrogen bond acceptors for the OH groups of phenolic resin than were the CO groups of the PCL and PLLA blocks. Curing of phenolic with the templates and hexamethylenetetramine resulted in excluded and confined PCL or PLLA phases, depending on the phenolic content. This effect led to the formation of various composition-dependent nanostructures, including disordered structures, bicontinuous gyroids, hexagonally packed cylinders, and spherical micelle structures. Small-angle X-ray scattering and transmission electron microscopy revealed that self-organized mesoporous phenolic resin formed at phenolic contents of only 30–50 wt % as a result of an intriguing balance among the contents of phenolic and the PEO, PCL, and PLLA blocks. An interesting closed-loop mesoporous structure existed in the phase diagram of the mesoporous phenolic resins templated by the PEO-<i>b</i>-PCL-<i>b</i>-PLLA triblock copolymers