Mediated Competitive Hydrogen Bonding Form Mesoporous\nPhenolic 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\ntriblock 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,\nhave been blended with phenolic resin. FTIR spectra revealed that\nthe ether groups of the PEO blocks were stronger hydrogen bond acceptors\nfor the OH groups of phenolic resin than were the CO groups\nof the PCL and PLLA blocks. Curing of phenolic with the templates\nand hexamethylenetetramine resulted in excluded and confined PCL or\nPLLA phases, depending on the phenolic content. This effect led to\nthe formation of various composition-dependent nanostructures, including\ndisordered structures, bicontinuous gyroids, hexagonally packed cylinders,\nand spherical micelle structures. Small-angle X-ray scattering and\ntransmission electron microscopy revealed that self-organized mesoporous\nphenolic resin formed at phenolic contents of only 30–50 wt\n% as a result of an intriguing balance among the contents of phenolic\nand the PEO, PCL, and PLLA blocks. An interesting closed-loop mesoporous\nstructure existed in the phase diagram of the mesoporous phenolic\nresins templated by the PEO-<i>b</i>-PCL-<i>b</i>-PLLA triblock copolymers.