Diffusion-regulated interfacial copolymerization of poly(ester amide) thin film composite membranes using trihydroxybenzene monomers

Interfacial polyesterification provides an alternative approach for fabricating thin film composite (TFC) membranes, yet the governing physicochemical factors remain unclear. This work elucidates the key factors of phenolate-based film formation using biomass-derived trihydroxybenzene (BTO) isomers. Kinetic analysis indicates that a base catalyst is required to generate reactive phenolate species. Two-phase diffusion assays demonstrate that BTO exhibits negligible partitioning into the organic phase (diffusivity ≈ 5.33 ± 0.88 · 10⁻⁸ cm²·s⁻¹), three orders of magnitude lower than the diffusive transport of m-phenylenediamine (MPD, diffusivity ≈ 3.69 ± 0.15 · 10⁻⁵ cm²·s⁻¹) in conventional polyamide TFC chemistry. This kinetic confinement restricts the film growth within the aqueous–organic interface, yielding ultrathin, smooth, and structurally continuous selective layers. Comparative screening identifies 1,2,3-BTO (pyrogallol) as the optimal isomer over 1,2,4-BTO (hydroxyquinol) and 1,3,5-BTO (phloroglucinol). Subsequent stoichiometric optimization of the catalyst, nucleophile (BTO), and electrophile (trimesoyl chloride) concentrations defines the boundary conditions for structurally continuous film formation. Furthermore, interfacial copolymerization using a mixture of MPD and BTO to form poly(ester amide) TFC membrane exploits transport asymmetry to engineer the layer architecture. The optimal MPD/BTO mixture composition (0.23:0.77 mass ratio) achieves a Rose Bengal rejection of 99.6% and a separation factor of 212 for Rose Bengal (973.67 Da)/Chrysoidine G (248.71 Da), with a two-fold increase in permeance relative to MPD-only polyamide membranes. Moreover, compared to the MPD-only polyamide TFC membrane, the MPD-BTO copolymerized poly(ester amide) network demonstrates enhanced chlorine and compaction resistance during 24 h of continuous operation. This work establishes a diffusion-regulated framework for tailoring the morphology and separation performance of polyesteramide TFC membranes.