Robust porous polymers enabled by a fast trifluoroacetic acid etch with improved selectivity for polylactide

Abstract

Polylactide is a widely used sacrificial block for the preparation of porous polymers from ordered block copolymers. Although numerous etching strategies were developed in the past decade, demonstrations to date are limited by slow etch rates that require as long as a week for the etching of few-mm thick films. Recent studies have also shown that NaOH etching of thin-films can degrade the morphology, highlighting the need for more selective processes. Here we report an aqueous trifluoroacetic acid etchant that results in an enhanced etch rate of 14 nm s⁻¹ with greatly improved selectivity for poly(styrene-block-lactide). The high etch rate enables the complete removal of polylactide from 2 mm thick block copolymer films in 19 h. Furthermore, the improved etch selectivity enables the macroscopic preservation of morphologies as confirmed by both SAXS and SEM and yields pristine porous PS as confirmed by NMR and GPC.