Routes to Alkene and Epoxide Functionalized Nanoporous Materials from Poly(styrene-b-isoprene-b-lactide) Triblock Copolymers

Abstract

Nanoporous materials with inherently tunable surface chemistries are poised to have a considerable impact in catalysis, separations, and nanopatterning. Using core−shell cylinder forming polystyrene-b-polyisoprene-b-polylactide (PS−PI−PLA) triblock terpolymers as templates, we were able to prepare aligned PI-coated nanoporous PS monoliths via the degradative removal of the cylindrical PLA cores. PS−PI−PLA precursors were synthesized using a combination of anionic (PS, PI) and ring-opening (PLA) polymerizations. The degree of order, alignment, and PLA degradation achievable was a strong function of molecular weight at a given triblock terpolymer composition. For intermediate molecular weight samples (25−28 kg mol-1), greater than 95% of the PLA was hydrolyzed through exposure of the monolith to a 0.1 wt % sodium dodecyl sulfate (SDS) solution in 0.5 N NaOH. However, low (17.5 kg mol-1) and high (46.8 kg mol-1) molecular weight samples of identical composition showed considerable resistance to PLA degradation. Treatment of the degraded monoliths with m-chloroperoxybenzoic acid in aqueous tert-butyl alcohol solutions permitted the controlled epoxidation of up to 75−80% of the PI alkene units. Despite some loss in pore alignment, scanning electron microscopy and small-angle X-ray scattering verified the retainment of the nanoporous structure following epoxidation.