Low-temperature reactive coupling at polymer-polymer interfaces facilitated by supercritical CO₂

Supercritical CO₂ (scCO₂) has been used to facilitate reactions in thin film bilayers between functionalized polystyrene and poly(methyl methacrylate) at temperatures far below the glass transition temperatures of the respective polymers. Secondary ion mass spectrometry (SIMS) is used to monitor the reaction progression directly by measuring the interfacial excess of deuterated PS. Complementary X-ray reflectometry (XR) yields the interfacial width and surface roughness of bilayer films for reactive systems with and without the addition of scCO₂, and comparisons are made with unreactive reference systems. From XR and SIMS analyses, the interfacial width and roughness have been found to be effectively independent of the reaction conditions employed here, and the primary impact of incorporated scCO₂ is enhanced mobility of the reactive polymer chains. The use of scCO₂ can change polymer mobility significantly enough over a very small temperature range (ΔT∼15 °C) so that both diffusion- and reaction-controlled type behavior can be observed for otherwise identical systems.