The Impacts of Tacticity and Repeat Unit Structure on the Growth of Irreversibly Adsorbed Poly(alkylmethacrylate) Layers

Abstract

The properties of polymer thin films confined to <100 nm in thickness have been shown to deviate substantially from bulk polymer properties with thickness, due to a large surface area to volume ratio and enhanced interfacial influences. Recently, deviations in glass transition temperature (Tg) have been shown to correlate with the growth of a residual irreversibly adsorbed layer, which remains following the coating, annealing and washing of polymer thin films onto a substrate. Since their discovery, a fairly standard procedure has been used to prepare irreversibly adsorbed layers. As a result, it is not well understood how variations in polymer structure and film processing can affect adsorbed layer growth. This project provides a greater understanding of the specific interactions between the polymer and substrate that lead to irreversibly adsorbed layers, and investigates the extent to which preparation methods affect their growth. Three independent investigations were conducted: the effects of poly(methyl methacrylate) (PMMA) tacticity using isotactic, syndiotactic, and atactic PMMA; the effects of poly(alkylmethacrylate) monomer size using PMMA, poly(ethyl methacrylate) (PEMA) and poly(butyl methacrylate) (PBMA); and the sensitivity to variations in preparation methods including substrate pre-treatment and washing. Results confirm that PMMA tacticity, poly(alkylmethacrylate) repeat unit structure, substrate preparation and washing methods all impact polymer-substrate interfacial interactions, and therefore the growth of irreversibly adsorbed layers. Data collected on adsorbed layer growth yields insight into the strength of interfacial interactions present, providing the link by which adsorbed layer growth and thin film property deviations with thickness are connected.