As the semiconductor industry strives to create devices with features smaller than 40 nm in the next five to ten years, a number of technical challenges must be overcome. The key step in the production of such devices requires manufacturing stable polymer nanostructures with large aspect ratios and nanoscopic lateral dimensions. One of the major challenges that must be overcome is that the properties of polymer materials change from their bulk values when they are confined to such small geometries. It is well-established in the literature that confinement can reduce the glass transition temperature, leading to a softening of the material and collapse during normal semiconductor processing. Here, we use molecular simulations to provide insight into how confinement affects the properties of polymers, and how additives can be used to create more stable nanostructures. We have developed a coarse-grained model that exhibits antiplasticization, a phenomenon where the addition of low molecular weight solvent molecules can increase the density and stiffness of a polymer glass while reducing the glass transition temperature. This is in contrast to the more widely-studied plastification of a material, where the elastic constants, density, and glass transition temperature decrease. Using our model, we have shown how antiplasticizer molecules can reduce the effects of confinement on the properties of polymers by reducing the size of the cooperative rearrangements. This effect is explained through the fragility of glass-formation, where antiplasticization is associated with reducing the fragility of our glass-forming polymer. A reduction in fragility is commonly associated with a decrease in the size of cooperative rearrangements within the framework of the Adam-Gibbs theory of glass-formation. In addition, our results are in excellent agreement with experimental results published in the literature.