text: The addition of polyethylene glycol (PEG) to the process causes silica particles to aggregate into a macroporous continuous block, allowing access to a monolithic morphology. PEG polymers with allyl or silyl end groups with a molecular weight of greater than 2000 g mol are required. The Stöber process is initiated under neutral pH conditions, so that the PEG polymers will congregate around the outside of the growing particles, providing stabilization. Once the aggregates are sufficiently large, the PEG-stabilized particles will contact and irreversibly fuse together by "sticky aggregation" between the PEG chains. This continues until complete flocculation of all the particles has occurred and the monolith has been formed, at which point the monolith may be calcined and the PEG removed, resulting in a macroporous silica monolith. Both particle size and sticky aggregation can be controlled by varying the molecular weight and concentration of PEG.