(552a) Degrafting of Polymer Assemblies from Silica Surfaces: Nuisance or Opportunity?

We discuss spontaneous degrafting of polyelectrolyte brushes and on-demand degrafting of neutral polymer grafts from silica surfaces. Spontaneous degrafting occurs in strong and weak polyelectrolyte brushes via hydrolysis of ester/amide linkers and siloxane bonds in the initiator molecule due to mechanical tension in the grafted chains. Sources of tension include high grafting density of polymer brushes on the surface (σ) as well as swelling and electrostatic repulsion associated with increasing degree of deprotonation (α) of repeat units in weakly charged polyelectrolyte brushes. On-demand degrafting of polymer assemblies and small molecule silanes from surfaces occurs by means of tetrabutyl ammonium fluoride (TBAF). We employ this degrafting approach to determine the molecular weight distribution of polymer grafts prepared by surface-initiated controlled radical polymerization on flat silica supports. We also demonstrate the application of TBAF for creating spatial degrafting patterns of polymers and organosilane modifiers on silica substrates. Desired in-plane patterns in polymer brush layers in millimeter scale are created by using a microcontact printing TBAF with a stamp made of agarose gel. Position-dependent gradients of the degrafted areas form by dipping substrates featuring homogeneous polymer coatings into TBAF solution. The use of TBAF for degrafting is appealing because it cleaves selectively Si-O bonds, does not alter chemically the structure of the degrafted moieties, and activates hydroxyl groups on silicon surfaces to enable deposition of organosilane-based initiators for growth of fresh polymer brush layers and organosilane monolayers.