Kinetic Study of Degrafting Poly(methyl methacrylate) Brushes from Flat Substrates by Tetrabutylammonium Fluoride

Abstract

Polymer degrafting is a process in which surface-attached polymer brushes are removed from the substrate by breaking a chemical bond in proximity to the substrate. This paper provides insight into the kinetics of degrafting poly­(methyl methacrylate) (PMMA) brushes using tetrabutyl­ammonium fluoride (TBAF) and demonstrates how the process can be modeled using a series of degrafting reactions. The trichlorosilane-based polymerization initiator utilized here to synthesize PMMA grafts by surface-initiated atom transfer radical polymerization anchors to the silica substrate by up to three potential attachment points. During the degrafting sequence this anchoring reduces to two and one chemical bond and finally results in complete liberation of the PMMA macromolecule from the substrate. We investigate the effect of TBAF concentration, the initial grafting density of PMMA grafts on the substrate, and TBAF exposure time on degrafting of PMMA by monitoring the instantaneous areal grafting density of PMMA on the substrate.

Spontaneous Degrafting of Weak and Strong Polycationic Brushes in Aqueous Buffer Solutions

“…In our previous paper, we attributed the initial degrafting data to removing multilayers/ imperfectly bound chains present at the very surface that would be liberated first from the grafted polymer layer. 41 Employing the "data-shifting" procedure brings all experimental data to a master curve. The inset in Figure 5 displays a linear dependence of the employed time shift as a function of the initial normalized grafting density of polymer brushes (h 0 / h N ).…”

“…In our analysis, we omitted the first degrafting point. In our previous paper, we attributed the initial degrafting data to removing multilayers/imperfectly bound chains present at the very surface that would be liberated first from the grafted polymer layer . Employing the “data-shifting” procedure brings all experimental data to a master curve.…”

“…The fluorine ions in TBAF selectively cleave the Si-O bonds, leading to degrafting. [38][39][40][41] We classified this mode as "on-demand degrafting (ODD)". In a series of studies, we reported that polyanionic brushes detached from substrates upon increasing pH of the solutions that induced strong swelling due to electrostatic charging and concurrent hydrolysis of ester bonds in the initiator.…”

“…Many researchers have attempted to comprehend breaking a covalent bond in grafted polymers to disclose the mechanism of chain breaking by considering click chemistry, photo-cleaving, − sonication-induced chain scission, , strong acid or base, − and so forth. − In our own previous work, we considered degrafting of polymer brushes from silicon substrates using tetrabutylammonium fluoride (TBAF). The fluorine ions in TBAF selectively cleave the Si–O bonds, leading to degrafting. − We classified this mode as “on-demand degrafting”. In a series of studies, we reported that polyanionic brushes detached from substrates upon increasing pH of the solutions that induced strong swelling due to electrostatic charging and concurrent hydrolysis of ester bonds in the initiator. − This is considered as “spontaneous degrafting”.…”

Synthetic strategies to enhance the long-term stability of polymer brush coatings

“…82 Yet, in most dense brush systems, the polymers are reported to degraft at their substrate anchors, where, depending on the type of anchor, bonds can be weaker 83 and tension is the highest. 84 This degrafting can be intentional [85][86][87] (e.g. to characterize the molecular weight of the polymers) or unintentional.…”