Impact of ATRP Initiator Spacer Length on Grafting Poly(methyl methacrylate) from Silica Nanoparticles

Abstract

We quantified the impact of the carbon spacer length (CSL) of immobilized alkoxysilanes initiators on grafting poly(methyl methacrylate) (PMMA) from the surfaces of monodisperse silica nanoparticles. PMMA was grafted using surface-initiated atom transfer radical polymerization (SI-ATRP), a facile technique to produce well-controlled polymer brushes. The polymerizations were carried out in environmentally friendly 4:1 (v/v) methanol-water solutions at room temperature. Monoethoxysilane initiators of 3, 11, and 15 carbon spacer lengths were synthesized and characterized with (1)H NMR and (13)C NMR. The initiators were then used to modify the surfaces of monodisperse silica nanoparticles in methyl isobutyl ketone, producing dense initiator monolayers with site densities between 1.8-3.6 initiators/nm(2). PMMA was subsequently grafted from the functionalized nanoparticles using both CuCl and CuBr catalysts. We found that polymerizations performed with CuBr were uncontrolled, whereas those with CuCl were controlled. PMMA graft densities ranged between 0.10-0.43 polymers/nm(2), which increased with the initiator carbon spacer length (CSL). Interestingly, longer CSLs make nanoparticle surfaces hydrophobic, causing nanoparticle aggregation in methanol-water solutions. Our results indicate that surface hydrophobicity correlates to increases in PMMA graft density through the adsorption of hydrophobic MMA monomers on initiators with longer CSLs. Thus, to augment PMMA graft densities, a subtle balance must be struck between enabling particle stability and increasing MMA adsorption in methanol-water solutions.

Self-healing polymer nanocomposites based on Diels-Alder-reactions with silica nanoparticles: The role of the polymer matrix

“…The remaining particle solution was transferred to iso-butyl methylketone (IBMK) by adding the high boiling solvent (500 mL) to the methanol solution and removing methanol in vacuo. [20] For a complete exchange, IBMK (250 mL) was added and again 250 mL solvent were removed. This was repeated three times to afford 250 mL particle solution in IBMK containing 15 g SiO2-nanoparticles.…”

“…The surface functionalization was carried out applying a solvent-exchange method, which results in a high surface coverage and a low agglomeration of the modified silica particles. [20] In this procedure, IBMK was added to the freshly prepared silica particles in methanol and the methanol was removed in vacuo. Using IBMK as the medium during the modification results in ionized OH-groups due to the high dielectric constant of the solvent (Ɛ = 13.1).…”

Grafting of amphiphilic polymers containing quaternary ammonium group on SiO2 surface via surface-initiated ATRP

“…Among the numerous reported examples of inorganic/organic hybrid nanoparticles, silica/polymer hybrid nanoparticles have been extensively studied [18][19][20][21]. Despite the increasing studies on silica/polymer hybrid nanoparticles, they all have the specific applications owing to the hydrophobic property of the polymers deposited on the silica surface, such as polystyrene [22,23], poly (methyl methacrylate) [24][25][26], and so on. However, due to the ease of the synthesis and the particular properties, such as heat resistance, mechanical performance [27][28][29], silica nanoparticles can be applied in highway, bridge, railway, and any other areas.…”

Designer nanoparticles as efficient nucleation agents in polymer foaming

“…137 This silane based chemistry can for example be used to tether an atom transfer radical polymerization (ATRP) initiator to the silica nanoparticle surface, to be able to polymerize a polymer shell around the particle, or to be used as reactive sites to couple polymers with functional groups by the grafting to method. 11,[138][139][140][141][142][143] The next section will focus on the formation of silica polymer core shell nanoparticles.…”