Surface‐Initiated Atom Transfer Radical Polymerization of Oligo(ethylene glycol) Methacrylate: Effect of Solvent on Graft Density

Abstract

Summary: Oligo(ethylene glycol) methacrylate (OEGMA) was grafted from silicon wafer surfaces by surface‐initiated atom transfer radical polymerization (ATRP) with CuIBr/2,2′‐bipyridine (bpy) as a catalyst and various water/alcohol mixtures as solvents. The ellipsometric thickness of the poly(OEGMA) layer on the surface increased linearly with monomer conversion in solution. High graft densities were achieved in alcohols. The graft density of poly(OEGMA) in methanol was found to be 0.26 chains · nm−2, which is 50% higher than that in water/methanol (30:70, v/v). The differences in graft density were correlated to the conformation of tethered poly(OEGMA) chains. Large poly(OEGMA) coils on the surface in the presence of water limited the access of initiation sites to the catalyst complex and monomer molecules.Development of poly(OEGMA) layer thickness on the silicon surface vs monomer conversion.imageDevelopment of poly(OEGMA) layer thickness on the silicon surface vs monomer conversion.

Substrate-Independent Method for Growing and Modulating the Density of Polymer Brushes from Surfaces by ATRP

“…With methanol and water in varying proportions, Feng et al found that thicker graft layers were obtained as the polarity of the solvent decreased. 48 We have verified this with ethanol/water solutions (not previously compared) and showed that use of the less polar solution resulted in grafted layers greater than twice as thick. The use of water as a cosolvent with alcohol has many advantages for SI-ATRP of PEGMA.…”

Characterization of protein resistant, grafted methacrylate polymer layers bearing oligo(ethylene glycol) and phosphorylcholine side chains by neutron reflectometry

“…33,34 For both OEGMA and MPC grafting, Cu͑I͒Br/bpy was used as the catalyst and methanol as the solvent. A sacrificial initiator was added to the mixture for the following reasons: ͑1͒ to provide enough deactivator ͓Cu͑II͒Br͔ through the redox reaction between Cu͑I͒Br and the sacrificial initiator, which in turn better controls the ATRP grafting of polymers from the Si; and ͑2͒ to control the polymer chain length under the assumption that the chains grown from the Si surface and in solution have similar molecular weights.…”

The Effect of [CuI]/[CuII] Ratio on the Kinetics and Conformation of Polyelectrolyte Brushes by Atom Transfer Radical Polymerization

“…It has previously been shown that the grafting density can be controlled by the density of initiator groups on the surface, [15,16] and in some cases, also by the quality of the solvent. [17] However, any attempt to control the grafting density of polymer brushes should also consider the 'speed' of polymerization. The rationale for this consideration is the hypothesis that very rapid brush growth will inevitably lead to more termination reactions during the initial stages of the polymerization and hence to lower grafting densities of the remaining 'living' chain ends.…”