Photoinitiated Synthesis of Mixed Polymer Brushes of Polystyrene and Poly(methyl methacrylate)

Abstract

We describe the synthesis of mixed, or binary, polymer brushes containing polystyrene (PS) and poly(methyl methacrylate) (PMMA). These films were synthesized by a grafting-from (GF) strategy from gold substrates that were coated with a bis-thiol free radical photoinitiator, similar to 2,2‘-azobis(isobutyronitrile) (AIBN). The PS layer was 70 nm thick for all substrates, and the PMMA was varied up to 700 nm. The number-average molecular weight (M n) of the ungrafted polymers was determined by gel permeation chromatography (GPC) and multiangle light scattering (MALS); the M n for bulk PS and PMMA was ∼57 000 and ∼515 000 Da, respectively. The air/liquid interface was probed by static water contact angles (θ) and X-ray photoelectron spectroscopy (XPS). We found that both θ and the oxygen concentration varied depending on whether the substrate was immersed in a nonselective solvent (tetrahydrofuran) or selective solvent for PS (cyclohexane) or PMMA (isobutanol). The morphology was monitored by atomic force microscopy (AFM), and we observed a dimple-type structure in cyclohexane and isobutanol, with less nanophase separation after immersion in tetrahydrofuran. Reflection−absorption infrared spectroscopy (RAIRS) was used to quantify the % PMMA in the binary brushes, which ranged from 0 to 90%, and was confirmed by XPS. These substrates exhibited reversible switching, and both lateral and layered nanophase separation were observed. The elasticity of a mixed brush was probed by AFM and was found to lie between that of neat PS and PMMA.

Surface-initiated ATRP of PMMA, PS and diblock PS-b-PMMA copolymers from stainless steel modified by 11-(2-bromoisobutyrate)-undecyl-1-phosphonic acid

“…An analysis of this energy range evidences the presence of four peaks centered at 285.0, 285.7, 286.8 and 289.1 eV which correspond to the different bonding situations in which the carbon atoms occur in the PMMA repeat unit as depicted in Fig. 6b [50,66,67]. The relative amounts of each type of carbons are listed in Table 4 and are close to the theoretical values calculated on the basis of the polymer structure.…”

“…A useful check of the surface state of the PMMA and PS homopolymers is given by their water contact angle values, 72 • and 95 • , respectively (Table 3) which fit well with corresponding data (74 • and 96 • ) obtained on the same polymers synthesized on sil- ica substrates [41,67,[70][71][72]. These measurements are sensitive to composition and structural changes at a depth of approximately 0.5-1 nm.…”

“…Also observable is the shake-up satellite associated to the π → π * transition of the phenyl ring and located around 292.2 eV [50,67]. A small signal of bromine (Br 3d: 73 eV) is observed in PMMA and PS which is consistent with the fact that the Br atoms present in the catalytic system CuBr/PMDETA are propagated to the surface as the chains grow (Scheme 2) [48].…”

Induction heating for surface triggering styrene polymerization on titanium modified with ATRP initiator

“…Using a conventional heating method lead to a more hydrophilic surface (64.4°± 0.9°) than using induction heating which leads to a much more hydrophobic surface (92.0°± 0.7°). A value of 95°± 1°has been observed in the literature for the ATRP of styrene during 24 h with a conventional heating at 90°C [20,[44][45][46][47]. In other words, using induction heating allows us to obtain hydrophobicity properties similar to the one obtained after a 24 h ATRP with conventional heating in only 1 h. In order to characterize the morphology of the polymer layers formed with these two different heating conditions, the treated samples were observed by SEM.…”

Spatiotemporally Controlled Formation of Two‐Component Counterpropagating Lateral Graft Density Gradients of Mixed Polymer Brushes on Planar Au Surfaces

“…An exception is the work of Zhao, [8] in which mixed-gradient poly-(methylmethacrylate) (PMMA)/polystyrene (PS) brushes were prepared from a binary gradient-mixed initiator layer by combining ATRP and nitroxide-mediated radical polymerization activated at different temperatures. However, as discussed by Dyer and co-workers, [34] several stringent criteria must be satisfied for this scheme to be successful. A reproducible binary gradient-mixed initiator layer must be formed; the polymerization efficiency of the two different initiators must be approximately equal; and it is problematic to tether mixed polymer brushes on Au, because alkanethiolate self-assembled monolayers (SAMs) are less stable above 60°C.…”