Side-Chain-Grafted Random Copolymer Brushes as Neutral Surfaces for Controlling the Orientation of Block Copolymer Microdomains in Thin Films

Abstract

Random copolymers of P(S-r-MMA-r-HEMA)s with a distribution of surface reactive hydroxyl groups were synthesized to formulate neutral surface layers on a SiO2 substrate. The layers were designed to drive vertical orientation of lamellar microdomains in a top P(S-b-MMA) thin film. Copolymers with a styrene weight fraction (f(St)) of 0.58 and a HEMA fraction (f(HEMA)) ranging from 0.01 to 0.03, with a corresponding MMA fraction (f(MMA)) ranging from 0.41 to 0.39, in the P(S-r-MMA-r-HEMA) copolymer showed neutral surface characteristics. The morphology of block copolymer thin films was studied by scanning electron microscopy (SEM). P(S-r-MMA-r-HEMA) copolymers prepared by both living and classical free-radical polymerizations were equally effective in demonstrating the neutrality of the surface. These side-chain-grafted random copolymer brushes showed faster grafting kinetics than the end-chain-grafted P(S-r-MMA) because of multipoint attachment to the surface. The modified surfaces had a very thin layer of random copolymer brush (5-7 nm), which is desirable for effective pattern transfer. Furthermore, neutral surfaces could be obtained even when the grafting time was reduced to 3 h. These results indicate that the composition of the random copolymer brush, rather than its PDI or molecular weights, is the most important factor in controlling the neutrality of the surface. These results also demonstrate the feasibility of using a third comonomer (C) in the random copolymer brush P(A-r-B-r-C) to alter the interfacial and surface energies of a diblock copolymer (A-b-B).

Preparation of stable polymeric grafted layers on poly(ethylene terephthalate) by thermal annealing

“…The molecular weight distributions of the copolymers are 1.86 and 2.04, respectively. Although these two copolymers possess different molecular weights and polydispersities, previous studies showed that the grafting efficiency does not depend on the polymer's molecular weight or polydispersity 17 . Hence these two copolymers were used for grafting studies as follows.…”

“…The copolymer-coated PET samples were then annealed at 130°C for 48 h. This annealing condition was first selected because it was similar to that of previous work where HEMA-containing copolymers were grafted on oxide substrates 17 . According to the literature, the grafting process occurs through the condensation reaction between surface hydroxyl groups and hydroxyl groups of the copolymer.…”

“…www.scienceasia.org Recently, hydroxyl groups have been used as surface linker to graft polymers 17 and rheniumbipyridine dyes 18 onto oxide substrates by thermal annealing. By simple heating at 140-160°C, the hydroxyl groups of an organic material and oxide surface condense to form an ether linkage resulting in organic layers chemically bonded onto the surface.…”

Extending the scope of poly(styrene)-block-poly(methyl methacrylate) for directed self-assembly

“…Finally, for the 62% underlayer a number of raised features were observed, which were characteristic of one block preferentially interacting with the substrate in a film that had a thickness that was incommensurate with the long period of the block copolymer. [61,62] Qualitative analysis of these images suggested that the 65% PS may be a neutral surface for the PS-b-PMMA (38k-b-37k) with 20% IL. To investigate the morphology of the thin film further the PS-b-PMMA (38k-b-37k) with 20% IL on the 65% PS underlayer was analyzed using grazing incidence small angle X-ray scattering and a 2D scattering profile is shown in Figure 4a.…”

Di-Stimuli Responsive Poly(<i>N</i>-Isopropylacrylamide-co-Diethylaminoethylmethacrylate) Copolymer: Synthesis, Characterization and Investigation of Aqueous Dispersion Properties

“…Among the polymerization methods, controlled radical polymerizations (such as ringopening polymerization (ROP), 17,18 nitroxide-mediated polymerization (NMP), 19,20 atom transfer radical polymerization (ATRP), [21][22][23], and reversible addition-fragmentation chain transfer (RAFT) polymerization, 24,25 have rendered the grafting-from approach more prevailing) are used for synthesis of well defined structural block polymers. Thermo-responsive polymers, which undergo a reversible phase transition in response to temperature, have been extensively studied and utilised.…”