From Self-Assembled Monolayers to Coatings: Advances in the Synthesis and Nanobio Applications of Polymer Brushes

In this review, we describe the latest advances in synthesis, characterization, and applications of polymer brushes. Synthetic advances towards well-defined polymer brushes, which meet criteria such as: (i) Efficient and fast grafting, (ii) Applicability on a wide range of substrates; and (iii) Precise control of surface initiator concentration and hence, chain density are discussed. On the characterization end advances in methods for the determination of relevant physical parameters such as surface initiator concentration and grafting density are discussed. The impact of these advances specifically in emerging fields of nano- and bio-technology where interfacial properties such as surface energies are controlled to create nanopatterned polymer brushes and their implications in mediating with biological systems is discussed

Bulk and Thin Film Morphological Behavior of Broad Dispersity Poly(styrene-<i>b-</i>methyl methacrylate) Diblock Copolymers

We describe the morphological implications of broad molecular weight dispersity on the bulk and thin film self-assembly behavior of seven model poly­(styrene-<i>block</i>-methyl methacrylate) (SM) diblock copolymers. Derived from sequential nitroxide-mediated polymerizations, these unimodal diblock copolymers are comprised of narrow dispersity S blocks (<i>Đ</i> ≤ 1.14) and broad dispersity M blocks (<i>Đ</i> ∼ 1.7) with total molecular weights <i>M</i>_n,total = 29.2–42.9 kg/mol and M volume fractions <i>f</i>_M = 0.35–0.63. Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) analyses demonstrate that these diblock copolymers microphase separate into lamellar and cylindrical morphologies with substantially larger microdomain spacings at lower overall molecular weights as compared to their narrow dispersity analogues. The observed microphase-separated melt stabilization is also accompanied by a substantial shift in the lamellar phase composition window to higher values of <i>f</i>_M. In thin films, these polydisperse copolymers form perpendicularly oriented morphologies with modest degrees of lateral order on substrates functionalized with P­(S-<i>ran</i>-MMA) neutral polymer brush layers

Post-Fabrication Placement of Arbitrary Chemical Functionality on Microphase-Separated Thin Films of Amine-Reactive Block Copolymers

We report an approach to the post-fabrication placement of chemical functionality on microphase-separated thin films of a reactive block copolymer. Our approach makes use of an azlactone-containing block copolymer that microphase separates into domains of perpendicularly-oriented lamellae. These thin films present nanoscale patterns of amine-reactive groups (reactive stripes) that serve as handles for the immobilization of primary amine-containing functionality. We demonstrate that arbitrary chemical functionality can be installed by treatment with aqueous solutions under mild conditions that do not perturb underlying microphase-separated patterns dictated by the structure of the reactive block copolymer. This post-fabrication approach provides a basis for the development of modular approaches to the design of microphase-separated block copolymer thin films and access to coatings with patterned chemical domains and surface properties that would be difficult to prepare by the self-assembly and processing of functionally complex block copolymers

Phase Behavior of Poly(4-hydroxystyrene-<i>block</i>-styrene) Synthesized by Living Anionic Polymerization of an Acetal Protected Monomer

We have synthesized a series of poly­(4-(2-tetrahydropyranyloxy)­styrene) [P­(OTHPSt)] homopolymers by living anionic polymerization of the protected monomer (OTHPSt) in tetrahydrofuran at −78 °C, with excellent control over molecular weight and dispersity. The high <i>T</i>_g of P­(OTHPSt) led to facile purification and isolation of the polymer as a powder. Characterization of the POTHPSt homopolymer by nuclear Overhauser effect spectroscopy confirms the strong preference for the axial position of the relatively sterically demanding alkoxy phenyl group. By sequential monomer addition, a series of low to high molecular weight P­(OTHPSt-<i>b</i>-styrene) BCPs with narrow dispersities were synthesized. Quantitative deprotection of the THP groups yielded poly­(4-hydroxystyrene-<i>b</i>-styrene) with tunable molecular weights and compositions. The solid-state and melt-phase self-assembly of these diblocks was investigated using synchrotron small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Mean-field theory analysis of the temperature-dependent correlation-hole scattering for a disordered diblock was used to determine the interaction parameter as χ_HS/S(<i>T</i>) = (4.39 ± 0.83)/<i>T</i> + (0.109 ± 0.002), which is approximately 4 times larger than that of poly­(styrene-<i>b</i>-methyl methacrylate) with the same disproportionately high contribution of entropy to the free energy of mixing

A Dual Functional Layer for Block Copolymer Self-Assembly and the Growth of Nanopatterned Polymer Brushes

We present a versatile method for fabricating nanopatterned polymer brushes using a cross-linked thin film made from a random copolymer consisting of an inimer (<i>p</i>-(2-bromoisobutyloylmethyl)­styrene), styrene, and glycidyl methacrylate (GMA). The amount of inimer was held constant at 20 or 30% while the relative amount of styrene to GMA was varied to induce perpendicular domain orientation in an overlying P­(S-<i>b</i>-MMA) block copolymer (BCP) film for lamellar and cylindrical morphologies. A cylinder forming BCP blend with PMMA homopolymer was assembled to create a perpendicular hexagonal array of cylinders, which allowed access to a nanoporous template without the loss of initiator functionality. Surface-initiated ATRP of 2-hydroxyethyl methacrylate was conducted through the pores to generate a dense array of nanopatterned brushes. Alternatively, gold was deposited into the nanopores, and brushes were grown around the dots after removal of the template. This is the first example of combining the chemistry of nonpreferential surfaces with surface-initiated growth of polymer chains