Hydrogen Bond Assisted Assembly of Well-Ordered Polyhedral Oligomeric Silsesquioxane Block Copolymer Composites

Blends of nanoscale fillers and polymers are of interest for a wide range of applications. Among these, block copolymer (BCP) nanocomposites are an interesting class of materials in which the block copolymer can guide the spatial location and periodic assembly of the additives. 4 This approach exploits differences between the chemical nature of the constituent blocks to direct the organization of additives, including small molecules, homopolymers and nanoparticles. 11 The selective incorporation of additives within one of the phases can create functional materials or enhance differences in the chemical and/or physical characteristics of the domains. In block copolymer lithography, for example, the etch resistance of one of the phases can be enhanced by selective incorporation of materials with high etch resistance. BCP composites can also find use as low line edge roughness resists for nanoscale electronics and as templates for the fabrication of nanoscale microelectronic structures, including high density data storage media. 16 A recent review summarizes the use of BCP nanostructures in electronics. BCP composites materials are also of interest for photovoltaics 20 and photonics. 23 Other applications include their use as templates for the fabrication of inorganic mesostructured materials via phase selective reactions 26 or the formation of nanoporous polymeric materials by treating the BCP composites to remove the minority phase. 29 In some cases, the additives have been used to influence domain orientation. 33 Many applications and materials synthesis schemes would benefit from high concentrations of an additive within an ordered block copolymer composite, however entropic penalties associated with BCP chain stretching can severely limit additive loadings. Recently Wiesner and co-workers demonstrated one specific example of a highly loaded and well-ordered polymer nanoparticle assembly using strong interactions between ionic liquid ligands bound to the surface of Pt nanoparticles and a specially designed BCP. Microphase separation of BCPs is thermodynamically governed by the segregation strength between the chemically dissimilar blocks. A measure of segregation strength is provided by the product χN where χ is the Flory Huggins interaction parameter between segments of the dissimilar blocks andN is the total number of repeat units. When the segregation strength is high, BCPs containing two chemically dissimilar blocks form spherical, cylindrical, or lamellar morphologies depending upon the relative volume fractions of the dissimilar blocks. However,