S.R. Nowak, T.S. Thomas, J.P. Reeds, L.R. Sita
University of Maryland,
Keywords: self-assembly, nanostructure, ultra-thin film, bioinspired, sugar conjugate, polyolefins
Summary:The self-assembly of amphiphilic materials comprised of chemically linked polar and non-polar segments gives rise to a variety of nanostructures in solution and the solid state that are instrumental for a wide range of existing and future technological applications. As such, there has long been a corollary interest in the development of new classes of molecular and macromolecular building blocks for amphiphilic systems that are amenable to programmed structural changes as a means by which to exert control over the relative magnitudes of entropic and enthalpic contributions to the self-assembly process and thereby over the final nanostructure that is formed. Traditionally, the ability to direct the architecture of such nanostructures has been inhibited by the limited ability to control the structure and properties of the amphiphilic materials from which they are prepared. This presentation summarizes the synthesis and characterization of poly(α- olefinate)-sugar hybrid conjugates, a new class of amphiphilic materials, which can be prepared with exquisite control over molecular structure and composition via a unique living coordination chain transfer polymerization (LCCTP) technique. The self-assembly of poly(α-olefinate)-sugar hybrid conjugates, which consist of hydrophobic poly(α-olefinate) (PAO) “tails” chemically tethered to hydrophilic saccharide “head” groups, have been investigated in both bulk and thin-film forms by atomic force microscopy, electron microscopy, and x-ray scattering techniques, as well as spectroscopic, calorimetric, and chromatographic methods. xPAO amphiphilic hybrid conjugates display organized nanostructures within ultra-thin films with sub-10 nm features, the morphology of which can be manipulated through variation in the occupied volume of the xPAO domain, which can in turn be influenced through the fine control over its molecular structure and composition afforded by LCCTP technology. Importantly, conjugates consisting of the disaccharide (D)-(+)-Cellobiose as the head group and atactic polypropylene (aPP) as the tail (CB- aPP) undergo a unique reorientation of self-assembled domains from a perpendicular orientation to a parallel orientation upon low temperature ( ≥38 °C) thermal annealing. The development of living coordination chain transfer polymerization (LCCTP) has provided a viable path to scalable quantities of structurally-well defined polyolefins that are further characterized by having tunable molecular weight, narrow polydispersity and end-group functionality, including –OH, -I, -N3 and –COOH chemical moieties. End-group functionalized poly(α-olefinates) (xPAOs) are further attractive as building blocks for new types of polyolefin materials with novel polymer architectures and properties.