Random Copolymer Effect in Self-Assembled Hydrogen-Bonded P(S-co-4VP)(PDP) Side-Chain Polymers

Random copolymers of styrene and 4-vinylpyridine P(S(1-x)-co-4VP(x)) were synthesized to study the effect of the random copolymer "repulsion" on the self-assembly in hydrogen-bonded complexes with pentadecylphenol (one PDP molecule per 4VP group). The major trends observed as a function of the fraction of styrene monomers 1 - x in the random copolymer are a decrease in order-disorder transition temperature, T(ODT), and a decrease in the periodic length scale of the ordered lamellar state. The lower T(ODT) results from a partial shielding in the disordered state of the highly unfavorable styrene/4-vinylpyridine interactions by the PDP alkyl tails. The reduced layer thickness in the ordered state is due to the relaxation into a more coil-like conformation of the alkyl tails of the PDP amphiphiles, made possible by the presence of styrene units. The self-assembly properties of P(S(1-x)-co-4VP(x))(PDP)(1.0) are compared with those of the lamellar self-assembled homopolymer-based P4VP(PDP)(x) system, where x denotes the number of PDP molecules per 4VP repeat unit. As in P(S(1-x)-co-4VP(x))(PDP)(1.0), in P4VP(PDP)(x) also only a fraction x of the total number of monomers of the macromolecule may potentially hydrogen bond with PDP molecules at any given instant. In contrast to P(S(1-x)-co-4VP(x))(PDP)(1.0), for P4VP(PDP),, however, the long period is found to increase for decreasing values of x

Annealing-Induced Changes in Double-Brush Langmuir-Blodgett Films of α-Helical Diblock Copolypeptides

The effect of annealing on the structure and the helix orientation in Langmuir-Blodgett (LB) monolayers of diblock copolymers (PLGA-b-PMLGSLGs) of poly(α-L-glutamic acid) (PLGA) and poly(γ-methyl-L-glutamate-ran-γ-stearyl-L-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) with unidirectional helix orientation deposited on hydrophilic silicon substrates was characterized by means of small-angle X-ray reflectivity, transmission Fourier transform infrared spectroscopy, and atomic force microscopy. Upon annealing at 100 °C for 24 h, the α-helices became less tilted toward the substrate surface normal. Surface area shrinkage accompanied the change in tilt, indicated by an increase in both film thickness and electron density, resulting in more compact and uniform films. The enhancement of the helix orientation by thermal annealing was greater for the PMLGSLG block and for the diblock copolymers with the shorter block lengths. For these diblock copolymers, annealing resulted in postorientation of the PMLGSLG block helices almost perpendicular to the substrate surface. This effect originates from a considerable increase in intermolecular packing of the PLGA block caused by hydrogen bonds between the carboxylic groups upon annealing, as well as the high mobility of the PMLGSLG block helices for rearrangement favored by the melted side chain mantle at elevated temperatures.

Hierarchical Terrace Formation in PS-b-P4VP(PDP) Supramolecular Thin Films

The terrace formation behavior of chloroform vapor annealed thin films of asymmetric, low molecular weight comb-shaped supramolecules consisting of a short polystyrene (PS) block and a long supramolecular block of poly(4-vinylpyridine) (P4VP) hydrogen bonded with pentadecylphenol (PDP) on silicon oxide (SiO2) was examined with atomic force microscopy. During annealing, PS microphase separated from the disordered P4VP(PDP) comb, resulting in the formation of terraces of parallelly oriented microdomains of PS in a matrix of P4VP. Upon evaporation of the solvent, the P4VP(PDP) combs dropped below their order-disorder transition, and formed alternating layers of P4VP and PDP, which for high P4VP(PDP) fractions were also oriented parallel to the substrate. This resulted in terraces of the short P4VP(PDP) length scale within terraces of the PS-P4VP long length scale. Washing away PDP from the thin films with ethanol provided an effective means of studying the morphology of the lowest terrace of the thin films and, for a particular system, also resulted in a uniform monolayer of cylinders with a PS core and a P4VP corona.

The influence of grain size on the alignment of hexagonally ordered

In situ SAXS is used to investigate the shear-induced alignment of a supramolecular system consisting of a polyisoprene-b-poly(2-vinylpyridine) diblock copolymer and octyl gallate (OG), where OG is hydrogen-bonded to the vinylpyridine block of the PI-b-P2VP copolymer. Due to microphase separation, the PI-b-P2VP(OG) system self-assembles forming a domain structure of hexagonally ordered P2VP(OG) cylinders embedded in the PI matrix. The results of the alignment showed that the orientation mobility of the cylinders, lying within the (10) planes parallel to the shear plane, is strongly dependent on the size of the cylindrical domains. Subjected to large amplitude oscillatory shear for 15 min a freshly loaded sample with a small grain size structure exhibited much better alignment compared to that of a pre-aligned/squeezed sample with a considerably larger grain size where the orientation had been first partly destroyed by squeezing.

The influence of grain size on the alignment of hexagonally ordered cylinders of self-assembled diblock copolymer-based supramolecules

In situ SAXS is used to investigate the shear-induced alignment of a supramolecular system consisting of a polyisoprene-b-poly(2-vinylpyridine) diblock copolymer and octyl gallate (OG), where OG is hydrogen-bonded to the vinylpyridine block of the PI-b-P2VP copolymer. Due to microphase separation, the PI-b-P2VP(OG) system self-assembles forming a domain structure of hexagonally ordered P2VP(OG) cylinders embedded in the PI inatrix. The results of the alignment showed that the orientation mobility of the cylinders, lying within the (10) planes parallel to the shear plane, is strongly dependent on the size of the cylindrical domains. Subjected to large amplitude oscillatory shear for 15 min a freshly loaded sample with a small grain size structure exhibited much better alignment compared to that of a pre-aligned/squeezed sample with a considerably larger grain size where the orientation had been first partly destroyed by squeezing. (c) 2007 Elsevier Ltd. All rights reserved

Nanorod engineering by reinforcing hexagonally self-assembled PS–b–P4VP(DDP) with PPE

Nanorods consisting of a polystyrene core and a poly(4-vinylpyridine) shell produced via the self-assembly route of comb-shaped supramolecules exhibit very poor mechanical properties. Adding a sufficient amount of poly(2,6-dimethyl-1,4-diphenyl oxide) introduces entanglements to the PS-core resulting in nanorods with much better properties, which can be used as templates for e.g. transition metal oxide tubes.

Supramolecular Triblock Copolymer Complexes

Four different poly(tert-butoxystyrene)-b-polystyrene-b-poly(4-vinylpyridine) (PtBOS-b-PS-b-P4VP) linear triblock copolymers, with a P4VP weight fraction varying from 0.08 to 0.39, were synthesized via sequential anionic polymerization. The values of the unknown interaction parameters between styrene and tert-butoxystyrene and between tert-butoxystyrene and 4-vinylpyridine were determined from random copolymer blend miscibility studies. All triblock copolymers synthesized adopted a P4VP/PS core/shell cylindrical self-assembled morphology. From these four triblock copolymers supramolecular complexes were prepared by hydrogen bonding a stoichiometric amount of pentadecylphenol (PDP) to the P4VP blocks. Three of these complexes formed a triple lamellar ordered state with additional short length scale ordering inside the P4VP(PDP) layers. The difference in morphology between the triblock copolymers and the supramolecular complexes is due to the change in effective composition and the reduction in interfacial tension between the PS and P4VP containing domains