Solvent induced phenomena in a dendronized linear polymer (original) (raw)

Dendronized Polymers: Molecular Objects between Conventional Linear Polymers and Colloidal Particles

ACS Macro Letters, 2014

The term molecular object (MO) is introduced to describe single, shape persistent macromolecules that retain their form and mesoscopic dimensions irrespective of solvent quality and adsorption onto a surface. The concept is illustrated with results concerning homologous series of dendronized polymers (DP). In particular, we discuss imaging experiments quantifying deformation upon adsorption, defect characterization, and atomistic molecular dynamics simulations of DP structure. We argue that MOs such as high generation DP, with their large dimensions and high internal density, provide an opportunity to address fundamental questions regarding the onset of bulk-like behavior in single molecules. Illustrative examples of such questions concern the smallest MO exhibiting a glass transition, glassy behavior or a constant bulk density. The characteristics of DP MO are highlighted by comparison to polymer beads, polymeric micelles, globular proteins, and carbon nanotubes. We discuss future research directions and speculate on possibilities involving multiarmed and toroid DP and the effect of DP on friction and rheology, as well as their utilization for nanoconstruction.

Computer simulation of dendronized polymers: Organization and characterization at the atomistic level

Rsc Advances, 2013

Atomistic molecular dynamics simulations in chloroform and solvent-free environments are used to build and study a homologous series of neutral dendronized linear polymers (DPs), whose repeat units are regularly branched dendrons of generations g = 1-7, excluding g = 5. We find that a DP with g ¡ 4 displays an elongated conformation, while a DP with g = 6 exhibits a helical backbone. The conformations essentially differ in their alternating (elongated) or regular (helical) twist with respect to the macromolecular axis, at similar average distance between repeat units (2.1-2.3 Å). With increasing g the dendrons tend to induce an increasing strain, stiffness and overall cylindrical shape onto the DP; the existence of DPs with g ¢ 7 is excluded. The fractal dimensionality of the backbone appears similar for DPs with g ¡ 4, while a discontinuous fractal behavior found for g = 6 is consistent with its helical backbone.

Interactions in dendronized polymers: intramolecular dominates intermolecular

Soft Matter, 2014

In an attempt to relate atomistic information to the rheological response of a large dendritic object, interand intramolecular hydrogen bonds and p,p-interactions have been characterized in a dendronized polymer (DP) that consists of a polymethylmethacrylate backbone with tree-like branches of generation four (PG4) and contains both amide and aromatic groups. Extensive atomistic molecular dynamics simulations have been carried out on (i) an isolated PG4 chain and (ii) ten dimers formed by two PG4 chains associated with different degrees of interpenetration. Results indicate that the amount of nitrogen atoms involved in hydrogen bonding is 1111% while 1115% of aromatic groups participate in p,pinteractions. Furthermore, in both cases intramolecular interactions clearly dominate over intermolecular ones, while exhibiting markedly different behaviors. Specifically, the amount of intramolecular hydrogen bonds increases when the interpenetration of the two chains decreases, whereas intramolecular p,pinteractions remain practically insensitive to the amount of interpenetration. In contrast, the strength of the corresponding two types of intermolecular interactions decreases with interpenetration. Although the influence of complexation on the density and cross-sectional radius is relatively small, interpenetration affects significantly the molecular length of the DP. These results support the idea of treating DPs as long colloidal molecules.

Tuning Polymer Thickness: Synthesis and Scaling Theory of Homologous Series of Dendronized Polymers

Journal of the American Chemical Society, 2009

The thickness of dendronized polymers can be tuned by varying their generation g and the dendron functionality X. Systematic studies of this effect require (i) synthetic ability to produce large samples of high quality polymers with systematic variation of g, X and of the backbone polymerization degree N, (ii) a theoretical model relating the solvent swollen polymer diameter, r, and persistence length, λ, to g and X. This article presents an optimized synthetic method and a simple theoretical model. Our theory approach, based on the Boris-Rubinstein model of dendrimers predicts r ∼ n 1/4 g 1/2 and λ ∼ n 2 where n ) [(X -1) g -1]/(X -2) is the number of monomers in a dendron. The average monomer concentration in the branched side chains of a dendronized polymer increases with g in qualitative contrast to bottle brushes whose side chains are linear. The stepwise, attach-to, synthesis of X ) 3 dendronized polymers yielded gram amounts of g ) 1-4 polymers with N ≈ 1000 and N ≈ 7000 as compared to earlier maxima of 0.1 g amounts and of N ≈ 1000. The method can be modified to dendrons of different X. The conversion fraction at each attach-to step, as quantified by converting unreacted groups with UV labels, was 99.3% to 99.8%. Atomic force microscopy on mixed polymer samples allows to distinguish between chains of different g and suggests an apparent height difference of 0.85 nm per generation as well as an increase of persistence length with g. We suggest synthetic directions to allow confrontation with theory. Airaud, C.; Xu, Y.; Mueller, A. H. E.; Harnau, L.; Rosenfeldt, S.; Lindner, P.; Ballauff, M.

Micellar behavior of a well-defined dendritic polymer (PS2PI)3: the effects of architecture and solvent selectivity

European Polymer Journal, 2004

The micelles formed when a dendritic polymer of polystyrene (PS) and polyisoprene (PI), having the overall structure (PS 2 PI) 3 , were examined in two solvents, dimethylformamide (DMF) and dimethylacetamide (DMA). Both solvents are good solvents for polystyrene and non-solvents for polyisoprene. The aggregation behavior was studied by a combination of static and dynamic light scattering and viscometry. In both systems star-like micelles were formed which followed the hard sphere model. The aggregation number was much lower for the micelles formed in DMA. The polymer-solvent interaction parameters indicate that the interactions are stronger between both PS-DMA and PI-DMA than for either polymer block with DMF. The effects of solvent selectivity are exacerbated by the structure of the polymer. With each polymer molecule contributing six soluble arms to the micelle, in the better solvent (DMA) increased repulsive interactions between the extended polystyrene lead to lower aggregation numbers.

Effect of the Branching Pattern of Hydrophobic Dendrons on the Core Structure of Linear-Dendritic Copolymer Micelles

Hydrophobic dendrons based on different branching patterns, viz. 3,5-di-and 3,4,5-trisub-stituted phenyl rings, consist of the same backbone but exhibit different sizes, shapes, and hydrophobic densities. These dendrons are attached to poly(ethylene glycol) and the core properties of the copolymer micelles are investigated in tetrahydrofuran (THF)/water mixtures by neutron scattering. Two polymers with intermediate hydrophobicity are studied further with variations in the solvent composition and the temperature. The aggregation numbers for 3,4,5-based dendron copolymers are lower, with more THF molecules of solvation compared with the 3,5-based dendron copolymer, the difference being greater at higher generations due to different molecular shapes. The micellar core size increases in small steps with dendron size so that dye encapsulation is tuned.