Branched Polymer Architectures Research Articles

Bidispersity Improves the Toughness and Impact Resistance of Star-Polymer Thin Films.

Branched polymer architectures are used to tune the mechanical properties of impact-resistant thin films through parameters, such as chain length and grafting density. While chain dispersity affects molecular properties, such as interpenetration and entanglements, structure-property relationships accounting for dispersity are challenging to obtain experimentally and are often neglected in computational models. We employ molecular dynamics simulations to model the high-rate tensile elongation and nanoballistic impact of thin films composed of bidisperse star polymers with varying arm lengths. We find that, at fixed molecular weight, high dispersity can significantly enhance the toughness and impact resistance of the films without decreasing their elastic modulus. Bidisperse stars with fewer longer arms are less entangled, but stretch and interpenetrate for longer times during crazing, leading to increased toughness. These findings highlight controlled dispersity as a design strategy to improve the mechanical properties of polymer composites across Pareto fronts.

Fast and Scalable Synthetic Route to Densely Grafted, Branched Polystyrenes and Polydienes via Anionic Polymerization Utilizing P2VP as Branching Point.

Defined, branched polymer architectures with low dispersity and architectural purity are of great interest to polymer science but are challenging to synthesize. Besides star and comb, especially the pom-pom topology is of interest as it is the simplest topology with exactly two branching points. Most synthetic approaches to a pom-pom topology reported a lack of full control and variability over one of the three topological parameters, the backbone or arm molecular weight and arm number. A new, elegant, fast, and scalable synthetic route without the need for post-polymerization modification (PPM) or purification steps during the synthesis to a pom-pom and a broad variety of topologies made from styrene and dienes is reported, with potential application to barbwire, bottlebrush, miktoarm star, Janus type polymers, or multi-graft copolymers. The key is to inset short poly(2-vinyl-pyridine) blocks (<2 mol% in the branched product) into the backbone as branching points. Carb anions can react at the C6 carbon of the pyridine ring, grafting the arms onto the backbone. Since the synthetic route to polystyrene pom-poms has only two steps and is free of PPM or purification, large amounts of up to 300g of defined pom-pom structures can be synthesized in one batch.

Utilising the effect of reaction concentration to tune the physical properties of hyperbranched polymers synthesised using transfer-dominated branching radical telomerisation (TBRT)

TBRT allows the control of cyclisation within branched polymer architectures by simply changing dilution. Increased cyclisation leads to changes in physical properties, therefore, tunig of behaviour is available without changing starting materials.

Theory of Y‐ and Comb‐Shaped Polymer Brushes: The Parabolic Potential Framework

AbstractThe parabolic approximation for self‐consistent molecular potential is widely used for theoretical analysis of conformational and thermodynamic properties of polymer brushes formed by linear or branched macromolecules. The architecture‐dependent parameter of the potential (topological coefficient) can be calculated for arbitrary branched polymer architecture from the condition of elastic stress balance in all the branching points. However, the calculation routine for the topological coefficient does not allow unambiguously identifying the range of applicability and the accuracy of the parabolic approximation. Here the limits of applicability of parabolic approximation are explored by means of numerical self‐consistent field method for brushes formed by Y‐shaped and comb‐like polymers. It is demonstrated that violation of the potential parabolic shape can be evidenced by appearance of multimodal distribution of the end monomer unit in the longest elastic path of the macromolecule. The asymmetry of branching of Y‐shaped polymers does not disturb the parabolic shape of the potential as long as the degree of polymerization of the root segment remains sufficiently large. The same applies to comb‐shape polymers with sufficiently long main chain and large number of branching points. For short comb‐like polymers multiple modes in the distribution of the end monomer unit of the main chain are observed and related to deviation from the parabolic shape of the potential.

Branched and Dendritic Polymer Architectures: Functional Nanomaterials for Therapeutic Delivery

AbstractBarriers to therapeutic transport in biological systems can prevent accumulation of drugs at the intended site, thus limiting the therapeutic effect against various diseases. Advances in synthetic chemistry techniques have recently increased the accessibility of complex polymer architectures for drug delivery systems, including branched polymer architectures. This article first outlines drug delivery concepts, and then defines and illustrates all forms of branched polymers including highly branched polymers, hyperbranched polymers, dendrimers, and branched–linear hybrid polymers. Many new types of branched and dendritic polymers continue to be reported; however, there is often confusion about how to accurately describe these complex polymer architectures, particularly in the interdisciplinary field of nanomedicine where not all researchers have in‐depth polymer chemistry backgrounds. In this context, the present review describes and compares different branched polymer architectures and their application in therapeutic delivery in a simple and easy‐to‐understand way, with the aim of appealing to a multidisciplinary audience.

Molecular dynamics simulation study of linear, bottlebrush, and star-like amphiphilic block polymer assembly in solution.

In this study we investigate the effect of varying branched polymer architectures on the assembly of amphiphilic block polymers in solution using coarse-grained molecular dynamics simulations. We quantify assembly structure (e.g., aggregation number, assembly morphology, and micelle core size) and thermodynamics (e.g., unimer to micelle transition conditions) as a function of increasing solvophobicity of the solvophobic block in the copolymer for three broad categories of polymer architectures: linear, 'bottlebrush' (with many short side chains on a long backbone), and 'star-like' (with few long side chains on a short backbone). Keeping the total number of coarse-grained beads in each polymer (or polymer molecular weight) constant, as we go from either linear or 'star-like' to 'bottlebrush' polymer architectures, the micelle aggregation number and micelle core size decrease, and the solvophobicity required for assembly (i.e., transition solvophobicity) increases. This trend is linked to the topological/steric hinderance for making solvophobic bead contacts between neighboring polymers for the 'bottlebrush' polymer architecture compared to the linear or 'star-like' architectures. We are able to identify some universal trends in assembly by plotting the assembly structure and thermodynamics data as a function of branching parameter defined as the ratio of the branched chain to the linear chain radius of gyration in the unimer state, and the relative lengths of the backbone versus side chain. The results in this paper guide how one could manipulate the amphiphilic block polymer assembly structure and thermodynamics by choosing appropriate polymer architecture, block sequence, and composition.

Analysis of hydrophobically modified ethylene oxide urethane rheology modifiers by comprehensive two dimensional liquid chromatography

Hydrophobically modified ethylene oxide urethane (HEUR) rheology modifiers are polymers used widely in waterborne coatings and other consumer products. The incorporation of hydrophobic end-groups significantly affects the thickening performance of HEURs. Therefore, understanding the degree of incorporation of hydrophobic end-groups on the polymer chain can help gain important insights on the structure/property relationship for HEUR rheology modifiers.A comprehensive two-dimensional liquid chromatography (2D-LC) method was developed for separating polymeric HEUR rheology modifiers based on the number of hydrophobic end-groups incorporated on the polymer chain. Our 2D-LC method uses a size exclusion chromatography (SEC) separation in the first dimension (1D) using an ultra-high performance Advance Polymer Chromatography (APC) column and a gradient reversed-phase liquid chromatography (RPLC) separation in the second dimension (2D). A low flow rate was used in the first dimension SEC separation to minimize the strong organic eluent transferred to the second dimension LC column. A small inner diameter (ID) LC column was used for the second dimension to reduce the total solvent consumption for routine analysis of process samples. The 1D flow rate, 2D transfer volume and gradient profile were all optimized to avoid polymer breakthrough and to achieve optimal separation of the polymer chains based on end-groups. Three types of polymer chains with 0, 1, and 2 terminal hydrophobes were successfully separated using this method. The total run time was further reduced by implementing flow programing in the first dimension separation. The 2D-LC method was applied to study how the polymerization process recipes affected hydrophobe incorporation and how the hydrophobe incorporation correlated with thickening efficiency. The method was also used to separate HEUR rheology modifier with branched polymer architecture.

Effect of Chain Transfer to Polymer in Conventional and Living Emulsion Polymerization Process

Emulsion polymerization process provides a unique polymerization locus that has a confined tiny space with a higher polymer concentration, compared with the corresponding bulk polymerization, especially for the ab initio emulsion polymerization. Assuming the ideal polymerization kinetics and a constant polymer/monomer ratio, the effect of such a unique reaction environment is explored for both conventional and living free-radical polymerization (FRP), which involves chain transfer to the polymer, forming polymers with long-chain branches. Monte Carlo simulation is applied to investigate detailed branched polymer architecture, including the mean-square radius of gyration of each polymer molecule, &lt;s2&gt;0. The conventional FRP shows a very broad molecular weight distribution (MWD), with the high molecular weight region conforming to the power law distribution. The MWD is much broader than the random branched polymers, having the same primary chain length distribution. The expected &lt;s2&gt;0 for a given MW is much smaller than the random branched polymers. On the other hand, the living FRP shows a much narrower MWD compared with the corresponding random branched polymers. Interestingly, the expected &lt;s2&gt;0 for a given MW is essentially the same as that for the random branched polymers. Emulsion polymerization process affects branched polymer architecture quite differently for the conventional and living FRP.

Quaternized triethanolamine-sebacoyl moieties in highly branched polymer architecture as a host for the entrapment of acid dyes in aqueous solutions

This paper reports the synthesis of a hyperbranched polymer by a cost-effective one-step copolymerization of A3 and B2 monomers, namely, triethanolamine and sebacoyl chloride, respectively, followed by methylation of tertiary amine groups. The structure of the hyperbranched polymer QTEAS as an efficient material for the removal of acid dyes was demonstrated by Fourier transform infrared spectroscopy (FTIR), cross polarization magic angle spinning (CPMAS) 13C NMR, thermogravimetric analysis (TGA), powder X-ray diffraction (DRX) and scanning electron microscopy (SEM). The removal of indigo carmine (IC) and Evans blue (EB) was expected to be driven by the electrostatic attraction between positively charged quaternary ammonium groups within the hyperbranched polymer and the negatively charged dyes. The removal process was found to be closely connected to the total number of sulfonate groups on the surface of the dyes. Nonetheless, the ionic strength does not affect the dyes' removal efficiency by the hyperbranched polymer. The sorption capacities at saturation of the monolayer qmax were determined to be 213.22 mg g−1 and 214.13 mg g−1, for IC and EB, respectively, thus showing the greater affinity of QTEAS sorbent for both dyes. Despite its extended molecular structure, EB is removed with the same effectiveness as IC. Finally, the great efficiency of the highly branched polymer for dye removal from colored wastewater was clearly demonstrated.

Ring opening metathesis polymerization of cyclopentene using a ruthenium catalyst confined by a branched polymer architecture

A Grubbs-type Ru alkene metathesis catalyst has been covalently anchored in the core of a globular star polymer. The spatially-confined catalyst is capable of efficient ring-opening metathesis polymerization of cyclopentene, a low-strain monomer.

Template-Directed Synthesis of Structurally Defined Branched Polymers

A grand challenge in materials chemistry is the synthesis of macromolecules and polymers with precise shapes and architectures. In this work, we describe a hybrid synthetic strategy to produce structurally defined branched polymer architectures based on chemically modified DNA. Overall, this approach enables precise control over branch placement, grafting density, and chemical identity of side branches. We utilize a two-step scheme based on polymerase chain reaction (PCR) for site-specific incorporation of non-natural nucleotides along the main polymer backbone, followed by copper-free “click” chemistry for grafting side branches at specific locations. In this way, linear DNA backbones are first synthesized via PCR by utilizing the promiscuity of a high yield thermophilic DNA polymerase to incorporate nucleotides containing bioorthogonal dibenzocyclooctyne (DBCO) functional groups at precise locations along one strand of the DNA backbone. Following PCR, copper-free “click” chemistry is used to attach synt...

Branched polythiophenes by Ni-catalyzed Kumada coupling

The controlled synthesis of branched polythiophenes via Ni-catalyzed Kumada type coupling of branched AB2 monomers prepared in situ from 5,5′′-dibromo-2,2′:3′,2′′-terthiophene (3TBr2) and 5,5′,5′′-tribromo-2,2′:3′,2′′-terthiophene (3TBr3) is presented. The access to highly branched polymer architectures with rather high molecular weights is a key benefit of this one-pot polymerization with respect to standard oxidative polymerization procedures. Our synthetic route further allows the in situ endgroup functionalization as shown exemplarily for pentene functionalized branched polythiophenes and eases thereby the access to branched polythiophenes with tailor-made properties. In particular a comparison of the optical properties allows conclusions about the architecture of the obtained materials with respect to linear and fully branched systems. Energy levels are obtained by cyclic voltammetry measurements in thin films. DFT calculations provide further guidance on the interpretation of the possible molecular structure of the polymer (i.e. branching density) in correlation with their properties.

Modulating Two Copper(I)-Catalyzed Orthogonal “Click” Reactions for the One-Pot Synthesis of Highly Branched Polymer Architectures at 25 °C

Controlling the rates of orthogonal “click” reactions in one-pot provides a method for designing highly branched macromolecular architectures. In this work, we constructed third generation (G3) den...

ChemInform Abstract: Hyperbranched and Highly Branched Polymer Architectures—Synthetic Strategies and Major Characterization Aspects

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Hyperbranched and Highly Branched Polymer Architectures—Synthetic Strategies and Major Characterization Aspects

“Life is branched” was the motto of a special issue of Macromolecular Chemistry and Physics1 on “Branched Polymers”, indicating that branching is of similar importance in the world of synthetic macromolecules as it is in nature. The significance of branched macromolecules has evolved over the last 30 years from just being considered as a side reaction in polymerization or as a precursor step in the formation of networks. Important to this change in perception of branching was the concept of “polymer architectures”, which formed on new starand graft-branched structures in the 1980s and then in the early 1990s on dendrimers and dendritic polymers. Today, clearly, controlled branching is considered to be a major aspect in the design of macromolecules and functional material. Hyperbranched (hb) polymers are a special type of dendritic polymers and have as a common feature a very high branching density with the potential of branching in each repeating unit. They are usually prepared in a one-pot synthesis, which limits the control on molar mass and branching accuracy and leads to “heterogeneous” products with a distribution in molar mass and branching. This distinguishes hyperbranched polymers from perfectly branched and monodisperse dendrimers. In the last 20 years, both classes of dendritic polymers, dendrimers as well as hb polymers, have attracted major attention because of their interesting properties resulting from the branched architecture as well as the high number of functional groups.2 The challenging synthesis of the dendrimers attracted especially scientists with a strong organic chemistry background and led to beautifully designed macromolecules, which allowed a deeper insight into the effect of branching and functionality. Dendrimers have been considered as perfect “nano-objects” where one can control perfectly size and functionality, which is of high interest in nanotechnology and biomedicine. hb polymers, however, were considered from the beginning as products suitable for larger-scale application in typical polymer fields like coatings and resins, where a perfect structure is sacrificed for an easy and affordable synthetic route. Thus, the first structures that were reported paralleled the chemistry used for linear polymers like typical polycondensation for polyester synthesis. More recently, unconventional synthetic methods have been adopted also for hb polymers and related structures. Presently, a vast variety of highly branched structures have been realized and studied regarding their properties and potential application fields. Excellent reviews appeared covering synthesis strategies, properties, and applications, like the very recent tutorial by Carlmark et al.,3 the comprehensive book on hyperbranched polymers covering extensively synthesis and application * E-mail: voit@ipfdd.de; lederer@ipfdd.de. Chem. Rev. 2009, 109, 5924–5973 5924

On growth patterns of branched polymer architectures

AbstractIn nature trees may have many different forms and so have all natural branched structures. Differences in branched architectures of synthetic polymers can only be explained by kinetics. We compare radical polymerization of low density Polyethylene (PE) and PE polymerization with Constrained Geometry Catalyst (CGC) metallocene. The architectures generated by our synthesis algorithms revealed marked differences between the two PE‐systems. Metallocene‐PE turned out to be more comb‐like. This could partially be explained by analyzing growth patterns of the two PE types as incorporated in the architecture synthesis algorithms.

Synthesis of Branched Polymer Architectures from Molecular Weight and Branching Distributions for Radical Polymerisation with Long-Chain Branching, Accounting for Topology-Controlled Random Scission

Synthesis of Branched Polymer Architectures from Molecular Weight and Branching Distributions for Radical Polymerisation with Long-Chain Branching, Accounting for Topology-Controlled Random Scission

Synthesis of Branched Polymer Architectures from Molecular Weight and Branching Distributions for Radical Polymerisation with Long-Chain Branching, Accounting for Topology-Controlled Random Scission

Synthesis of Branched Polymer Architectures from Molecular Weight and Branching Distributions for Radical Polymerisation with Long-Chain Branching, Accounting for Topology-Controlled Random Scission

Hyperbranched Polyether Polyols: A Modular Approach to Complex Polymer Architectures

A versatile modular system for complex branched polymer architectures has been developed through exploitation of the multibranching polymerization chemistry of glycidol. This report summarizes recent advances in the preparation of these novel polymers and describes the modular concept used to tailor their topology to give functional materials, such as the dye-loaded molecular nanocapsule depicted in the Figure.

Preparation of Hyperbranched Polymer Films Grafted on Self-Assembled Monolayers

In this paper we report the preparation of thin films of new highly branched polymers which are relevant to boundary layer phenomena such as adhesion, wetting, and chemical sensing. Specifically, we synthesized surface-grafted, hyperbranched poly(acrylic acid) (PAA) films on self-assembled organomercaptan monolayers. These films grow in discrete steps, but unlike most layer-by-layer approaches, film thickness increase nonlinearly as a function of the number of layers because of the branched polymer architecture. Moreover, these polymer films contain a high density of carboxylic acid groups, which can selectively bind metal ions or serve as reactive sites for subsequent derivatization. Hyperbranched polymer films thus provide new platforms for chemical sensing applications and for tailoring polymer surface properties for a wide variety of technological applications. 24 refs., 4 figs.