Hyperbranched Molecules with Epoxy-Functionalized Terminal Branches: Grafting to a Solid Surface

Transformations of Thermosensitive Hyperbranched Poly(ionic liquid)s Monolayers

We synthesized amphiphilic hyperbranched poly(ionic liquid)s (HBPILs) with asymmetrical peripheral composition consisting of hydrophobic n-octadecylurethane arms and hydrophilic, ionically linked poly(N-isopropylacrylamide) (PNIPAM) macrocations and studied low critical solution temperature (LCST)-induced reorganizations at the air-water interface. We observed that the morphology of HBPIL Langmuir monolayers is controlled by the surface pressure with uniform well-defined disk-like domains formed in a liquid phase. These domains are merged and transformed to uniform monolayers with elevated ridge-like network structures representing coalesced interdomain boundaries in a solid phase because the branched architecture and asymmetrical chemical composition stabilize the disk-like morphology under high compression. Above LCST, elevated individual islands are formed because of the aggregation of the collapsed hydrophobized PNIPAM terminal macrocations in a solid phase. The presence of thermoresponsive PNIPAM macrocations initiates monolayer reorganization at LCST with transformation of surface mechanical contrast distribution. The heterogeneity of elastic response and adhesion distributions for HBPIL monolayers in the wet state changed from highly contrasted two-phase distribution below LCST to near-uniform mechanical response above LCST because of the hydrophilic to hydrophobic transformation of the PNIPAM phase.

The design and biomedical applications of self-assembled two-dimensional organic biomaterials

Self-assembling 2D organic biomaterials exhibit versatile abilities for structural and functional tailoring, as well as high potential for biomedical applications.

Ultralow dielectric, high performing hyperbranched epoxy thermosets: synthesis, characterization and property evaluation

The present work addresses the major drawbacks, such as low toughness character and high dielectric constant, of conventional epoxy thermosets through macromolecular engineering.

Self-assembly of hyperbranched polymers and its biomedical applications

Hyperbranched polymers (HBPs) are highly branched macromolecules with a three-dimensional dendritic architecture. Due to their unique topological structure and interesting physical/chemical properties, HBPs have attracted wide attention from both academia and industry. In this paper, the recent developments in HBP self-assembly and their biomedical applications have been comprehensively reviewed. Many delicate supramolecular structures from zero-dimension (0D) to three-dimension (3D), such as micelles, fibers, tubes, vesicles, membranes, large compound vesicles and physical gels, have been prepared through the solution or interfacial self-assembly of amphiphilic HBPs. In addition, these supramolecular structures have shown promising applications in the biomedical areas including drug delivery, protein purification/detection/delivery, gene transfection, antibacterial/antifouling materials and cytomimetic chemistry. Such developments promote the interdiscipline researches among surpramolecular chemistry, biomedical chemistry, nano-technology and functional materials.

Immobilization of a hyperbranched polyester via grafting-to and electron beam irradiation

Stable thin films of an aromatic-aliphatic hyperbranched polyester with hydroxyl groups were fabricated on silicon substrates using electron beam irradiation and a grafting-to approach. We present a detailed study on the influence of the dose, dose rate, and temperature on the film properties and degradation behavior of the polyester immobilized by electron beam irradiation. A patterned polyester film was prepared on the substrate using a masking technique. In the second part of this work, we report on a method for the strong binding of the hyperbranched polyester onto the surface of an "activated" silicon substrate without using any coupling agent. The results are compared with the grafting-to of the hydroxyl-terminated polyester using thin PGMA anchoring layers ( Reichelt et al. Macromol. Symp. 2007, 254, 240- 247 ). The optimal conditions and mechanism of the anchoring procedures were investigated. The surface and film properties of all immobilized polymer films were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), electrokinetic measurements, contact-angle measurements by drop-shape analysis, spectroscopic and imaging ellipsometry, and infrared spectroscopy. It is shown that all immobilization methods can be optimized in such a way that the polymer surface properties remain unchanged compared to those of nongrafted polyesters.

Photolabile carboxylic acid protected terpolymers for surface patterning. Part 1: Polymer synthesis and film characterization

We present the synthesis and characterization of a series of photolabile phenacyl derivative polymers and their subsequent thin film preparation. These systems are composed of up to three methacrylate units: a photolabile component including a p-methoxyphenacyl moiety which after selective irradiation (UV/laser) can provide free carboxylic groups in specific areas for further modification; an anchoring unit, trimethoxysiloxane or glycidyl methacrylate derivative, which allows the covalent attachment of the polymer to the substrate; and a spacer, methyl methacrylate or styrene, which in the appropriate proportion ensures the formation of films with good quality. Structural and thermal properties of these materials have been analyzed by means of NMR, FTIR, elemental analysis, UV, gel permeation chromatography, differental scanning calorimetry, and thermogravimetric analysis. The polymers have been subsequently processed by spin coating to render ultrathin films (<50 nm). Topographic and structural characterization studies of the films have been carried out with atomic force microscopy, contact angle measurements, and X-ray photoelectron spectroscopy. The extent of the substrate attachment of the polymers depending on the nature of the anchoring groups have been studied by ellipsometry and FTIR.

Assembly of coordination nanostructures via ligand derivatization of oxide surfaces

A scheme is presented for the construction of coordination nanostructures on oxide surfaces (glass, Si/SiO2, quartz), based on application of epoxy-terminated monolayers as anchors for covalent grafting of ligands. Two ligands bearing amine groups were reacted with epoxysilane monolayers on oxide surfaces, providing ligand-terminated substrates. The ligands employed were (i) a pyridine moiety, used for subsequent binding of cobalt tetraphenylporphine (CoTPP), and (ii) deferoxamine (DFX), which contains hydroxamic acid moieties, used for subsequent construction of various Zr4+-based coordination layers. The results suggest that a dense ligand layer was obtained in both cases, allowing the formation of coordination overlayers on the oxide surfaces. The growth of coordinated layers was similar to analogous overlayers assembled on Au substrates, indicating that high ligand coverage is achieved by the epoxy-amine surface reaction. Epoxy-based functionalization of oxide substrates is a mild and efficient method for preparing high-quality coordination overlayers. Moreover, the method makes use of commercially available silane and amine reactants, providing the basis for wide application.

Dendritic structures based on bis(hydroxymethyl)propionic acid as platforms for surface reactions

In this paper we present results related to the self-assembly of different generations of disulfide-cored 2,2-bis(hydroxymethyl)propionic acid-based dendritic structures onto gold surfaces. These molecular architectures, ranging from generation 1 to generation 3, contain removable acetonide protecting groups at their periphery that are accessible for hydrolysis with subsequent formation of OH-terminated surface-attached dendrons. The deprotection has been investigated in detail as a versatile approach to accomplish reactive surface platforms. A special focus has been devoted to the comparison of the properties of the layers formed by hydrolysis of the acetonide moieties directly on the surface and in solution, prior to the layer formation.

Polymer grafting via ATRP initiated from macroinitiator synthesized on surface

Macromolecular anchoring layer approach was used for preparation of an effective macroinitiator for the synthesis of grafted polymer layers by atom transfer radical polymerization (ATRP) initiated from the surface. For the initial surface modification, a thin layer of poly(glycidyl methacrylate) (PGMA) was deposited on the surface of a silicon wafer. The ATRP macroinitiator was synthesized on the substrate surface by the reaction between epoxy groups of PGMA and carboxy functionality of bromoacetic acid (BAA). Variation of the time and temperature of the BAA deposition as well as PGMA layer thickness allowed control over the amount of BAA attached to the surface. The PGMA anchoring layer allowed the achievement of initiator surface density significantly higher than that reported for a self-assembled monolayer of ATRP initiators. Polymer brushes were synthesized on the PGMA/BAA-modified substrates by ATRP. Different surface concentrations of BAA were used in our grafting experiments to acquire knowledge about the relationship between the amount of initiator anchored to the surface through PGMA and the rate of the grafted layer formation. The increase in the surface density of the initiating moieties led to the increase in the grafting rate. However, a cutoff initiator concentration beyond which no increase of the thickness of the grafted layer was observed. From comparison between the surface densities of the initiator and the attached polymer it was determined that the efficiency of the initiation from the surface was on the level of 5-15%.

Assembling of Amphiphilic Highly Branched Molecules in Supramolecular Nanofibers

We found that the amplification of weak multiple interactions between numerous peripheral branches of irregular, flexible, polydisperse, and highly branched molecules can facilitate their self-assembly into nanofibrillar micellar structures at solid surfaces and the formation of perfect long microfibers in the course of crystallization from solution. The core-shell architecture of the amphiphilic dendritic molecules provides exceptional stability of one-dimensional nanofibrillar structures. The critical condition for the formation of the nanofibrillar structures is the presence of both alkyl tails in the outer shell and amine groups in the core/inner shell. The multiple intermolecular hydrogen bonding and polar interactions between flexible cores stabilize these nanofibers and make them robust albeit flexible. This example demonstrates that one-dimensional supramolecular assembling at different spatial scales (both nanofibers and microfibers) can be achieved without a tedious, multistep synthesis of shape-persistent molecules.

Mixed polymer brushes by sequential polymer addition: anchoring layer effect

Smart surfaces can be described as surfaces that have the ability to respond in a controllable fashion to specific environmental stimuli. A heterogeneous (mixed) polymer brush (HPB) can provide a synthetic route to designing smart polymer surfaces. In this research we study HPB comprised of end-grafted polystyrene (PS) and poly(2-vinyl pyridine) (P2VP). The synthesis of the HPB involves the use of an "intermolecular glue" acting as a binding/anchoring interlayer between the polymer brush and the substrate, a silicon wafer. We compare anchoring layers of epoxysilane (GPS), which forms a self-assembled monolayer with epoxy functionality, to poly(glycidyl methacrylate) (PGMA), which forms a macromolecular monolayer with epoxy functionality. The PS and P2VP were deposited onto the wafers in a sequential fashion to chemically graft PS in a first step and subsequently graft P2VP. Rinsing the HPB in selective solvents and observing the change in water contact angle as a function of the HPB composition studied the switching nature of the HPB. Scanning probe microscopy was used to probe the topography and phase imagery of the HPB. The nature of the anchoring layer significantly affected the wettability and morphology of the mixed brushes.