[Show abstract][Hide abstract] ABSTRACT: The synthesis of isomeric, functionalized 4-vinyl-1,2,3-triazole and 5-vinyl-1,2,3-triazole monomers is demonstrated using heterogeneous copper (copper-in-charcoal)-catalyzed azide−alkyne cycloaddition (CuAAC) or homogeneous ruthenium (Ru)-catalyzed azide−alkyne cycloadditions (RuAAC) “click” protocols. These reactions are regiospecific, exclusively forming 1,4- and 1,5-disubstituted triazoles as determined by 1H NMR, 13C NMR, and X-ray crystallography analysis. Polymerizations were performed using living free radical procedures to yield materials with divergent properties. In the case of the 1,5-triazole materials, glass transition temperature were significantly higher that for the 1,4-derivatives while solubility was decreased.
[Show abstract][Hide abstract] ABSTRACT: We describe a new method to covalently link a wide variety of molecules to the surface of colloidal polymer microspheres using the Cu(I)-catalyzed azide-alkyne reaction, most commonly known under the class of reactions identified by the term click chemistry. The method is generic and readily applied to a spectrum of colloidal particle systems allowing surfaces to be tailored with virtually any desired functionality. To demonstrate this method, polystyrene microspheres were functionalized with two different polyethylene oxide-based polymers, and changes in hydrodynamic radii after functionalization were measured using dynamic light scattering. Control of surface functional groups was demonstrated by fluorescently labeling the colloidal microspheres using the same Cu-catalyzed azide-alkyne cycloaddition reaction.
[Show abstract][Hide abstract] ABSTRACT: Using facile, highly modular synthetic approaches, a new monomer family based on a 1,2,3-triazole-4-vinyl building block has been prepared, and various functional derivatives have been obtained. Subsequent homo- and copolymerization of these novel functionalized monomers gives polymeric materials with unique physical properties, combining many attractive features of more traditional monomers, such as styrene, vinylpyridine, and meth/acrylates.
Journal of the American Chemical Society 10/2006; 128(37):12084-5. DOI:10.1021/ja0648209 · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Molecular-recoginition-controlled construction of nanoparticles using photochemical crosslinking of recognition-induced polymersomes (RIPs), which provide vesicular systems with enhanced stability and size control, is discussed. It was observed that irradiated polymersomes exhibit complete stability in solvents such as methanol, ethanol, tetrahydrofuran, and water, which competitively accept and/or donate hydrogen bonds, disrupting the three-point hydrogen bonds that drive polymersomes formation. Photoirradiated polymersomes retain their spherical structure after removal from solution, in stark contrast to native, unirradiated polymersomes that form an amorphous film after drop-casting from solution. Molecular self-assembly with the phase-separated characteristics of vesicular templates presents a new opportunity for the creation of highly structured construct featuring new structural and dynamic properties.
[Show abstract][Hide abstract] ABSTRACT: Random polystyrene copolymers grafted with complementary recognition elements were combined in chloroform producing vesicular aggregates, that is, recognition-induced polymersomes (RIPs). Reflection interference contrast microscopy (RICM) in solution, coupled with optical microscopy (OM) and atomic force microscopy (AFM) on solid substrates, were used to determine the wall thickness of the RIPs. Rather than a conventional mono- or bilayer structure (approximately 10 or approximately 20 nm, respectively) the RIP membrane was 43+/-7 nm thick. Structural arrangement of the polymer chains on the RIP wall were characterized by using angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The interior portion of the vesicle membrane was found to be more polar, containing more recognition units, than the exterior part. This gradient suggests that a rapid self-sorting of polymers takes place during the formation of RIPs, providing the likely mechanism for vesicle self-assembly.
[Show abstract][Hide abstract] ABSTRACT: The development of selective chemistries that are orthogonal to the diverse array of functional groups present in many polymeric systems is becoming an important tool for the synthesis and use of macromolecules in fields ranging from biomedical devices to nanotechnology. By combining copper-catalyzed cycloaddition chemistry with other synthetic transformations such as esterification, amidation, etc., highly efficient and modular simultaneous and cascade functionalization strategies have been developed. These single-step strategies for preparing multifunctional macromolecules represent a significant advance as compared to traditional multistep approaches, and the utility of these concepts is demonstrated by selective preparation of a diverse range of orthogonally functionalized vinyl polymers.
Journal of the American Chemical Society 11/2005; 127(42):14942-9. DOI:10.1021/ja0549751 · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Polystyrene functionalized with diamidopyridine (DAP) recognition units self-assembles in nonpolar media to form thermally reversible micrometer-scale spherical aggregates. The size and the thermal stability of these microspheres can be controlled by the molecular weight of the polymer. The addition of thymine-functionalized polymer to these self-assembled microspheres converted them into vesicular aggregates with a controlled size. The morphology change was reversible: the addition of DAP-functionalized polymer converted the vesicles back to microspheres.
Journal of the American Chemical Society 11/2004; 126(45):14773-7. DOI:10.1021/ja047643p · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The concepts of molecular recognition present powerful tools for the control of polymer assemblies. In recent years, numerous researchers have coupled supramolecular chemistry with polymer synthesis and engineering, creating a discipline located squarely at the interface of chemistry and polymer science. This review will present an overview of the field of supramolecular polymer science, establishing fundamental differences between main- and sidechain supramolecular polymers and demonstrating the utility of these methodologies in polymer structure control, guest sensing, surface deposition, and in the formation of microscale aggregates.
[Show abstract][Hide abstract] ABSTRACT: Bis-thymine units were used to noncovalently cross-link a complementary diamidopyridine-functionalized copolymer. Upon combination in noncompetitive solvents, discrete micron-scale spherical aggregates were formed arising from specific three-point polymer-cross-linker hydrogen bonding interactions. The diameter of these microspheres could be controlled through spacer structure. The cross-linking process was fully thermally reversible, with complete dissolution observed at 50 degrees C and reformation of the aggregates upon return to ambient temperature. This process could be repeated multiply, with lower particle dispersity observed arising from the annealing process.
Journal of the American Chemical Society 10/2003; 125(37):11249-52. DOI:10.1021/ja034868b · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Specific hydrogen-bonding interactions between polymers and surface-tethered recognition elements were used to selectively modify self-assembled monolayers (SAMs) on gold. The interfacial recognition processes were followed by observing frequency changes of thymine-SAM modified quartz crystal microbalance (QCM) chips during adsorption of diamidopyridine-functionalized (DAP) polystyrene from a nonpolar solvent. QCM studies combined with X-ray photoelectron spectroscopy (XPS), water contact angle, and ellipsometry measurements of the polymer-modified surfaces demonstrate the selectivity of the polymer−surface hydrogen-bonding interactions. These studies also indicate that the degree of recognition element functionalization of both the polymer and the surface is crucial in determining the rate, selectivity, and coverage of polymer on the surface.
[Show abstract][Hide abstract] ABSTRACT: We have explored the interactions of mono- and multivalent guests with Recognition-Induced Polymersomes (RIPs) formed from complementary random copolymers featuring diamidopyridine and thymine functionality. Addition of monovalent guests featuring imide functionality to these RIPs induced a temporary swelling of the vesicles, followed by dissociation of the vesicles due to competitive binding of the guest. Conversely, multivalent thymine-functionalized nanoparticle guests were rapidly incorporated into the RIPs, inducing a contraction of RIP diameter over time. These mono- and multivalent interactions were extremely specific: highly analogous control systems showed no interaction with the RIP structures. Taken together, these studies demonstrate highly selective molecular "lock and key" control over higher-order assembly and recognition processes.
Journal of the American Chemical Society 01/2003; 124(51):15249-54. DOI:10.1021/ja026418+ · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Applying the concepts of molecular recognition to the self-assembly of macromolecules provides a powerful tool for the creation of higher-order supramolecular assemblies. The unprecedented formation of vesicles from these random copolymers lacking defined headgroups presents a new method for the creation of supramolecular assemblies. Moreover, the recognition-induced polymersomes (RIPs) interact specifically with guests featuring appropriate recognition functionality, providing a novel means for the control of self-assembled structures.
[Show abstract][Hide abstract] ABSTRACT: Flavin mononucleotide (FMN, 1) provides a dynamic conformational probe for studying the covalent cross-linking of dopants into silica. Excitation of FMN 1 leads to photodecomposition only when the side chain is in an appropriate geometry to allow a six-membered ring transition state. Our investigations indicate that the rate of photodecomposition dramatically changes in the sol−gel through the course of the gelation and aging process. Rapid changes in the decomposition rate were observed in the sol very early in the gelation process, indicating that the hydroxyl groups of 1 become covalently fixed within the silicate matrix and that silicate structure is formed around this site very early in the sol−gel process.