Antibiofouling hybrid dendritic Boltorn/star PEG thiol-ene cross-linked networks.

A series of thiol-ene generated amphiphilic cross-linked networks was prepared by reaction of alkene-modified Boltorn polyesters (Boltorn-ene) with varying weight percent of 4-armed poly(ethylene glycol) (PEG) tetrathiol (0-25 wt%) and varying equivalents of pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) (0-64 wt%). These materials were designed to present complex surface topographies and morphologies, with heterogeneity of surface composition and properties and robust mechanical properties, to serve as nontoxic antibiofouling coatings that are amenable to large-scale production for application in the marine environment. Therefore, a two-dimensional matrix of materials compositions was prepared to study the physical and mechanical properties, over which the compositions spanned from 0 to 25 wt% PEG tetrathiol and 0-64 wt% PETMP (the overall thiol/alkene (SH/ene) ratios ranged from 0.00 to 1.00 equiv), with both cross-linker weight percentages calculated with respect to the weight of Boltorn-ene. The Boltorn-ene components were prepared through the esterification of commercially available Boltorn H30 with 3-butenoic acid. The subsequent cross-linking of the Boltorn-PEG-PETMP films was monitored using IR spectroscopy, where it was found that near-complete consumption of both thiol and alkene groups occurred when the stoichiometry was ca. 48 wt% PETMP (0.75 equiv SH/ene, independent of PEG amount). The thermal properties of the films showed an increase in T(g) with an increase in 4-armed PEG-tetrathiol wt%, regardless of the PETMP concentration. Investigation of the bulk mechanical properties in dry and wet states found that the Young's modulus was the greatest at 48 wt% PETMP (0.75 equiv of SH/ene). The ultimate tensile strength increased when PETMP was constant and the PEG concentration was increased. The Young's modulus was slightly lower for wet films at constant PEG or constant PETMP amounts, than for the dry samples. The nanoscopic surface features were probed using atomic force microscopy (AFM), where it was observed that the surface of the amphiphilic films became increasingly rough with increasing PEG wt%. On the basis of the physicochemical data from the diverse sample matrix, a focused compositional profile was then investigated further to determine the antifouling performance of the cross-linked Boltorn-PEG-PETMP networks. For these studies, a low, constant PETMP concentration of 16 wt% was maintained with variation in the PEG wt% (0-35 wt%). Antifouling and fouling-release activities were tested against the marine alga Ulva. Spore settlement densities were low on these films, compared to that on standards of polydimethylsiloxane and glass.

Evaluation of Isoprene Chain Extension from PEO Macromolecular Chain Transfer Agents for the Preparation of Dual, Invertible Block Copolymer Nanoassemblies.

Two RAFT-capable PEO macro-CTAs, 2 and 5 kDa, were prepared and used for the polymerization of isoprene which yielded well-defined block copolymers of varied lengths and compositions. GPC analysis of the PEO macro-CTAs and block copolymers showed remaining unreacted PEO macro-CTA. Mathematical deconvolution of the GPC chromatograms allowed for the estimation of the blocking efficiency, about 50% for the 5 kDa PEO macro-CTA and 64% for the 2 kDa CTA. Self assembly of the block copolymers in both water and decane was investigated and the resulting regular and inverse assemblies, respectively, were analyzed with DLS, AFM, and TEM to ascertain their dimensions and properties. Assembly of PEO-b-PIp block copolymers in aqueous solution resulted in well-defined micelles of varying sizes while the assembly in hydrophobic, organic solvent resulted in the formation of different morphologies including large aggregates and well-defined cylindrical and spherical structures.

A new porous reaction layer for developing addressable molecular libraries.

A new diblock copolymer-derived porous reaction layer for microelectrode arrays has been tested for its stability and its compatibility with both site-selective synthesis and electrochemical signaling experiments. The diblock copolymer consisted of a cinnamoyl-substituted polymethacrylate block for attachment to the surface of the array and a bromo-substituted polystyrene block for selective functionalization of the surface proximal to microelectrodes in the array. Site-selective Suzuki, Heck, and Cu(I)-coupling reactions were all performed on the new reaction layer along with electrochemical impedance studies.

Amphiphilic cross-linked networks produced from the vulcanization of nanodomains within thin films of poly(N-vinylpyrrolidinone)-b-poly(isoprene).

Diblock copolymers of poly(N-vinylpyrrolidinone) (PNVP) and poly(isoprene) (PIp) were employed as building blocks for the construction of complex cross-linked networks that present surfaces having amphiphilic character, imparted by covalent trapping of compositionally heterogeneous phase-separated morphologies. The kinetics for the homopolymerization of N-vinylpyrrolidinone by reversible addition-fragmentation chain transfer (RAFT) techniques was studied, and the initially obtained PNVP-based macro-RAFT agents were then extended to PNVP-b-PIp block copolymers. Therefore, the PNVP chain length was held constant at a number-averaged degree of polymerization of 120, while the PIp chain length was varied to afford a series of three PNVP120-b-PIpx block copolymers (where x=710, 53, and 25). These materials were then cross-linked individually using sulfur monochloride, to produce complex amphiphilic networks. The nanoscopically resolved topographies of these films were analyzed using atomic force microscopy, and their compositional heterogeneities were probed by X-ray photoelectron spectroscopy and internal reflectance infrared imaging techniques. Additionally, the surfaces were analyzed to determine the extent of surface reorganization under aqueous conditions.

Perfluorocarbon-loaded Shell Crosslinked Knedel-like Nanoparticles: Lessons regarding polymer mobility and self assembly.

Reversible addition-fragmentation chain transfer polymerization was employed to synthesize a set of copolymers of styrene (PS) and 2,3,4,5,6-pentafluorostyrene (PPFS), as well as block copolymers with tert-butyl acrylate (PtBA)-b-PS-co-PPFS, with control over molecular weight and polydispersity. It was found that the copolymerization of styrene and PFS allowed for the preparation of gradient copolymers with opposite levels of monomer consumption, depending on the feed ratio. Conversion to amphiphilic block copolymers, PAA-b-(PS-co-PPFS), by removing the protecting groups was followed by fitting with monomethoxy poly(ethylene glycol) chains. Solution-state assembly and intramicellar crosslinking afforded shell crosslinked (SCK) block copolymer nanoparticles. These fluorinated nanoparticles (ca. 20 nm diameters) were studied as potential magnetic resonance imaging (MRI) contrast agents based on the (19)F-nuclei, however, it was found that packaging of the hydrophobic fluorinated polymers into the core domain restricted the mobility of the chains and prohibited (19)F-NMR spectroscopy when the particles were dispersed in water without an organic cosolvent. Packing of perflouro-15-crown-5-ether (PFCE) into the polymer micelle was demonstrated with good uptake efficiency, however, it was necessary to swell the core with a good solvent (DMSO) to increase the mobility and observe the (19)F-NMR signal of the PFCE.