Robert T. Mathers

A scanning tip electrospinning source for deposition of oriented nanofibres

We present a method for controlled deposition of oriented polymeric nanofibres. The method uses a microfabricated scanned tip as an electrospinning source. The tip is dipped in a polymer solution to gather a droplet as a source material. A voltage applied to the tip causes the formation of a Taylor cone, and at sufficiently high voltages, a polymer jet is extracted from the droplet. By moving the source relative to a surface, acting as a counter-electrode, oriented nanofibres can be deposited and integrated with microfabricated surface structures. For example, we deposited fibres of polyethylene oxide with diameters ranging from 100 to 1800 nm, with the diameter primarily depending on the concentration of the polymeric solution. In addition to the uniform fibre deposition, the scanning tip electrospinning source can produce self-assembled composite fibres of micro-and nanoparticles aligned in a polymeric fibre. We also deposited oriented conductive polymeric fibres of polyaniline and investigated the conductivity of these fibres as components for polymeric nanoelectronics.

Nanofluidic channels with elliptical cross sections formed using a nonlithographic process

We fabricated nanofluidic channels that have elliptical cross sections with major and minor radii of less than 100 nm, without the use of electron-beam or other high-resolution lithography. The channels were formed by thermal removal of sacrificial polymer nanofibers. The sacrificial template fiber was deposited on a target substrate by electrospinning and encapsulated by a spin-on glass. The elliptical shape of the channels eliminates sharp corners, at which fluid flow is hindered, and provides convenient boundary conditions for theoretical modeling of fluid flow in the channels. Also, the spin-on glass is optically transparent and compatible with chemical analysis, thereby opening up application in biomolecular separation and single molecule analysis. Hundreds of parallel channels have also been formed by the oriented spinning process.

Towards sustainable polymer chemistry with homogeneous metal-based catalysts

In the last two decades, numerous catalytic methods have become woven into the fabric of green and sustainable chemistry. In order to qualitatively evaluate and construct a tangible meaning for sustainable processes in polymer chemistry, this perspective outlines ten desirable attributes of homogeneous metal-based catalysts to prepare monomers and polymers within the context of sustainability. Catalysts were evaluated with respect to their activity, composition, and potential environmental impact. In many cases, the most pertinent catalysts tolerate a wide range of functional groups and eliminate purification or synthetic steps. Desirable catalysts also exhibit low toxicity, diminish chemical waste, and allow replacement of toxic chemicals with benign alternatives. Ideally, catalysts operate with extended lifetimes and only require minimal catalyst loadings.

A biodegradable thermoset polymer made by esterification of citric acid and glycerol.

A new biomaterial, a degradable thermoset polymer, was made from simple, economical, biocompatable monomers without the need for a catalyst. Glycerol and citric acid, nontoxic and renewable reagents, were crosslinked by a melt polymerization reaction at temperatures from 90 to 150°C. Consistent with a condensation reaction, water was determined to be the primary byproduct. The amount of crosslinking was controlled by the reaction conditions, including temperature, reaction time, and ratio between glycerol and citric acid. Also, the amount of crosslinking was inversely proportional to the rate of degradation. As a proof-of-principle for drug delivery applications, gentamicin, an antibiotic, was incorporated into the polymer with preliminary evaluations of antimicrobial activity. The polymers incorporating gentamicin had significantly better bacteria clearing of Staphylococcus aureus compared to non-gentamicin gels for up to 9 days.

Cross metathesis functionalization of polyolefins.

A cross metathesis strategy is reported for the post-polymerization functionalization of the pendant vinyl groups present in a range of polyolefin architectures. This represents a general strategy for the synthesis of tailored random and block copolymers as well as homopolymers.

Synthesis and Polymerization of Renewable 1,3‐Cyclohexadiene Using Metathesis, Isomerization, and Cascade Reactions with Late‐metal Catalysts

Synthesis and subsequent polymerization of renewable 1,3-cyclohexadiene (1,3-CHD) from plant oils is reported via metathesis and isomerization reactions. The metathesis reaction required no plant oil purification, minimal catalyst loading, no organic solvents, and simple product recovery by distillation. After treating soybean oil with a ruthenium metathesis catalyst, the resulting 1,4-cyclohexadiene (1,4-CHD) was isomerized with RuHCl(CO)(PPh3)3. The isomerization reaction was conducted for 1 h in neat 1,4-CHD with [1,4-CHD]/[RuHCl(CO)(PPh3)3] ratios as high as 5000. The isomerization and subsequent polymerization of the renewable 1,3-CHD was examined as a two-step sequence and as a one-step cascade reaction. The polymerization was catalyzed with nickel(II)acetylacetonate/methaluminoxane in neat monomer, hydrogenated d-limonene, and toluene. The resulting polymers were characterized by FTIR, DSC, and TGA.

Diglycerol‐Based Polyesters: Melt Polymerization with Hydrophobic Anhydrides

The melt polymerization of diglycerol with bicyclic anhydride monomers derived from a naturally occurring monoterpene provides an avenue for polyesters with a high degree of sustainability. The hydrophobic anhydrides are synthesized at ambient temperature via a solvent-free Diels-Alder reaction of α-phellandrene with maleic anhydride. Subsequent melt polymerizations with tetra-functional diglycerol are effective under a range of [diglycerol]/[anhydride] ratios. The hydrophobicity of α-phellandrene directly impacts the swelling behavior of the resulting polyesters. The low E factors (<2), large amount of bio-based content (>75%), ambient temperature monomer synthesis, and polymer degradability represent key factors in the design of these sustainable polyesters.

Streamlining the conversion of biomass to polyesters: bicyclic monomers with continuous flow

A three-step transformation of 1,4-cyclohexadiene (1,4-CHD) using continuous flow produced an aliphatic bicyclic monomer for polyester synthesis. The monomer synthesis involved catalytic alkene isomerization of 1,4-CHD to 1,3-CHD using a heterogeneous Na2O/Na/Al2O3 catalyst, a Diels Alder reaction with maleic anhydride, and hydrogenation of the bicyclic monomer. A partially continuous strategy was compared with a fully continuous method. The continuous flow process streamlined the transformation of waste by-product biomass by minimizing workup procedures and reducing the synthesis time from ∼1 day for batch processes to ∼2.5 h. The monomer synthesis was easily scalable and allowed recycling of the catalysts for alkene isomerization and hydrogenation. The resulting bicyclic monomers were polymerized with glycerol and 1,4-butanediol (BDO) to obtain renewable polyesters with high thermal stability and tunable glass transition temperatures.

Reaction of polymeric organolithium compounds with ethylene oxide in hydrocarbon solution: determination of extent of oligomerization

The functionalization of poly(styryl)lithium with excess ethylene oxide in benzene solution has been reexamined to determine if oligomerization of ethylene oxide occurs under normal conditions. No 13 C NMR peaks were observed at b = 69-70 and 72-73 ppm as expected for a chain end with two ethylene oxide units. These peaks were not observed even when 3.3 equivalents of 13 C-labeled ethylene oxide (98 atom % 13 C) was utilized. No peak corresponding to two ethylene oxide units at the chain end (at m/z 104n + 210 + 44 Daltons) was observed in the MALDI-TOF mass spectrum of the functionalization product. The main series of peaks (Ag + -cationized) appeared at m/z 104n + 210, corresponding to the expected C 4 H 9 and CH 2 CH 2 OH end groups with a number average degree of polymerization of n. A small peak ( ca. 3 %) corresponding to two ethylene oxide units at the chain end was observed in the mass spectrum of the functionalization product obtained using 10 equivalents of ethylene oxide.

Indirect Measurements of Microstructure Development in Magnetorheological Fluids

Magneto-induction experiments have been devised to measure the microstructure response of quiescent magnetorheological (MR) fluids to an applied magnetic field. Unlike many previous techniques this measurement technique is well suited for MR fluids of high iron loading. Two distinct time scales of microstructure formation have been observed within the range of 10-3 to 10-1 seconds. These two time constants are thought to be associated with floc or chain formation and chain growth and migration. The dependency of the time response upon volume fraction, carrier viscosity and applied field is in partial agreement with contemporary theories and models of particle aggregation.