N‐methylolmaleimide–benzene photoadduct: A novel monomer for the synthesis of functionally modified polyimides

A novel polycyclic dihydroxy diimide monomer was synthesized through the photocycloaddition of N‐methylolmaleimide to benzene and the reaction of maleimide–benzene photoadduct with formaldehyde. The monomer, which evolved formaldehyde at about 165 °C, was subsequently used to prepare low molecular weight polyamineimides and polyurethaneimides. Soluble polyamineimides, prepared with three different aromatic diamine monomers, exhibited initial decomposition temperatures between 277 and 329 °C and glass‐transition temperatures between 180 and 219 °C. An aliphatic polyamineimide prepared from 1,6‐hexanediamine was insoluble and had glass‐transition and initial decomposition temperatures of 225 °C and 294 °C, respectively, with prior loss of formaldehyde from end groups. Polyurethaneimides prepared with two aromatic diisocyanates showed loss of formaldehyde in the approximate range of 160–169 °C followed by loss of CO₂ and glass‐transition temperatures of 219 and 233 °C. Attempts to prepare polyamideimides resulted in oligomers with a low nitrogen content. Attempts to prepare polyesterimides were unsuccessful. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2645–2651, 2000     

Transient Voltammetry Under Hydrodynamic Conditions

The channel flow cell has been shown to be a powerful tool with which to study analytical, mechanistic and kinetic processes. In this article we describe a numerical strategy which provides an efficient and flexible alternative to previous computational techniques for simulating channel electrode problems. It is demonstrated that the finite element method can accurately simulate the transient currents measured in hydrodynamic systems under mass transport control, at both macro- and micro-electrodes. Results are compared to analytical theory where available, and to previously established methods of simulation.     

New recursive methods for transversal covers

A transversal cover is a set of gk points in k disjoint groups of size g and a minimum collection of transversal subset s, called blocks, such that any pair of points not contained in the same group appear in at least one block. The case g = 2 was investigated and completely solved by Sperner, Renyi, Katona, Kleitman, and Spencer. For all g, asymptotic results are known, but little is understood for small values of k. Sloane and others have initiated the investigation of g = 3. The present article is concerned with constructive techniques for all g and k. One of the principal constructions generalizes Wilson's theorem for transversal designs. This article also discusses a simulated annealing algorithm for finding transversal covers and gives a table of the best known transversal covers at this time. © 1999 John Wiley & Sons, Inc. J Combin Designs 7: 185–203, 1999     

The role of non-coordinating anions in homogeneous olefin polymerization

We present an overview of homogeneous olefin polymerization catalysts in which chain initiation and propagation involves a metallocenium ion (e.g. Cp₂ZrMe⁺) that can be produced by equilibrium or irreversible CH₃⁻ transfer. The Kaminsky catalyst is an example of the former. Complexes of (C₆F₅)₃B with water, alcohols, mercaptans, silanols and oximes are strong acids which can protonate dialkylmetallocenes to produce weakly-coordinated metallocenium salts that are hydrocarbon soluble and which produce high molecular weight poly-1-olefins. Polymer molecular weight is correlated with the steric and electronic effects of the ligands attached to the metal.     

Toward high-performance computational chemistry: II. A scalable self-consistent field program

We discuss issues in developing scalable parallel algorithms and focus on the distribution, as opposed to the replication, of key data structures. Replication of large data structures limits the maximum calculation size by imposing a low ratio of processors to memory. Only applications which distribute both data and computation across processors are truly scalable. The use of shared data structures that may be independently accessed by each process even in a distributed memory environment greatly simplifies development and provides a significant performance enhancement. We describe tools we have developed to support this programming paradigm. These tools are used to develop a highly efficient and scalable algorithm to perform self-consistent field calculations on molecular systems. A simple and classical strip-mining algorithm suffices to achieve an efficient and scalable Fock matrix construction in which all matrices are fully distributed. By strip mining over atoms, we also exploit all available sparsity and pave the way to adopting more sophisticated methods for summation of the Coulomb and exchange interactions. © 1996 by John Wiley & Sons, Inc.     

Brillouin light scattering studies of the mechanical properties of polystyrene/polyisoprene multilayered thin films

We have used Brillouin light scattering (BLS) to investigate the mechanical properties of thin polystyrene (PS) and polyisoprene (PI) films incorporated in a multilayer geometry consisting of alternating layers of the two polymers. All samples had a total thickness h ∼ 1600 Å, and consisted of between 2 and 10 individual polymer films; individual layer thicknesses were as small as 160 Å. Ellipsometry was used to determine the thickness of the PS and PI layers. The velocities of several high-frequency film-guided mechanical waves were measured using BLS and the results are compared with values calculated using an effective medium approach. The effective elastic constants of the multilayered films were obtained from those determined for thick films of PS and PI. Remarkable agreement was obtained between the measured and calculated velocities even for samples in which the individual layer thicknesses were much less than the unperturbed size of the polymer molecules. These results suggest that the mechanical properties of polymers change very little even when the molecules are forced into highly confined geometries. © 1996 John Wiley & Sons, Inc.     

Phase separation morphology of thin films of polystyrene/polyisoprene blends

We present the results of a study of the morphology of phase separation in a thin film blend of polystyrene (PS) and polyisoprene (PI) in a common solvent of toluene. The blend is quenched by rapid solvent evaporation using a spincoating technique rather than a temperature quench. The mass fraction of polystyrene is varied to determine the effect of the substrate on thin film phase separation morphology. We compare the phase separation morphology for very thin films of the PS/PI blend cast onto three different substrates: Si(001) with a native oxide layer (Si (SINGLEBOND) SiO_x), Si(001) etched in hydrofluoric acid (Si-H), and a Au/Pd alloy sputtered onto Si(001). We observe large differences between the morphologies of 1000 Å thick blend films on the Si(SINGLEBOND) SiO_x and Si-H substrates as the mass fraction is varied due to the difference in the wetting properties of PS on the two substrates. Smaller differences are observed between the films on the Si(SINGLEBOND) SiO_x and Au/Pd substrates only for film thicknesses h < 600 Å. © 1996 John Wiley & Sons, Inc.     

Differences in Human Plasma Protein Interactions between Various Polymersomes and Stealth Liposomes as Observed by Fluorescence Correlation Spectroscopy

A significant factor hindering the clinical translation of polymersomes as vesicular nanocarriers is the limited availability of comparative studies detailing their interaction with blood plasma proteins compared to liposomes. Here, polymersomes are self-assembled via film rehydration, solvent exchange, and polymerization-induced self-assembly using five different block copolymers. The hydrophilic blocks are composed of anti-fouling polymers, poly(ethylene glycol) (PEG) or poly(2-methyl-2-oxazoline) (PMOXA), and all the data is benchmarked to PEGylated “stealth” liposomes. High colloidal stability in human plasma (HP) is confirmed for all but two tested nanovesicles. In situ fluorescence correlation spectroscopy measurements are then performed after incubating unlabeled nanovesicles with fluorescently labeled HP or the specific labeled plasma proteins, human serum albumin, and clusterin (apolipoprotein J). The binding of HP to PMOXA-polymersomes could explain their relatively short circulation times found previously. In contrast, PEGylated liposomes also interact with HP but accumulate high levels of clusterin, providing them with their known prolonged circulation time. The absence of significant protein binding for most PEG-polymersomes indicates mechanistic differences in protein interactions and associated downstream effects, such as cell uptake and circulation time, compared to PEGylated liposomes. These are key observations for bringing polymersomes closer to clinical translation and highlighting the importance of such comparative studies.