Polyurethane Block Polymers

My research on Polyurethane block polymers and other multiphase thermoplastic elastomers seeks a fundamental understanding of these system's morphology and physical properties. Small angle x-ray scattering is used to determine domain size, shape and degree of phase separation in order to determine microphase separation and intermolecular bonding in these high performace polymers. The material's morphology is correlated with thermal and mechanical properties determined by differential calorimetry, dynamic mechanical testing and stress-strain analysis.

Polyurethane chemistry is well suited to the design of a variety of high performance materials used in specialized applications. Among the materials systems studied in our laboratory are polyurethane acrylates which can be crosslinked by ultraviolet or electron beam radiation, silicone rubber-based polyurethances for low temperature applications and polyurethanes containing ionic functionalities spaced along the polymer backbone. The mechanical and transport properties of these ion-containing polymers are strongly influenced by aggregation of the ionic groups. In order to better understand the sturcture of such aggregates we are using techniques such as x-ray and neutron scattering. We are also interested in the solution properties of ionomers where we are using rheological measurements, inelastic light scattering and neutron scattering to study aggregation phenomena.

Polymers for Biomedical Application

The occurrence of blood clotting, or thrombosis, at the blood-polymer interface presents major difficulties in the design of artificial organs and cardiac assist devices. In order to examine how surface properties affect blood-materials interactions, a number of polyurethane block polymers have been synthesized and studied in our laboratory. The surface properties of these materials are characterized by a variety of techniques which include X-ray photoelectron spectroscopy (XPS), attenuated multiple total internal reflection-infared spectroscopy (ATR_IR), scanning electron microscopy (SEM) and contact angle measurements. We are investigating a new generation of functionalized polyrethane surfaces which possess markedly improved blood compatibility. In-vitro techniques also have been developed to study protein adsorption, platelet deposition and aggregation and their interactions with polymer surfaces. We are currently studying the adsorption characteristics of the cell adhesive proteins, fibrinogen, fibronectin and vitronectin as well as the anti-adhesive protein, high molecular weight kininogen. Our interest is in discovering the role these proteins have on white blood cell activation and implant infection.

A state of the art video-microscopy facility has been constructed to study bacteria-surface and leukocyte surface interactions in a radial flow field. This system allows efficient study of shear rate effects on cell-surface interactions. Recent research has involved creating antifouling surfaces using antimicrobial cationic polyurethanes and polyurethanes containing cationic dendrimer pendant groups. Finally we have initiated research in the area of tissue engineering using a platform of low glass transition acrylic terpolymers which contain cell binding ligands.