Unique Polymeric Materials by Novel Processes

University Of Akron, Akron OH

Investigators

Abstract

This proposal consists of three research thrusts, each focusing on the creation by novel strategies of unique polymeric materials of potential use for medical and high technology applications. The first thrust concerns "smart" (stimuli-responsive) amphiphilic networks and membranes that rapidly change their micromorphology depending on the surrounding medium. The aim of this thrust is to synthesize, characterize and evaluate conceptually new tricomponent tricontinuous amphiphilic membranes with improved O2, permeability, mechanical properties, and precisely designed pore dimensions. The immediate objective will be to prepare immunosiolatory capsules for beta cells for the treatment of diabetes. The walls of the capsules will be novel membranes that contain a continuous hydrophilic poly (ethylene glycol) (PEG) phase for the transport of water and aqueous solutions, a continuous oxyphilic polydimethylsiloxane (PDMS) phase for O2 transport, and a continuous polypentamethylcyclosiloxane (PD5) phase that provides crosslinking of the PEG and PDMS moieties, and reinforcement. Polysiloxanes are known to possess high O2 permeability, and thus will yield channels for O2 transport across the membrane; Thus O2 will diffuse through membrane walls via water-mediated transport by water-swollen PEG phases and by oxyphilic (oxygen-specific) PDMS/PD5 channels. The synthesis of these novel amphiphilic membranes is based on a recently discovered cohydrosilation/hydrolysis/polycondensation process: Thus, vinyl-telechelic PEG and -PDMS moieties will be cohydrosilated by pentamethylcyclosiloxane (D5H), the residual SiH functions of D5H will be hydrolyzed to SiOH groups, and the latter will crosslink to give novel membranes. Well-defined molecular weight PEG and PDMS prepolymers will be used which will result in well-controlled structures. Earlier research with first generation bicomponent membranes will provide guidance toward the preparation of improved biocompatible membranes that will be jointly evaluated with biologists and medical scientists. These unique membranes will be designed to become components that will be jointly evaluated with a bioartificial pancreas to correct diabetes. The second thrust is built upon the recent discovery that D5H can be readily polymerized in the presence of a hydrosilation (Karstedt's) catalyst and water to PD5, a new material with a combination of unprecedented properties, i.e., the lowest Tg on record (~150 degree C), high thermal resistance, etc. The mechanism of the D5H-> PD5 polymerization will be studied (role of water, stoichiometry, etc.), and efforts will be made to define conditions for the synthesis of PD5 clusters of defined sizes, volumes and morphology. A further objective is to create by new processes, and by the use of a combination of inexpensive linear- and cyclic polysiloxanes, unique elastic networks that exhibit outstanding heat and oxidative stability. These networks will be synthesized by the use of HO-PDMS-OH and PD5, and will be based on the discovery that PD5 contains a small but sufficient number of SiH groups that will combine with the HO-telechelic PDMS to give thermally resistant elastic networks. Indeed, preliminary experiments have indicated that the proposed synthesis is feasible. The aim of the third thrust is the synthesis, characterization and testing of novel fully aliphatic thermoplastic elastomers (TPEs). These TPEs will be tri-and star-blocks of soft PIB inner segments bonded to high Tg (~300degrees C) polynorbornadiene outer segments. The objective will be reached by first preparing by living cationic polymerization PIB blocks or stars fitted with tert-chlorine termini, and using these groups, in conjuction with TiCl4, to induce the polymerization of norbornadiene. The characteriztion and testing of these new polymeric materials are integral parts of the thrusts. All the necessary instrumentation, major equipment, and expert advise are available to complete the tasks. These studies will be of significance for the generation of a new family of aliphatic TPEs with potential electronic applications. The envisioned activities will significantly advance discovery and understanding, while fostering teaching and training of young professionals (graduate students and postdoctorals). Various collaborations with researchers at The University of Akron, neighboring universities and hospitals (both in Akron and in Cleveland), and research institutes in Germany and Hungary are in place and will be continued. Students will, as before, participate at local, national, and international meetings and workshops. Special mentoring of undergraduates and graduate students has started and will continue. The envisioned research in inherently multidisciplinary and will lead to extensive participation in interdisciplinary symposia and conferences. Results of this research will be published in highest quality professional journals and presented at meetings.