Taeyi Choi

Polydimethylsiloxane-Based Polyurethanes: Phase-Separated Morphology and In Vitro Oxidative Biostability

Three series of segmented polyurethane block copolymers were synthesized using 4,4′-methylenediphenyl diisocyanate (MDI) and 1,4-butanediol (BDO) or 1,3-bis(4-hydroxybutyl)tetramethyl disiloxane (BHTD) as the hard segments, and soft segments composed of poly(dimethyl siloxane) (PDMS)-based and poly(hexamethylene oxide) (PHMO) macrodiols. Copolymers synthesized with the PDMS macrodiol and PDMS and PHMO macrodiol mixtures consist of three microphases: a PDMS phase, hard domains, and a mixed phase of PHMO (when present), PDMS ether end-group segments and some dissolved hard segments. Degrees of phase separation were characterized using small-angle X-ray scattering by applying a pseudo two-phase model, and the morphology resulting from unlike segment demixing was found to be closely related to the in vitro oxidative biostability of these segmented polyurethanes.

Novel Hard-Block Polyurethanes with High Strength and Transparency for Biomedical Applications

Novel hard-block-only polyurethanes are prepared from 1,4-butanediol (BDO) and a pre-polymer synthesized separately from 1,3-bis (4-hydroxybutyl) tetramethyl disiloxane (BHTD) and 4,4′-diphenylmethane diisocyanate (MDI). Three (co)polymers using different proportions of these chain extenders were synthesized using reaction injection moulding, and their microstructure, mechanical properties and in vitro oxidative biostability were evaluated. These materials were found to form a single-phase system, and exhibit optical transparency, high elastic modulus and tensile strength, as well as significant in vitro oxidative biostability. By controlling the BDO/BHTD composition, the ductility can be tuned over orders of magnitude. These polyurethanes may be potentially suitable for biomedical applications, like electronic headers for defibrillators, pacemakers and neurostimulators, and orthopedic nail encapsulation.